CORRELATION OF TURBIDITY WITH INDIAN REMOTE-SENSING SATELLITE-1A DATA

Indian Remote Sensing Satellite-IA Linear Imaging Self Scanning System (IRS-1A-LISS-I) multispectral digital data acquired over the Tawa reservoir region have been analysed to evaluate the turbidity in the surface water. Tawa reservoir water samples were collected on 20 October 1988 concurrent with an IRS-1A overpass. The turbidity was measured at each sampling point in the field with a nephelometer. Reservoir water samples were analysed for total suspended matter, grain size and mineralogy. IRS-1A-LISS-I computer-compatible tapes were obtained from the National Remote Sensing Agency (NRSA), India. The relationship between the LISS-I digital data of 20 October 1988 and the measured values of turbidity was established. The results indicate that, in the turbidity range between 15-45 NTU (nephelometric turbidity units), a positive relationship exists between the turbidity and the visible wavelength band 1, 2 and 3 (0.45 to 0.68-mu-m) mean pixel values. Shorter wavelengths, especially in band 3 (0.62-0.68-mu-m), are more useful than longer wavelengths (near infrared) in quantifying turbidity. The concentration, mineralogy and grain size of the suspended matters are the main factors which influence the reflected radiance at low concentration levels (15-45 NTU) of turbidity. There is a positive correlation between reflectance, turbidity and suspended sediment concentration. It can be concluded that, as turbidity increases in the 15-45 NTU range, the spectral response increases. It appears that IRS-1A-LISS-I data could he developed as a practical tool in water quality monitoring.