ESTIMATING CROP ACREAGE IN SMALL IRRIGATED DISTRICTS VIA GROUND-GATHERED AND SATELLITE DATA

Remote sensing is an important tool for monitoring and evaluating agricultural areas. In the semi-arid part of Spain which are dependent upon irrigation, problems connected with water scarcity, the environment and marketing necessitate the obtention of rapid and accurate crop inventories in each irrigated district. The classical method of area frame sampling corrected by regression estimator has been adapted to the crop acreage in 3 irrigated districts of the central Ebro basin (northeastern Spain). The small size of the districts involved pushes the method to the limits of its applicability; higher ground sampling rates were therefore tested. The statistics of summer land use in these districts have been presented. Computer processing of one single Landsat TM image reduces the coefficient of variation for estimation of the acreages of maize, alfalfa, rice and tilled land (either with natural vegetation or bare soil). The acreage estimation was inaccurate only for minor crops (sunflower, fruit tree and horticultural crops) that are sparsely planted and in particular for those with a heterogeneous spectral signature.