The thesis describes and tests a method to combine satellite measurements of the geoid height with shipboard and terrestrial measurements of the freeair gravity anomally using Fourier transform techniques. Fast Fourier transforms can process very large data sets quickly but require the data to be available on a complete and regular grid. New methods were devised that grid altimeter and marine gravity data, and which remove the long-wavelength errors associated with these measurements. Satellite altimeter data distributed along widely spaced groundtracks are differenced along track to reduce long-wavelength orbit errors, and any repeat track observations are averaged to reduce time-dependent oceanographic noise. The ascending and descending along-track slopes are then gridded separately, using a kernel designed to extrapolate the observations smoothly into the gaps between tracks, while retaining the high along-track resolution of the data. The spectral properties of the gridding operation, were analysed by calculation of a transfer function. In a development of Sandwell's method, the grids of along-track slopes are transformed using vector algebra to grid-easting and -northing deflections of the vertical. Vertical deflection grids from any number of satellite missions may now be combined, then converted using Fourier techniques to give a grid of the geoid height. This grid is easily converted to a grid of the freeair anomaly. The effect of datum errors in the shipboard gravity data is also reduced by processing not gravity but along-track gravity gradient. An incomplete grid of freeair gravity anomalies is generated from the observed along-track gravity slopes, constrained by, and improving the altimeter-derived freeair anomaly grid. Land gravity measurements are interpolated directly onto a separate grid as there is no similar long-wavelength error in the data. The combination algorithm performs a weighted superposition of the geoid height and freeair anomaly grids in an iterative process, until self-consistent. The algorithms were first tested on a simulated dataset, extracted from accurate, high-resolution and self-consistent geoid and freeair anomaly models of the British Isles and North Sea. The geometry of real altimeter tracks from an area of equal size in the North Atlantic were superimposed on the British geoid, and simulated readings interpolated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653473 |
| Date | January 1996 |
| Creators | Kirby, Jonathan Frank |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15179 |
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