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Development of an airborne geiod mapping system for coastal oceanography

Exploitable results

To study the dynamic sea surface topography, large progress has been achieved with the performance of satellite missions like ERS-1 and ERS-2. But there are still deficiencies in coastal areas (islands, shoals, local tides, etc), and in the polar regions (covered by sea ice and only partly covered by satellite observations). In addition, satellite missions can not recover the short and ultra-short waves (1 to 200 km) of the Earth's gravity field. To overcome these drawbacks an additional flexible, fast and cost saving system has become necessary. The new airborne gravity and altimetry system is based on most advanced sensor technology (accelerometer, laser and radar altimeter, global positioning system (GPS), inertial navigation system (INS)) for gravity and sea surface height data acquisition. Because of the homogeneity of these data, they are well suited for assimilation with satellite data to develop more detailed geoid and sea surface models in regions of interest. First demonstration projects and a full application project has been performed. The obtained results reveal an accuracy at the 5 to 10 cm level regarding geoid (distance depending), and +/- 2 mGal (20 µm/s{2}) with 6 km spatial resolution regarding gravity anomalies. This is derived from a comparison with available data, and simultaneous shipborne ground truth measurements (gravity, acoustic Doppler current profiler (ADCP), CTD). The airborne and shipborne measurements along the ERS-2 and Topex and Poseidon tracks allowed a direct comparison of the different techniques and show the advantages of each system. To increase the number of potential users, the employment of the airplane based system can be offered for geophysical objectives in the field of geodynamics research or resource exploration. The hardware can be operated over sea as well as over land (including deserts, polar regions), therefore bridging important data gaps.
To study the dynamic sea-surface topography, large progress has been achieved with the performance of satellite missions like ERS-1 and ERS-2. But there are still defi-ciencies in coastal areas (islands, shoals, local tides etc.), and in the polar regions (covered by sea ice and only partly covered by satellite observations). In addition, satellite missions can not recover the short and ultra-short waves (1 ... 200 km) of the Earth´s gravity field. To overcome this drawbacks an addi-tional flexible, fast and cost saving system has become necessary. The new airborne gravity/altimetry system is based on most advanced sensor technology (accelerometer, laser and radar altimeter, GPS, INS) for gravity and sea surface height data acquisition. Because of the homoge-neity of these data, they are well suited for assimilation with satellite data to develop more detailed geoid and sea surface models in regions of interest. First demonstration projects (Skagerrak/1996, Fram Strait/1997) and a full applica-tion project (Azores/1997) has been performed. The obtained results reveal an accuracy at the 5 to 10 cm level regarding geoid (distance depending), and ±2 mGal (20 mm/s2) with 6 km spatial resolution regarding gravity anomalies. This is derived from a comparison with available data, and simultaneous shipborne "ground truth" measurements (gravity, ADCP, CTD). The airborne and shipborne measu-rements along the ERS-2 and Topex/Poseidon tracks allowed a direct comparison of the different techniques and show the advantages of each system. This new airborne system has defined a new state-of-the-art in airborne gravimetry with respect to accuracy and the spatial resolution. In future applications, a combination of the airborne geoid mapping system (Þ regional geoid with ± 5 cm) with satellite altimetry data (Þ instantaneous sea-surface height ±1 ... 3 cm with ENVISAT or Topex/Poseidon) can deliver the dynamic sea-surface topography within the subdecimeter level of accuracy.