SUBMITTED BY

MUNISH KUMAR B.V.C.O.E.(3 rd Year) Now in 4 th .

IMD

The India Meteorological Department was established in 1875. It is the National Meteorological Service of the country and the principal government agency in all matters relating to meteorology, seismology and allied subjects The beginnings of meteorology in India can be traced to ancient times. Early philosophical writings of the 3000 B.C. era, such as the Upanishads, contain serious discussion about the processes of cloud formation and rain and the seasonal cycles caused by the movement of earth round the sun. Varahamihira's classical work, the Brihatsamhita, written around 500 A.D., provides clear evidence that a deep knowledge of atmospheric processes existed even in those times. It was understood that rains come from the sun (Adityat Jayate Vrishti) and that good rainfall in the rainy season was the key to bountiful agriculture and food for the people. Kautilya's Arthashastra contains records of scientific measurements of rainfall and its application to the country's revenue and relief work. Kalidasa in his epic, 'Meghdoot', written around the seventh century, even mentions the date of onset of the monsoon over central India and traces the path of the monsoon clouds.

To take meteorological observations and to provide current and forecast meteorological information for optimum operation of weather-sensitive activities like agriculture, irrigation, shipping, aviation, offshore oil explorations, etc. To warn against severe weather phenomena like tropical cyclones, norwesters, dust storms, heavy rains and snow, cold and heat waves, etc., which cause destruction of life and property. To provide meteorological statistics required for agriculture, water resource management, industries, oil exploration and other nation-building activities. To conduct and promote research in meteorology and allied disciplines. To detect and locate earthquakes and to evaluate seismicity in different parts of the country for development projects.

Agriculture meteorology Civil aviation Climatology Hydro-meteorology Instrumentation Meteorological telecommunication

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Regional specialized meteorological center Positional astronomy Satellite meteorology Seismology Training

SERVICES PROVIDED BY IMD

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INTRODUCTION TO COMMUNICATION SYSTEMS

Communication is the process of establishing connection or link between to points for information exchange.

Communication is simply the process of conveying message at distance or commuication is the basic process of exchange information.

Fig. shown below shows the block diagram of a general Communication system in which different functional elements are represented by blocks. The essential components of a communication system are:

1. Information source .2. Input transducer.3. Transmitter .4. Channel .5. Receiver.6. Output transducer.7. Distortion and noise.

Examples of Communication Systems1. E-mail2. Voice Mail - Fax 3. Smart Phone - instant messaging 4. Telecommuting - Video-conferencing 5. Groupware - Telephony6. E-Commerce - The Internet7. Bulletin board system - The Web8. Global positioning system

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BLOCK DIAGRAM OF A GENERAL COMMUNICATON SYSTEM

1. Information source : Information sources can be: speech, T.V., facsimile and personal computer. Function of information is to produce required message, which has to be transmitted.

2. Input transducer : A transducer is a device which converts one form of energy to other form. The message from the information source may or may not be electrical in nature. In case when the message from the source is not electrical in nature, an input transducer is used to convert it into time-varying electrical signal. For example in radio-broadcasting, a microphone converts the message (which is in sound waves) into corresponding electrical signal.

3. Transmitter : The function of transmitter is to process the electrical signal from different aspects. For example, in radio broadcasting, the electrical signal obtained from sound signal Is processed to restrict its range of audio frequencies (upto 5 kHz in amplitude modulation) and is often amplified.

4. The channel and the noise : There are two types of channels, namely point-to-point channels and broadcast channels (where multiple stations receive from single station) . The other various examples are:i) Telephone channels.ii) Optical channels.iii) Mobile radio channels.iv) Satellite channels.

5. Receiver : It’s main function is to reproduce the message signal in electric form from the distorted received signal. This reproduction of the original signal is accomplished by a process known as “demodulation or detection”.

6. Destination : It is the final stage which is used to convert an electrical signal to it’s original form. For example, in radio broadcasting, the destination is a loudspeaker, which works as a transducer i.e. it converts the original electrical to the original sound signal.

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TYPES OF COMMUNICATION SYSTEMS

1.)DIGITAL COMMUNICATION SYSTEM

2.)ANALOG COMMUNICATION SYSTEM

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SATELLITE COMMUNICATION SYSTEMA satellite is an object which has been placed into orbit by human endeavor. Suchobjects are sometimes called artificial satellites to distinguish them from natural satellitessuch as the Moon.

Introduction

a) A satellite is something that goes around and around a larger something, like the earth or another planet. Some satellites are natural, like the moon, which is a natural satellite of the earth. Other satellites are made by scientists and technologists to go around the earth and do certain jobs.

b) Some satellites send and receive television signals. The signal is sent from a station on the earth’s surface. The satellite receives the signal and rebroadcasts it to other places on the earth. With the right number of satellites in space, one television program can be seen all over the world.

c) Some satellites send and receive telephone, fax, and computer communications.

d) Satellites make it possible to communicate by telephone, fax, Internet, or computer with anyone in the world.

e) Other satellites observe the world’s weather, feeding weather information into giant computer programs that help scientists know what the weather will be. The weather reporters on your favorite T.V. news show get their information from those scientists.

f) When a satellite is launched, it is placed in orbit around the earth. The earth’s gravity holds the satellite in a certain path as it goes around the earth, and that path is called an "orbit." There are several kinds of orbits. Here are three of them.

1.)LEO, or Low Earth Orbit

a) A satellite in low earth orbit circles the earth 100 to 300 miles above the earth’s surface. Because it is close to the earth, it must travel very fast to avoid being pulled out of orbit by gravity and crashing into the earth.

b) Satellites in low earth orbit travel about 17,500 miles per hour. These satellites can circle the whole earth in about an hour and a half.

2.)MEO, or Medium Earth Orbit

(a) Satellites circling 6,000 to 12,000 miles above the earth are in medium altitude orbit. In these larger orbits they stay in sight of a ground receiving station for 2 hours or more, compared to about 10 minutes for LEOs. It takes MEO satellites from 4 to 8 hours to go around the earth.

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3.)GEO, or Geostationary Earth Orbit

(a) A satellite in geosynchronous orbit circles the earth in 24 hours—the same time it takes the earth to rotate one time. If these satellites are positioned over the equator and travel in the same direction as the earth rotates, they appear "fixed" with respect to a given spot on earth— that is, they hang like lanterns over the same spot on the earth all the time.

(b) Satellites in GEO orbit 22,282 miles above the earth. In this high orbit, GEO satellites are always able to "see" the receiving stations below, and their signals can cover a large part of the planet. Three GEO satellites can cover the globe, except for the parts at the North and South poles.

History of artificial satellites:

1) The first artificial satellite was Sputnik 1, launched by the Soviet Union on 4 October 1957, and initiating the Soviet Sputnik program, with Sergei Korolev as chief designer and Kerim Kerimov as his assistant. This in turn triggered the Space Race between the Soviet Union and the United States.

2) Sputnik 1 helped to identify the density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere. Because the satellite's body was filled with pressurized nitrogen, Sputnik 1 also provided the first opportunity for meteoroid detection, as a loss of internal pressure due to meteoroid penetration of the outer surface would have been evident in the temperature data sent back to Earth. The unanticipated announcement of Sputnik 1's success precipitated the Sputnik crisis in the United States and ignited the so-called Space Race within the Cold War. Sputnik 2 was launched on November 3, 1957 and carried the first living passenger into orbit, a bitch named Laika.

3) In May, 1946, Project RAND had released the Preliminary Design of an Experimental World-Circling Spaceship, which stated, "A satellite vehicle with appropriate instrumentation can be expected to be one of the most potent scientific tools of the Twentieth Century. The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy. The United States Air Force's Project RAND eventually released the above report, but did not believe that the satellite was a potential military weapon; rather, they considered it to be a tool for science, politics, and propaganda.

4) On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the fall of 1957. Following pressure by the American Rocket Society, the National Science Foundation, and the International Geophysical Year, military interest picked up and in early 1955 the Air Force and Navy were working on Project Orbiter, which involved using a Jupiter C rocket to launch a satellite. The project succeeded, and Explorer 1 became the United States' first satellite on January 31, 1958. In June 1961, three-and-a-half years after the launch of Sputnik 1, the Air Force used resources of the United States Space Surveillance Network to catalog 115 Earth-orbiting satellites.

The largest artificial satellite currently orbiting the Earth is the International Space Station.

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What Does a Satellite Do?

Satellites do many things for people. Their most important job is helping people communicate with other people, wherever they are in the world.

A satellite can carry a camera as it travels in its orbit and take pictures of the whole earth. Mapmakers can use these pictures to make more accurate maps. Satellite pictures can also help experts predict the weather, because from the satellite, the camera can actually see the weather coming. When you watch the weather forecast on TV, you are seeing pictures of the earth taken by a camera riding on a satellite.

