Cropland inventory in the command area of Krishnarajasagar project using satellite data

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Abstract
Inter-state disputes on water utilization from the Cauvery river have necessitated an accurate and timely estimate of the irrigated crop area in each season to optimise the water supply through the canal system and to suggest a departure from the traditional system of protective kharif irrigation to productive rabi irrigation. An inventory of the cropland in the command area of Krishnarajasagar Project was made by visually interpreting satellite imagery. Satellite data showed a reduction of about 6 per cent in the irrigated area from 1973 to 1986. Effect of scale of imagery and percentage of boundary pixels on accuracy of estimated irrigated area was studied. 1:250000 scale was found to be adequate for this large command area. The accuracy of estimated irrigated crop area was within 5 per cent of the DES estimate for the entire command area. At taluk-level, total enumeration gave an overestimate of irrigated area by 13 per cent compared to an overestimation of about 18 per cent using multistage-proportionate-probability sampling with a grid size of 2-5 km by 2-5 km. The per hectare cost of estimating the crop land using satellite remote sensing was found to be two to five times cheaper than the conventional system. An attempt was also made to evaluate various vegetation indices derived from Landsat-TM for identifying irrigated croplands and IRS-1A/LISS-II data for identification of crop types. It was concluded, from the results of this study, that satellite remote sensing is an effective time saving techqniue for providing seasonal assessment of irrigated cropland in the command areas.

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