COMPARISON OF ALONG-TRACK RESOLUTION OF STACKED GEOSAT, ERS-1, AND TOPEX SATELLITE ALTIMETERS

Cross-spectral analysis of repeat satellite altimeter profiles was per formed to compare the along-track resolution capabilities of Geosat, E RS 1 and TOPEX data. Geophysical Data Records were edited, differentia ted, low-pass-filtered, and resampled at 5 Hz. All available data were then loaded into three-dimensional files where repeat cycles were ali gned along-track (62 cycles of Geosat/Exact Repeat Mission; 16 cycles of ERS 1, 35-day orbit; 73 cycles of TOPEX). The coherence versus wave number between pairs of repeat profiles was used to estimate along-tr ack resolution for individual cycles, eight-cycle-average profiles, an d 31-cycle-average profiles (Geosat and TOPEX only). Coherence, which depends on signal to noise ratio, reflects factors such as seafloor gr avity amplitude, regional seafloor depth, instrument noise, oceanograp hic noise, and the number of cycles available for stacking (averaging) . Detailed resolution analyses are presented for two areas: the equato rial Atlantic, a region with high tectonic signal and low oceanographi c noise; and the South Pacific, a region with low tectonic signal and high oceanographic variability. For all three altimeters, along-track resolution is better in the equatorial Atlantic than in the South Paci fic. Global maps of along-track resolution show considerable geographi c variation. On average globally, the along-track resolution (0.5 cohe rence) of eight-cycle stacks are approximately the same, 28, 29, and 3 0 km for TOPEX, Geosat, and ERS 1, respectively. TOPEX 31-cycle stacks (22 km) resolve slightly shorter wavelengths than Geosat 31-cycle sta cks (24 km). The stacked data, which are publicly available, will be u sed in future global gravity grids, and for detailed studies of mid-oc ean ridge axes, fracture zones, sea mounts, and seafloor roughness.