Satellites in orbit can send messages to a special receiver carried by someone on a ship in the ocean or in a truck in the desert, telling that person exactly where he or she is.

A satellite can relay your telephone call across the country or to the other side of the world. If you decide to telephone your friend in Mexico City, your call can be sent up in space to a satellite, then relayed to a ground station in Mexico and sent from there to your friend’s telephone.

A satellite can relay your computer message, fax message, or Internet data as well. With the help of satellites, we can fax, e-mail, or download information anyplace in the world. When the satellite sends a message from your computer or fax to another computer or fax, it’s called data transmission. The satellite is transmitting, or sending, information or data.

A satellite can transmit your favorite TV program from the studio where it is made to your TV set—even if the studio is in Japan and your TV set is in Inglewood. From the studio where it is made, a TV program is broadcast to a satellite. This is called an uplink. Then it is rebroadcast from the satellite to another place on the earth. This is called a downlink. To link means to connect. So uplink is connecting upward to the satellite and downlink is connecting downward to earth.

When words or pictures or computer data are sent up to a satellite, they are first converted to an invisible stream of energy, called a signal. The signal travels up through space to the satellite and then travels down from the satellite to its destination, where it is converted back to a voice message, a picture, or data, so that the receiver can receive it.

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What’s Inside a Satellite?

Satellites have a great deal of equipment packed inside them. A satellite has sevensubsystems, and each one has its own work to do.

The P ropulsion subsystem includes the electric or chemical motor that brings the spacecraft to its permanent position, as well as small thrusters (motors) that help keep the satellite in its assigned place in orbit. Satellites drift out of position because of solar wind or gravitational or magnetic forces. When that happens, the thrusters are fired to move the satellite back into the right position in its orbit.

The power subsystem generates electricity from the solar panels on the outside ofthe spacecraft. The solar panels also store electricity in storage batteries, which providepower when the sun isn’t shining on the panels. The power is used to operate the communicationssubsystem. A Boeing 702 generates enough power at the end of its servicelife to operate two hundred 75-watt light bulbs.

The communications subsystem handles all the transmit and receive functions. Itreceives signals from the earth, amplifies or strengthens them, and transmits (sends)them to another satellite or to a ground station.

The structures subsystem distributes the stresses of launch and acts as a strong, stable framework for attaching the other parts of the satellite.

The thermal control subsystem keeps the active parts of the satellite cool enoughto work properly. It does this by directing the heat that is generated by satellite operationsout into space, where it won’t interfere with the satellite.

The attitude control subsystem maintains the communications "footprint" in the correct location. Satellites can’t be allowed to jiggle or wander, because if a satellite is not exactly where it belongs, pointed at exactly the right place on the earth, the television program or the telephone call it transmits to you will be interrupted. When the satellite gets out of position, the attitude control system tells the propulsion system to fire a thruster that will move the satellite back where it belongs.

Operators at the ground station need to be able to transmit commands to the satellite and to monitor its health. The telemetry and command subsystem provides a way for people at the ground stations to communicate with the satellite.

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Microwave Band designations used in satellite communications

Band Downlink frequency

range

Uplink frequency

range

Bandwidth Beam Satellite spacing

Atmospheric effect

C 3.7-4.2 GHz 5.925-6.425 GHz

500 MHz wide 40 less

Ku 10.9-11.7 GHz

14.00-14.5 GHz

500 Hz narrow 10 more

Ka 17.7-21.2 GHz

27.5-31.0 GHz

3.5 GHz narrower <10 severe

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Indian National Satellite System

INSAT or the Indian National Satellite System is a series of multipurpose Geo-stationary satellites launched by ISRO to satisfy the telecommunications, broadcasting, meteorology, and search and rescue needs of India.

Commissioned in 1983, INSAT is the largest domestic communication system in the Asia Pacific Region. It is a joint venture of the Department of Space, Department of Telecommunications, India Meteorological Department, All India Radio and Doordarshan. The overall coordination and management of INSAT system rests with the Secretary-level INSAT Coordination Committee.

INSAT satellites provide 199 transponders in various bands (C, S, Extended C and Ku) to serve the television and communication needs of India. Some of the satellites also have the Very High Resolution Radiometer (VHRR), CCD cameras for metrological imaging. The satellites also incorporate transponder(s) for receiving distress alert signals for search and rescue missions in the South Asian and Indian Ocean Region, as ISRO is a member of the Cospas-Sarsat programme.

INSAT SYSTEM

The Indian National Satellite (INSAT) system was commissioned with the launch of INSAT-1B in August 1983 (INSAT-1A, the first satellite was launched in April 1982 but could not fulfill the mission). INSAT system ushered in a revolution in India’s television and radio broadcasting, telecommunications and meteorological sectors.

It enabled the rapid expansion of TV and modern telecommunication facilities to even the remote areas and off-shore islands. Today, INSAT has become the largest domestic communication satellite system in the Asia-Pacific region with ten satellites in service—INSAT-2E, INSAT-3A, INSAT-3B, INSAT-3C, INSAT-3E, KALPANA-1, GSAT-2, EDUSAT, INSAT-4A and INSAT-4B. Together, the system provides 199 transponders in C, Extended C and Ku bands for a variety of communication services.

Some of the INSATs also carry instruments for meteorological observation and data relay for providing meteorological services. KALPANA-1 is an exclusive meteorological satellite. The satellites are monitored and controlled by Master Control Facilities that exist in Hassan and Bhopal.

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SATELLITE BEING USED IN IMD

1.)INSAT-3A

The multipurpose satellite, INSAT-3A, was launched by Ariane in April 2003. It is located at 93.5 degree East

longitude. The payloads on INSAT-3A are as follows:

12 Normal C-band transponders (9 channels provide expanded coverage from Middle East to South East Asia with an EIRP of 38 dBW, 3 channels provide India coverage with an EIRP of 36 dBW and 6 Extended C-band transponders provide India coverage with an EIRP of 36 dBW).

6 Ku-band transponders provide India coverage with EIRP of 48 dBW.

A Very High Resolution Radiometer (VHRR) with imaging capacity in the visible (0.55-0.75 µm), thermal infrared (10.5-12.5 µm) and Water Vapour (5.7-7.1 µm) channels, provide 2x2 km, 8x8 km and 8x8 km ground resolutions respectively.

A CCD camera provides 1x1 km ground resolution, in the visible (0.63-0.69 µm), near infrared (0.77-0.86 µm) and shortwave infrared (1.55-1.70 µm) bands.

A Data Relay Transponder (DRT) having global receive coverage with a 400 MHz uplink and 4500 MHz downlink for relay of meteorological, hydrological and oceanographic data from unattended land and ocean-based automatic data collection-cum-transmission platforms.

A Satellite Aided Search and Rescue (SAS&R) SARP payload having global receive coverage with 406 MHz uplink and 4500 MHz downlink with India coverage, for relay of signals from distress beacons in sea, air or land. See also Cospas-Sarsat.

For meteorological observation, INSAT-3A carries a three channel Very High Resolution Radiometer (VHRR) with 2 km resolution in the visible band and 8 km resolution in thermal infrared and water vapour bands. In addition, INSAT-3A carries a Charge Coupled Device (CCD) camera which operates in the visible and short wave infrared bands providing a spatial resolution of 1 km. A Data Relay Transponder (DRT) operating in UHF band is incorporated for realtime hydrometeorological

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data collection from unattended platforms located on land and river basins. The data is then relayed in extended C-band to a central location.

INSAT-3A also carries another transponder for Satellite Aided Search and Rescue (SAS & R) as part of India's contribution to the international Satellite Aided Search and Rescue programme.

Mission

Spacecraft Massonboard power

Stabilization

Propulsion

Payload

Launch date

Launch site

Launch vehicle

Orbit

Telecommunication, broadcasting and Meteorology

2,950 (Mass at Lift – off) 1,348Kg (Dry mass)

3,100 W

3 – axis body stabilized in orbit using momentum and reaction wheels, solar flaps, magnetic torquers and eight 10 N and eight 22 N reaction control thrusters.

440 N Liquid Apogee Motor with MON 3 (Mixed Oxides of Nitrogen) and MMH (Mono Methyl Hydrazine) for orbit raising

Communication payload

- 12 C – band transponders,- 6 upper extended C band transponders- 6 Ku band transponders- 1 Satellite Aided Search & Rescue transponders

Meteorological payload

- Very High Resolution Radiometer (VHRR) with 2 km resolution in visible band and 8 km resolution in infrared and water vapour band

- Charged Coupled Device (CCD) camera operating in visible, near infrared and shortwave infrared band with 1 km resolution.

