Correlation of Total suspended Sediments and Reflectance of Landsat TM in Laguna De Bay, Philippines
Fay F. Mancebo, Romeo C. Bruce, Zenaida B. Catalan, Medel P. Lim suan, Ben S. Malayang III
Institute of Environmental Science and Management,
University of the Philippines
Los Banos, college, Laguna, 4030 Philippines
Tel. (63)-049-5362251; Fax: (63)-049-5364101
E-mail : stm@mudspring.uplb.edu.ph
Abstract
This exploratory study attempted to apply the integrationof Remote Sensing (RS) and Geographic Information System (GIS) technologies in monitoring and assessment of the water quality of Laguna de Bay. More specifically, the study determined the correlation between TSS and reflectance of Bands 1,2,3,4,5,7 in Landsat TM utilizing the LLDA and NAMRIA data, taken in February 1992, March and April 1993.
Using the pearson's Correlation Analysis results have been shown that TSS values were significantly corrected to the reflectance of Bands 2 and 3. A reclassified image for TSS with the highest correlation was generated showing four reflectance ranges as indicated by the colors. These findings have shown that the two technologies with some validations could be an alternative tool for monitoring and assessment of the lake.
Introduction
Under pressure from human activities, aquatic ecosystems such as lakes, rivers and coastal areas have undergone profound environmental changes resulting in impairments or loss of the services they provide to humans. In Laguna de Bay, one of the pressures from human activities is the continuous discharge of sediment into it that seems to worsen the turbidity of the lake. This condition appears to be due to the presence of high levels of suspended solids in its waters and at certain times of the year, of phytoplankton population. Turbidity is considered to be one of the major environmental factors limiting the lake's productivity (Nielsen, 1983; Santiago, 1991; Batac-Catalan, 1995).
The technology used for measuring suspended solids is in situ measurement or collection of water samples for successive laboratory analysis. However, the need to provide both spatial and temporal variability becomes imperative for faster monitoring of the lake. The technologies that offer such capabilities are the Remote Sensing and GIS.
Suspended solids in water produce visible changes in the surface of the waters and in the reflected solar radiation. Such changes in the spectral signal from surface water can be captured by the satellite (Ritchie, 1990)
In View of these concerns, this exploratory study was conducted to monitor and assess the water quality of the lake. More specifically, it aimed to determine the correlation between the total suspended solids (TSS) in situ and the reflectance in the Landsat TM of Laguna de Bay utilizing the Laguna Lake Development Authority (LLDA) and National Mapping Resource Information Agency (NAMRIA) data, taken in February 1992, and in march and April 1993, respectively.
Methodology
Locale of Study
The Laguna Lake Basin is situated in Region 4 (Southern Tagalog) at coordinates 14o 11.6'to 14o 32.2' north longitude and 120o 2.7' to 121o 28.7' east latitude. It has a surface area of 90,000 ha. And is considered to be the largest feshwater body in the Philippines and the second largest freshwater lake in Southeast Asia (URSI, 1989). The areas of interest are the sampling points set by LLDA in 1992 and 1993. These are located in the West, south, Central and East Bays (Figure 1).
Collection of Available Secondary Data
The available raw landsat TM digital data (11 Feb 1992 and 2 April 1993) were provided by NAMRIA. The secondary data of TSS close to the Landsat TM dates obtained from LLDA. Other secondary data such as topographic maps with a scale 1:50,000 were obtained from NAMRIA for geometric correction. The climatological data were also taken from the Department of AGRO -Meteorology, UPLB and the Philippine Atmospheric Geophysical Astronomical Services Administration (PAG-ASA). The status of the napindan Hydraulic Control Structure (NHCS) was obtain from the Department of Public Works and Highways (DPWH).
Analysis of Data
Remote Sensing Phase
The geometrically-corrected satellite data stored in an exabyte tape was downloaded to the ERMapper network image processing system for image preprocessing. The pixels in the image wre then located using the longitude and latitude coordinates obtained from the field. When the exact pixel location was determined, the reflectance of bands 1,2,3,4,5 and 7 was shown in the data set text profile menu in the ERMapper.
Finally, Person's correlation analysis was used to determine the relationship of TSS and reflectance of bands. All inferential inferential test of hypothesis wee carried out at the 5% and 1% levels of significance.
