Ruecker, Gernot 
  
severely affected by wildfires during a drought period in 1997/1998 in East Kalimantan, Indonesia. Vegetation 
fires significantly alter land surface properties. The surface structure changes since leaves and parts of the 
branches are consumed by fire. A greater portion of the incoming radar beam therefore is reflected or scattered 
by the ground, while scattering from canopy or volume scattering from stands becomes less important (French et 
al. 1996, Siegert and Ruecker, 2000). Due to changes in the surface and soil hydrology induced by burning, soil 
moisture patterns are altered (Holdsworth and Uhl 1997). These fire induced soil moisture and vegetation cover 
changes are affecting ERS-1/2 C-Band radar backscatter to a varying degree depending on vegetation type, site 
ecology and weather conditions prevailing during image acquisition (Wang et a. 2000). Thus, French et al. 
(1996) found in Alaska, that Radar backscatter increased after a forested site was affected by fire. They 
attributed this effect to changes in soil moisture, namely an increase in soil water content due to melting of the 
underlying permafrost. Siegert and Ruecker (2000) also suggested that soil moisture has a strong influence on 
radar backscatter from burned surfaces in Indonesia. It was found that radar backscatter decreased strongly after 
a fire event when weather conditions are dry, but increased when rain fell on the burned surfaces. In this case, 
backscatter increases strongly due to the higher dielectric constant of the wet soil, but also from wet living 
vegetation. Discrimination of burned from unburned surfaces is thus hampered by an overall higher backscatter 
and a noisier picture. Generally, backscatter behaviour seemed to be dependending on the type of vegetation 
existing in each area before the fire impact and on the degree of damage each particular vegetation type suffered 
from fire. 
The study presented here was commissioned by a cooperation of the Integrated Fire Management Project and 
the Sustainable Forerst Management Project, both of GTZ (Deutsche Gesellschaft für technische 
Zusammenarbeit mbH) and operating in Samarinda, East Kalimantan during the exceptional fire event that 
struck this Indonesian province in late 1997 and early 1998. It aimed at producing a map of fire damage at a 
scale of 1:200,000 for almost the entire province discriminating the most severely affected areas from the less 
damaged. This is of great importance for regional planning endeavours in the fire’s aftermath. Prior studies 
mapping the fire damage (Liew et al. 1998, Fuller and Fulk 2000) were hampered by availability of optical data 
due to cloud and haze coverage, did no provide the required spatial resolution or were conducted before the fires 
came to an end. Since no optical data at the desired spatial resolution were available, it was decided to make use 
of the cloud-penetrating capabilities of satellite-born imaging radar. Results of a pilot study have already been 
published elsewhere (Siegert and Ruecker 1999, Siegert and Ruecker 2000, Siegert and Hoffmann 2000). In this 
article we shall describe results of an empirical study about the ability to discern degrees of vegetation damage 
by fire in tropical lowland ecosystems with the help of C-band imaging radar. We also present the fire damage 
map compiled from a multitemporal mosaic of 46 ERS-2 SAR images. 
1.2 The study area 
The study area covered about 130,890 km? or 66% of the territory of the Indonesian province of Kalimantan 
Timur on the island of Borneo. This comprises more than 90% of the province’s lowland area. The province of 
Kalimantan Timur is divided in basins and mountain ridges. From north to south, there are three basin areas with 
large river systems, the largest of them being the Mahakam basin, which is also the region most inhabited and 
most severely affected by fire. The major part of the central mountains of Borneo with large inaccessible forest 
areas in the West of the province was not struck by fire. Only part of this mountain area was covered by the radar 
satellite mosaic. The Mahakam basin area is marked by large central wetland and swamp areas which are quite 
inaccessible as well as three lakes with populated shores and shifting cultivation by villagers along the river. 
Further away from the centre large plantations and forest concessions are to be found. The province’s southern 
and coastal areas are more populated and land cover is dominated by degraded vegetation, agriculture and 
plantations. A large part of the province is covered by lowland dipterocarp rainforests of varying degree of man- 
induced degradation. 
2 MATERIAL AND METHODS 
2.1 Radar image processing 
A total of 48 ERS-2 SAR Precision Images from three adjacent orbits was used to investigate changes in radar 
backscatter in areas affected by fires of different severity and to map the total burned area in the province of 
Kalimantan Timur. Images were acquired for three dates: August 1997 (at the beginning of the fire season), 
April 1998 (at the end of the fire season) and July 1998 (after the fires had been extinguished by heavy rainfall). 
Due to failure to record images from two satellite orbits in April, only images for the central orbit were available 
for April. While images from August and April were acquired under extremely dry weather conditions, the 
images from July 1998 was recorded during a period of heavy rainfall. 
Images were subsampled to a pixel size of 25 meters, calibrated to represent radar backscatter, co-registered, and 
mosaiced together to cover about two third of the province of Kalimantan Timur. Calibration was done to linear 
  
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 1287