September 2006 1 SAR Processing Jeremy Nicoll
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September 2006 1
SAR Processing
Jeremy Nicoll
September 2006 2
Outline
• Sonar Echoes • Definitions• What do we measure?• Target detection• Convolution• Range compression• Azimuth Compression
September 2006 3
Hello!
Sonar Echoes
September 2006 4
Some definitions
Azimuth
Range
Swath
September 2006 5
What do we measure?
• At the satellite– Radar signal strength as a function of time
• After processing– Radar Cross Section per piece of dirt
September 2006 6
Target detection
September 2006 7
Target detection:Short pulse
• Power problem– We need a short pulse for resolution– We need a lot of power for detection
September 2006 8
Target detection:Long pulse
• Power problem– We need a short pulse for resolution– We need a lot of power for detection
September 2006 9
Target detection:Chirp
• Can go from low to high or high to low frequency• Can be much more complicated
September 2006 10
Target detection:Chirp pulse
September 2006 11
Convolution
• Run simulation
September 2006 12
Convolution:Constructive interference
27 28 29 30 31 32
ReceiveConvolutionTransmit
September 2006 13
Convolution:Destructive interference
27 28 29 30 31 32
ReceiveConvolutionTransmit
September 2006 14
Convolution
ReceiveConvolutionTransmit
September 2006 15
Range Compression
• Convolve the received range signal with the chirp you sent out.
• Range line looks similar to that of a short pulse –We have “compressed” the chirps in the signal to short pulses.
September 2006 16
Azimuth:Real Aperture Radar
• Good resolution in range, poor resolution in azimuth
September 2006 17
Azimuth:The Doppler effect
September 2006 18
Azimuth compression
• Carl Wiley, in 1951, observed that two point targets at different azimuth positions, will have distinct Doppler frequency shifts. [Curlander, McDonough, 1991]
• We can compress the pulse in azimuth in the same fashion we compressed it in range.
• Convolve an azimuth line with the azimuth reference function:
September 2006 19
Synthetic Aperture Radar
• Raw data
• Range compressed
• Azimuth compressed
September 2006 20
Range compression
• each element of the raw data is multiplied by the complex conjugate of the corresponding element of the range reference function
September 2006 21
Range compression
September 2006 22
Azimuth reference function
September 2006 23
Range cell migration
• range cell migration realigns all the returns for a single target into an appropriate single line of data
September 2006 24
Azimuth compression
• each element of the data is multiplied by the complex conjugate of the corresponding element of the azimuth reference function
September 2006 25
Range compression
September 2006 26
SAR training processor
September 2006 27
Input file selection menu
Choice of start lineprocessing data patch
Choice of Doppler parameters for processing
September 2006 28
Choice of performing steps during processing
Select to save individualintermediate product
Select to save allintermediate products
September 2006 29
Processing flow withdetailed description of respective processing step
September 2006 30
Preview of intermediateproduct
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