Ocean Color Satellite Observation of Borneo Red Tide 2004
Can We See The Red Tide from Satellite?
The Observation Using MODIS True Color 250m Resolution Imagery
Normally, the satellite sensors that designed for the land application have very limited ability for ocean observation. However, some of these sensors having higher resolution than the ordinary ocean monitoring sensor, which giving advantages to the local and smaller scale observation. As the consequences, the higher resolution land sensor may capture the area of red tide efficiently.
MODIS true color imagery (250m resolution) from MODIS Rapid Response System had been downloaded and examined its possibility for detecting red tide. Figure 1 and 2 show the MODIS 250m true color images before and after enhancement, respectively. The image was enhanced using root enhancement technique. In figure 1, we can distinguish the difference between land, cloud and sea easily. The coastal water appears to be more greenish color, while some area in the Brunei Bay showing brownish color, which was loaded with high sedimentation. At the top right of the image, we can see the Mengalum Island and some shallow shoal. After the enhancement, features in the ocean become clearer. The turbid coastal water can be clearly seen, and its distribution pattern can be studied. While, we are try to look for red tide, and two darker spot in the ocean had been highlighted. By comparing these two spots with the chlorophyll a image, we understand that this was the area of phytoplankton bloom. Besides, some area around Brunei and in the Brunei bay also displayed slight darker color.
The possible theory behind this is the pigment of phytoplankton that will absorb light, especially at blue spectrum. When the phytoplankton concentration become very high, strong absorption will occur at the green spectrum too. However, the shadow of cloud cover will also create the same result. Careful examination must be done in order to avoid any misinterpretation. Up to present level, the observation of these two spots are not yet been confirmed by any in-situ information.
Figure 1. MODIS 250m true color on 31 January 2004
Figure 2. Enhanced MODIS 250m true color image on 31 January 2004
Figure 3. MODIS Level 2 (1km) chlorophyll a image
Prepared on 16 March 2004
By C. K. Tan