Satellite Monitoring of Coastal Topography in La Union,
Northwestern Luzon, Philippines
Salvador, J.H.G.1, Kanbara,H.2, Sato, T.2, Machida,S3, Almeda, R.1,Garelan, S.4, and Laserna, S.1
1Mines and Geosciences Boreau,
North Ave., Diliman, QC, 1101 Philippines.
Fax (632)928-8544
2Nikko Exploration and Development,
Condition., Ltd., 7-10 Toranomon 2-Chrome,
Minatoku,Tokyo, Japan.
Fax(81)3-3508-9785
3Earth Remote Sensing Data Analysis Center,
Roppongi First Bldg., Tokyo, Japan
4Mines and Geosciences Bureau,
Regional Office No. 1,
San Fernando, La Union, Philippiness
Abstract
Eight different datasets that include the 1946 aerial photographs, the Landsat MSS, Landsat TM and JERS-1 OPS from 1972 and 1994 covering La union, Philippines were studied. The images documented the change in the beach line configuration of the Santo Tomas Spit due to rapid coastal erosion. In particular, there is regression of about 200 meters along the coastline and growth of the spit landform by more than one kilometer southward.
Introduction
This study is a part of the three-year Philippines-Japan cooperative undertaking by the Philippines Mines and Geosciences Bureau (MGB) under the Dept. of Environment and Natural Resources (DENR), the Nikko Exploration and Devt. Condition., Ltd. (NED) and the Earth Remote Sensing Data Analysis Center (ERSDAC) of Japan. The main objective is to apply remote sensing technology to the management of the coastal environment and resources in Luzon.
The Sto. Tomas Spit is located along the coast of La Union in northwestern Luzon. It is bounded by latitudes 16014'30" N to 16020'00"N and longitudes 120020'00"E to 120025'00"E. It is about two km at its widest portion and eight km long tapering gradually to the south. The Santo Tomas Spit is probably formed by the action of south-flowing longshore currents. The Aringay-Pugo River on the northeast is probably the source of quaternary materials that make up the spit (Duna, 1963).
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.
Methodology
False color composites were prepared from available Landsat TM, MSS and JERS-1 POS images (Table 1). The images were geometrically corrected to a 1:50,000 scale topographic map. These images and the 1946 aeraial photograph were superimposed (Figs. 1,2 and 3). The changes in the configuration of the coastline over time were interpreted from the superimposed images. A fieldwork was conducted to verify some results.
Table 1-The various data used for the study.
| Data |
Path/Row |
Acquisition Date |
| Aerial Photograph |
125/49 |
21 November 1946 |
| Landsat MSS |
125/49 |
18 November 1972 |
| Landsat MSS |
125/49 |
10 May 1976 |
| Landsat MSS |
125/49 |
21 February 1979 |
| Landsat TM |
117/49 |
27 April 1988 |
| Landsat TM |
117/49 |
24 May 1992 |
| Landsat TM |
117/49 |
11 March 1994 |
| JERS-1 OPS |
91/273 |
06 November 1993 |
