A data compression algorithm for the LRPT direct broadcast link on future polar orbit missions

The LRPT (Low Rate Picture Transmission), a new direct-broadcast digital link standard, will first appear on the ESA MetOp-1 satellite and will provide an overall 72 Kbps bandwidth. The main user of this link will be the AVHRR-3 (Advanced Very High Resolution Radiometer) instrument, a push-broom, 6 channels, multispectral imager producing data at a rate of 600 Kbps. In order to fit the allocated bandwidth of 40 Kbps a data compression algorithm was designed. The selected algorithm is a modified version of the JPEG standard in which a nonlinear rate control loop provides a quasi-fixed output data rate at the expense of a modest computation overhead. This paper describes the selected algorithm together with some optimisation issues. Also, the results of the algorithm implementation on the ADSP21020 processor (which is now available in rad-hard technology) are presented.