 Commission
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Study Group 2.3 Satellite altimetry: data quality improvement and coastal applications Exchange of software Publications of membersCheinway Hwang Dept of Civil Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 300, Taiwan
In a previous IAG SSG, namely, SSG3.186, members have put effort to develop best methodologies for deriving gravity anomaly, geoid, sea surface topography and bathymetry from satellite altimeter data. Despite some achievements, a number of problems in coastal applications of altimetry are not resolved. For example, altimeter data at the immediate vicinity of shores are eliminated due to bad quality. However, for purposes such as coastal geoid and gravity determinations, shallow-water tide modeling and coastal ocean circulation determination, such “bad” data are badly needed. Do we really need to eliminate these altimeter data? Can we improve the quality of coastal altimeter data and how? One important application of satellite altimetry is to determine local coastal geoid models. Coastal areas are largely heavily populated. Most countries in the world will need a high-precision coastal geoid model for purposes such as national vertical datum determination and connection (for countries with scattered islands), GPS leveling, coastal circulation study and coastal topography mapping. However, satellite altimetry alone cannot fulfill this need, and satellite and terrestrial gravity data (at land and sea) and elevation data (for terrain effects) should be included. The question is how to best combine these heterogeneous data. It has been shown that use of retracked altimetry can produce improved results in altimetric applications. Currently, only retracked ERS-1 altimetry is used for purposes such as marine geoid and gravity determinations in only a limited number of coastal areas (e.g., polar regions and the China Seas). Retracked altimetry can be also used in shallow-water tide modeling and sea surface topography determination for oceanography.. Another dense data set, namely, Geosat/GM, has not been retracked for coastal applications. The geodetic and earth science communities will surely benefit from a global set of combined retracked ERS-1 and Geosat/GM altimeter data. One objective of this current SSG will be to freely provide a database of retracked ERS-1 and Geosat/GM for members interested in applications of these retracked altimeter data.
1) Retrack global shallow-waters ERS-1 and Geosat/GM altimeter data and establish a database for members to use. 2) Investigate geophysical, geodetic and oceanographic signals with altimetric products using rates higher than 1 Hz. In addition to the radar altimetry, high-rate laser altimeter data from ICESat, which are not corrupted near coasts, will be used. Impact of using JASON-2 WSOA and CRYOSAT altimeter data will be investigated. 3) Improve models of geophysical corrections over shallow waters using, e.g., improved shallow-waters tide models, sea state bias estimates and tropospheric corrections and improve quality of altimeter data over shallow waters by, e.g., waveform retracking, adaptive filtering and outlier detection. Selected "difficult" regions of scientific interest such as the Hawaiian Ridges, the Cayman Trench, and the southeast Asia waters will be investigated. The improved models should be distributed to all members. 4) Combine coastal altimetry, satellite gravity, land gravity, marine gravity (shipborne or airborne) to enhance the accuracy of coastal geoid (at sea and land). 5) Combine altimetry data, LIDAR and remote sensing data for coastal bathymetry determination. LIDAR onboard an aircraft is able to determine ocean depths up to 50 m. Optical sensor data from, e.g., Landsat, can be used to determine depths at shallow waters, provided that a careful calibration is made. Here altimetry data help to determine bathymetry at the deeper part of the oceans. But how exactly do we combine them? 6) Define a standard, including theory and data type, to obtain the current best results in marine gravity, geoid and bathymetry from altimetry data. 7) Investigate the possibility of determining coastal ocean circulations from satellite altimetry and numerical modeling. 8) Create long-term averaged satellite altimetry database for geodetic purposes.
Geosat ERS-1 TOPEX/POSEIDON GEOSAT-FOLLOW-ON JASON-1 ENVISAT CRYOSAT Geosat ERS-1 TOPEX/POSEIDON
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