Minimize Processing Levels

There are different data products associated with the three levels of processing of altimeter data:

  • Level-0 is the raw telemetered data
  • Level-1B is the Level-0 data corrected for instrumental and geometrical effects
  • Level-2 is the Level-1 data corrected for geophysical effects.


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:

  • one Level-1B SRAL product
  • one Level-1B MWR product
  • a set of dynamic ancillary or auxiliary data.

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).