Altimeter Signal Processing 

Altimeter Signal Processing

As part of Steps 1 and 2 of the QA4EO Five Steps, namely define the measurand and document the traceability with a diagram, we need to consider where the measured signal comes from.

Any type of satellite altimeter measurement will require some level of processing from the raw signal to the final deliverable data product. Within the processing chain, calculations, assumptions, approximations or corrections will be made, and it is important to document those. Each step in the processing chain will introduce uncertainties associated with input data, any auxiliary information and the approximations and assumptions. 

The diagram below describes the core steps for data processing, as related to the altimeter, from raw onboard signal processing to corrections for sea state bias and ionosphere correction. Corrections relating to the atmosphere and tides are covered elsewhere (and not yet included in the uncertainty analysis. You can select highlighted sections of the diagram or use the buttons below to find out more about individual processes.

The top left section (light blue) relates to processing of the raw signal, mostly onboard the satellite, with the calibration of the waveforms performed in level 1 processing. The bottom left (grey section) represents how the model used in the retracker is derived and the assumptions that are built into the retracker and the final part of this diagram (yellow section) represents the processing of the wind speed, sea state bias correction and ionosphere correction.