What is the horizontal resolution of the TOPEX/Poseidon altimeters?
The measurement geometry and operation principles of the TOPEX Altimeter are very well described in D. B. Chelton, et als, “Pulse compression and sea level tracking in satellite altimetry”, J. Atmospheric and Oceanic Tech., Vol 6, #3, June 1989. The altimeter footprint for ocean applications (or other very flat surfaces, relief less than 100 m) is determined by the compressed pulse length (3.125 nsec), the satellite altitude, and the significant wave height. At the TOPEX altitude of 1335 km, the footprint diameter varies from 2.0 km at 0 m SWH (not very realistic) to 5.5 km at 3 m SWH (typical of open ocean) to 11.7 km at 15 m SWH (about the highest observed during the TOPEX mission). Measurement values are reported at approximately 1 per second, although high rate data at 10/sec are also given. In 1 sec the satellite nadir point moves about 6 km along the Earth’s surface. For land or ice applications, the beam width of the antenna may be important as returns may come from anywhere wit
