CryoSat-2 NRT issues remain

Gridded sea-ice thickness from near-real time CryoSat-2 data in October displays a few orbits with large thickness values in the Russian Arctic (see figure below). These are the result of an anomaly in the processing chain/input data and are under investigation. A temporary solution is to omit the orbits entirely from the daily orbit data until a fix has been developed.

The offline reprocessed (rep) CryoSat-2 data is not affected.

Update 04 Nov 2020 

The source of the issue has been identified as imprecise satellite altitude values (l1b parameter `alt_20_ku`) since some orbits rely on the predicted orbits (`vector_source: fos predicted`) instead of observed (`vector_source: doris_navigator`). Both orbit solutions differ from the final solution in the offline reprocessed L1b data (`vector_source: doris_precise`), but the altitude of the predicted orbit may vary in the orders of several meters with respect to the final solution. For some orbits this effect is non-linear and negatively effects the estimation of the sea-level anomaly which in turn impacts freeboard and thickness.

As a fix, orbit data with (`vector_source: fos predicted`) will be excluded from the processing leading to reduced data availability in the Russian Arctic.