Browsing by Subject "Radar in hydrology"
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Item Characterizing surface drainage systems in selected areas of central Texas using spaceborne imaging radar(Texas Tech University, 1993-05) Garcia, Salvador RodolfoThis study involves an examination of certain hydrologic features within five scenes of SIR-B (Shuttle Imaging Radar B) sensor digital data of Central Texas. The imagery, a subset of Datatake 81.2 (a 40km. wide swath extending from northwest of San Antonio to southeast of Dallas), provides an opportunity for synoptic planimetric mapping and studies of river morphology, surface limnology, and drainage basins. The analysis centers on the feature extraction potential of the imagery by highlighting the planimetric geometry and extent of surface drainage systems. The use of spaceborne imaging radar data for drainage analysis, like that of SIRB, provides land-use planners, and flood control specialists with an additional tool for doing synoptic mapping. Previous work in hydrologic analysis employing radar has been done primarily with Side Looking Airborne Radar (SLAR) from airplane platforms. However, the advantages for using spaceborne radar include the potential for multitemporal and multispatial data acquisition as well as remote sensing from higher altitudes, thus providing less distortion. Radar's capability of illuminating targets under most weather conditions, day or night, is an obvious advantage over other spaceborne sensors. The unique characteristics of spaceborne imaging radar, like SIR-B, that make it an ideal sensor for mapping hydrologic catchment systems, includes the ability to vary direction of illumination at various incidence angles and look directions at specified radar frequencies and polarization. The SIR-B radar is also sensitive to soil moisture and vegetation, as well as geologic boundaries. The resulting imagery provides a marked contrast between smooth and rough terrain, and variations which depend on target dielectric. It was theorized that maps derived from the SIR-B data could be used for drainage studies, such as: (1) calculations of river morphology, like stream length, meander wavelength and belt width, sinuosity index, wavelength radius-to-river-width ratio, cluster analysis of river curvature, and stream confluence; (2) areal limnological calculations, like lake and reservoir shoreline length, area, and shoreline development index; and (3) drainage basin calculations, like estimates of linear distributions of water impoundments, and basin geometry. Feature extraction from the SIR-B imagery for a number of hydrologic features involving drainage basin characteristics was possible in most instances, but difficult in others. Probable explanations for interpretation difficulty include misspecification of incidence angle and illumination direction (Radar incidence angle needs to be specified in accordance with the local incidence angle, and illumination direction needs to correspond with terrain slope). Suggestions for future coverage of this geographical area include optimizing radar system configuration and flight path.Item Delineating contributing areas for karst springs using NEXRAD data and cross-correlation analysis(2008-08) Budge, Trevor Jones, 1974-; Sharp, John Malcolm, 1944-The use of cross-correlation analysis on spring discharge and precipitation data in karst aquifer basins has been used for many years to develop a conceptual understanding of an aquifer and estimate aquifer properties. However, to this point, the application of these processes has relied on gaged precipitation at discrete locations. The use of spatially varying precipitation data and cross-correlation analysis provides a means of spatially characterizing recharge locations on a karst aquifer. NEXRAD provides a spatial estimate of precipitation based by combining reflectivity measurements from radar stations and traditional precipitation gages. This study combines NEXRAD precipitation data with spring discharge data to develop maps of contributing areas for two karst springs in Central Texas. By calculating the cross-correlation of each NEXRAD measurement to spring flow data for the same period of time a map showing the locations hydraulically connected to the spring can be developed. Both numerical experiments and field applications were conducted as part of the study. The numerical experiments conducted by Padilla and Pulido-Bosch are revisited using the numerical groundwater model MODFLOW. This allowed the introduction of spatially varying parameters into the model. The results show that spatially varying parameters can be inferred based on the results cross-correlation of spatially varying precipitation with respect to a single spring discharge location. Also, contributing area maps are prepared for both Barton Springs and Jacob’s Well. Barton Springs has a precise estimate of the recharge area. The current map of the recharge area and the NEXRAD derived map show good agreement with the cross-correlation results. Conversely, Jacob’s Well has not been sufficiently studied to delineate a contributing area map. This study provides an preliminary estimate of the area contributing to flow at Jacob’s Well. Finally, the development of these maps can also be applied to the construction of regional groundwater models. An application of this methodology with the groundwater availability model for the Barton Springs portion of the Edward’s aquifer is introduced. The application of spatial cross-correlation analysis to constrain recharge in the model showed a reduction in the objective function with respect to discharge at Barton Springs of 15%.