3. Procedure: 
3.1 Percent reflectance: The data collection consists of first 
determining the sun irradiation. This was done by using ground 
glass filters on the four sensors of the ERTS Spectro radiometer 
and focussing perpendicularly on the sky from top of the ladder. 
The procedure is repeated to collect the radiance from water 
using plane glass filters and focussing the instrument on the 
water. 
Radiance and irradiance values were determined between 11 A.M. 
and 3 P.M. in order to maintain uniformity of sun angle and 
other factors. All readings were taken on clear sunny days only. 
3.2 Secchi Depth: Secchi depth measurements were made by immersing 
Secchi disc in the water to a depth at which the disc first dis- 
appears and the relevant depth noted. The mean depth and maximum 
depth of water were measured using a meter stick. 
3.3 Extinction Depth: To measure the bottom reflectance effect 
the white plate is immersed at various depths and the corresponding 
radiance from the plate measured. This was done by two persons, 
one standing in the water and holding the plate at various depths 
and the other focussing the instrument vertically on the plate. 
The percent reflectance of the white plate which is 85 percent 
outside the water reduces as the depth is increased and finally 
it remains constant. The depth at which the percent reflectance 
remains constant is the depth beyond which the water bottom does 
not contribute to the measured reflectance of the water body. 
A water sample is collected from the site of data collection and 
later analysed using a Colorimeter and the relative turbidity of 
the water determined.