Abstract's details
Atmospheric corrections for altimetry studies over inland water
CoAuthors
Event: 2014 Ocean Surface Topography Science Team Meeting
Session: Science Results from Satellite Altimetry: Inland waters (multi-mission and long-term monitoring)
Presentation type: Type Oral
Contribution: PDF file
Abstract:
Originally designed for applications over the ocean, satellite altimetry has been proven to be a useful tool for hydrologic studies. Altimeter products, mainly conceived for oceanographic studies, often fail to provide atmospheric corrections suitable for studies over continental water bodies. Consequently, in various altimetric products the corrections are often not handled properly and in a consistent way.
This study addresses the main issues associated with the atmospheric corrections that need to be applied to the altimeter range to get precise water level heights. Rather than being a review of the relatively well-known issues, the main problems identified in the atmospheric corrections in most of the present altimetric products are discussed, identifying the main sources of error and suggesting suitable approaches.
Some of the addressed topics include:
1) Handling of the height dependence of the tropospheric corrections. In contrast to the ocean domain, inland water studies require the handling of height dependent dry and wet tropospheric corrections. While the dry tropospheric correction is one of the most precise range corrections over oceans (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. This is due to the fact that some products provide the correction at sea level instead of at surface level or, when provided at surface level, it may also contain large errors coming from the interpolation of surface pressure grids from numerical weather models. The correct handling of the dry correction from sea level pressure grids further reduced to surface height is presented.
2) Errors in the wet tropospheric correction related to the land contamination in the on-board microwave radiometer and inconsistencies in the handling of the correction derived from numerical weather models. The most suitable models for deriving this correction are discussed.
3) Issues associated with the uncertainty in the dual-frequency ionospheric correction due to the different land effects in the Ku and C (or S) bands and the ability to perform the necessary along-track smoothing of this correction. The most suitable models and climatologies are presented.
Examples illustrating the impact of these errors on water level measurements are given.
This study addresses the main issues associated with the atmospheric corrections that need to be applied to the altimeter range to get precise water level heights. Rather than being a review of the relatively well-known issues, the main problems identified in the atmospheric corrections in most of the present altimetric products are discussed, identifying the main sources of error and suggesting suitable approaches.
Some of the addressed topics include:
1) Handling of the height dependence of the tropospheric corrections. In contrast to the ocean domain, inland water studies require the handling of height dependent dry and wet tropospheric corrections. While the dry tropospheric correction is one of the most precise range corrections over oceans (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. This is due to the fact that some products provide the correction at sea level instead of at surface level or, when provided at surface level, it may also contain large errors coming from the interpolation of surface pressure grids from numerical weather models. The correct handling of the dry correction from sea level pressure grids further reduced to surface height is presented.
2) Errors in the wet tropospheric correction related to the land contamination in the on-board microwave radiometer and inconsistencies in the handling of the correction derived from numerical weather models. The most suitable models for deriving this correction are discussed.
3) Issues associated with the uncertainty in the dual-frequency ionospheric correction due to the different land effects in the Ku and C (or S) bands and the ability to perform the necessary along-track smoothing of this correction. The most suitable models and climatologies are presented.
Examples illustrating the impact of these errors on water level measurements are given.