- Data Relay Transponders (DRT)

10.04.2003

French Guyana

Ariane -5

Geostationary (93.5 deg East longitude)

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Orbit Mission life 12 Years

INSAT-3A is launched by European Ariane-5G Launch Vehicle into a Geosynchronous Transfer Orbit (GTO) with a perigee of 200 km and an apogee of 35,980 km. The satellite is manoeuvered to its final orbit by firing the satellite's apogee motor. Subsequently, the deployment of solar array, antennae and the solar sail is carried out and the satellite is commissioned after in-orbit checkout.

  Nation: IndiaType /

Application:Communication, Meteorology

Operator: InsatContractors: ISRO

Equipment:

12 C-band transponders, 6 ext. C-band transponders, 6 Ku-band transponders, 1 Ku beacon, 1 S-band transponder, VHRR, CCD Camera, DR Transponder

Configuration:

Insat-2/-3 Bus

Propulsion: 440 Newton thrust liquid apogee motorLifetime:

Mass: 2950 kg (1348 kg dry) Orbit: GEO

 

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2.)KALPANA-1/METSAT-1

METSAT (Meteorological Satellite), launched by PSLV, is the first exclusive meteorological satellite built by ISRO. So far, meteorological services had been combined with telecommunication and television services in the INSAT system. METSAT will be a precursor to the future INSAT system that will have separate satellites for meteorology and telecommunication & broadcasting services. This will enable larger capacity to be built into INSAT satellites, both in terms of transponders and their radiated power, without the design constraints imposed by meteorological instruments.

For meteorological observation, METSAT carries a Very High Resolution Radiometer (VHRR) capable of imaging the Earth in the visible, thermal infrared and water vapour bands. It also carries a Data Relay Transponder (DRT) for collecting data from unattended meteorological platforms. METSAT will relay the data sent by these platforms to the Meteorological Data Utilization Centre at New Delhi. Such platforms have been installed all over the country.

At the time of its launch, METSAT weighed 1055 kg including about 560 kg of propellant. The propellant carried by METSAT is mainly required to raise the satellite from the Geosynchronous Transfer Orbit to its final geostationary orbit. METSAT will be located at 74 deg East longitude.

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METSAT has been designed using a new spacecraft bus employing lightweight structural elements like Carbon Fiber Reinforced Plastic (CFRP). The satellite has a solar array generating 550 watts of power.

On 5. February 2003 METSAT 1 was renamed Kalpana 1 to honour the late Indian born astronaut Kalpana Chawla, who died in the Columbia STS-107 accident.

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Nation: IndiaType /

Application:Meteorology

Operator: ISROContractors: ISRO

Equipment:3-band VHRR instrument, Data Relay Transponder

Configuration: I-1K (I-1000) BusPropulsion: LAM engine

Lifetime:Mass: 1060 kg Orbit: GEO

 Satellite Date LS   Launcher Remarks:METSAT 1/ Kalpana 1 12.09.2002  Sr PSLV (3)

3.)INSAT-3C

Indian National Satellite (Insat) is a multipurpose space system for communication, broadcasting and meteorological services.

MAIN FEATURES OF INSAT-3A

MISSION Communication, broadcasting and Meteorology

SPACECRAFT MASS 2,650 Kg (Mass at Lift - off)

1218 Kg (Dry mass)

ORBOARD POWER2765 W

PROPULSION Liquid Apogee Motor with fuel and oxidizer stored in separate titanium tanks and pressuring in Kevlar wound titanium tank.

TRANSPONDERS 24 C band transponders

6 Extended C - band Transponders

2 S - band Transponders

LAUNCH DATE 24.01.2002

LAUNCH SITE French Guyana

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LAUNCHVEHICAL Ariane -5

ORBIT Geostationary (74 deg East longitude)

MISSION LIFE Very long

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OUTDOOR UNIT OF EARTH STATION

ANTENNA FEED LNA (LOW NOISE AMPLIFIER)

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ANTENNA SYSTEM

a) Antennas are another part of satellite communication subsystem. In fact the antennas on board the satellite serve as an interface between the Earth stations on the ground and various satellite sub-systems during operations. Antennas receive the uplink signal and transmit to downlink signals. In addition they provide single link for the satellite telemetry, command and ranging systems which in conjunction with attitude control subsystem provides beacon tracking signals for precise pointing of the antenna towards the Earth coverage areas.

b) The design of satellite antenna is conditioned by the required coverage. It should be remembered that antennas are the one of the key elements in a satellite communication system since their gain values directly determine the amount of received power.

c) Antennas demonstrate a property known as reciprocity, which means that an antenna will maintain the same characteristics regardless if it is transmitting or receiving. Most antennas are resonant devices, which operate efficiently over a relatively narrow frequency band.

d) An antenna must be tuned to the same frequency band of the radio system to which it is connected; otherwise the reception and the transmission will be impaired. When a signal is fed into an antenna, the antenna will emit radiation distributed in space in a certain way. A graphical representation of the relative distribution of the radiated power in space is called a radiation pattern.

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BASIC TERMINOLOGIES USED WITH ANTENNAS

1.) Bandwidth, Beamwidth, and Polarization

Bandwidth, beamwidth, and polarization are three important terms dealing respectively with the operating frequency range, the degree of concentration or the radiation pattern, and the space orientation of the radiated waves.

1.1) Bandwidth

a) The term bandwidth refers to the range of frequencies the antenna will reflect effectively; i.e., the antenna will perform satisfactorily throughout is size of frequencies. When the antenna power drops to ½(3 dB), the upper and lower extremities of these frequencies have been reached and the antenna no longer perform satisfactorily.

b) Antennas that operate over a wide frequency range and still maintain satisfactory performance must have compensating circuits switched into the system to maintain impedance matching, thus ensuring no deterioration of the transmitted signals.

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1.2) Beamwidth

a) The beamwidth of an antenna is described as the angles created by comparing the half-power points (3 dB) on the main radiation lobe to its maximum power point.

b) In an example, the beam angle is 300, which is the sum of the two angles created at the points where the field strength drops to 0. 0’ field strength is measured in u/V/m) of the maximum voltage at the center of the lobe.(These points are known as the half-power points.).

1.3) Polarization

a) Polarization of an antenna refers to the direction in space of the E field (electric vector) portion of the electromagnetic wave being radiated by the transmitting system.

b) Low-frequency antennas are usually vertically polarized because of ground effect (reflected waves, etc.) and physical Construction methods. High-frequency antennas are generally horizontally polarized.

1.4) Aperture

The effective aperture of an antenna Ae is the area presented to the radiated or received signal. It is a key parameter, which governs the performance of the antenna.

The aperture efficiency depends on the distribution of the illumination across the aperture. If this is linear then Ka= 1. This high efficiency is offset by the relatively high level of sidelobes obtained with linear illumination. Therefore, antennas with more practical levels of sidelobes have an antenna aperture efficiency less than one (Ae< A).

1.) Major and Side Lobes (Minor Lobes) a) The pattern shown in the upper figures has radiation concentrated in several lobes. The radiation

intensity in one lobe is considerably stronger than in the other. The strongest lobe is called major lobe; the main beam (or main lobe) is the region around the direction of maximum radiation (usually the region that is within 3 dB of the peak of the main beam). The main beam in Figure 1 is northbound.

b) The others are (minor) side lobes. Since the complex radiation patterns associated with arrays frequently contain several lobes of varying intensity, you should learn to use appropriate terminology. In general, major lobes are those in which the greatest amount of radiation occurs. Side or minor lobes are those in which the radiation intensity is least.

c) The sidelobes are smaller beams that are away from the main beam. These sidelobes are usually radiation in undesired directions which can never be completely eliminated. The sidelobe level (or sidelobe ratio) is an important parameter used to characterize radiation patterns. It is the maximum value of the sidelobes away from the main beam and is expressed in Decibels. One sidelobe is called backlobe. This is the portion of radiation pattern that is directed opposing the main beam direction.

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2.) Front-to-Back Ratio

The front-to-back ratio of an antenna is the proportion of energy radiated in the principal direction of radiation to the energy radiated in the opposite direction. A high front-to-back ratio is desirable because this means that a minimum amount of energy is radiated in the undesired direction.

Figure 2: The same antenna pattern in a rectangular-coordinate graphFigure 1: Antenna pattern in a polar-coordinate graph

3.) ANTENNA GAIN Independent of the use of a given antenna for transmitting or receiving, an important characteristic of this antenna is the gain. Some antennas are highly directional; that is, more energy is propagated in certain directions than in others. The ratio between the amount of energy propagated in these directions compared to the energy that would be propagated if the antenna were not directional (Isotropic Radiation) is known as its gain. When a transmitting antenna with a certain gain is used as a receiving antenna, it will also have the same gain for receiving.

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TYPES OF ANTENNAS USED IN IMD

1.) Parabolic antenna

A parabolic antenna for Erdfunkstelle Raisting, the biggest facility for satellite communication in the world, based in Raisting, Bavaria, Germany.

