A Review of the Range and Geophysical Corrections for Altimetry Studies over Inland Water
Fernandes, M. Joana1; Scharroo, Remko2; Lazaro, Clara1; Nunes, Alexandra L.3; Bos, Machiel4
1Univ. Porto; CIIMAR, PORTUGAL; 2Altimetrics LLC, UNITED STATES; 3ISEP-IPP; CIIMAR-UP, PORTUGAL; 4CIIMAR, PORTUGAL
Although primarily designed for ocean and ice studies, satellite radar altimetry has been successfully used in the monitoring of continental water surfaces. Being freely available and due to its all-weather, day and night capability, it may be the only source of information in some remote areas.
A correct handling of the range and geophysical corrections is of major importance for hydrological studies, in parallel with the improvement of the range estimates from dedicated retracking.
The determination of lake or sea surface height above some reference surface requires the measured radar distance to be corrected for a number of effects to account for the interaction of the radar signal with the atmosphere and with the water surface, and a number of geophysical effects such as tides. This study addresses the main issues associated with the range and geophysical corrections that shall be applied to the radar altimetry measurements over continental water bodies.
For inland water studies using satellite radar altimetry, the most relevant corrections are those from the troposphere (dry and wet), from the ionosphere and tides (solid earth and ocean tide loading).
In contrast to the ocean domain, inland water studies require the handling of height dependent dry and wet tropospheric corrections. Since most radar altimeter products have been designed for oceanographic purposes, they often fail to provide valid corrections over continental water regions. The major problems related with the height dependence of tropospheric corrections and land contamination on the onboard microwave radiometer will be discussed, identifying the main sources of error and suggesting suitable approaches. For example, while over the ocean the dry tropospheric correction is one of the most precise range corrections (better than 1 cm), in some of the present altimeter products it is the correction with the largest errors for inland water studies, up to several decimetres. Although the emphasis is put on the tropospheric corrections, the main issues related with the other range and geophysical corrections will also be summarised, in particular for the ionosphere, sea state bias and tides.