1. Compression for Synthetic Aperture Sonar Signals
Thomas Higdon
MDDSP
May 1, 2008

2. What is synthetic aperture processing?
Collect sensor data at a series of physical locations.
Aggregate the data and process it to form an image.

3. Typical SAS Image
Edge detection
Speckle noise reduction

4. Why compression is needed
Data for a typical sonar array might arrive at many megabytes/sec.
Storage on autonomous vehicles is limited.
Compression might allow data to be reasonably transmitted via underwater communication links.

5. SPIHT Wavelet transform-based
[Said, Pearlman,. 1996]
Wavelet transform-based
Transmits wavelet coefficients with more information first.
Capable of very low bit rates by recording only decisions made by the encoder.
Capable of arbitrary bit rates.

6. Basic SPIHT Algorithm ci,j – wavelet coefficients
μn – number of coefficients in the range

7. Spatial Orientation Tree
Each pixel has four descendants.
SPIHT uses each pixel’s descendants to decide if a pixel is significant.

8. Wavelet Packet Transform
Each subband is divided further, based on some metric.

9. Wavelet Packet Transform
The irregular tree structure makes the spatial orientation tree more complex than in traditional SPIHT.

10. 0.1 bpp, 80:1 compression

11. 0.1 bpp

12. .025 bpp 320:1 compression

13. .015 bpp, 533:1 compression

14. 0.05 bpp, 160:1 compression

15. 0.01 bpp 800:1 compression

16. PSNR

17. WSNR

18. UQI

19. Questions