A parabolic antenna is a high-gain reflector antenna used for radio, television and data communications, and also for radiolocation (RADAR), on the UHF and SHF parts of the electromagnetic spectrum. The relatively short wavelength of electromagnetic (radio) energy at these frequencies allows reasonably sized reflectors to exhibit the very desirable highly directional response for both receiving and transmitting.

With the advent of TVRO and DBS satellite television, the parabolic antenna became a ubiquitous feature of urban, suburban, and even rural, landscapes. Extensive terrestrial microwave links, such as those between cellphone base stations, and wireless WAN/LAN applications have also proliferated this antenna type. Earlier applications included ground based and airborne radar and radio astronomy. The largest "dish" antenna in the world is the Arecibo observatory's radio telescope at Arecibo, Puerto Rico, but, for beam-steering reasons, it is actually a spherical, rather than parabolic, reflector.

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Parabolic Dish

Antennas based on parabolic reflectors are the most common type of directive antennas when a high gain is required. The main advantage is that they can be made to have gain and directivity as large as required. The main disadvantage is that big dishes are difficult to mount and are likely to have a large wind age

The basic property of a perfect parabolic reflector is that it converts a spherical wave irradiating from a point source placed at the focus into a plane wave. Conversely, all the energy received by the dish from a distant source is reflected to a single point at the focus of the dish. The position of the focus, or focal length, is given by:

Where D is the dish diameter and c is the depth of the parabola at its center.

The size of the dish is the most important factor since it determines the maximum gain that can be achieved at the given frequency and the resulting beam width. The gain and beam width obtained are given by:

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f = D^2 / 16*c

G = {(pi*D) ^2 / wave lenth^2}*n

BW = 70*wavelength / D

Design: Main types of parabolic antennas

CASSEGRAIN ANTENNA

a) Cassegrain antennas are widely used in today’s world of millimeter wave communications. Due to the high gain and pencil-sharp beam width they are mostly used for point-to-point links and mesh network terminals, but also works well for radar and satellite communication applications.

b) The fact of Cassegrain antennas popularity is based on a general rule, that if the diameter of the main reflector is greater than 100 wavelengths, the Cassegrain system is a contending option compare to other antenna types.

picture of cassegrain antenna used in IMD (earth station) Used for satellite downlink for KALPANA

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c) The main reflector is most expensive part of the of Cassegrain antenna and usually made from a metal-coated composite plastic or machined from a chunk of metal. Plastic reflectors are cheaper but are subjected to hogging under direct sunlight and curling of coating at the regions with a wet climate. The other problem associated with plastic reflectors is a technology processing complexity to make an ideal fidelity hyperbola with a micron tolerance for high frequencies from a plastic material. That’s why steel or aluminum dishes are used to design Cassegrain antennas for serious commercial products on broadband communications market.

Cassegrain antenna used in IMD for satellite downlink of INSAT 3A

Disadvantage :- Complex design The sub reflector of a Cassegrain type antenna is fixed by bars. These bars and the secondary

reflector constitute an obstruction for the rays coming from the primary reflector in the most effective direction.

Advantages :- Feed radiator is more easily supported The antenna is geometrically compact Its maintenance and repairing is easy as compare to prime feed.

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OFFSET ANTENNA

a) An offset dish antenna is a type of satellite dish. It is so called because the antenna feed is offset to the side of the reflector, in contrast to a typical circular parabolic antenna where the feed is in front of the center of the reflector.

b) The offset dish antenna still uses a parabolic dish with the driven element at the focus of the parabola; however, the curve of the dish is taken from one side of the parabola instead of the center.

c) Offset feed antennas are most commonly found on Ku Band DBS satellite dishes or ‘mini-dishes’. The benefit of the offset configuration is that it positions the feed horn away from the dish itself so that it does not cast a shadow on the dish. Offset dishes are often referred to as ‘asymmetrical’.

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PRIME FOCUS

a) The signal reflects from the satellite dish and concentrates towards the center, where the LNB is mounted to catch the signal.

Prime focus parabolic

antenna used in IMD

Description :-

A typical parabolic antenna consists of a parabolic reflector with a small feed antenna at its focus.

The reflector is a metallic surface formed into a paraboloid of revolution and (usually) truncated in a circular rim that forms the diameter of the antenna. This paraboloid possesses a distinct focal point by virtue

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of having the reflective property of parabolas in that a point light source at this focus produces a parallel light beam aligned with the axis of revolution.

Disadvantages :- Its maintenance is difficult Gain is low

ADVANTAGE OF CASSEGRAIN AND OFFSET

Both generally called as “DUAL OPTICS” because of the use of secondary reflector, which allows better control over “COLLIMATED” beam.

They allow antenna feed system to be more compact.

The feed element is usually located in a "feed horn" which protrudes out from the main reflector, with the Rx and Tx equipment located immediately behind the center of the primary reflector. This setup is used when the feed element is bulky or heavy such as when it contains a pre-amplifier or even the actual receiver or transmitter. Parabolic antenna theory closely follows optics theory. So a Gregorian antenna can be identified by the fact that it uses a concave sub-reflector, while a Cassegrain antenna uses a convex sub-reflector.

2.) Horn Antenna

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a. Description: The Horn Antenna at Bell Telephone Laboratories in Holmdel, New Jersey, was

constructed in 1959 to support Project Echo—the National Aeronautics and Space Administration's passive communications satellite project.

a) The antenna is 50 feet (15 m) in length with a radiating aperture of 20 by 20 feet (6 by 6 m) and is made of aluminum. The antenna's elevation wheel is 30 feet (10 m) in diameter and supports the weight of the structure by means of rollers mounted on a base frame. All axial or thrust loads are taken by a large ball bearing at the apex end of the horn. The horn continues through this bearing into the equipment cab. The ability to locate receiver equipment at the apex of the horn, thus eliminating the noise contribution of a connecting line, is an important feature of the antenna. A radiometer for measuring the intensity of radiant energy is found in the equipment cab.

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3.) Helical antenna

a) Helical antenna for WLAN communication, working frequency app. 2.4 GHz.

b) A helical antenna is an antenna consisting of a conducting wire wound in the form of a helix. In most cases, helical antennas are mounted over a ground plane. Helical antennas can operate in one of two principal modes: normal (broadside) mode or axial (or end fire) mode.

B: Central Support,C: Coaxial Cable,E: Spacers/Supports for the helixR: Reflector/Base,S: Helical Aerial Element

c) In the normal mode, the dimensions of the helix are small compared with the wavelength. The far field radiation pattern is similar to an electrically short dipole or monopole. These antennas tend to be inefficient radiators and are typically used for mobile communications where reduced size is a critical factor.

d) A Tesla coil secondary coil is also an example. In the axial mode, the helix dimensions are at or above the wavelength of operation. The antenna then falls under the class of waveguide antennas, and produces true circular polarization. These antennas are best suited for animal tracking and space communication, where

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the orientation of the sender and receiver cannot be easily controlled, or where the polarization of the signal may change. Antenna size makes them unwieldy for low frequency operation, so they are commonly employed only at frequencies ranging from VHF up to microwave.

APPLICATIONS

The relative amplitudes of — and constructive and destructive interference effects among — the signals radiated by the individual antennas determine the effective radiation pattern of the array. A phased array may be used to point a fixed radiation pattern, or to scan rapidly in azimuth or elevation. Simultaneous electrical scanning in both azimuth and elevation was first demonstrated in a phased array antenna at Hughes Aircraft Company, Culver City, CA, in 1957 (see Joseph Spradley, “A Volumetric Electrically Scanned Two-Dimensional Microwave Antenna Array,” IRE National Convention Record, Part I – Antennas and Propagation; Microwaves, New York: The Institute of Radio Engineers, 1958, 204-212). When phased arrays are used in sonar, it is called beam forming. The phased array is used for instance in optical communication as a wavelength-selective splitter.

1.)Broadcasting

In broadcast engineering, phased arrays are required to be used by many AM broadcast radio stations to enhance signal strength and therefore coverage in the city of license, while minimizing interference to other areas. Due to the differences between daytime and nighttime ionospheric propagation at mediumwave frequencies, it is common for AM broadcast stations to change between day (groundwave) and night (skywave) radiation patterns by switching the phase and power levels supplied to the individual antenna elements (mast radiators) daily at sunrise and sunset. More modest phased array longwire antenna systems may be employed by private radio enthusiasts to receive longwave, mediumwave (AM) and shortwave radio broadcasts from great distances.

2.)Naval usage

Phased array radar systems are also used by warships of several navies including the Chinese, Japanese, Norwegian, Spanish, Korean and United States' navies in the Aegis combat system. Phased array radars allow a warship to use one radar system for surface detection and tracking (finding ships), air detection and tracking (finding aircraft and missiles) and missile uplink capabilities. Prior to using these systems, each surface-to-air missile in flight required a dedicated fire-control radar, which meant that ships could only engage a small number of simultaneous targets.

