Bathymetry in clear waters from Landsat-5 Satellite Data
Dr. Mohd Ibrahim Seeni Mohd, Samsudin Ahmad, Mohamad Yem
Centre Remote Sensing
Faculty of Surveying
Universiti Teknology Malaysia
Locked Bag 791
80990 Johor Bahru
Malaysia
Abstract
The coastal waters of the world are o importance to navigation. However, the sea bottom topography in these areas undergo frequent changes due to coastal process such as erosion and siltation. As a result , hydrographic charts in these areas have to be updated frequently for safe navigation. Satellite remote sensing techniques can be used together with limited water depth measurements from conventional methods to chart the coastal areas in a cost-effective manner.
This paper reports on a study to obtain water depths in the coasts! Waters of Pulau Tioman, Malaysia using the Landsat-5, Thematic Mapper data that were acquired on 1 April 1990. Band 1 ( 0.45 – 0.52 mm ) of the data was used since it has the best depth penetration capability in the relatively clear waters of Pulau Tioman. A computer program was written to correct the satellite data for atmospheric effects prior to computation of water depths. An algorithm which expresses the exponential relationship between water depth and pixel intensities were used together with a few in-situ calibration depths that were taken at the time of satellite pass. Comparisons of calculated depths with in-situ measured depths at some check points indicate an error of 0.5. – 2.0 m in depths of up to about 50 m of water.
1. Introduction
Hydrographic surveying by conventional shipborne sounding techniques is slow, hazardous and expensive. As a result , interest has been generated in the application of remote sensing techniques at last in the critical shallow areas which are frequently used by ships approaching or leaving ports or harbours. Satellites can provide an extremely effective means of carrying out preliminary surveys over wide areas, especially in remote regions. Ships need then be used only in those areas where closer investigation is indicated and in this way the sending of ships on unproductive surveys may frequently be avoidea. In the preparation of hydrographic charts satellite data may be used to fill in contours between lines of ship soundings and may reduce the number of soundings required and hence the cost. Furthermore, because of the frequent over flights satellites provide an effective means of monitoring changes to the coast and seabed.
The possibility of using remote sensing technology was addressed as early as the late 1960s (Brown et al. 1971) These studies led to the NASA/ Cousteau Ocean Bathymetry Experiment in 1975 which demonstrated the feasibility of using Landsat high-gain multispectral scanner (MSS) data in bathymetry ( Polcyn 1976 ). Since then, a number of studies have been carried out.
