Workshop on Radio Frequencies for Meteorology Earth Exploration-Satellite Service - Active...

Workshop on Radio

Frequencies for Meteorology

Earth Exploration-Satellite Service - Earth Exploration-Satellite Service - Active Spaceborne Remote Sensing and Active Spaceborne Remote Sensing and

OperationsOperations

Bryan HUNEYCUTT (NASA/JPL)

WMO, Geneva, Switzerland7 October 2002

Oil Spills SAR Image of anSAR Image of anOil Slick on the OceanOil Slick on the Ocean

FloodsFloods

SAR Image ofSAR Image ofMissouri River Flood, 1993Missouri River Flood, 1993

Earthquakes

SAR Interferogram ofSAR Interferogram ofSurface DisplacementSurface Displacement

Along Earthquake FaultAlong Earthquake Fault

EARTH-IMAGING RADAR SATELLITE MISSION

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Frequencies for Meteorology Active Sensor TypesActive Sensor Types

• SYNTHETIC APERTURE RADARS - Sensors looking to one side of nadir track, collecting phase and time history of coherent radar echo from which typically can be produced a radar image or topographical map of the Earth surface

• ALTIMETERS - Sensors looking at nadir, measuring the precise time between a transmit event and receive event to extract the precise altitude of ocean surface

• SCATTEROMETERS - Sensors looking at various aspects to the sides of the nadir track, using the measurement of the return echo power variation with aspect angle to determine wind direction and speed on Earth ocean surface

• PRECIPITATION RADARS - Sensors scanning perpendicular to nadir track, measuring the radar echo from rainfall to determine the rainfall rate over Earth surface, usually concentrating on the tropics

• CLOUD PROFILE RADARS - Sensors looking at nadir, measuring the radar echo return from clouds, to determine cloud reflectivity profile over Earth surface

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Frequencies for Meteorology ACTIVE SENSOR AND ACTIVE SENSOR AND SERVICE DEFINITIONSSERVICE DEFINITIONS

Active Sensor: a measuring instrument in the Earth exploration-satellite service or in the space research service by means of which information is obtained by transmission and reception of radio waves (RR)

Earth Exploration-Satellite Service: a radiocommunication service between earth stations and one or more space stations, which may include links between space stations, in which:

- information relating to the characteristics of the Earth and its natural phenomena including data relating to the state of the environment is obtained from active sensors or passive sensors on earth satellite;

- similar information is collected from airborne or earth-based platforms;

- such information may be distributed to earth stations within the system concerned

Space Research Service: a radiocommunications service in which spacecraft or other objects in space are used for scientific or technological research purposes

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Frequencies for Meteorology Active Sensors Applications Active Sensors Applications by Sensor Typeby Sensor Type

Active Sensor Type

Active Sensor Applications

SARS Low frequency SARs can provide knowledge of deep and undercanopy soil moisture which is critical for several Earth science disciplines and public welfare and policy making processes. These applications in-clude, but are not limited to: long-term weather forecasts, studying the long- and short-term climate varia-tions through quantifying elements of the energy and water cycle, for Carbon cycle science studies, and for studies and management of underground water resources and aquifers.

Atimeters The data obtained by radar altimeters will be used to study ocean dynamics and their effects on climatology and meteorology. Dual frequency altimeters also operate at 5.3 GHz to provide data to compensate for uncertainties in height measurements caused by ionospheric effects on the 13.5 GHz measurement. The radar altimeter will provide precise measurements of the distance from the satellite to the Earth’s surface and also of the power and the shape of the returned echoes from ocean, ice and land surfaces, eventually allowing us to improve our knowledge of climatology and environmental change detection.

Scatterometers Scatterometers will measure surface wind speeds and directions over at least 90% of the oceans every two days in all weather and cloud conditions. Winds are a critical factor in determining regional weather pat-terns and global climate. Scatterometers will play a key role in scientists efforts to understand and predict complex global weather patterns and climate systems.

Precipitation Radars

One precipitation radar is the first space mission dedicated to measuring tropical and subtropical rainfall using several microwave and visible/infrared sensors. Major objectives of the PR are 1) to provide a 3-dimensional rainfall structure, 2) to achieve quantitative rainfall measurement over land as well as over ocean, and 3) to improve the accuracy of a microwave imager measurement by providing the rain structure information.

