Centre for Remote Imaging, Sensing and Prcessing (CRISP)	CRISP's Research
Contact: crisp@nus.edu.sg	Copyright © CRISP, 2001

Red Tide Monitoring

It is important to monitor occurrences of algal blooms due to their strong social, economic and health impacts. Traditional monitoring programmes by in situ point measurements are expensive, time consuming and inadequate since they do not have sufficient spatial and temporal coverage to monitor the complex dynamic phenomena occurring during a red tide episode. It is believed that many blooms are occurring but are not detected.

Satellite remote sensing measurement of ocean colour provides a feasible complementary tool for red tide monitoring. As the individual phytoplankton pigments are characterised by their unique light absorption features, detection of specific optical features can discriminate individual pigments. This property allows detection of algal blooms by ocean colour remote sensing technique.

Research on Remote Sensing Monitoring of Red Tides

In a project partially funded by the National Space Development Agency of Japan (NASDA) through the Economic and Social Commission for Asia and the Pacific (ESCAP), CRISP and collaborators studied the feasibility of detecting red-tides by remote sensing. Collaborators in this project include the NUS Departments of Biological Sciences and Civil Engineering, Tropical Marine Science Institute of NUS, and the Marine Science Institute of the University of Philippines. The Royal Observatory of Hong Kong has rendered valuable assistance to the project team members when they were on field trips in Hong Kong.

The project team makes regular field trips in Singapore, and visited the Manila Bay and Hong Kong during red-tide outbreaks in 1998. Water samples are collected and sea surface reflectance is measured with a hand-held spectrometer. The water quality parameters measured were, among other things, the total suspended solid (TSS), chlorophyll-a (Chl-a), dissolved organic matter (DOM), total phosphate, total nitrogen and plankton cell count.

	Water Samples during field trips are collected for analysis of Water Quality Parameters
	Phytoplankton samples are collected using a phytoplankton net
	Reflectance spectra of water are collected using a portable spectroradiometer with 256 bands (350 to 1000 nm, at 2 nm bandwidth)
	Phytoplankton Cell Count and Species Identification are carried out in the laboratory

In the project period, red-tide blooms due to several different species of phytoplanktons have been observed. It was found that the reflectance spectra of the different types of blooms exhibit distinct characteristics. Based on the measured spectra, the responses of satellite-borne ocean colour sensors (existing and future systems) are simulated. The results suggest that satellite sensors such as the MODIS, and future MERIS and GLI will be able to detect red-tide blooms and, in favourable conditions, to identify the type of the blooms.

Reflectance spectra of algal bloom classes (Dinoflagellates) collected by a portable spectroradiometer

Reflectance spectra of algal bloom classes (Diatoms and Cyanobacteria) collected by a portable spectroradiometer

Results of spectral analysis of the sea water surface reflectance measured around Singapore show that it is possible to distinguish case II waters of different total suspended solids and chlorophyll-a loadings using the reflectance spectra. Attenuation coefficients of the case II waters can also be derived from reflectance.

(i) What are Red Tides; (ii) Ocean Colour Remote Sensing Satellite Sensors;