Irrigated area determination by NOAA-Landsat upscaling techniques, Zayandeh River Basin, Isfahan, Iran
The processing and analysis of a set of NOAA-14/AVHRR images, obtained from the Satellite Active Archive (SAA) for 1995 and 1999, is discussed. The NDVI values were calculated using channel 1 and channel 2 reflection values after standard radiometric and geometric corrections. The average Normalized Difference Vegetation Index (NDVI) of the main irrigation systems in the Zayandeh Rud Basin, Isfahan, Iran, was then determined for each image. This made it possible to analyse the temporal evolution of these NDVI values for the individual irrigated areas during 1999. The National Oceanic and Atmospheric Administration (NOAA) NDVI values can, in principle, also be used for the determination of the size of the actual irrigated areas of the principal systems. However, calibration of the method proved necessary, because in most NOAA pixels the vegetation is only a fraction of the pixel area. Through the use of Geographic Information System (GIS) operations on a Landsat 7 image (1 August 1999), the actual irrigated areas in Borkhar, Abshar Left and Right, Nekouabad Left and Right, were determined for that particular date. Five NOAA images were then selected for the period July-August 1999. This made it possible to establish regression relations linking NOAA NDVI values to the size of the net irrigated systems, which were then applied to the 1995 dataset.
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