Cloud Profiling Radars

The cloud profiling radar has been widely recognized as a key sensor to measure global distribution of clouds, which is a critical issue in understanding the cloud role in earth’s radiation budget and thereby predicting the global warming. The objective of spaceborne CPR is to measure global three –dimensional cloud distribution. The clouds which always cover about half area of the whole earth surface, play a sig-nificant and complicated role in the earth’s radiation budget. Especially, the vertical structure of clouds is a critical parameter to decide whether clouds contribute to warming or cooling of the atmosphere.

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Frequencies for Meteorology Active Sensor Active Sensor

CharacteristicsCharacteristicsSensor Types Characteristics

SAR Altimeter Scatterometer Precipitation Radar

Cloud Radar

Viewing Geometry

Side-looking @20-55 deg off nadir

Nadir-looking

(1) Six fan beams in azimuth (2) Two conical scanning beams

Nadir-looking Nadir-looking

Footprint/ Dynamics

(1) Fixed to one side

(2) ScanSAR

Fixed at nadir

1.0 Fixed in azimuth

(2) Scanning

Scanning across nadir track

Fixed at nadir

Antenna Beam Fan beam Pencil beam (1) Fan beams

(2) Pencil beams

Pencil beam Pencil beam

Radiated Peak Power

1500-8000 W 20 W 100-5000 W 600 W 1000-1500 W

Waveform Linear FM pulses

Linear FM pulses

Interrupted CW or

Short Pulses

Short pulses Short pulses

Spectrum Width

20-300 MHz 320 MHz 5- 80 kHz 0.6 MHz 300 kHz

Duty Factor 1-5 % 46 % 31 % 2 % 1-14 %

Service Area Land/coastal/ Ocean Ocean/Ice Ocean/Ice/Land Land/Ocean Land/Ocean

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Frequencies for Meteorology Active Sensor ExamplesActive Sensor Examples

SAR-Radar Image Honolulu,HI

Altimeter-Sea Level

Cloud Radar-Cloud Reflectivity Profile

Scatterometer-Wind Speeds

Precipitation Radar-Rain Rates

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Frequencies for Meteorology Synthetic Aperture Radars Synthetic Aperture Radars

(SARs)(SARs)

v

h

s

X a

Chirp Spectrum

SAR Illumination

Swath

• Provide radar images of the Earth’s surface

• RF center frequency depends on the Earth’s surface interaction with the EM field

• RF bandwidth affects the resolution of the image pixels

• Allowable image pixel quality degradation determines allowable interference level

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Frequencies for Meteorology AltimetersAltimeters

(a)

(b)

(c)

(d) tr td

t

t

t t

t2

t1

• Provide altitude of the Earth’s ocean surface

• RF center frequency depends on the ocean surface interaction with the EM field

• Dual frequency operation allows ionospheric delay compensation

• TOPEX/POSEIDON uses frequencies around 13.6 GHz and 5.3 GHz

• Allowable height accuracy degradation determines the allowable interference level Illustration of Altimeter Return

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Frequencies for Meteorology ScatterometersScatterometers

• Provide the wind direction and speed over the Earth’s ocean surface

• RF center frequency depends on the ocean surface interaction with the EM field and its variation over aspect angle

• Narrow RF signal bandwidth provides the needed measurement cell resolution

• Allowable wind speed accuracy degradation determines the allowable interference level

0 40 80 120 150 200 240 280 320 360

30

15

10

5

0

5.5 ms Horizontal Polarization 5.5 ms Vertical Polarization12.8 ms Horizontal Polarization12.8 ms Vertical Polarization

-1

-1

-1

-1

12.8 ms -1

5.5 ms -1

HH

HH

VV

VV

Azim uth Angle (degrees)

Rad

io s

catt

erin

g C

oeffi

cie

nt (

dB)

Variation of Backscatter with Aspect

Angle

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Frequencies for Meteorology ScatterometersScatterometersSub-Satellite

Track

Sub-SatellitePoint

M onitorCells

175km

175km

600 km 600 km

Left Wind VectorSwath

Right Wind VectorSwath

-45 o

-65 o

-135 o

135 o

115 o

45 o

Sea W indsO rbit Track

800 km

Nadir Track

Cross Track

250 to 800 km Swath*

900 km

700 km

Nadir

46 Degree B eam

40 deg

NSCAT illuminates the Earth’s surface at several different fixed aspect angles

SEAWINDS scanning pencil beam illuminates scans at two different look angles from nadir, and scans 360 degrees about nadir in azimuth

