Outline: definition of remote sensing components of system electromagnetic radiation nature of...

Outline:Outline: definition of remote sensing

components of system

electromagnetic radiation

nature of an image

light interaction with atmosphere and surface

types of remote sensors

Remote Sensing

science and art of obtaining information about something from a distance.

analysis of collected data to obtain information about the objects, areas or phenomenon under investigation.

Remote Sensing

Components of System

propagation through the atmosphere

energy interactions with earth surface features

transmission through the atmosphere

Data Analysis:Data Analysis:

examining the data using various viewing and interpretation devices to analyze pictorial data and/or a computer to analyze digital sensor data (i.e. GIS).

Components of System

Energy Sources:Energy Sources:

energy available from sun is described by electromagnetic spectrum

Electromagnetic Radiation

Wavelength - distance from one wave crest to another.

Frequency - number of wave crests passing a fixed point in a given period of time. Measured in hertz (1 cycle per second)


Electromagnetic RadiationAmplitude - height of each peak. Measured as spectral irradiance

Ultraviolet Radiation - 0.4 micrometers

not much is done with UV for remote sensing since these shorter wavelengths are easily scattered by the atmosphere


Visible Radiation

BLUE (.4-.5 micrometers)

GREEN (.5-.6 micrometers)

RED (.6-.73 micrometers)


Infrared Radiation - .72 - 15 micrometers

1. Near Infrared - reflected, can be recorded on film

2. Mid Infrared - reflected, can be detected using electro-optical sensors.

3. Thermal Infrared - emitted, can only be detected using electro-optical sensors


Microwave Radiation - radar sensors, wavelengths range from 1mm to 1m


most systems rely on the sun to generate all the EM energy needed to image terrestrial surfaces - passive sensors.

other sensors generate their own energy, called active sensors, transmits that energy in a certain direction and records the portion reflected back by features within the signal path


atmospheric modification of incoming and outgoing EM radiation includes scattering, refraction and absorption

Light Interaction with Atmosphere

Scattering

redirection of light by particles

can be in any direction

General Effects of Scattering

causes skylight (allows us to see in shadow)

forces image to record the brightness of the atmosphere in addition to the target.

directs reflected light away from the sensor, decreasing spatial detail (fuzzy images)

tends to make dark objects lighter and light objects darker (reduces contrast)


Refraction

bending of light when it passes through two media

degrades spectral signatures on hot- humid days


Absorption

mostly caused by three atmospheric gases: ozone, carbon dioxide and water vapour


no attenuation attenuation

Reflection

the bouncing of electromagnetic energy from a surface

type of reflection is dependent on the size of the surface irregularities relative to the incident wavelength.

Light Interaction with Surface

1. Specular Reflectance

light is reflected in a single direction - 'mirror' reflection

specular reflectance helps and hinders remote sensing


2. Diffuse/Lambertian Reflectance

energy is reflected equally in all directions

many natural surfaces act as a diffuse reflector to some extent.


image – model target features described through the use of spectral reflectance

software and hardware specially designed to analyze these images give us the ability to see a pictorial rendition of targets.

images that we see on a computer screen are made up of picture elements called pixels.

Nature of the Image

Pixel - picture element having both spatial and spectral properties.

the spatial property defines the "on ground" height and width.

the spectral property defines the intensity of spectral response for a cell in a particular band

Nature of the image

Nature of the Image

when only one band of the EM spectrum is sensed, the output device (colour monitor) renders the pixels in shades of grey

Nature of the Image

multispectral sensors detect light reflectance in more than one or two bands of the EM spectrum. these bands represent different data - when combined into the red, green, blue guns of a color monitor, they form different colors

Nature of the Image

multispectral image is composed of 'n' rows and 'n' columns of pixels in each of three or more spectral bands

Nature of the Image

most common, versatile and economic form of remote sensing

spectral range 0.3 to 0.9 mm (visible portion of spectrum).

photogrammetry is the science, art and technology of obtaining reliable measurements, maps, other derived products from photographs.

