Browsing by Author "Morrison, K."
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Item Open Access Polarimetric calibration strategy for long-duration imaging with a ground-based SAR(2006-05-04T15:02:52Z) Morrison, K.; Cookmartin, G.; Bennett, J. C.; Quegan, S.; Race, A.The Ground-Based Synthetic Aperture Radar (GB-SAR) facility in the UK provides high-resolution, fully polarimetrically calibrated L- through X-band SAR imagery, principally of targets of remote sensing interest such as soils and vegetation. The facility consists of an indoor laboratory and a portable outdoor imaging system. Details of the polarimetric calibrations of both systems are discussed, with consideration given to the special requirements of field operation. Because of the need to mechanically scan the real antenna to build up a synthetic aperture, the SAR imaging process is significantly longer than its airborne and satellite counterparts. Some of the extended imaging schemes, such as those used in three-dimensional tomographic imaging and diurnal monitoring campaigns, can last from hours to days. However, calibration is normally only possible just prior to, and just after, imaging, leaving the data susceptible to nonlinear system sensitivity fluctuations during the imaging process itself. To address this problem, a novel scheme is discussed that utilizes the signal that arises from the imperfection in the rf isolation of the antenna head as a diagnostic to account for sensitivity fluctuations. Variations of several decibels were seen on a time scale of hours over an extended 2 day measurement. Excellent agreement was found with radar cross section (RCS) fluctuations retrieved from contemporaneous SAR imagery of reference trihedrals placed in the scene.Item Open Access Three-dimensional X-band SAR imaging of a small conifer tree(2006-05-04T15:25:08Z) Morrison, K.; Bennett, J. C.; Cookmartin, G.; McDonald, A. J.; Race, A.; Quegan, S.High spatial resolution 3-D SAR imagery was recorded by the UK’s Natural Environment Research Council GB-SAR Microwave Measurement Facility at the University of Sheffield. X-band V V polarisation measurements were made using a near-field monostatic imaging system inside an anechoic chamber. The measurement process employs vector network analyser techniques to sample backscatteredsignals over a 2-D aperture, allowing a 3-D reconstruction of a target. This technique is used to provide a detailed 3-D map of the spatial scattering behaviour of a small Colorado Blue Spruce tree (Picea pungens glauca). The images produced are at a su“ ciently high spatial resolution ( ~ 5 cm) that individual plant components can be discerned. An ability to select any volume pixel from within the target allows features in the microwave reconstruction to be readily associated with structures in the tree. The scattering behaviour associ-ated with the uppermost set of branches shows it to be dominated by scattering from the branch tips.Item Open Access A very high resolution X- and Ku-band field study of a barley crop in support of the SWINTOL Project(2016-08-10) Bermejo, J. P.; Morrison, K.SAR Wave INteraction for Natural Targets Over Land (SWINTOL) is a project funded by the European Space Agency. The study’s goal is to better understand the interaction of high frequency radar (> X-band) with vegetation and soils, in order to drive the development of a high-frequency electromagnetic model to simulate SAR imagery at high resolution (< 1 m). Existing models work well at C and X band frequencies, but do not work properly at higher frequencies. Cranfield University’s role in this project was to provide the field data necessary for model validation and development. Radar imagery was taken of a barley crop over an entire growing season. The portable outdoor GB-SAR system used the tomographic profiling (TP) technique to capture polarimetric imagery of the crop. TP is a scheme that provides detailed maps of the vertical backscatter pattern through a crop canopy, along a narrow transect directly beneath the radar platform. Fully-polarimetric imagery was obtained across overlapping 6.5 GHz bandwidths over the X- and Ku-band frequency range 8-20 GHz. This gave the opportunity to see the detailed scattering behaviour within the crop at the plant component level, from emergence of the crop through to harvesting. In combination with the imagery, full bio-geophysical characterisation of the crop and soil was made on each measurement date. Surface roughness characterisation of the soil was captured using a 3D optical stereoscopic system. This work details the measurements made, and provides a comparative assessment of the results in terms of understanding the backscatter in relation to biophysical and radar parameters.