USING REMOTE SENSING TO MAP THE DISTRIBUTION OF SAGO PALMS IN NORTHEASTERN MINDANAO, PHILIPPINES: RESULTS BASED ON LANDSAT ETM+ IMAGE ANALYSIS

摘要

We present in this paper the results of our study that aims to map the distribution of the sago palm (Metroxylon sagu) in Agusan del Sur province in northeastern Mindanao, Philippines using remote sensing data and techniques. The sago palms have been reported to exist in marshlands and wetlands of northeastern Mindanao which are difficult to access and would be costly if mapped using conventional field mapping techniques. We tested the viability of Landsat ETM+ image to locate the distribution and abundance of the sago palm in the Agusan del Sur province. After radiometric calibration and atmospheric correction, the image was subjected to Maximum Likelihood classification to produce a land cover map showing the distribution of sago palms and other land-cover types. The classifier was trained and the accuracy of the results assessed using ground truth data of sago palm and other land-cover types that were collected between February and August 2012. Results of the supervised classification using combination of all the multispectral bands, NDVI and SRTM DEM showed an overall classification accuracy of 94.88%. A total of 597 hectares of sago palms were detected from the image analysis. The sago palm classification has 80.18% Producer's Accuracy and 82.66% User's Accuracies. This relatively low Producer and User's Accuracies of the sago palm classification may be attributed to three factors: (ⅰ) the similarities in the spectral characteristics of sago palm with other palm vegetation, especially coconut and oil palm; (ⅱ.) the 30-m spatial resolution of the Landsat ETM+ image may not be optimal for classifying specific vegetation species such as the sago palms, especially in areas where sago palms are interspersed with other land-cover types; and (ⅲ.) the differences in the date of image acquisition and the date of field surveys when the sago ground truth data were collected. Despite these low accuracies for sago palms, the location, extent and distribution of sago palms depicted in the derived land-cover map provides vital information as to where sago palms are deemed to be abundant in Agusan del Sur province.