3.)Space probe communication

The MESSENGER spacecraft is a mission to the planet Mercury (arrival 18 March 2011). This spacecraft is the first deep-space mission to use a phased-array antenna for communications. The radiating elements are linearly-polarized, slotted waveguides. The antenna, which uses the X band, uses 26 radioactive elements but can gracefully downgrade.

CONCLUSION

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An antenna is a structure—generally metallic and sometimes very complex designed to provide an efficient coupling between space and the output of a transmitter or the input to a receiver.

Like a transmission line, an antenna is a device with distributed constants, so that current, voltage and impedance all vary from one point to the next one along it. This factor must be taken into account when considering important antenna properties, such as impedance, gain and shape of radiation pattern. Thus artificial satellites are become the very important thing not only for the Science and research purpose but also in our day to day life.

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SATELLITE SYSTEM OVERVIEW1. The system comprises of outdoor and indoor equipment. The outdoor equipment is consisting of 6.1

meter antenna with feed, motor drives, and limit switches alongwith (1+1) low noise amplifier assembly etc. The indoor equipment consists of antenna control unit, down converters, encoders, demodulators, encoders, demodulator for DCP data and Personal computers all mounted in 5 different racks.

2. Ext-C band amplified signal received from L.N.A.

3. Received signal downconverted to 70MHz IF.

4. IF 70MHz signal demodulated & decoded to get VHRR & CCD data.

5. Ext-C band signal downconverted to 140MHz IF.

6. IF 140MHz signal demodulated by DDRGS to get DCP raw data.

7. DCP raw data processed by Xconnect software to get engineering unit DCP data.

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ANTENNA CONTROL SYSTEM

1. This unit does the tracking and control of antenna.

2. 6.1 meters antenna with 46dB gain receives Ext C band signal form satellite.

3. It can be positioned to receive INSAT 3A, KALPANA and INSAT 2E.

4. It controls the movement in elevation 10 to 90° and azimuth 150° in two phases. Polarization control is also provided.

5. Manual & auto track mode for tracking purpose- manual mode, position track mode, program mode & step track mode.

6. For auto tracking control, the system makes use of Beacon Tracking Receiver.

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L.N.A. (LOW NOISE AMPLIFIER)

A low noise amplifier is an electronic device used to filter out the noise of input signals received at the front of communication systems. They are widely used in a variety of applications such as RF communication systems including wireless computer networks and mobile phones.

A low noise wideband amplifier has been designed for use in DVB satellite, TV receivers using a

(cheaper) fourth generation BFG520/X wideband transistor. The LNA will enhance the performance of modern satellite down converter IC’s, such as the TDA8060A [1], ensuring optimum receiver sensitivity.

1+1 L.N.A. CONTROL SYSTEM

1. It has a minimum gain of 60 dB.

2. Noise temperature less than 45 degree K.

3. Two LNA’s are connected in redundant configuration.

4. A fault condition in the on-line LNA, or an operator generated command will switch the standby LNA to the on-line position.

5. Outdoor amplifier/switch assembly which mounts at the antenna hub.

6. Mode of operation is either auto/manual.

7. Monitoring and control is via remote computer.

Fig 1 Dual band CMOS L.N.A. Figure 2 shows the LNA circuit.

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BLOCK DIAGRAM OF 1+1 L.N.A.CONTROL SYSTEM

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INDOOR EARTH STATION UNIT

The main components used in indoor section of earth station are as follows:-

DOWNCONVERTOR DECODER BIT SYNCHRONISER IMD COMPUTER PROCESSING SECTION

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DOWNCONVERTER

1. It downconverts the frequency varies from 4.5 to 4.8GHz range to 70 ±20MHz.

2. Dualconversion method is used to achieve 70MHz output.

3. First local oscillator (L.O.): 5.58GHz to 5.88GHz.

4. Second L.O.: 1150MHz.

5. R.F. input frequency 4.5 to 4.8GHz.

6. Mode setting is either local or remote.

7. Output attenuation 0-30dB to be set; so that output level is suitable for demodulator input.

8. 32 setups can be stored in memory.

9. For remote monitoring RS485 interface is used.

Front View

Rear View

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Some important features

Down conversion frequency (4.5-70) MHz

Conversion type Dual to achieve 70 MHz output

o/p attenuation 0-30 dB

Mode of operation Auto or manual

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BLOCK DIAGRAM OF DOWNCONVERTER

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Digital Direct Readout Ground Station (D.D.R.G.S.)

1. RF signal at 4.5 GHz downconverted to 140 MHz and fed to DDRGS. 2. DDRGS downconverts the signal to 10 MHz suitable for A/D conversion.

3. Signal digitized and demodulated (4 channels can be simultaneously demodulated)

4. Raw data extracted and sent on demand to PC.

5. XCONNECT software on PC processes the data into engineering units suitable for generating reports and export files in PDF, EXCEL, ASCII and other standard formats.

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DEMODULATOR Depending upon the data received from satellite the demodulation technique is used at the

reception point Mainly two types of data are received at earth station which are NUMERICAL and

PICTOURIAL from satellite payloads For numerical data to be transmitted QPSK is used and for pictorial data BPSK is used.

BPSK

BPSK (also sometimes called PRK, Phase Reversal Keying, or 2PSK) is the simplest form of phase shift keying (PSK). It uses two phases which are separated by 180° and so can also be termed 2-PSK.

TIMING DIAGRAM OF B.P.S.K.

QPSK

QPSK can encode two bits per symbol, shown in the diagram with Gray coding to minimize the BER — twice the rate of BPSK. Analysis shows that this may be used either to double the data rate compared to a BPSK system while maintaining the bandwidth of the signal or to maintain the data-rate of BPSK but halve the bandwidth needed.

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DEMODULATOR USED IN IMD IMD used arraycom CM 601 demodulator The IF Rx input signal is input at the BNC connector on the modem card.

The input passes through an AGC amplifier. The AGC amplifier section has a wide dynamic range and is control to keep its output signal at an optimal level, regardless of the input signal level.

The first digital block encountered after the analog-to-digital convertor is a digital baseband filter.

Symbol time clock and AGC amplifier (through the filter ASIC), all under digital control. The carrier and clock frequency tracking loops are digitally controlled using direct digital synthesizer (DDS) ASIC is in the IF synthesizer and digital clock synthesizer blocks.

The demodulator function mixes the IF carrier down to the baseband. The demodulated channel symbol are then;

Decoded by a sequential decoder depending upon the installed modem card and the ordered options.

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The data is direct back to the modem card where it is converted to the appropriate electrical level and then passed to the user.

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DECODER

In telecommunication, a line code (also called digital baseband modulation) is a code chosen for use within a communications system for baseband transmission purposes. Line coding is often used for digital data transport.

Line coding consists of representing the digital signal to be transported by an amplitude- and time- discrete signal that is optimally tuned for the specific properties of the physical channel (and of the receiving equipment). The waveform pattern of voltage or current used to represent the 1s and 0s of a digital signal on a transmission link is called line encoding. The common types of line encoding are uni- polar, polar, bi-polar and Manchester encoding.

The signal received from the demodulator is in the form of RS-422 electrical signal. A decoder is used to decode the received signal into desired TTL form data.

For CCD signal, I and Q is separated and differentially decoded and again converted to RS-422 form and 75 TTL form.

The output of DECODER-100 is RS-422 clock and data and TTL-75 Ohms driver clock and data.

There are two types of signals, which the decoder can receive:

1. VHRR BPSK NRZ-S Encoded bit rate-526.5 kbps

2. CCD QPSK NRZ-L Encoded bit rate- 1.28875 Mbps

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POWER LEVEL DIAGRAM

This diagram shows the variations that occur in the power level of the RF waves during the reception through earth station’s antenna and its down conversion through the Down Converter.

The power received by the antenna is at -150dbm power level; as it goes through various stages of amplifications,

its final level at the demodulator reaches -27dbm.

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SATELLITE PAYLOADSEvery satellite is composed of a bus—that is, the set of systems that keep it going—and a payload that accomplishes its mission. The bus plays a supporting role; its functions include power generation and distribution, attitude control, and propulsion.

On a communication satellite, the payload is the communication subsystem, which carries out the communications mission (receiving and transmitting information). The payload of a communication satellite has one or more antennas, receivers, and transmitters, as well as hardware and software that perform some information processing.

V.H.R.R. (Very High Resolution Radiometer)

It operates in three bands, visible, infrared and near infra red called water vapour. Visible channel provide resolution of 2 Km X 2Km and 8X8 Km in infra red region and water vapour.

It has 3 types of scanning modes: normal scan (14 deg. In N-S and 20 deg. E-W), full scan (20 deg. X 20 deg.) and sector scan.

Normal mode scan completes in 23 min’s, full scan mode in 33 min’s The VHRR data rate and format shall be complited with the existing ground system for data

reception and processing.

