First Earth Observation images compressed by the new FAPEC-CILLIC algorithm onboard ESA’s OPS-SAT
The European Space Agency (ESA) launched OPS-SAT on 18 December 2019 into a circular, polar orbit at 515 km altitude.
OPS-SAT is a technology demonstration nanosatellite based on the cubesat standard. The satellite is only 30cm x 10cm x 10cm, but it brings powerful technology and instrumentation onboard, such as a fine Attitude Determination Control System, a GPS receiver, an X-band transmitter (up to 50 Mbps downlink) or a Software Defined Radio front-end.
It also includes a high-performance data processing platform (based on a dual-core ARM Cortex-A9 processor) and a high-resolution camera (based on an RGB Bayer filter) with a bit depth of 12 bits per pixel and a ground resolution of up to 80m x 80m per pixel.
When preparing for this mission, ESA issued a call for experimenters willing to test their technologies in orbit. One of the submitted (and accepted) experiments is the FAPEC data compression software – a versatile and efficient solution for lossless and lossy compression of images and of a large variety of instrumental data.
FAPEC is already being used by a satellite constellation to compress payload data onboard. However, its image compression capabilities had not been demonstrated in orbit yet. Furthermore, FAPEC was recently improved with a new image decorrelation algorithm (named CILLIC), presented at the ESA/CNES On-Board Payload Data Compression workshop (OBPDC) on 22 September 2020. FAPEC, with its CILLIC configuration, offers lossless and lossy image compression performances similar to those achieved by wavelet transforms but at a fraction of their computational cost.
On 28 November 2020, FAPEC was uploaded to OPS-SAT. The day after, and for the very first time in orbit, it was invoked by the payload data processing system to compress two images of our planet taken from Space.
Each of the two images, with a resolution of 4 Mpix and weighting 7.6 MB, were reduced to nearly 800 KB in about 0.8 seconds in a single computing thread.
Once received on ground, they were “de-bayered” with the ImageJ software to obtain the original colour images, which are shown below.
First FAPEC-compressed images from ESA’s OPS-SAT. The colour pictures shown here have been obtained by applying a standard de-bayer algorithm on ground, without any colour correction or white balancing in this case.
Shortly after this, more images were acquired and, again, compressed with FAPEC to be later downlinked to the ground station. These ones better illustrate the high resolution of the camera:
Some of the Earth Observation images acquired by ESA’s OPS-SAT and compressed by FAPEC onboard. In this case, some colour correction (white balancing) was applied.
With this, FAPEC has been the first user non-ESA experiment to be activated onboard OPS-SAT, achieving two important goals. First, it demonstrates the feasibility of uploading and activating new experiments onboard this technology demonstration mission. And second, thanks to the efficient collaboration with ESA and OPS-SAT experts, it can provide an interesting data compression service to other experimenters having to download many images from the satellite.
FAPEC is an excellent data compression solution especially for cubesat-based missions, which use to have strong limitations in onboard computing capabilities and in the downlink. The highly optimized, versatile and portable FAPEC software allows for an agile integration in the payload data handling system while offering a compression throughput comparable to hardware-based solutions. Even satellites with just a low-range onboard computer can use it. Science return of EO missions can significantly be increased in this way.
- OBPDC’20 and CILLIC:
Disclaimer: The view expressed herein can in no way be taken to reflect the official opinion of the European Space Agency.