The processing of hexagonally sampled signals with standard rectangular techniques: application to 2D large aperture synthesis interferometric radiometers
In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10-20 km, a radiometric resolution of 1 K and a revisit time of 1-3 days. Compared to total power radiometers aperture synthesis inter...
| Autores: | , , , |
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| Formato: | artículo |
| Fecha de publicación: | 1997 |
| País: | España |
| Recursos: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/1970 |
| Acesso em linha: | https://hdl.handle.net/2117/1970 |
| Access Level: | acceso abierto |
| Palavra-chave: | Radiometry Remote sensing Microwave measurements Radar Equipment and supplies Boundary layer (Meteorology) UHF measurement fast Fourier transforms geophysical signal processing geophysical techniques hydrological techniques moisture measurement oceanographic techniques radiometry remote sensing soil Fourier based iterative inversion UHF radiometry Y-shaped array brightness temperature distribution hexagonal sampling grid hexagonally sampled signal processing hydrology interferometric radiometry large aperture synthesis measurement technique ocean passive low frequency measurement radiowave emission sea surface salinity signal processing soil moisture spatial Fourier transform standard rectangular technique triangular-shaped array two dimensional method Radiometria Sensors remots Microones -- Mesurament Radar Capa límit (Meteorologia) Àrees temàtiques de la UPC::Enginyeria de la telecomunicació::Radiocomunicació i exploració electromagnètica::Teledetecció |
| Resumo: | In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10-20 km, a radiometric resolution of 1 K and a revisit time of 1-3 days. Compared to total power radiometers aperture synthesis interferometric radiometers are technologically attractive because of their reduced mass and hardware requirements. In this field it should be mentioned the one-dimensional (1D) linear interferometer ESTAR developed by NASA and MIRAS a two-dimensional (2D) Y-shaped interferometer currently under study by European Space Agency (ESA). Interferometer radiometers measure the correlation between pairs of nondirective antennas. Each complex correlation is a sample of the “visibility” function which, in the ideal case, is the spatial Fourier transform of the brightness temperature distribution. Since most receiver phase and amplitude errors can be hardware calibrated, Fourier based iterative inversion methods will be useful when antenna errors are small, their radiation voltage patterns are not too different, and mutual coupling is small. In order to minimize on-board hardware requirements-antennas, receivers and correlators-the choice of the interferometer array shape is of great importance since it determines the (u,v) sampling strategy and the minimum number of visibility samples required for a determined aliasing level. In this sense, Y-shaped and triangular-shaped arrays with equally spaced antennas are optimal. The main contribution of this paper is a technique that allows the authors to process the visibility samples over the hexagonal sampling grids given by Y-shaped and triangular-shaped arrays with standard rectangular FFT routines. Since no interpolation processes are involved, the risk of induced artifacts in the recovered brightness temperature over the wide held of view required in Earth observation missions is minimized and signal to noise ratio (SNR) is preserved. |
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