V.H.R.R. ELECTRONICS The VHRR electronics onboard the spacecraft shall convert the analog image into digital form

after which the auxiliary data shall be inserted into the data stream and transmitted to earth. The electronics shall have total redundancy (including detector electronics). Data conversion equipments interfacing with its 4 GHz transmitter shall be self-contained with

adequate redundancy. The linearity and accuracy of electronics equipments should be such that they do not degrade the

basic accuracy and linearity of optical and detector system. The VHRR data shall be transmitted to the earth station in real time.

Schematic of V.H.R.R. Payload

1. METSAT VHRR works in the three spectral bands: visible, water vapor (W.V.) and thermal (T.I.R.).

2. The patch on which IR detectors were placed had to be carefully controlled at 100K for proper functioning of IR channel. VHRR patch area, which is exposed to the space on the northern face of the

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spacecraft, was heated from 12 to 19 September (approx. for 168h), so that the contaminants from the spacecraft outgasssing do not condense and settle in the IR detector area.

3. In addition to the VHRR, METSAT also carries a DRT for collection of meteorological data from the unattended data collection platforms to meteorological data utilization centre (M.D.U.C), India Meteorological Department, Delhi.

Table 1. Imaging modes of METSAT V.H.R.R. payload

Imaging Mode Coverage Repeatability in (mins)Full scan 20° N–S and 20° E–W 33Normal scan 14° N–S and 20° E–W 23Sector scan 4.5° N–S and 20° E–W 23 (3 times)

Table 2. V.H.R.R. specifications

Channel Number of detectors Modulation transfer function

Dynamic Range Noise Performance

Visible Four with four redundant

>0.23 approx. 0-100% albedo 6:1 min at 2.5% albedo

Thermal One with one redundant

>0.21 approx. 4-340K 0.25 K at 300 K

Water Vapor One with one redundant

>0.21 approx. 4-320K 0.5 K at 300 K

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C.C.D.

A charge coupled device (CCD) is an analog shift register that enables the transportation of analog signal (electric charges) through successive stages (capacitors), controlled by a clock signal. “CCD” refers to the way that the image signals is read out from the chip. Under the control of an external circuit, each capacitor can transfer its electric charge to one or another of its neighbors. It is used in photography & astronomy.

Basics of operation:

In a CCD for capturing images, there is a photoactive region (an epitaxial layer of silicon), and a transmission region made out of a shift register (the CCD, properly speaking). An image is projected through a lens onto the capacitor array (the photoactive region), causing each capacitor to accumulate an electric charge proportional to the light intensity at that location.

Once the array has been exposed to the image, a control circuit causes each capacitor to transfer its contents to its neighbor (operating as a shift register). The last capacitor in the array dumps its charge into a charge amplifier, which converts the charge into a voltage.

By repeating this process, the controlling circuit converts the entire contents of the array in the semiconductor to a sequence of voltages. In a digital device, these voltages are then sampled, digitized, and usually stored in memory; in an analog device (such as an analog video camera), they are processed into a continuous analog signal (e.g. by feeding the output of the charge amplifier into a low-pass filter) which is then processed and fed out to other circuits for transmission, recording, or other processing.

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Use in meteorology:

The CCD works on three detectors:

I. Visible (0.6 um - 0.68um)II. Near IR (0.77um – 0.86um)

III. Short wave IR (1.55um-1.69um)

CCD PAYLOAD PERFORMANCE REQUIREMENTS

1.) MODES OF OPERATION AND FRAME TIME: The payload shall have

the capability of operating in two modes:

a.) NORMAL MODE:

In this mode of operation, the payload covers about 9.5°. In the North-South direction (from 40° North to 15° South latitude); while the East-West coverage is 50° longitude centered on India. The scan time for normal mode will be about 25 minutes.

b.) PROGRAM MODE:

Program mode produces 10° (East-West) by N*0.5° (1<N<3), (N being integer); North-South image with provision to position the image anywhere in the frame of 20*20° with 0.5° step. The sector scan shall continue to scan the same sector M(1<M<3), (M being integer) times. Time taken for a sector to be scanned once shall be about N minutes. N and M shall be selectable by ground command. The rate of positioning for such sector scans within the normal frame shall be at least 10 times the step rate.

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2.)SPECTRAL BANDS:

The CCD Payload system shall be capable of imaging simultaneously in the following spectral bands:

a.) VISIBLE CHANNEL

The bandwidth of the visible channel shall be such that:

i. 50% of maximum response shall be at 0.62±0.02 micrometer and 0.68±0.02 micrometer.

ii. Both 5% and 80% response points of the sensor output shall be 0.01 micrometers or less from the corresponding 50% response point.

iii. The response of the sensor shall not be less than the 80% response value for any points between 80% response points, stated in (ii) above.

iv. For a solar spectrum input defined in Spectral Distribution table, the visible channel output signal beyond 5% response points on either side shall be less than 3% of the integrated signal between 5% response points for the same radiance input.

b.) NEAR INFRARED CHANNEL

The bandwidth of the NIR channel shall be such that

i. 50% of maximum response shall be at 0.77±0.02 micrometer and 0.86±0.02 micrometer.

ii. Both 5% and 80% response points of the sensor output shall be 0.015 micrometers or less from the corresponding 50% response point.

iii. The response of the sensor shall not be less than the 80% response value for any points between 80% response points, stated in (ii) above.

iv. For a solar spectrum input defined in Spectral Distribution table, the visible channel output signal beyond 5% response points on either side shall be less than 3% of the integrated signal between 5% response points for the same radiance input.

c.) SHORTWAVE INFRARED CHANNEL

i. 50% of maximum response shall be at 1.55±0.02 micrometer and 1.69±0.02 micrometer.

ii. Both 5% and 80% response points of the sensor output shall be 0.02 micrometers or less from the corresponding 50% response point.

iii. The response of the sensor shall not be less than the 80% response value for any points between 80% response points, stated in (ii) above.

iv. For a solar spectrum input defined in Spectral Distribution table, the visible channel output signal beyond 5% response points on either side shall be less than 3% of the integrated signal between 5% response points for the same radiance input.

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d.) RESPONSE MATCH:

Where more than one detector are used for any channel, the spectral response for all the detectors for a particular channel shall be within the tolerance specified earlier and the sensor output shall be the same within 10% for the same radiance input.

3.) RESOLUTION: The system shall have an instantaneous geometric field of view (IFOV);

so as to produce an element of not more than 1*1 km for all three channels at the sub-satellite point from the geo-stationary orbit.

The IFOV is defined as the angular distance between the two closest angles at which the channel response to a slit source of width less than 20% of the theoretical IFOV and aligned perpendicular to the detector edge is 50% of the peak response of the channel during the scan. The voltage response to the light source at ant angular distance from the centre of the IFOV equal to or greater than 2 IFOV shall be 5% or less of the maximum response when in the field of view in both the direction.

TABLE 7.1

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μm L(W/M²-ster-μm)

0.30 4.9

0.32 6.8

0.34 8.3

0.36 9.2

0.38 9.8

0.40 12.3

0.42 15.3

0.44 16.2

0.46 17.2

0.48 17.2

0.50 15.8

0.52 14.9

0.54 15.8

0.56 15.1

0.58 14.9

0.62 13.9

0.64 13.2

0.66 12.7

4.)SPECTRAL DISTRIBUTION

Spectral distribution of energy in the solar radiation incident on the Earth’s upper atmosphere when the Earth as at its mean distance from the Sun. These values correspond to 2.5% reflectance.

5.)MODULATION TRANSFER FUNCTION

The modulation transfer function of the overall system shall not be less than 0.21 for all channels. These values shall be attained both in the scan and cross scan directions.

6.)CCD PAYLOAD ELECTRONICS The CCD Payload electronics onboard the spacecraft shall convert the analog image data into digital form after which the auxiliary data shall be inserted into the data stream and transmitted to Earth.The following auxiliary data shall be included in the data stream:

i. Scan mode and offset status.ii. Line identification.

iii. Scanner/electronic temperature.iv. Spacecraft altitude sensor data.v. Spacecraft TM data.

The CCD Payload data transmitted from the spacecraft shall be such that when received on ground it could be processed by adding only time and ephemeris data regarding spacecraft position in space obtained from the Master Control Facility (MCF) of the INSAT 2 system. The data for all channels shall be digitized to at least 256 levels (8 bits/sample).

CCD PAYLOAD SPECIFICATIONS

S. No. Specification Data Value

1. Spatial Resolution 1Km×1Km

2. Frame Size 10°×10°.

3. Frame Time 23 minutes.

4. Repetivity 30 minutes.

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5. Data Rate 1.3 Mbps.

6. Integration time 10.4 ms.

7. M.T.F. >0.23 all bands.

8. S.N.R.(at 100% Albedo)At 2.5%Albedo

>3.

