Of more than 7,600 [1] islands in the Philippines, Palawan — touted as the country’s last ecological frontier — is lauded to be one of the world’s best and finest tourist destinations [2]. It is considered to be among the best not only because of its crystal-clear waters and extensive white beaches, but also due to its biodiversity, which provides different ecological functions and services.
The island is geographically situated between the West Philippine Sea and the Sulu Sea. Having a total land area of almost 1.5 million hectares, this long and narrow island is the country’s largest province by land area. More than half of its land area is total forest cover, a home to hundreds of endemic wildlife, including the Palawan peacock-pheasant, Palawan horned frog, and Philippine mouse-deer. Underneath the ocean surface is a vast distribution of seagrass beds and coral reefs, which serve as breeding and nursing grounds to countless and diverse marine species [3]. Due to its biodiversity, extensive land area, and topography, the entire province has been declared by the United Nations Educational Scientific and Cultural Organization (UNESCO) as a Biosphere Reserve [4].
As of 2015, Palawan, excluding Puerto Princesa City, accommodates approximately 849,000 inhabitants, making it the fastest growing province in the MIMAROPA region with an annual population growth rate of 1.84% during the 2010–2015 period [5]. Currently, the major socio-economic endeavors in Palawan include agriculture, fisheries, mineral extraction, and tourism activities. The rapid population increase and heightened socio-economic activities in the province could have implications on the pristine condition of the island,, including biodiversity loss, pollution, and depletion of natural resources of the local environment. Monitoring developments in Palawan has therefore been a priority to maintain its position as a UNESCO Biosphere Reserve and a Protected Area under the National Integrated Protected Areas System (NIPAS) Act of 1992.
For the first time, the Diwata-1 team has successfully produced a contiguous photograph of a large portion of the Philippines — its largest such contiguous photograph to date. On December 21, 2016, Diwata-1 successfully captured a contiguous set of images of Palawan through its Spaceborne Multispectral Imager (SMI). By harnessing Diwata-1’s capability of capturing images in the visible and near-infrared regions, the microsatellite’s SMI could provide remotely sensed information on some of the current environmental issues in Palawan that is well beyond the capabilities of ordinary digital cameras. The technique paves the way for highly detailed photographs of the entire country that could give scientists a clearer visual understanding of local atmospheric and geophysical conditions.
A portion of the densely-vegetated island was described by the mosaicked 60-meter-resolution true-color SMI image, covering the Municipality of Brooke’s Point in the south all the way to the City of Puerto Princesa up north (Figure 1). The summits and ridges of Mount Victoria and Thumb Peak and their dense tropical rainforests can be clearly observed, along with several neighboring small islands and coastlines, as well as the famous tourist destination Honda Bay.
Possible sediment plumes from river systems along coastal waters near the municipalities of Brooke’s Point and Sofronio Española are noticeable in the RGB image (Figure 2). The increased concentration of suspended sediments in both municipalities are possibly due to natural or human-induced soil erosion. The topography of Palawan — narrow mountain ranges, steep runoff slopes, and meandering rivers — makes the watershed reserves susceptible to soil erosion, especially when forest cover has been affected [6].
A heavy rainfall could break down soil aggregates in the steep mountains and flat agricultural lands, which would be transported via rainwater surface runoff towards streams and rivers and consequently towards the open sea. Brooke’s Point and Sofronio Española have vast agricultural lands and plantations, and agricultural activities in these areas (such as plowing and other tilling methods) can induce soil erosion in their vicinities. The application of fertilizers and pesticides may also complicate the situation as excess nutrients and chemicals could leach out and be transported to the coasts through surface runoff — this can impact the coastal marine ecosystem via eutrophication [7]. These observations may give rise to further investigation whether the apparent siltation along the coast of Sofronio Espanola is caused by suspended natural or man-made sediments, or if it is not siltation at all and just the shallower part of the coast.
Figure 2. Zoomed in RGB image showing sedimentation along the coastal waters of Palawan.
The SMI onboard Diwata-1 is also capable of seeing beyond the ability of the naked human eye. Utilizing both visible and near-infrared images allows the calculation of the Normalized Difference Vegetation Index (NDVI), a widely-used metric for estimating vegetation health and density.
Diwata-1 SMI was able to take a snapshot of a site with bare soil situated in Sofronio Española (Figure 3). In the NDVI map to the right, high values are represented by colors orange to red, indicating healthy and dense vegetation cover. Conversely, green to blue colors indicate low values, denoting areas with sparse to no vegetation cover (e.g. bare land, water or clouds, built-up areas, shadows). Since sites such as urban areas, mining sites, unused agricultural regions and real estate development projects are largely bare soil by classification, the site in question has lower NDVI values compared to the surrounding forest cover. Moreover, other land features that are not visible in the true-color image such as the meandering river system and the coastline could also be highlighted using the NDVI image. Since river systems are agents of sediment transport toward the coastal areas, it is important to consider these tracks to monitor potential sources of contamination.
Figure 3. A true-color image of the municipality of Sofronio Española derived from Diwata-1’s SMI sensor and its corresponding NDVI product, showing a site with bare soil (encircled). A river system (traced by broken lines) can also be highlighted using the NDVI image. © PHL-Microsat
References
[1] Retrieved from http://cnnphilippines.com/videos/2016/02/20/More-islands-more-fun-in-PH.html
[2] Retrieved from http://www.travelandleisure.com/worlds-best/islands#intro 4
[3] Retrieved from http://www.palawan.gov.ph/environment.php
[4] Retrieved from https://pcsd.gov.ph/palawan-biosphere-reserves-official-logo/
[5] Retrieved from https://www.psa.gov.ph/content/population-region-iv-b-mimaropa-based-2015-census-population
[6] Fuentes, R.T. et al. (2015). The Role of UNESCO’s Man and Biosphere Reserves in Climate Change Adaptation: Experience from Palawan Biosphere Reserve in the Philippines. Our Palawan 1(1): pp. 49–60 Retrieved from http://www.pkp.pcsd.gov.ph/ourpalawan/OUR%20PALAWAN%205.pdf
[7] Retrieved from http://www.nature.com/scitable/knowledge/library/eutrophication-causes-consequences-and-controls-in-aquatic-102364466
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