Pasture land cover in eastern Australia from NOAA-AVHRR NDVI and classified Landsat TM

A method for constructing a pasture Tend cai;er classification for the high rainfall zone of eastern Australia from the U.S. National Oceanic and Atmo spheric Administration's advanced very high resolution radiometer normalize d difference vegetation index (NOAA-AVHRR NDVI) data is described. The meth od uses an established classification of pasture growth potential from sing le date, springtime, Landsat thematic mapper (TM) data to provide measures of subpixel mixture composition in mosaicked classes in the absence of grou nd truth or control sites. A sequence of AVHRR data front 1993 was transfor med into a vegetation index and then classified to define pasture classes w ith differing patterns of NDVI. High-resolution classifications of pasture were constructed for ten selected sites within the study area by using Land sat TM scenes. The study area rc;as split into a northern and southern zone on the basis of the temporal pattern of moisture(re indices. The pasture l and cover classes were described irt terms of the shape of the NDVI profile s, their geographical location, and the subpixel composition front Landsat Tn data. The classified NDVI data were combined with local government area (LGA) boundary data to allow the particular pasture state of each LGA to be estimated. The NDVI-Landsat TM procedure identified 21 and 22 classes in t he northern and southern zones, respectively. These classes could be broadl y grouped into eight types: seton perennial pastures, sown perennial pastur es with woodland seton annual pastures (southern zone only), mixed pasture and cropping, native pastures, native pastures with woodland, degraded or r evegetated areas, and forest. This eight-class classification, combining th e two zones appeared to represent regional distribution of the major types quite well. The pasture land cover classification was evaluated for selecte d LGAs by using agricultural statistics and a specialist pasture survey. Lo cal estimates of proportions of major pasture types were sometimes in-accur ate owing to difficulties in distinguishing between perennial, annual, and native types where seasonal conditions caused rapid senescence or where ope n woodland confused profiles between improved and native pastures. The meth od is nevertheless usefull where ground truth or definitive spectral signat ures for cover types are unavailable and IL;where description lit terms of art average or predominant cover type within a landscape mosaic is acceptab le. (C) Elsevier Science Inc., 1998.