Export 3 results:
Sort by: [ Author  (Asc)] Title Type Year
A B C D E F G H I J K L M N O P Q R S T U V W X [Y] Z   [Show ALL]
Yale, MM, Sandwell DT.  1999.  Stacked global satellite gravity profiles. Geophysics. 64:1748-1755.   10.1190/1.1444680   AbstractWebsite

Gravity field recovery from satellite altimetry provides global marine coverage but lacks the accuracy and resolution needed for many exploration geophysics studies. The repeating ground tracks of the ERS-1/2, Geosat, and Topex/Poseidon altimeters offer the possibility of improving the accuracy and resolution of gravity anomalies along widely spaced (similar to 40-km spacing) tracks. However, complete ocean coverage is usually needed to convert the sea-surface height (br along-track slope) measurements into gravity anomalies. Here we develop and test a method for constructing stacked gravity profiles by using a published global gravity grid (Sandwell and Smith, 1997), V7.2, as a reference model for the slope-to-gravity anomaly conversion. The method is applied to stacks (averages) of Geosat/ERM (up to 62 cycles), ERS-1/2 (up to 43 cycles), and Topex (up to 142 cycles) satellite altimeter profiles. We assess the accuracies of the ERS-1/2 profiles through a comparison with a gravity model of the northern Gulf of Mexico (profiles provided by EDCON Inc.). The 40 ERS profiles evaluated have a mean rms difference of 3.77 mGal and full wavelength resolution (0.5 coherence) of 24 km. Our processing retains wavelengths as short as 10 km so smaller, large-amplitude features can be resolved, especially in shallow ocean areas (<1000 m deep). We provide an example of combining these higher resolution profiles with lower resolution gravity data in the Caspian Sea.

Yale, MM, Sandwell DT, Smith WHF.  1995.  Comparison of Along-Track Resolution of Stacked Geosat, Ers-1, and Topex Satellite Altimeters. Journal of Geophysical Research-Solid Earth. 100:15117-15127.   10.1029/95jb01308   AbstractWebsite

Cross-spectral analysis of repeat satellite altimeter profiles was performed to compare the along-track resolution capabilities of Geosat, ERS 1 and TOPEX data. Geophysical Data Records were edited, differentiated, low-pass-filtered, and resampled at 5 Hz. All available data were then loaded into three-dimensional files where repeat cycles were aligned 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-track resolution for individual cycles, eight-cycle-average profiles, and 31-cycle-average profiles (Geosat and TOPEX only). Coherence, which depends on signal to noise ratio, reflects factors such as seafloor gravity amplitude, regional seafloor depth, instrument noise, oceanographic noise, and the number of cycles available for stacking (averaging). Detailed resolution analyses are presented for two areas: the equatorial Atlantic, a region with high tectonic signal and low oceanographic 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 Pacific. Global maps of along-track resolution show considerable geographic variation. On average globally, the along-track resolution (0.5 coherence) of eight-cycle stacks are approximately the same, 28, 29, and 30 km for TOPEX, Geosat, and ERS 1, respectively. TOPEX 31-cycle stacks (22 km) resolve slightly shorter wavelengths than Geosat 31-cycle stacks (24 km). The stacked data, which are publicly available, will be used in future global gravity grids, and for detailed studies of mid-ocean ridge axes, fracture zones, sea mounts, and seafloor roughness.

Yale, M, Sandwell D, Herring A.  1998.  What are the limitations of satellite altimetry? The Leading Edge. 17:73-76.: Society of Exploration Geophysicists   10.1190/1.1437832   AbstractWebsite

Radar altimeter measurements of the marine geoid collected during the Seasat altimeter mission gave geophysicists hope of uncovering the gravity field over all the ocean basins. However, because of insufficient track density, it has taken 16 years for the full potential of the satellite altimeter to be realized. The high‐density coverage obtained by ERS-1 during its geodetic mapping phase (April 1994–March 1995) prompted the U.S. Navy to declassify all of the Geosat altimeter data in June 1995. The combination of these two high‐density data sets provided the first global view of all the ocean basins at a wavelength resolution of 20–30 km.