Determination of Local Empirical Covariance Functions from Residual Terrain Reduced Altimeter Data
Abstract
Local empirical covariance functions have been estimated from cross- over adjusted high-pass filtered SEASAT/GEOS-3 altimeter data in three local 2 x 2 deg areas in the North Atlantic ocean. The high-pass filtering was needed in order to remove remaining long wavelength parts of the gravity field due to errors in the spherical harmonic expansion that was used, and effects from sea surface topography and correlated parts of radial orbit errors. After a subtraction of noise variances geoid height variances associated with harmonic degrees above 180 of 0.213 sq.m, 0.112 sq.m, and 1.217 sq.m were obtained in the three local areas respectively. Then residual terrain effects were computed from Airy-Heiskanen isostatic earth models using Fourier techniques and SYNBAPS bathymetry. The depths of compensation were increased in order to simulate regional Vening Meinesz models. Comparisons of altimetric and bathymetric geoid heights showed that the magnitudes of the unmodelled parts of the gravity fields practically were unaffected by changes in the depths of compensation from 50 km to 70 km. Estimations of local empirical covariance functions from the terrain reduced altimetry showed that the geoid height variances were reduced by about 3 dB, and 9 dB to values of 0.096 sq.m, 0.108 sq.m. and 0.147 sq.m respectively. The variances have hereby decreased to about the same level. Finally Tscherning/ Rapp covariance function models were adjusted to fit the empirical covariance values.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1988
- Accession Number
- ADA208678
Entities
People
- Per Knudsen
Organizations
- Ohio State University