An Evaluation of Multi-Band/Multipolarised SAR Data For Vegetation Discrimination, In Malaysia
N.Laili, H. mariamni and K.M. Noh
Malaysian center for Remote Sensing (MACRES)
CB 100, 5th Floor, city Square Centre, Jalan Tun Razak
50400 kuala Lumpur
Malaysia
E-mail: laili@macres.gov.my
Abstract
Optical and conventional SAR data such as Landsat TM, SPOT, ERS-1, Radarsat are being used widely fro mapping and monitoring of vegetation and other application in Malaysia. However these data, the optical and the conventional SAR , have some limitation due to cloud cover and single polarization & single frequency, respectively. The AISRF data of multi-polarization and multi-frequencies captured on a single date could minimize those obstacles.
In this study, AIRSAR data of bands L-HH, L-VV, L-HV, P-HH, P-VV and P-HV were analyzed for their potential in extracting information on vegetation such as forest, oil palm, rubber and non-vegetation such as clear-cut area and suburban, and radar backscattering coefficient (
s0) derived for these classes were compared graphically, visual and statistically . the preliminary results proved a good discrimination, for vegetated and non-vegetated area. The oil palm and rubber could be discriminated in L band at all polarization, while rubber, natural forest and plantation forest are hardly discriminated.
Introduction
Land cover classification from SAR imagery is an important and continually developing application of microwave remote sensing. Advances in microwave technology have provided an improved measurement capability, allowing development of employing multiple-frequencies and multi-polarizations. The characterization and classification of land-cover using polar metric SAR data has been extensively invested and reported on. Diane L. Evans et al, 1998 had discriminated the vegetated and clear-cut area with polarization. Recently, K.S. Chen at. Al , 1996 analysed the radar respond of crop types to frequency and polarization for classification based on three configuration:1) multifrequency and single polarization images; 2) single-frequency and multi polarization images; and 3) multifrequency and multipolarizaiton images. Adoption of neural network and the classifier to classification show the p band multipolarizaiton images and multiband HH polarization images have better classification accuracy, while with a full configuration, namely multiband and multipolarizaiton gives the best discrimination capability.
This paper focuses on the multifrequecies and polar metrics classification of land cover from airborne radar image . different frequency and polarization extraction of backscatter have been implemented and compared.
Rubber
Rubber trees are either grown on large estate in units of hundred hectares or more, or by small holders on fields with size of only to few hectares. In both cases, the plantation is subject to characteristic planting and growing schedule. Young plants, some 1.2 m tall are planted on cleared areas were roots and trunk from previous vegetation have been removed. The ground is normally even and covered with short grass and legume. On flat and gently undulating terrain, the trees are planted in straight rows, normally in N-S or E-W direction, while terrace planting is practiced in undulating and rolling areas. The planting densities vary between 380-540 trees per ha. The trees grow to a total height of 12.20m , depending on the soil and terrain conditions. The trunk diameter seldom exceeds 30 cm. The leaves, some 7 by 13.cm in size, are shed once per year during the major dry season in December/February. After 20-25 year the productivity of latex decreased and if the plantation is abandoned, the trees will eventually start to cut off . before this happens, however, the fields are normally cleared and new generation of trees is planted.
Oil Palm
Oil palm trees are grown on large estates in units of hundred hectares or more, or by smallholders on field with size of only a few hectares. The trees are normally grown to a total height of between 12-20 m's including the large fronds , or branches, which fan out from the top of a straight, single trunk. Each fronds consists of an oblong stem from which some hundred long slender leaves extend out on opposite sides. The frond will reach lengths of 5 to 8m with in a few years after planting, exceeding a width of 2 at the center . The surface of the trunks is rough and covered with scale-like remnants of old fronds that have been cut off as the tree has grown. The palm trees are normally planted in asymmetrical triangular pattern on flat or gently undulating ground and in terraces in more hilly terrain. The ground is covered with grow of legumes and subsequently as the trees grow, with stacks of dead fronds. After 20-25 years the productivity decreases, the plantation are then normally cleared and new trees are transplanted.
Forest
Consist of tnatural forest and forest plantation. Natural forest consist of -(a) higland forest which has strongly mixed natural and very denser canopy in which the highest story ranges from 30-40m and the lower story is bushes and small trees; and (b) lowland forest in which tree species tend to be taller and larger than the high altitude rain forest trees. Forest plantations which consists of trees, bushes and other crops for commercial or industrial purposes which are monocrop.