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Frequencies for Meteorology Precipitation RadarsPrecipitation Radars• Provide precipitation rate over the Earth’s

surface, typically concentrating on rainfall in the tropics

• RF center frequency depends on the precipitation interaction with the EM field


• Tropical Rainfall Measurement Mission (TRMM) uses only 0.6 MHz RF bandwidth

• Allowable minimum precipitation reflectivity degradation determines the allowable interference level

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Frequencies for Meteorology Cloud Profile RadarsCloud Profile Radars

• Provide three dimension profile of cloud reflectivity over the Earth’s surface

• RF center frequency depends on the ocean surface interaction with the EM field and its variation over aspect angle

• Antennas with very low sidelobes so as to isolate the cloud return from the higher surface return illuminated by the sidelobes


• Allowable reflectivity accuracy degradation determines the allowable interference level

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Frequencies for Meteorology Active Sensor Active Sensor

Interference And Interference And Performance CriteriaPerformance Criteria

.

Sensor Type I/N Criteria Data Availability Criteria

Systematic Random

Synthetic Aperture Radar

Altimeter

Scatterometer

Precipitation Radar

Cloud Profile Radar

-6 dB

-3 dB

-5 dB

-10 dB

-10 dB

99 %

99 %

99 %

N/A

99 %

95 %

95 %

95 %

99.8 %

95 %

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Frequencies for Meteorology Typical Interference Typical Interference

Levels at Earth’s SurfaceLevels at Earth’s Surface

Parameter Sensor Type

SAR Altimeter Scatterometer Precipitation Radar

Cloud Radar

Radiated Power, W 1500 20 100 578 630

Antenna Gain, dB 36.4 43.3 34 47.7 63.4

Range, km 695 1344 1145 350 400

PFD, dB(W/m2) -59.67 -77.25 -78.17 -46.55 -31.64

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Frequencies for Meteorology Compatibility StudiesCompatibility Studies

Frequency Band (GHz)

User Objectives Allocation Status Allocation Needs Users Comments

0.420-0.470 Forest monitoring (biomass)

None PRIMARY or secondary P-band SAR WRC-99 agenda, Res. 712, Reslv 2

1.215-1.300 Wave structure, geology, soil moisture, interfer. (DEM)

PRIMARY RR NOs. 5.332 & 335

Same L-band SAR (JERS-1, SIR-C, PALSAR)

Subband 1270-1295 MHz for wind profilers

3.1-3.3 Geology Secondary PRIMARY S-band SAR, Altimeter (Envisat RA-2 second freq)

Interf. From shipborne radar to SAR

5.15-5.25 Geology, oceanography, sea ice, land use, interf. (DEM)

None PRIMARY High resolution radar altimeters (Jason)

Difficult sharing with NGSO FSS


PRIMARY RR NOs. 5.447D, 5.448A,B

PRIMARY SAR, scatterometers, altimeters (AMI, ASCAT, ASAR, ALT/dual, IKAR-N)

Compatibility analysis of sharing with wireless LAN systems


None PRIMARY Wideband SAR, altimeters

Compatibility analysis of sharing with wireless LAN systems

8.55-8.65 High resolution SAR applications (tactical) plus snow and ice

PRIMARY (WRC-97) RR NOs. 5.468 and 5.469

PRIMARY Not identified


PRIMARY RR NO. 5.476A

PRIMARY X-band SAR, Okean-( SLR


Secondary RR No. 5.479

Not identified Not identified

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Workshop on Radio

Frequencies for Meteorology Compatibility StudiesCompatibility Studies

Frequency Band (GHz)

User Objectives Allocation Status Allocation Needs Users Comments

13.25-13.75 Wind, ice, geoid PRIMARY RR NOs. 5.498A, 5.501A,B

PRIMARY Ku-band scatterometers, altimeters (NSCAT, ALT/dual, PR, R225, IKAR-D&N, RA, RA-2, DPR)

17.2-17.3 Vegetation, snow, rain, wind

PRIMARY RR NO. 5.513A

Rain radars, precipitation radar, scatterometers

24.05-24.25 Rain Secondary PRIMARY Rain radars, precipitation radars (IKAR-D&N)

35.5-36.0 Ice, wind, geoid, snow PRIMARY RR NO. 5.551A

Altimeters, scatterometers, precipitation radars (IKAR-N, DPR)