9. Target Power Consumption ~40 Watts (regulated) average.

10. Target Weight 45.0 Kg.

11. Spectral Bands(type)

Band 1: 0.63-0.69 micron.Band 2: 0.77-0.86 micron.Band 3: 1.55-1.70 micron.

12. Detector Linear Si CCD array for Bands 1 & 2.Linear Si CCD array for Bands 3.

13. Digitization 10 bits.

14. Special Features E-W offset capability. Commendable Gain

Selection independently for the three bands.

Smaller frame size.

DATA RELAY TRANSPONDER (DRT)

The DRT on board INSAT/METSAT receives the data bursts at 402.75 MHz from AWS, down converts 28 MHz,

filters and up converts to the down-link frequency of 4506.05 MHz in case of KALPANA-1 satellite, amplifies

and transmits towards the Earth.DRT is on board and is part of INSAT.

It consists of the following components:

1. UHF receiving antenna for 402.75 MHz

2. Down converter (402.75 to 28 MHz)

3. Filter

4. Up converter (28 to 4506.05) MHz

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5. Power amplifier

6. Transmitting antenna

PARAMETERS OF SATELLITE COMMUNICATION (MATHEMATICAL ANALYSIS)

BACK OFF LOSS :

High- power amplifier used in the earth station transmitter and the travelling wave tubes typically used in satellite transponders are non-linear tubes.

There gain is independent on input signal, the amount of output level is back off from rated levels is the equivalent to the loss & is approximately called “back of loss”.

TRANSMIT POWER AND BIT ENERGY:

To operate as efficiently as possible a power amplifier should be as close as possible to saturation. The saturated output power is designated P0 (sat) or simply pt.

The output power of a typical satellite earth station transmitter is much higher than the output from the terrestrial microwave power amplifier.

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Consequently, when dealing with satellite system, Pt is generally expressed in dBW rather than dbm.

Most modern satellite system either use phase shift keying (FSK) or QAM (quadrature amplitude modulation) rather than conventional FM modulation. With PSK and QAM. The input baseband is generally a PCM encoded, time-division multiplexed signal that is digital in nature.

Also, with PSK and QAM, several bits may be encoded in a single transmit signaling element. Consequent, a parameter more meaningful than carrier power is “energy per bit Eb”

where Eb = energy of a single bit

Pt = total saturated output power

Tb = time of a single bit

EFFECTIVE ISOTROPICALLY RADIATED POWER (EIRP):

Effective isotropically radiated power as an equivalent transmit power and is expressed mathematically as –

Where, Pin = antenna input power

At = transmit antenna gain

Expressed as a log,

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Eb = Pt*Tb

EIRP = Pin* At

EIRP (dBW) = Pin (dBW) + At (dB)

EQUIVALENT NOISE TEMPERATURE :

With territorial microwave systems, the noise introduced in a receiver or a component within a receiver is commonly specified by a parameter noise figure.

In satellite communication system, it is necessary to differentiate systems, it is necessary to differentiate or measure noise in increments as small as a tenth or a hundredth for precise calculations.

Consequently, it is common to use environmental temperature (T) and equivalent noise temperature (Te) when evaluating the performance of a satellite system. Total noise power was expressed mathematically as-

NOISE DENSITY

Noise density (N0) is the noise power normalized to 1-Hz bandwidth, or present in a 1-Hz bandwidth. Mathematically, noise density is

Where, N0 = noise density (watts per hertz) = 1 joule per cycle

N = total noise power (watts)

B = Boltzmann’s constant (joules per Kelvin)

Te = equivalent noise temperature (Kelvin)

CARRIER TO NOISE DENSITY :

C/N0 is the average wideband carrier power-to-noise density ratio. The wideband carrier power is the combined power of the carrier and its associated sidebands.

The noise density is the thermal noise present in a normalized 1-Hz bandwidth. The carrier-to-noise density ratio also is written as a function of noise temperature. Mathematically-

ENERGY OF BIT TO NOISE DENSITY RATIO :

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T = N/KB

N0 = N/B = (KTeB)/B = KTe

C/N0 = C/KTe

Eb/N0 is the most important and most often used parameters when evaluating a digital

system. The Eb/Nb is the equivalent way to compare digital system that use different transmission rates, modulation schemes, or encoding techniques. Mathematically, Eb/N0

is

Eb/N0 is a convenient term used for digital system calculation and performance comparisons, but in the real world, it is more convenient to measure the wideband carrier power-to-noise density ratio and convert it to Eb /N0. rearranging above equation:

The Eb/N0 ratio is the product of carrier-to-noise ratio (C/N) and the noise bandwidth-to-bit rate ratio (B/fb) expressed as a log,

GAIN TO EQUIVALENT NOISE TEMPERATURE RATIO :

Gain-to-eq. noise temperature ratio (G/Te) is a figure of merit used to represents the quality of a satellite or an earth station receiver.

The G/Te of a receiver is the ratio of the receive antenna gain to the equivalent noise temperature (Te) of the receiver.

Because of the extremely small receiver carrier powers typically located at the feed point of the antenna.

When the antenna plus the gain of the LNA to the equivalent noise temperature. Mathematically, gain-to-eq. noise temperature ratio is.

Expressed in logs, we have

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Eb/N0 = (c/fb) / (N/B) = CB/Nfb

Eb/N0 = (C/N) * (B/fb)

Eb/N0 (dB) = (C/N) (dB) + (B/fb) (dB)

G/Te = {Ar + A (LNA)} /Te

G/Te (dB/K) = {Ar (dB) + A (LNA) (dB)} – Te (dBK)

G/Te is a useful parameter for determining the Eb/N0 and C/N ratios at the satellite transponder and earth station receivers. G/Te is essentially the only parameter required at a satellite or an earth station receiver when completing a link budget.

DOWN-LINK BUDGET ANALYSIS When evaluating the performance of digital satellite system, the uplink and downlink

parameters are first considered separately, & then the overall performance is determined by combining them in proper manner.

In our project we are only considering the reception from satellite, hence only downlink equation is used which considers the ideal gain and loss and effects of thermal noise associated earth- station receiver.

DOWN-LINK EQUATION

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C/N0 = EIRP (dBW) – Lp (dB) + G / Te (dB/K) – K (dBWK)

Where, EIRP = effective Isotropic Radiated Power Lp = Free Space Path Loss G/Te = gain to noise temperature ratio K = Boltzmann’s constant

SYSTEM PARAMETER GRAPHS

To determine the system parameters the following graphs have been used which are as follows:

Fig-1: Determination of C/N ration

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P(e) performance of M-ary PSK, QAM, QPR and M-ary APK coherent systems. The rms C/N is specified in the double sided Nyquist bandwidth.FIG-2 : Determination of Eb/N0 ratio

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FIG-3 : Determination of Antenna Gain

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Antenna gain on the gain eqn. for a parabolic antenna:

Where D = antenna diameter W.V = wavelength N = antenna efficiency = 0.55

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A (dB) = {10 log n (3.14 D/W.V) 2 }

FIG-4 : Determination of free space path loss (Lp)

Free space path loss (Lp) determine from:

Elevation angle = 900, Distance = 35930 Km

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Lp = 183.5 + 20 log f (GHz)

CALCULTION FOR SYSTEM PARMETERS AND DOWNLINK BUDGET ANALYSIS

EFFECTIVE ISOTROPIC RADIATED POWER (EIRP) :

EIRP = 22.0 Db for CCD of INSAT – 3A, the value is given for each payload of satellite.

FREE SPACE PATH LOSS (Lp) :

Lp = 183.5 + 20logf (GHz),Here f = 4.5 GHz (given) Lp = 183.5 + 20log (4.5) So,

The calculated value of Lp can be verified using graph no. 4 which gives the characteristics of relation between free space path loss and frequency in GHz.

DATA RATE:

A data rate is the rate at which the signals are being received at the earth station unit. This rate varies with payloads. Egg- data rate of CCD is 1.28875 mbps

Eb/N0 :

Energy of one bit it noise density ratio at error is

Here B is bandwidth Fb is bit rateC/N can be calculated by using graph 1 & for BPSK, B = fb = 20 MHz, in log:

Eb/N0 = (C/N) + (B/fb) = 10.8 + 10log ((20*10^6)/ (20*10^6))

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Lp = 196.5 dB = 197.0 dB

Eb/N0 = (C/N) * (B/fb)

Eb/N0 = 10.8 dB

At bit error of 10^-6

DEMODULATION IMPLIMENTATION MARGIN : This value is

predetermined & is a constant value. Here we have taken this margin as 2.0 dB.

Eb/N0 RATIO : Now, EB/N0 ratio would be the sum of the calculated value & demodulated margin.

Hence, Eb/N0 = 10.8 + 2.0

C/N0 RATIO : carrier to noise density ratio. The required C/N0 ratio is predetermined & has a value of 73.9 dBHz.

