Ocean
Color Satellite Observation of Borneo Red Tide 2004
A
Preliminary Analysis of Ocean Color Data
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
Link to MODIS Rapid Response Website
http://rapidfire.sci.gsfc.nasa.gov/
Prepared on 16 March 2004
By C. K. Tan