AVHRR analysis of a savanna site through a fire season in Brazil
A temporal sequence of images form the Advanced Very High Resolution Radiometer (AVHRR) orbital sensor along 1.5 year was used to study the response of a savanna site that burnt in the dry season. The Emas National Park of Brazil was monitored with 1.1 km high resolution afternoon images from June 1992 to October 1993 through the responses of channels 1 (0.6 m), 2 (0.9 m), 3 (3.7 m), and of the Normalized Difference Vegetation Index (NDVI) combination of channels 1 and 2. A fire consumed 23% of the park's 1300 km2 surface in August 1992; based on a subsequent Landsat Thematic Mapper image, three sub-areas that burnt were chosen for a detailed AVHRR comparative analysis with five sub-areas that did not burn. From the 344 images recorded on different days only 26 were effectively useful. Channel 1 showed little difference for burnt and unburnt vegetation. Channel 2 and NDVI displayed strong evidence of the fire for up to 13 months, while in channel 3 this period was less than 8 months. However, channel 3 and NDVI presented the strongest evidence of the fire occurrence on a short-term basis. The results support the use of AVHRR products based on channels 2 and 3 to monitor and evaluate the extent of vegetation burn and regrowth in savannas, important information for tropical vegetation.