Geoenvironmental Monitoring of the Lingayen Gulf, Northwestern Luzon, Philippines Using Remote Sensing Technology
The present study aims to document the changes that occurred over the Lingayen Gulf area using remote sensing technology. The satellite-based images will provide the basic information on the geoenvironmental condition of the Gulf area for a span about 22 years, form 1972 to 1994. The information obtained will be an input into the region's development plan.
1.1 Location and Accessibility
The Lingayen Gulf area in NW Luzon can be accessed via the North Expressway through private vehicles or by public utility buses. Air fights to San Fernando, La Union is available. Sea ports are present in San Fernando, La Union and Currimao in llcos Norte.
1.2 General Topographic and Geologic Setting
Generally, the Lingayen Gulf area comprise the lowland area. This lowland is composed essentially of quaternary alluvial deposits and several limestone units. To the NE is the highlands of the BMD where igneous rocks intrude undifferentiated older rocks. In between the gulf area and the BMD are the shale, sandstone and limestone units.
The Sto. Tomas spit, located along the coast of La Union, is about two km at its widest portion and eight km long tapering gradually to the south. The Sto. Tomas Spit is probably formed by the action of south-flowing longshore currents. The Aringay-Pugo River on the NE is probably the source of quaternary materials that make up the spit (Duna, 1963).
1.3 Drainage and Climate
The Agno River is the largest river flowing into the Lingayen Gulf. The total length of the river is about 270 km and the area covered by its drainage reaches 7,640 km
2. it flows through the mountain areas east of itogon Province characterized by deep valleys and rugged topography. It ten flows through the lowlands of Pangasinan before emptying to the Lingayen Gulf in the west.
The Study area has a type I climate. The dry season starts in November and ends in April. The rainy season is from May to October. The total annual rainfall in La Union is 2,409 mm. Typhoons and monsoons usually accompany the rainy season. The precipitation data from the US National Oceanic and Atmospheric Administration (NOAA) (1970 to 1980) and the Japan Meteorological Agency (JMA) (1981 to 1994) measured in Dagupan shows a high 2,659 mm monthly rainfall in July 1972. This was due to a major typhoon at that time.
2.0 Methodology
Several satellite images, Landat TM, MSS and JERS-1 OPS images, from 1972 to 1994 were obtained Table 1 shows the summary of the images used.
| Date | Path/Row | Acquisition Data |
| Landsat MSS | 125/49 | 18 November 1972 |
| Landsat MSS | 125/49 | 10 May 1976 |
| Landsat MSS | 125/49 | 21 February 1979 |
| Landsat TM | 116/49 | 31 January 1988 |
| Landsat TM | 116/49 | 03 December 1989 |
| Landsat TM | 116/49 | 02 April 1993 |
| Landsat TM | 117/49 | 27 April 1988 |
| Landsat TM | 117/49 | 24 may 1992 |
| Landsat TM | 117/49 | 11 March 19494 |
| JERS-OPS | 91/273, 274 | 06 November 1993 |
| JERS-1 SAR | 91/273, 274 | 07 May 1993 |
Table 1 - Summary table for the datasets used
False color composites were prepared from these available data. Each of the images were enhanced and geometrically corrected to a 1:50,000 map. Several interpretations were made on the processed images.
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A regional geological interpretation was made on the 1993 TM images to determine the geological and geomorphological boundaries and the lineament zones.
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A photogeomorphological interpretation map of the Agno River Basin with special emphasis on identifying landslide concavities was also made.
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A maximum likelihood classification was applied to the 1988 and 1993 TM images to identify open area, soil, weathered areas or barren ground areas before and after the July 1990 earthquake.
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A photogeological interpretation was made on the 1972 to 1993 images to document the extent of flood deposits in the Agno River Basin. The images were compared with each other to assess the trend.
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These images covering the Sto. Tomas Spit and an additional 1946 aerial photographs were superimposed. The changes in the configuration of the coastline over time were interpreted from the superimposed images.
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The distribution of coral reef and other reef communities were mapped from the images.
