Consiraints and refinement of radiative transfer model for bathymetric mapping from satellite remotely sensed data
Mazlan Hashim and Samsudin Ahmad
Center for Remote Sensing
University of Technology Malaysia
Locked Bag 791, 80990 Johor Bahru
Malaysia
Abstract
This paper examines the a customization of radioactive transfer model for correlating the reflectance to-depth of a typical turbid coastal water of Malaysia, hence enabling the bathymetric information be extracted from satellite remotely sensed data.
Introduction
Hence the launching of the Earth Resources Satellite Series (ERTS); (ANDSAI) 1,2,3,4,5, SPOT-1 various stations have been carried out for extracting bathymetric information from water covered area. Hammock (1977) had shown that multispectral scanner data (MSS ) within visible wavelength, band 4 00-5-0-6mm and band 5(0.6-0.7mm) are very useful for updating hydrographic charts. Misplaced or uncharted reefs and shoals could easily be detected and located. The near-infrared and infrared bands (0.7.1.1mm) are excellent for mapping the contact between land and water such as coastline. Studies by Gordon et.al. (1975) Poleyn and Lyzenga 91979) have also revealed that lands at 4 MSS data: band 4 under perfect weather condition has the capability of penetrating within the range of 24 to 40 meters while band 6 is about 2 meters. On using finer resolution data, Hallada and Lanis (1984) band that band 1 )0.45-0.52mm) and band 2 (0.52.0.60mm) of Lands at 4 Thematic Map per data were capable of penetrating 20 and 14 meters, respectively.
All the above-mentioned studies have obtained bathymetric information from satellite imagery based on radioactive transfer model which deal directly on using local in situ measurements such as water attenuation coefficient, bottom samples, sea surface state, etc. at the region being studied. Although this approach is most appropriate, a considerably large amount of effort is needed in collecting in-situ information and later much processing time is taken in reducing the field samples. Alternatively, this research will concentrate on a simplified approach of correlating the depth of a water body against its reflectance recorded by a satellite sensor. This hybrid radioactive transfer model : the single band and two reflectance models are adopted in computing the water depth from satellite digital data.
Study area and dcigital data
Four test area, located both in the eastern and western coasts of Peninsular Malaysia were distributed. The four test sites : southern waterway of Langkawi Island to Kuala perils : South port of Pelabuhan kelag; off Bandar Hilir to Fan Jung Keling, Melaka, and Tanjuna Leman to Tanjung Tenggaroh of Mersing .
The satellite digital data SPOT-1 and lands at 5 MSS were used in the study. These data were later geometrically corrected by registering to the corresponding nautical chart of the given area. A second degree polynomize transformation is employed in
establishing the framework for geometric correction. This is then followed by a resembling process.
Methodology and data manipulatrion
After the satellite imagery is correctly registered to the corresponding nautical chart, the shallowest and deepest points are identified. These two points are needed to verify the correlation of the reflectance values and the depth of the water column. In formulating the correlation, the period known depth obtained from nautical chart corrected for tidal height at the time of data acquisition was used.
