10/12/2015 1 Synthetic Aperture Radar (SAR) Basics and Theory Dr. M Jahanzeb Malik B.E. (Civil Engg.), NED University, Pakistan M.Sc (Geo information science and Earth Observation), ITC-UT, The Netherlands PhD (Remote Sensing and Land Surface Modeling), ITC-UT, The Netherlands Remote Sensing (RS) Electromagnetic spectrum: Wave and frequencies used in RS Why microwave RS…? Independence of the Sun as a source of illumination: all-hour Ability to penetrate clouds, haze, dust (and to some extent rain): all-weather Ability to penetrate more deeply into vegetation, snow, soils then optical waves Microwave RS complements Optical RS MODIS Aqua 5-Aug, 10 R,G,B 5(NIR),1(R),4(G) PALSAR ALOS L-Band 5-Aug, 10
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10/12/2015
1
Synthetic Aperture Radar (SAR)
Basics and Theory
Dr. M Jahanzeb Malik
B.E. (Civil Engg.), NED University, Pakistan
M.Sc (Geo information science and Earth Observation), ITC-UT, The Netherlands
PhD (Remote Sensing and Land Surface Modeling), ITC-UT, The Netherlands
Remote Sensing (RS)
Electromagnetic
spectrum: Wave and
frequencies used in RS
Why microwave RS…?
Independence of the Sun as asource of illumination: all-hour
Ability to penetrate clouds, haze,dust (and to some extent rain):all-weather
Ability to penetrate moredeeply into vegetation, snow,soils then optical waves
Microwave RS complementsOptical RS
MODIS
Aqua
5-Aug, 10
R,G,B
5(NIR),1(R),4(G)
PALSAR
ALOS
L-Band
5-Aug, 10
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Microwave RS complements Optical RS
ALOS: PALSAR, HH
ALOS: AVNIR, (R,G,B): (NIR,R,G)
Nawabshah/ Dadu, Sindh, Pakistan
Microwave RS complements Optical RS
Envisat, ASAR, WSM, C-Band, VV
01-Mar, 2006
Tibet, China
Basic operation of RADAR
RADAR: RAdio Detection And Ranging
Spaceborne radar RS
Radar Altimeters: measure the round trip time delay totargets to determine their distance from the sensor (e.g.,SIRAL on CryoSat-2)
Radar Scattromters: make measurements of the amount ofenergy backscattered from targets (e.g., Seawinds onQuikSCAT)
Synthetic Aperture Radars (SAR): measure the round triptime and amount of energy backscattered from targets (e.g.,TerraSAR-X, COSMO-SkyMed,RADARSAT)
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Imaging geometry of Side Looking RADAR
or pulse width
Bandwidth (B) = 1/τ
Common angles in radar imaging
slant range: the range along the radar line of sight, and
ground range: range from the nadir track along a smooth surface (the ground) to the
scatterer.
The incidence angle is the angle between the radar beam and ground surface
The look angle is the angle at which the radar looks at the surface
What does RADAR measure? Backscattering coefficient
units of m²
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Spatial resolution
What is spatial resolution…?
the size of the smallest possible feature that can be
detected
RS in visible region:
For a homogeneous feature to be detected, its size
generally has to be equal to or larger than the IFOV.
If the feature is smaller than this, it cannot be detectable
as the average brightness of all features in that IFOV will
be recorded
Road
IFOV IFOV
Spatial resolution
SLAR Case:
Slant range resolution
Ground range resolution
Along-track (or azimuth)
resolution
=pulse duration
Range resolution
In designing the signal pattern for a radar sensor, there is
usually a strong requirement to have as much energy as
possible in each pulse in order to enhance the signal-to-
noise ratio (SNR)
This can be done by increasing the transmitted peak
power or by using a longer pulse
peak power is usually strongly limited by the available
power sources
an increased pulse length, which leads to a worse range