The effect of spatial resolution on the ability on to monitor the status of agricultural lands

Monitoring regional and global changes in agricultural land use requires coarse spatial resolution imagery in order to keep data volumes reasonable and to allow sufficiently frequent temporal coverage. The viability of coarse spatial resolution data for monitoring the status of agricultural lands is evaluated using degraded multitemporal TM imagery. Areal estimates of productive land in Egypt's Western Desert are slightly underestimated at spatial resolutions of 120 m ad 240 m. Although error increases at 480 m and 960 m, estimates are within 10% of the original 30-m estimations. The area of old agricultural lands is more accurately estimated while reclaimed lands (cultivated after June 1985) show greater underestimation errors. These results suggest that the areal extent of these lands can be estimated accurately using multitemporal data with intermediary spatial resolutions such as the 250 m Bands 1 and 2 of the upcoming MODIS instrument. While overall map accuracies are good, the location of the reclaimed lands are poorly mapped. Fine spatial resolution data will still be needed to map the location of the fields. Also, the multitemporal maximum NDVI threshold differentiating productive and non-productive lands, identified in the original TM data, is relatively stable across the four coarse resolutions tested. (C) Elsevier Science Inc., 1997.