Aerial Photography/Airphoto

AADVANTAGES OF DVANTAGES OF AAERIAL ERIAL

PPHOTOGRAPHYHOTOGRAPHY

Five Basic Advantages

Improved vantage point

Capability to stop action

Permanent recording

Broadened spectral sensitivity

Increased spatial resolution and geometric fidelity

camera produces a large-format 23x23cm photo

contain high precision/well calibrated lenses that minimize spatial distortions

motor-driven film advances – 60% overlap between successive exposures


panchromatic, black-and-white, true-colour film

Aerial Photography/Airphoto Grey scale step wedge

Notes

Altimeter

Fiducial marks

Clock

Lens serial number

Focal length

Frame number

Mission name and date

Airphoto – Saudi Arabia


advantages: improves vantage point, capability to stop action, permanent recording, broadened spectral sensitivity, increased spatial resolution.

disadvantages: can’t get at elevation, not appropriate for urban areas (tall buildings block information)

applications: land use/land cover mapping, geologic and soil mapping, agricultural application, forest applications, wildlife ecology, etc.


currently there are 2777 satellites orbiting the earth (US – 878)

multi-purpose:

scientific

defense

communications

global positioning system (GPS)

Satellite Remote Sensors

geostationary orbiting satellites are those that remain stationary relative to a point on the surface of the earth

i.e. communications and meteorological satellites



polar-orbiting satellites are those in which the position of the satellite’s orbital plane is kept constant relative to the sun.

i.e. Landsat satellite series

Passive Remote Sensing

measure natural radiation emitted by target or/and radiation energy from other sources reflected from the target

examples: passive microwave radiometers, LandSat, SPOT

AACTIVE VS CTIVE VS PPASSIVE ASSIVE RREMOTE EMOTE

SSENSINGENSING

AACTIVE VS CTIVE VS PPASSIVE ASSIVE RREMOTE EMOTE

SSENSINGENSING

Active Remote Sensing

transmit their own signal and measure the energy that is reflected or scattered back from the target

advantages: ability to “see” regardless of time of day or season; use wavelengths not part of solar spectrum; better control of the way target is illuminated

sensors that operate in the microwave portion of the spectrum

advantages: capable of penetrating atmosphere under virtually all conditions, different view of the environment.

disadvantage: radar instruments have a hard time identifying water bodies because the wavelength is much longer than the general character of the surface roughness

applications: sea ice and snow, geologic features, ocean bottom contours, other planets.

Microwave Sensors

Microwave radiometer – narrow-beam antenna attached to a scanning device

soil moisture, water content of snow, geologic strata

Synthetic Aperture Radar – shorter antenna that emits and receives returned energy from ground objects

day/night, clouds/cloud free operation

Microwave Sensors

RADARSAT

launched in November 1995

developed by Canada to monitor environmental change and the planet’s natural resources

heart is synthetic aperture radar (SAR) – microwave instrument that sends pulsed signals to earth and processes the received reflected pulses.

Microwave Sensors

First RADARSAT Image

Microwave Sensors

ERS-2 Vancouver Island

Microwave Sensors

European SAR

sensors that operate in the optical portion of spectrum, which extends from approximately 0.3 to 14 mm.

can do more with these data because it is numbers.

look at differences in colors

look at differences over time

applications: meteorological, ocean monitoring (i.e. chlorophyll absorption).

Optical Sensors

show how much energy from the sun was being reflected or emitted off the Earth's surface when the image was taken.

clear water reflects little radiation, so it looks black.

pavement and bare ground reflect a lot of radiation, so they look bright.

urban areas usually look light blue-grey.

vegetation absorbs visible light but reflects infrared, so it looks red

Optical Sensors

Optical image of Montreal area during ice storm of 1998. Icesnow and clouds appear as various colors of white, vegetationis green.

GOES - Geostationary Operational Environmental Satellite (Visible to NIR, Thermal)

DMSP - Defense Meterological Satellite Program 600 m resolution (Visible to NIR, Thermal), urban heat island studies

Nimbus - CZCS - coastal zone color scanner, 825 m spatial resolution

AVHRR - Advanced Very High Resolution Radiometer – meteorological satellite (visible, NIR, thermal)

Optical Sensors

AVHRR - Advanced Very High Resolution Radiometer – meteorological satellite (visible, NIR, thermal)

Channel Wavelength Primary Use1 0.58 - 0.68 Daytime cloud/surface mapping

2 0.725 - 1.10 Surface water delineation, ice and snow melt

3A 1.58 - 1.64 Snow / ice discrimination (NOAA K,L,M)

3 3.55 - 3.93 Sea surface temperature, nighttime cloud mapping

4 10.30 - 11.30 Sea surface temperature, day and night cloud mapping

5 11.50 - 12.50 Sea surface temperature, day and night cloud mapping

AVHRR Channels

LANDSAT - visible, NIR spectral bands (Landsats 1,2,3), and MIR and Thermal (Landsats 4 and 5)

Multispectral scanner - 4 spectral bands – Green, Red, and 2 NIR

Thematic mapper - 7 spectral bands – Blue/Green, Green, Red, NIR, MIR, MIR, Thermal

Optical Sensors

LANDSAT MSS image - Grand Canyon

LANDSAT TM image - southwestern Utah and Southern Nevada

SPOT Image of the WTC Fires

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