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In selection of Mandya area for this project, our main consi- 
deration has been that Multispectral Scanner flights were being 
taken up by NRSA for another research Project in the same area. 
The area also provides water bodies with diverse turbidities. We 
have tried to include water bodies with wide ranging turbidity 
values. 
2.2 The following equipment were used for collection of data: 
I. ERTS Radiometer: It is a four channel radiometer having 
the same spectral bands as that of the Landsat (i.e.0.5-0.6um; 
0.6-0.7um; 0.7-0.8um). This instrument can be used to first 
determine the total irradiation from the sun and the radiance 
from the water. Using these two quantities, the percent re- 
flectance can be calculated as: 
Percent reflectance = Jradiance x 100 
Irradiance 
II. Secchi Disc: It is a circular disc of radius 20cm. which is 
painted black and white on alternate quadrants. The reflec- 
tance as measured in the laboratory is about 85 percent for 
white paint and 2.5 percent for Black paint. The Secchi Disc 
is used to measure Secchi depth (the depth at which the disc 
just becomes invisible in the water). Secchi depth is inversely 
proportional to the turbidity of the water. 
III.Modified Secchi Disc: A square Aluminium plate of side 20cm. 
which is painted white on one side and black on the other 
with reflectance values 85 percent and 2.5 percent respectively 
as measured in the laboratory. 
IV. Ground truth ladder and vehicle: A Landrover vehicle modified 
for collecting ground data has been used for this purpose. 
The top portion of the vehicle is modified to be used as the 
base of the ladder. The ladder which is assembled in the 
field consists of four stages and on full assembly extends 
to a height of about 9 meters. À 1 1/2 mtrs. x 1 1/2 mtrs. 
platform enables the investigator to stand on top with the 
instruments to collect the data. From this ladder which could 
be erected only at a water band we could collect information 
at a viewing angle of about 70$. 
V. Multispectral Scanner: This is an Eleven Channel digital 
multispectral scanner, which is operated from an aircraft 
platform, at an altitude of about 1000 meters. Eleven spectral 
bands of data are collected and recorded, 10 in the visible 
and reflective near-Infrared portion and one in the termal 
Infrared region. A brief description of the system can be 
found in Appendix A. 
Two ground data collection missions were taken up in the months 
of November and December 1977. The November data is used to test 
the equipment and methodology and to standardize the procedure. 
The December data collected from December 15-21 is used for 
analysis.