Keywords: SAR, forest biomass density, backscatter, remote sensing, JERS-1
Abstract:
It is difficult to acquire optical remote sensing data in tropical regions because these area are generally covered with thick cloud. However SAR (Synthetic Aperture Radar) data is very useful to tropical regions so it can penetrate the clouds. Moreover response from vegetation using optical and near-infrared sensor is only reflectance of canopy top but microwave penetrate canopy top of vegetation and enables to conduct physical measurement. In this study, the authors apply estimation method forest biomass density at several sites in Kalimantan Island using JERS-1 SAR data.
Introduction
As tropical regions are generally covered with thick cloud all the year around, it is difficult to measure biomass by spaceborne optical instruments. In additions, Response of vegetation from optical sensor can observe chlorophyll in the canopy. Therefore it is difficult to distinction land cover after logging between the primary forest and young trees. On the other hand, SAR instrument can acquire the data in depend on the weather because of the properties of microwave.
Backscatter from vegetation of microwave have three types (Figure 1):
- Direct backscatter from canopy top.
- Multiple scattering and volume scattering in the vegetation.
- Direct backscatter from land surface.
Rate of penetration to the canopy top is different from microwave wavelength (Figure 2). Short wavelengths like K band and X band are mainly scattering on canopy surface directly. Long wavelengths like L band and C band occur to multiple scattering in the vegetation - the leaf , branch and trunk and volume scattering.
As L band microwave is penetrative (Iisaka, 1998) and very sensitive (Luckman, et al., 1997) to the forest, JERS-1 SAR L band sensor data will be used in this research. Therefore the objective of this study is to estimate forest biomass density at several sites in Kalimantan Island using JERS-1 SAR data.
Figure 1. Variety of backscatter from vegetation (Iisaka, 1998)
Figure 2. Wavelength and Rate of penetration to the canopy(Iisaka, 1998)
Study Area and Field Data
Bukit Soeharto Experimental forest (BSEF) of Mulawarman University (Hutan Pendidikan UNMUL) was rather damaged by large scale fire in East Kalimantan region in 1983 (Figure 3). In 1997 before the fire, lowland dipterocarp survived from the fire of 1983, has the average height of 45m. While secondary forest of macaranga which have the height of 20m distributed like a pitch. The secondary forest was formed macaranga mainly after the fire. In the experimental forest, macaranga was almost burn down by the natural dryness and the fire in 1997 to 1998.
Field data in this study includes following two kinds of biomass density data.
- Lightly disturbed stand (LCD) biomass density
The canopy is almost covered with dipterocarp and it has been damaged very much before.
- Heavily disturbed stand (HDS) biomass density
The canopy is almost covered with macaranga and it has not been damaged so much before.
The locations of the field sites are following (Toma, 1999):
LDS: South latitude 0° 51' 44'', East longitude 177° 01' 66''
HDS: South latitude 0° 51' 68'', East longitude 177° 02' 46''
Figure 3. Bukit Soeharto Experimental forest in Kalimantan Island
