Monitoring agricultural lands in Egypt with multitemporal Landsat TM imagery: How many images are needed?

Multitemporal imagery is needed to -monitor agricultural landscapes characterized by high temporal variability. With the use of a database of 10 Landsat Thematic Mapper images dating frcrrn 1984 to 1993, the effects of the number and tuning o f images on area estimates of productive and nonproductive lands are evaluated for agricultural lands in Egypt. Average overestimation of nonproductive lands in. the Nile Delta ranges from 5% with data sets of nine images to more than 300% with data sets c f two images. Average underestimation of reclaimed lands in the Western Desert ranges frown 4% with six image data sets to 42% vith one-image data sets. Generally, data sets including more high-growth-.season imagery retilt in higher accuracie.s, although in. sonic eases a mixture of high- and low-growth-season imagery is more accurate. A single peak-growth image dominates results in both regions; data sets including this image are consistently more accurate than. those without it. The results indicate the critical significance of using extensive multiternporal data sets to rrunritor agricultural landscapes.