Detecting Tropical Deforestation Using Satellite Radar Data:
A Case Study From Central Sumatra, Indonesia
Belinda Arunarwati Yousif Ali Hussin Michael Weir
The International Institute for Aerospace Survey and Earth Science (ITC)
7500 AA, Enschede, The Netheralnds
Fax (31)53-4874-399
E-mail : HUSSIN@ITC.NL
Abstract
Indonesia is the most richly tropical forested national in southeast Asia. Over most of the country, forest land use is regulated by a system of land assessment known as TGHK or "consensus of forest land use". The key to wisely managing forest land and its resources in information. In the case of Indonesian deforestation, information is required not only about the rate and the extent of deforestation, but also about some other related information such as the presence of deforestation in relation to THK classes, its location within each class of TGHK, and also its type. Data derived from remote sensors are increasingly being utilized as a data source in GIS. Conventional methods of remote sensing using optical system have failed in some part of Indonesia due to cloud cover. Radar, being free from the time and weather restrictions may be a useful alternative sourced of the remote sensing data in Indonesia. The main objectives of this research was to investigate the potential of satellite radar data to detect, differentiate, and classify deforestation.
Introduction
It is generally recognized that forest resources should be sustainably managed to support the needs of present and future generations. The capability of the land to produce on a sustainable basis is, however, loggers want to fell trees for timber, and environmentalists want conservation and protection. The problems of deforestation and environmental degradation as a result of the activities of the former actors (farmers and loggers) are become alarming.
Deforestation is expressed by the rate of change of forest cover area caused by changing the use of forest land from forest to non forest. Several factors are directly responsible for the forest change, such as commercial logging, pasture, colonization programs or spontaneous migration, slash-and -burn agriculture, expansion of agricultural activities and other land use practices such the logging activity. It has been suggested that more than 80 percent of deforestation can be attributed to agricultural expansion (De gier, 1995). Logging, indirectly contributes to this major cause of deforestation by providing to farmer through the construction of timber extraction roads.
Indonesia, a part of Malaysian botanical region, is the richest tropical rainforest in the world. Indonesia's
forest represent 10 percent of the world remaining tropical rainforest. Of its total land area of 193 million
hectares, about 144 million hectares or nearly 75 percent are classified as "forest land". More than 95
percent of those forest land are outside java island (80 percent in Sumatra, Kalimantan, and Irian Jaya). A result of growing population pressure issues of land use have becoming increasingly important in Indonesia. On Java, the encroachment of landless farmer into upland forests have led to increasing soil erosion. Similar issues arise in the outer Java, where the conversion of forest land to agriculture use, is compounded by the commercial exploitation of forest resources.
In order to mange the forest land in sustainable way, the Government of Indonesia instigated classification the consensus of Forest Land Use of TGHK (Tata Guna Hutan Kesepakatan). Essentially, this consensus classifies the forest land into 5 categories according to their usage, namely: protection forest, convservation forest including national parks and reservation forests, limited production forests, permanent production forests, and convertible production (conversion) forest. A number of important issue related to spatial information such the location of deforestation within TGHK classes, and the deforestation pattern distribution, are worth investigation to support the decision maker's objectives in order to realize the sustainable forest management in Indonesia.
Remote sensing is an important source of spatial data. Remote sensing systems can be divided into active sensors (using their own energy), and passive sensors (using natural (sun) energy). Radar is an active sensor which transmits and receives a microwave signal. Some advantages of the use of radar in remote sensing are that it can be used during both day and nith, has all weather capability (cloud cover, rain, fog, atmospheric dust, etc.), and its energy has th ability to penetrate through some surficial features. Radar is expected to be used for a wide range of applications in forestry, including activities in forest management, monitoring of deforestation, shifting cultivation, colonization settlements, and land use change. The need for reliable information about deforestation within different forest land use (TGHK) classes, such as location, distribution, and probably also its types, is obviously important to monitor the deforestation occurring in relation the TGHK. Most tropical countries use satellite imagery as a source of data about their forest resource . Landsat TM and SPOT satellite image are the most important source, but problems due to lack of image quality as result of cloud cover occur in the tropical areas like Sumatra island in Indonesia (Sumatra is notorious area for cloud cover.) This problem can be solved with the use of radar images as data source. Radar can be used as an effective tool for detection the particular pattern of human activity such as logging, agriculture expansion, (shifting cultivation ) and illegal settlement in the tropical forest which objectives of this research was to investigate the ability of satellite radar data to detect, differentiate, and classify deforestation.
