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Improved Processing of
the CASIE SAR Data
Craig Stringham and David Long
Microwave Earth Remote Sensing Laboratory
Brigham Young University

2. About CASIE
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Characterization of Arctic Sea
Ice Experiment
When: Summer of 2009
Where: Fram Strait region
Why: Investigate how well remote
sensing can detect changes in sea ice
How: Using satellite and Unmanned
Aircraft System(UAS) observations

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CASIE UAS
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NASA SIERRA UAS equipped
with:
— High-Res Video Camera
— Laser altimeter
— Temperature Sensors
— Pyranometers
— Spectrometers
— MicroASAR Synthetic
Aperture Radar

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About the microASAR
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• LFM-CW SAR
• Size: 22.1x18.5x4.6cm
weight: 2.5kg
power: <35W
• Pseudo-monostatic
• C-Band
• 80-200 MHz Bandwidth
• 90-1000m Operational
Altitude
• 300-2500m Swath width

5. Image Source http://rst.gsfc.nasa.gov/Sect14/Sect14_14.html
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Previous Images
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• Processed using RDA
• 1m Resolution
• ~1km ground swath
• Sparse motion data
collected

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Backprojection Introduction
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— Time domain matched filter
— Accounts for all flight
conditions
— Inherently creates
georectified images
— Allows for sub-aperture
processing
— Computationally intensive

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Introduction to CUDA
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— Massively parallel
processing
— 30 streaming
multiprocessors @ 1.45 GHz
— 8 single precision
processors
— 2 special function units
— 1 double precision
— 16 KB shared memory

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Initial Results
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RDA BP

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Motion Measurement
Alignment
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— Recorded GPS synchronized 0
range compressed data + gps altitude
by a software interrupt 50 100
100
— High-precision GPS aligned 150
80
to SAR data by
range(m)
200
60
— Interpolating GPS data to 250
match the PRF 300 40
— Fine tune using minimum 350
entropy of a small image 400 20
450
250 300 350 400
time(s)

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Results with Aligned GPS
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RDA BP

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Estimating the System Delay
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— System Delay 0
range compressed data + gps altitude
— Cable delay 50 100
— RF component delay 100
80
150
— Feed-through appears in
range(m)
dechirped data as a single 200
60
sinusoid 250
300 40
— Estimating the System 350
Delay 400 20
450
— Isolate the feed-through 250 300 350 400
component time(s)
— Estimate feed-through using
MUSIC algorithm

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Estimating the System Delay
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— System Delay 0
range compressed data + gps altitude
— Cable delay 50 100
— RF component delay 100
80
150
— Feed-through appears in
range(m)
dechirped data as a single 200
60
sinusoid 250
300 40
— Estimating the System 350
Delay 400 20
450
— Isolate the feed-through 250 300 350 400
component time(s)
— Estimate feed-through using
MUSIC algorithm

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Altitude Offset
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— The GPS altitude
measurement were highly
biased 0
range compressed data + gps altitude
50 100
— Altitude bias varies with 100
altitude 150
80
range(m)
200
60
— Surface height can be 250
estimated from nadir 300 40
return 350
400 20
450
250 300 350 400
time(s)

15. Correcting altitude using Nadir
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— Using an initial subjective
estimate of the bias select
Range compressed data
a window of RC data 100
150
200
250
Range(m)
300
350
400
450
250 300 350 400
Time(s)

16. Correcting altitude using Nadir
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— Using an initial subjective
estimate of the bias select
a window of RC data Range compressed data
100
Windowed maximum
— Find the maximum in that 150
window 200
250
Range(m)
300
350
400
450
250 300 350 400
Time(s)

17. Correcting altitude using Nadir
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— Using an initial subjective
estimate of the bias select
a window of RC data Range compressed data
100
Windowed maximum
— Find the maximum in that 150 Median Filtered maximum
window 200
250
Range(m)
— Median filter 300
350
400
450
250 300 350 400
Time(s)

18. Correcting altitude using Nadir
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— Using an initial subjective
estimate of the bias select range compressed data + gps altitude
a window of RC data 100
150
— Find the maximum in that
200
window
250
Range(m)
— Median filter 300
350
— Correct GPS altitude using 400
linear error model 450
250 300 350 400
Time(s)

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Results with Altitude and
System Delay corrections
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BP without altitide BP with altitude
correction correction

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RDA Image (old)
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Back-projected Image
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Conclusions
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— Well focused images for the CASIE SAR data were
obtained using an external GPS record
— Processing of the full data set was made possible by the
GPU backprojection implementation
— Future work should be made to make images using
attitude information in the backprojection processing

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Special Thanks to:
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NASA
University of Colorado
Artemis
Brigham Young University