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

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

Typical SAS Image Edge detection Speckle noise reduction

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.

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.

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

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

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

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

0.1 bpp, 80:1 compression

JPEG @ 0.1 bpp

.025 bpp 320:1 compression

.015 bpp, 533:1 compression

0.05 bpp, 160:1 compression

0.01 bpp 800:1 compression

PSNR

WSNR

UQI

Questions