78-79 Altimetry (land and ice) at high spatial resolution

PRIMARY RR NO. 5.560

Radio altimeters

94.0-94.1 Cloud profiling PRIMARY RR NO. 5.562

PRIMARY Cloud profile radars (ESA CPR, CPR/NASA, IKAR-D&N)

Coordination with radioastronomers to avoid destructive main-to-main beam coupling

133.5-134 Cloud profiling PRIMARY RR NO. 5.562E

Cloud profile radars

237.9-238 Cloud profiling PRIMARY RR NO. 5.563E

Cloud profile radars

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Frequencies for Meteorology WRC’03 Issues/ConcernsWRC’03 Issues/ConcernsBANDS RES. OTHER SERVICES AGENDA ITEM

420-470 MHz Res. 727: 6 MHz for EESS (active) within 420-470 MHz; recognizes CPM-97 concluded incompatibility with terrestrial tracking radars

Fixed, mobile, radiolocation, amateur, mobile-satellite, meteorological satellite

1.38

1215-1300 MHz

Res. 606: New allocation for RNSS (space to Earth) in 1260-1300 MHz; need for pfd to protect radionavigation and radiolocation radars

EESS (active), radiolocation, SRS (active), amateur

1.15

5250-5570 MHz

Res. 736: Allocation to mobile service in 5150-5350 MHz and 5470-5725 MHz; allocation to fixed in 5250-5350 MHz in Region 3; additional allocation in 5460-5570 MHz for EESS (active); upgrading radiolocation in 5350-5650 MHz

EESS (active), radiolocation, SRS (active), aeronautical radionavigation, radionavigation, radionavigation maritime, amateur, space research (deep space)

1.5

35.5-36.0 GHz Res. 730: consider removal of restriction on 5.551A on spaceborne precipitation radars operating in EESS 35.5-35.6 GHz; consider studies with sharing feasible in 35.5-36.0 GHz

Meteorological Aids, EESS (active), radiolocation, SRS (active)

1.12

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Frequencies for Meteorology 420-470 MHZ BAND 420-470 MHZ BAND CURRENT STUDIESCURRENT STUDIES

The WRC-2003 resolution 727 resolves to consider provision of up to 6 MHz of frequency spectrum to the EESS (active) in the band 420-470 MHz.

Several studies from the spaceborne active sensor community has analyzed the interference from spaceborne SARs in the band 420-470 MHz into Earth stations, the radio amateur service, fixed service, and ISM equipment, concluding that although there may be occasional interference to the various other services, that the interference will be short in time and will have a very long interval of six months or longer and thus the affected service will not be rendered incapable of operating effectively; current studies include sharing analyses with terrestrial radars, military radiolocation systems, and amateur systems.

Another study by the the spaceborne active sensor community analyzes the interference levels of a lower power, lower sidelobe spaceborne SARs into the amateur and amateur satellite services and airborne radiolocation radars, offering that the SAR parameters can be chosen to reduce the interference level to acceptable levels. Mitigation techniques include lowering the antenna sidelobes in both azimuth and range, and lowering the average power with reduced backscatter sensitivity. Limiting operations to geographical regions, delineated by boxes of latitude, longitude may also be an option.

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Workshop on Radio

Frequencies for Meteorology 5460-5570 MHZ BAND 5460-5570 MHZ BAND CURRENT STUDIESCURRENT STUDIES

The WRC-2003 resolution 736 resolves to consider additional primary allocation for the EESS (active) and SRS (active) in the band 5460-5570 MHz.

For the 5460-5570 MHz band, the previous studies in the 5250-5460 MHz band showing

compatibility between spaceborne active sensors and the radiolocation/ radionavigation services, have been extended to the band 5460-5570 MHz.

For interference mitigation techniques as provided in the Rec. ITU-R SA.1280, the selection of

active spaceborne sensor emission characteristics can help to mitigate the interference potential to terrestrial radars. One consideration for this 5460-5570 MHz band is to use it for the wideband SARs with high time- bandwidth products, which tend to give high on-tune rejection factors and thereby lower the interference levels into terrestrial radars.

In addition, several studies from the spaceborne active sensor community have analyzed the

compatibility between spaceborne SARs in the band 5470-5570 MHz and wireless access systems including RLANs in the mobile service. The wider SAR bandwidths also give higher kTB system noise temperatures, allowing greater acceptable interference levels from other services, and further improves the sharing situation.

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