Minimize Level-2

There are three main steps in the Level-2 processing chain:

  1. Compute time-derived geophysical/environmental parameters.
  2. Perform re-tracking and compute physical parameters.
  3. Compute Level-2 altimeter/radiometer geophysical processing. 

Computing time-derived geophysical parameters involves:

  • re-computing altitude, orbital altitude rate, location and Doppler correction, accounting for updated orbit data
  • computing ionospheric corrections
  • computing non-equilibrium and equilibrium ocean tide heights, tidal loading, solid earth tide height, equilibrium long period ocean tide height and pole tide height (using pole locations)
  • computing the height of the mean sea surface above the reference ellipsoid
  • computing the mean dynamic topography, the height of the geoid and the ocean depth/land elevation.

Performing retracking and computing physical parameters (LRM mode) involves:

  • performing ocean re-tracking to waveforms, estimating waveform altimetric parameters such as epoch, composite sigma, amplitude or square of the mis-pointing angle
  • computing 20 Hz altimeter range and backscatter coefficient
  • computing 1 Hz estimates of the altimeter range, composite sigma, backscatter coefficients and square of the off-nadir angle (Ku-band only)
  • computing 1 Hz physical parameters (SWH and modelled corrections for both bands) and correcting 1 Hz physical parameters.

Performing retracking and computing physical parameters (SAR mode) involves:

  • discriminating echoes (ocean/lead, sea-ice, ice sheet margin or ocean/coastal)
  • performing retracking (ocean/lead, sea-ice, ice sheet margin or ocean/coastal)
  • computing physical parameters
  • merging snow depth (ocean/lead and sea-ice only)
  • performing a short-arc, along track ocean interpolation (ocean/lead and sea-ice only)
  • estimating freeboards (ocean/lead and sea-ice only)
  • performing a latitude limit check (ocean/lead and sea-ice only)
  • performing modified slope correction (ice sheet margin and ocean/coastal only).

Level-2 altimeter/radiometer geophysical processing involves:

  • inputting and checking Level-1 MWR products
  • computing and correcting physical parameters according to platform data
  • interpolating MWR data and computing MWR geophysical parameters
  • computing altimeter wind speed and rain/ice flags
  • computing wind, tropospheric corrections and inverted barometer according to meteorological data
  • computing HF fluctuations of the sea surface topography
  • computing sea state bias
  • computing dual frequency ionospheric corrections
  • building and checking Level-2 SRAL/MWR products.