Radar Remote Sensing Group
Department of Electrical Engineering
University of Cape Town
Tel: +27 (0)21 - 650 2792
Fax: +27 (0)21 - 650 3465
The ERS-1 satellite is equipped with a wind scatterometer, which produces estimates of ocean surface wind speed and direction over a 500 km wide swath or strip across the Earth's surface. However, because of orbital constraints, the swaths do not overlap, resulting in large areas between swaths where no wind field measurements are available. Since wind field data is important for a number of oceanographic, meteorological and climate studies, this project investigated the feasibility of interpolating wind field measurements between swaths.
The following interpolation and smoothing techniques for spatial data were investigated and compared:
From the results obtained the conclusion was drawn that it is feasible to interpolate and extrapolate wind field measurements obtained from satellite scatterometers using Ordinary Kriging.
This project culminated in a journal publication with the following reference:
M.R. Inggs and R.T. Lord, "Interpolating Satellite Derived Wind Field Data Using Ordinary Kriging, with Application to the Nadir Gap," IEEE Transactions on Geoscience and Remote Sensing, vol. 34, no. 1, pp. 250-256, January 1996. tgrs96.pdf (315K)
This thesis describes three methods to process stepped-frequency waveforms, namely
In addition to using stepped-frequency waveforms for RFI suppression, a number of other techniques have been investigated to suppress RFI. Of these, the notch filter and the least mean squares (LMS) adaptive filter have been implemented and applied on real P-band data obtained from the E-SAR system of the German Aerospace Center (DLR), Oberpfaffenhofen, and on real VHF-band data obtained from the South African SAR (SASAR) system. Both methods significantly suppressed the RFI in the real images investigated.
It was found that the number of range lines upon which the LMS adaptive filter could operate without adaptively changing the filter tap weights was often well above 100. This facilitated the re-writing of the LMS adaptive filter in terms of an equivalent transfer function, which was then integrated with the range-compression stage of the range-Doppler SAR processing algorithm. Since the range-compression and the interference suppression could then be performed simultaneously, large computational savings were achieved.
A technique was derived for suppressing the sidelobes which arise as a result of the interference suppression of the LMS adaptive filter. This method was also integrated with the range-compression stage of the range-Doppler processor, leading to a very efficient implementation of the entire RFI suppression routine.
A pdf copy of the thesis can be obtained here (11MB). Other research outputs can be viewed in the list of Published Papers.
During my stay at the DLR I was involved with the development of synthetic aperture radar (SAR) processing algorithms for the future German TerraSAR-X remote sensing satellite, which will launch in 2006. TerraSAR-X is a high-resolution X-band SAR based on active phased array technology, which allows operation in StripMap, ScanSAR and SpotLight modes in different polarisations, with scientific and commercial applications.
My work concentrated on the development of a spaceborne SpotLight SAR simulator, which can accurately simulate raw SpotLight SAR data. This simulated data was used to analyse the characteristics of a SpotLight SAR processor, which was developed by a colleague at the DLR. Any approximations, which are made by this SpotLight SAR processor, could accurately be analysed with the simulated data, regarding their effects on the impulse response function (IRF) and the resulting processing accuracy. Even the effects of satellite steering errors (for example inaccurate yaw-steering) could be analysed. Simulation results of worst-case scenarios were produced in terms of satellite position (latitude and longitude) and antenna pointing direction (off-nadir angle).
During my stay I wrote a number of technical notes, or was co-author of technical notes. These notes summarise most of the work I was involved with, including a study on the absolute orbit accuracy requirements for the TerraSAR-X satellite, calculation of Kepler orbits to simulate the satellite trajectory, calculation of the Earth ellipsoid intersection given the antenna pointing vector, and an investigation of the SpotLight processor approximations.
I gained significant work experience at the DLR in the field of radar remote sensing, and it was a pleasure working together with a highly professional team on the TerraSAR-X project.