REGIONAL FOREST COVER ESTIMATION VIA REMOTE-SENSING - THE CALIBRATIONCENTER CONCEPT

A method for combining Landsat Thematic Mapper (TM), Advanced Very Hig h Resolution Radiometer (AVHRR) imagery, and other biogeographic data to estimate forest cover over large regions is applied and evaluated a t two locations. In this method, TM data are used to classify a small area (calibration center) into forest/nonforest; the resulting forest cover map is then used in combination with AVHRR spectral data from th e same area to develop an empirical relationship between percent fores t cover and AVHRR pixel spectral signature; the resultant regression r elationship between AVHRR band values and percent forest cover is then used to extrapolate forest cover for several hundred kilometers beyon d the original TM calibration center. In the present study, the method was tested over two large regions in the eastern United States: areas centered on Illinois and on the Smoky Mountains on the North Carolina -Tennessee border. Estimates of percent forest cover for counties, aft er aggregating AVHRR pixel estimates within each county, were compared with independent ground-based estimates. County estimates were aggreg ated to derive estimates for states and regions. For the Illinois regi on, the overall correlation between county cover estimates was 0.89. E ven better correlations (up to r = 0.96) resulted for the counties clo se to one another, in the same ecoregion, or in the same major land re source region as the calibration center. For the Smokies region, the c orrelations were significant but lower due to large influences of pine forests (suppressed spectral reflectance) in counties outside the har dwood-dominated calibration center. The method carries potential for e stimating forest cover across the globe. It has special advantages in allowing the assessment of forest cover in highly fragmented landscape s, where individual AVHRR pixels (1 km2) are forested to varying degre es.