Modern hyperspectral imaging systems are able to acquire far more data than can be downlinked from a spacecraft. Onboard data compression helps to alleviate this problem, but requires a system capable of power efficiency and high throughput. Software solutions have limited throughput performance and are power-hungry. Dedicated hardware solutions can provide both high throughput and power efficiency, while taking the load off of the main processor. Thus a hardware compression system was developed. The implementation uses a fieldprogrammable gate array (FPGA).
The implementation is based on the fast lossless (FL) compression algorithm reported in “Fast Lossless Compression of Multispectral-Image Data” (NPO-42517), NASA Tech Briefs, Vol. 30, No. 8 (August 2006), page 26, which achieves excellent compression performance and has low complexity. This algorithm performs predictive compression using an adaptive filtering method, and uses adaptive Golomb coding. The implementation also packetizes the coded data. The FL algorithm is well suited for implementation in hardware. In the FPGA implementation, one sample is compressed every clock cycle, which makes for a fast and practical realtime solution for space applications. Benefits of this implementation are:
• The underlying algorithm achieves a combination of low complexity and compression effectiveness that exceeds that of techniques currently in use.
• The algorithm requires no training data or other specific information about the nature of the spectral bands for a fixed instrument dynamic range.
• Hardware acceleration provides a throughput improvement of 10 to 100 times vs. the software implementation.
A prototype of the compressor is available in software, but it runs at a speed that does not meet spacecraft requirements. The hardware implementation targets the Xilinx Virtex IV FPGAs, and makes the use of this compressor practical for Earth satellites as well as beyond-Earth missions with hyperspectral instruments.