CALCULATED C/N0 RATIO :

C/N0 = EIRP – Lp + G/Te – K = 22.0 – 197.0 + 26 – (-228.5)

Here, k – Boltzmann’s constant G/Te – antenna gain to noise temperature Now, G (dB) = 10log = 10log [(10.55)*((3.14*610) / (6.659)) ^2] = 46.5dB In log, G/Te = G- Te = 46.5 – 20

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Eb/N0 = 12.8dB

C/N0 = 79.6dBH

G/Te = 26.5 dB

DOWNLINK BUDGET’S FOR PAYOADS

INSAT- 3A (V.H.R.R)

Satellite EIRP 18.0 dBW FREE SPACE PATH LOSS (4.5 GHz) 197.0 dB DATA RATE 526.5 kbpsEb/N0,(required at bit error of 10^-6) 10.8 dBDEMODULATION IMPLIMENTATION MARGIN 2.0 dBEb/N0 12.8 dBC/N0 70.0 dBHzG/Te (6.1 m antenna 46 dB, T system 100 deg. K, 5 deg. elevation)

46 – 20 = 26 dB/K

C/N0 : EIRP – Lp + G/Te – K 75.6 dBHzREQUIRED C/N0 70.0 dBHzMARGIN 5.6 dB

INSAT-3A (C.C.D)

Satellite EIRP 22.0 dBW FREE SPACE PATH LOSS (4.5 GHz) 197.0 dB DATA RATE 1.28875kbpsEb/N0,(required at bit error of 10^-6) 10.8 dBDEMODULATION IMPLIMENTATION MARGIN 2.0 dBEb/N0 12.8 dBC/N0 73.9 dBHzG/Te (6.1 m antenna 46 dB, T system 100 deg. K, 5 deg. elevation)

46 – 20 = 26 dB/K

C/N0 : EIRP – Lp + G/Te – K 79.6 dBHzREQUIRED C/N0 73.9 dBHzMARGIN 5.7 dB

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KALPANA-1 (V.H.R.R)

Satellite EIRP 18.0 dBW FREE SPACE PATH LOSS (4.5 GHz) 197.0 dB DATA RATE 526.5 kbpsEb/N0,(required at bit error of 10^-6) 10.8 dBDEMODULATION IMPLIMENTATION MARGIN 2.0 dBEb/N0 12.8 dBC/N0 70.0 dBHzG/Te (6.1 m antenna 46 dB, T system 100 deg. K, 5 deg. elevation)

46 – 20 = 26 dB/K

C/N0 : EIRP – Lp + G/Te – K 75.6 dBHzREQUIRED C/N0 70.0 dBHzMARGIN 5.6 dB

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ACTIVITY

SPECTRUM ANALYSIS DIFFERENT METEOROLOGICAL PAYLOADS CARRIERS

The spectrum analysis of different meteorological payloads of INSAT-3A and KALPANA-I is done to study the

characteristics of the received data at different stages. The different figures obtained can be summarized as:

SATELLITE PARAMETERS (E.S.U.)

SATELLITES LOCATION LOOK ANGLE (º) SIZE OF

ANTENNA

INSAT-3A 93.5º E (Longitude)AZ = 148.5

EL = 52.16.1 meter

KALPANA-I 74º E (longitude)AZ = 168.0

EL = 56.47.5 meter

SATELLITES MET. PAYLOAD R.F. (MHz) I.F.(MHz) DATA RATE

INSAT-3AVHRR

CCD

DRT

SAR

4501.5

4508.9

4504.5

4505.7

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77.4

72.75

74.22

526.5 kbps

1.28875 Mbps

4.8 kbps

KALPANA-IVHRR

DRT

4503.5

4506

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74.5

526.5 kbps

4.8 kbps

The above data is now shown in the form of actual graphical representation. These graphs have been obtained by

using a spectrum analyzer.

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Automatic weather station

An automatic weather station (AWS) is an automated version of the traditional weather station, either to save human labor or to enable measurements from remote areas. An AWS will typically consist of a weather-proof enclosure containing the data logger, rechargeable battery, telemetry (optional) and the meteorological sensors with an attached

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Solar panel or wind turbine and mounted upon a mast. The specific configuration may vary due to the purpose of the system. The system may report in near real time via the Argos System and the Global Telecommunications System, or save the data for later recovery. In the past automatic weather stations were often placed where electricity and communication lines were available. Nowadays, the solar panel, wind turbine and mobile phone technology have made it possible to have wireless AWSs that are not connected to the electrical grid or telecommunications network.

Sensors

Most automatic weather stations have

Thermometer for measuring temperature Anemometer for measuring wind speed

Wind vane for measuring wind direction

Hygrometer for measuring humidity

Barometer for measuring pressure

Some of them even have

Ceilometers for measuring cloud height Rain gauge for measuring rainfall

Present weather sensor and/or visibility sensor

Unlike manual weather stations, automatic weather stations cannot report the class and amount of clouds. Also, precipitation measurements are difficult, especially for snow as the gauge must empty itself between observations. For present weather, all phenomena which do not touch the sensor, such as fog patches, remain unobserved.

A weather station is a set of weather measuring instruments operated by a private individual, club, association, or even business (where obtaining and distributing weather data is not a part of the entity's business operation). The quality and number of instruments can vary widely, and placement of the instruments, so important to obtaining accurate, meaningful, and comparable data, can also be very variable.

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Typical instrumentation includes an anemometer and wind vane, thermometer, hygrometer (for obtaining relative humidity), barometer, and rain gauge. More sophisticated stations may also measure the ultraviolet index, solar radiation, leaf wetness, soil moisture, soil temperature, water temperature in ponds, lakes, creeks, or rivers, and occasionally other data. Today's personal weather stations also typically involve a digital console that provides readouts of the data being collected. These consoles may interface to a personal computer where data can be displayed, stored, and uploaded to Web sites or data ingestion/distribution systems.

Personal weather stations may be operated solely for the enjoyment and education of the owner, but many personal weather station operators also share their data with others, either by manually compiling data and distributing it, or through use of the Internet or amateur radio. The Citizen Weather Observer Program (CWOP) is one such, and the data submitted through use of software, a personal computer, and internet connection (or amateur radio) are utilized by the National Weather Service when generating forecast models, and by many other entities as well. Each weather station submitting data to CWOP will also have an individual web page that depicts the data submitted by that station. The Weather Underground Internet site is another popular destination for the submittal and sharing of data with others around the world. As with CWOP, each station submitting data to The Weather Underground has a unique web page displaying their submitted data.

FUTURE SATELLITE FOR IMD SAT-MAT

It is an exclusive mission designed for enhanced meteorological observations and monitoring of land and ocean surfaces for weather forecasting and disaster warning. The three axis stabilized geostationary satellite is to carry two meteorological instruments: a six channel imager and an IR sounder along with the channel in visible, middle infrared, and water vapor and thermal infrared bands, the imager includes a SWIR channel for wider applications. The sounder will have eighteen narrow spectral channels in three IR bands in addition to a channel in visible bands.

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INSAT-3D is configured around standard 2000 kg 12k spacecraft bus with 7-years life. Several innovative technologies like on-the-fly correction of scan mirror pointing errors, biannual law rotation of spacecraft, micro stepping SADA, star sensors and integrated bus management unit have been incorporated to meet the stringent payloads requirements like pointing accuracies, thermal management of IR detectors and concurrent operation of both instruments.

Payloads of INSAT-3D ARE:

6-channle imager 19-channle sounder for obtaining data on vertical temperature profiles.

Services which would be provided by INSAT-3D:

Rainfall Sea surface temperature Clouds classification Cloud motion vectors (visible & infrared) and water vapor winds Vertical profiles of temperature, humidity & ozone Objective technique for estimation of intensity & position of tropical cyclones Assimilation of satellite data in global & regional numerical weather prediction

models.

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WESDIS interests include rainfall, aerosols, vegetation, health, sea surface temperature, clouds & winds.

Provision of source program along with the algorithm will result in easy implementation of generating the products from INSAT-3D which can be quickly made operational.

Once INSAT-3D is launched, algorithms will run on test sample data sets to derive products. Testing of products using in situational data is expected to provide a diagnostic understanding on the performance of the algorithms & their limitations. Further collaboration is envisioned in constant updating of research & derivation of products from future similar satellites.

Important feature of INSAT-3D

Nation India Type/application Meteorology

Operator INSATContractor ISROEquipment 19-channle sounder, a 6-channle imager,

DRT & SAR payloadsConfiguration Insat-2/-3 bus

Propulsion 440 Newton thrust liquid spogee motorLife time 7-years

Orbit Geostationary

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SATELLITE TRANSMITTER TO RECEIVER LINK WITH TYPICAL LOSSES AND NOISE SOURCES

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