The Image Compression Unit (ICU) has been developed for high data rate Optical Earth Observation Satellites. The JPEG (ISO 10918) algorithm is used to compress the digital image data, with an additional output bit rate regulation for a direct adaptation to the telemetry channel.
The SPOT5 (1rst generation) ICU included 3 compression boards, 2 reordering boards, 1 control board and 1 DC converter.
The 2nd generation ICU reuses flight proven SPOT5 technologies: algorithm, mechanics, and ASICs, that are embedded in a higher integration design. Now, instead of 7 boards, the same SPOT5 ICU would have only 4 boards :2 reordering/compression,1 control and 1 DC converter. Several 2nd generation Flight Models ICUs have already been shipped to their customers.
Design features :
• Mechanically modular : a base plate supports the framed boards, tied together using proven Airbus Defence and Space modular mechanics.
• Functionally modular: one compression board performs all input, processing & output functions. Compression boards are added as needed by throughput.
• Versatility : bit rate control and microcontrol of compression are performed by firmware adaptable to each mission. All firmware and parameters are stored in in-flight reprogrammable EEPROM
Functional features : I/O
• Flexible (FPGA) reordering of input pixels order to form the channels to compress.
• redundant interfaces (at input, control and output) for full cross-strapping capability
• Single compressed output multiplex per board
• Serial TM and TC (compression ratio, parameter selection)
Functional features: Processing
• A compression channel produces compressed data at constant rate.
• JPEG compression with DCT transform, flat quantization, Huffman coding.
• The output bit rate control (CNES patent) adjusts the volume of each Line of 8*8 Blocks.
• Many possible configurations of number of compression channels and data rate per channel.
The ICU is based on 3 types of modules : the RCR Compression board, the Control board and the DC/DC power Converter
The RCR Compression board (see also RCR product sheet) includes the following functions :
• Reordering of up to 4 input data streams,
• 3 JPEG compression modules,
• 1 rate regulation module,
• 1 output multiplexer and formatter module
Typically, a pair of RCR boards can compress one 48 Mpel/s PAN channel and 4 (B0, B1, B2, B3) 6 Mpel/s multispectral channels.
High resolution Image compression for Earth Observation.
SPOT5 and export programmes.