Improved Processing of the CASIE SAR Data.pdf
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Transcript of Improved Processing of the CASIE SAR Data.pdf
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BRIGHAM YOUNG UNIVERSITY
Improved Processing of the CASIE SAR Data
Craig Stringham and David Long Microwave Earth Remote Sensing Laboratory
Brigham Young University
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BRIGHAM YOUNG UNIVERSITY About CASIE
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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BRIGHAM YOUNG UNIVERSITY CASIE UAS
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 • 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
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Image Source http://rst.gsfc.nasa.gov/Sect14/Sect14_14.html
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Previous Images • Processed using RDA • 1m Resolution • ~1km ground swath • Sparse motion data
collected
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BRIGHAM YOUNG UNIVERSITY Backprojection Introduction
� Time domain matched filter
� Accounts for all flight conditions
� Inherently creates georectified images
� Allows for sub-aperture processing
� Computationally intensive
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BRIGHAM YOUNG UNIVERSITY Introduction to CUDA
� 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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BRIGHAM YOUNG UNIVERSITY Initial Results RDA BP
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Motion Measurement Alignment
� Recorded GPS synchronized by a software interrupt
� High-precision GPS aligned to SAR data by � Interpolating GPS data to
match the PRF
� Fine tune using minimum entropy of a small image
time(s)
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range compressed data + gps altitude
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BRIGHAM YOUNG UNIVERSITY Results with Aligned GPS
RDA BP
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BRIGHAM YOUNG UNIVERSITY Estimating the System Delay
� System Delay � Cable delay � RF component delay
� Feed-through appears in dechirped data as a single sinusoid
� Estimating the System Delay � Isolate the feed-through
component
� Estimate feed-through using MUSIC algorithm
time(s)
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e(m
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range compressed data + gps altitude
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BRIGHAM YOUNG UNIVERSITY Estimating the System Delay
� System Delay � Cable delay � RF component delay
� Feed-through appears in dechirped data as a single sinusoid
� Estimating the System Delay � Isolate the feed-through
component
� Estimate feed-through using MUSIC algorithm
time(s)
rang
e(m
)
range compressed data + gps altitude
250 300 350 400
0
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BRIGHAM YOUNG UNIVERSITY Altitude Offset
� The GPS altitude measurement were highly biased
� Altitude bias varies with altitude
� Surface height can be estimated from nadir return
time(s)
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range compressed data + gps altitude
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BRIGHAM YOUNG UNIVERSITY Correcting altitude using Nadir
� Using an initial subjective estimate of the bias select a window of RC data
Time(s)
Ran
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Range compressed data
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BRIGHAM YOUNG UNIVERSITY Correcting altitude using Nadir
� Using an initial subjective estimate of the bias select a window of RC data
� Find the maximum in that window
Time(s)
Ran
ge(m
)
Range compressed data
250 300 350 400
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Windowed maximum
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BRIGHAM YOUNG UNIVERSITY Correcting altitude using Nadir
� Using an initial subjective estimate of the bias select a window of RC data
� Find the maximum in that window
� Median filter
Time(s)
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Range compressed data
250 300 350 400
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Windowed maximumMedian Filtered maximum
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BRIGHAM YOUNG UNIVERSITY Correcting altitude using Nadir
� Using an initial subjective estimate of the bias select a window of RC data
� Find the maximum in that window
� Median filter
� Correct GPS altitude using linear error model
Time(s)
Ran
ge(m
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range compressed data + gps altitude
250 300 350 400
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Results with Altitude and System Delay corrections
BP without altitide correction
BP with altitude correction
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BRIGHAM YOUNG UNIVERSITY RDA Image (old)
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BRIGHAM YOUNG UNIVERSITY Back-projected Image
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BRIGHAM YOUNG UNIVERSITY Conclusions
� 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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BRIGHAM YOUNG UNIVERSITY Special Thanks to:
NASA
University of Colorado
Artemis
Brigham Young University