README_DH.txt

The file DH.grd is the height correction in mm as described in
Sandwell, D. T., and W. H. F. Smith, Slope Correction for Ocean Radar Altimetry, 
Journal of Geodesy, DOI 10.1007/s00190-014-0720-1, 2013.
http://topex.ucsd.edu/sandwell/publications/149.pdf

The file DH.grd is calculated for a nominal effective satellite altitude of 1000 km. The values in DH.grd are to be scaled by H_e/(1000 km), where H_e is the effective altitude of the satellite altimeter which is being corrected. For example, TOPEX has an effective altitude of 1112 km. To use DH.grd with TOPEX, multiply the values in DH.grd by 1.112.

This 3 May 2021 version of README_DH.txt by Eric W Leuliette updates the original version of 3 May 2017 by David T Sandwell. The update given here is to the effective elevations (H_e) given in Table 1 of the 2013 publication. This update uses revised mean altitudes (H) averaged over time for each mission. It also corrects a typo in the value for H_e provided for ERS-1/2, Envisat in the 2013 publication.

The revised and updated the effective elevations (H_e) of several altimeters are:

	                H(km)  H_e(km)
Seasat, Geosat	         797     708
ERS-1/2, Envisat, SARAL	 795     707
TOPEX, Jason-1/2/3	1347	1112
CryoSat-2 (LRM)          731     656
Sentinel-3 (PLRM)        813     721
HY-2                     971     843

Note that the slope correction applies to altimetry data processed with Low-Rate or Pseudo-Low-Rate retracking.

Note also that the correction should not be used with the mean sea surface models that have included the slope correction such as MSS_CNES_CLS-2015 or DTU18.