University of Twente Student Theses


Validation of RS Approaches to Model Surface Characteristics in Hydrology: A Case Study in Guareña Aquifer, Salamanca, Spain

Gebreyesus, Michael Gidey (2009) Validation of RS Approaches to Model Surface Characteristics in Hydrology: A Case Study in Guareña Aquifer, Salamanca, Spain.

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Abstract:Validation of RS methods capable of estimating variables like soil moisture and fluxes such as latent and sensible heat is vital for the use of RS models in ungaged and remote areas. In this study the validation of the surface energy balance system (SEBS) was carried out by estimating soil moisture and actual evapotranspiration for the Guareña catchment in Spain and comparing them against ground measurements. Thirteen atmospherically corrected MODIS images were processed and compared from ground information collected on 23 soil moisture loggers and 5 meteorological stations. The proportional relation of the relative soil moisture with the relative evapotranspiration was used for the estimation of soil moisture from RS as SEBS was primarily developed for the estimation of surface turbulent fluxes. A downscaling procedure to improve the comparison between point and RS information was accomplished using the temporal stability approach. The study reveals that there is a satisfactory correlation (r2=0.65) between the average field scale soil moisture estimates of the RS method SEBS and the ground measurements, allowing this methodology for modeling initialization. There is no correlation however between the pixel wise RS estimates and the measured soil moisture on the point scale level after the pixel level estimates were downscaled to the point scale ground measurements (0<r2<0.2).The AET estimates were compared with the complementary (advection–aridity) method. Results indicate good correlation between the two methods with coefficients of determination, r2, greater than 0.86 for all the pixels compared. The single crop coefficient was also computed based on the estimates of the evapotranspiration from the RS and the values are found to be in good agreement with the values in the FAO guide lines. Estimates of AET were higher by 3% to 40 % when NDVI was used as a surrogate for the land cover in estimating momentum roughness heights, which suggests against the use of non-interactive NDVI based methods for Zom retrievals. The conclusion from this study is that SEBS can provide satisfactory estimates of soil moisture at the field scale and can give reliable estimates of AET.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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