There are different data products associated with the three levels of processing of altimeter data:
The input data for Level-0 processing is the Instrument Source Packet (ISP). The ISP contains raw data expressed in instrument engineering units, not in international system (SI) units.
The input data for Level-1 processing are the Level-0 products. The main function of the Level-1 processing chain is to calculate the tracker range, the sigma0 scaling factor and the Level-1 waveforms, applying instrumental corrections to all of them.The Level-1 processing chain outputs three types of products: Level-1A , Level-1B-s and Level-1B products.
The input data for Level-2 processing are the Level-1 products. The first function of the Level-2 processing chain is to apply different re-tracking algorithms to the Level-1 waveforms to calculate the final altimeter range, backscatter coefficient, wind speed over ocean and SWH. There are different types of re-tracking algorithms according to the type of waveforms re-tracked (ocean, ice, sea-ice).
The Level-2 processing chain inputs are:
Figure 1: SRAL and MWR Level-1B Inputs and SRAL/MWR Level-2 Outputs (Credit: CLS)
The second function of the Level-2 processing chain is to compute and apply all geophysical corrections to the measurements. Examples of geophysical corrections are the tides or the reference surface used (e.g. geoid).