Monitoring Deforestation in Luzon Island, The Philippines using Satellite Data
4.1.2 Vegetation Cover Ratio
To evaluate the soil dryness information, Soil Dryness Index (SDI) was utilized. SDI, referred to as Soil Index (SI) by Fukuhara et al.(1979), is sensitive to the soil brightness, which depends on soil moisture and soil organic matter conditions. SDI is given by
| SDI=arctan |
P4-Band4
------------------
Band2-P2 |
(3) |
where P2 and P4 are the x-coordinate (Red) and the y-coordinate (NIR) of the pixel that has the maximum vegetation coverage, respectively. The higher the SDI value of a pixel, the drier the soil of the pixel is. Pixels were classified into 5 levels according to their SDI values from high to low.
4.1.3 Soil/vegetation matrix method
Each pixel was distributed over 5x 5 matrix of VCR and Sill, and they were classified into 8 classes according to their land cover conditions (Figure 3).
Figure 3. Soil/vegetation matrix according to VCR and SDI
4.1.4 Re- classification
Soil/vegetation matrix method was carried out to both images taken during the dry season and the rainy season that resulted in two sets of land use/land cover classified images. Using GIS overlay function, these two images were cross-examined to generate a re-classified land use map to make the land use classification more accurate. Classification classes were determined in order to keep the consistency with the classes derived from the existing map. Those are (1) Water, (2) Fish pond, (3Bare soil, (4) Upland farming field, (5) Paddy, and (6) Forest.
Land use information was extracted from an existing topographic map compiled and published NAMRIA in 1977. In order to maintain the consistency with the satellite-derived land use map, land use information was digitized with the aid of GIS software so that overlay analysis can be carried out. ..At the same time, major roads and rivers in this area were also digitized to make the geographical registration easier
4.3 Land use change analysis
Satellite-derived land use map and the land use map derived from the existing map were input into a GIS to perform an overlay analysis in order to detect the land use change happened between 1977 and p 1990. With the help of GIS, spatial distribution of land use change was also detected. Distinct deforestation as monitored during the period. Considerable amount of forest area deceased by. nearly half (Figure 4). Of4.6 x 102 km2 of forest area ill 1977,2.1 x 102 km2turned into paddy ill 1990. This explains 93.9 percent of the total loss of forest area (Figure 5).
Figure 4. Land use change for settlement, bare soil, paddy, upland field, and forest: 1977 to 1990.
Figure 5. Spatial distribution of land use change ( Forest (1977) Paddy (1990))
5. Conclusion
Deforestation in Luzon island, the Philippines was monitored and evaluated both numerically and spatially with the help of soil/vegetation matrix method and GIS technique. From 1977 to 1990, a considerable amount of forest area turned into paddy in the study area. Soil/vegetation matrix method, a land use classification method using the information on vegetation coverage and on soil dryness is effective to generate a land use map from satellite data. Using two sets of satellite data acquired during the dry season and the rainy season, respectively, makes the classification accuracy higher
Acknowledgments
Part of this study was made as the cooperative work with National Space Development Agency (NASDA) of Japan. The authors are grateful to NASDA for providing the MOS-1/MESSR data
References
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Fukuhara, M., Hayashi, H., Yasuda, Y., Asanuma, I., Emori, Y., and Iisaka, I., "Extraction of soil information from vegetated area., Machine Processing of Remotely Sensed Data Symposium, pp.242-252., 1979.
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