Hansen, MC, DeFries, RS, Townshend, JRG, Marufu, L, Sohlberg, R (2002). "Development of a MODIS tree cover validation data set for Western Province, Zambia". REMOTE SENSING OF ENVIRONMENT, 83(2-Jan), 320-335.
One of the annual land cover products to be made from Moderate Resolution Imaging Spectroradiometer (MODIS) data is the vegetation continuous fields layers. Of these fields, one is a global percent tree cover map. Using field measurements, IKONOS data, Enhanced Thematic Mapper Plus (ETM+) data, and ancillary map sources, a tree cover map was made and validated for two WRS path/rows in Western Province, Zambia. This map will be used in validating the 500-m global MODIS tree cover product. The map was made at the 30-m Enhanced Thematic Mapper Plus (ETM+) resolution and also scaled up to 250- and 500-m resolutions. Five IKONOS images were classified into crown cover/no crown cover maps at 4-m resolution. These maps were aggregated to 30 m to create a continuous training data set of percent crown cover. Three dates of ETM+ data were acquired to predict percent crown cover using a regression tree algorithm. Comparisons of training accuracies and field data to ETM+ tree estimates yielded root mean square errors (rinse) of similar to +/- 10% crown cover. When aggregating the 30-m map to 250- and 500-m MODIS cell sizes, the training errors are more than halved. The final 250-m map was assessed using a structural vegetation map of the area and an overall rmse of 8.5% is estimated. The 250-m map was sampled and used to derive a tree cover continuous field product using 3 Level 113 MODIS time slices, approximating the acquisitions of the ETM+ data. The results are promising as an overall root mean square error between the ETM+ derived tree crown cover map and an aggregated MODIS 500-m map was 5.2%. Results from this test in Zambia show that the MODIS 250-m bands should allow for improved depictions of percent tree cover. (C) 2002 Elsevier Science Inc. All rights reserved.