Abstract:
Satellite data has long been in use to estimate the water-spread area at different water levels of
a reservoir. Traditional approaches such as maximum likelihood classification and band
threshold method involve the per-pixel approach to delineate the water-spread area of a
reservoir. One of the limitations of the per-pixel approach is that the pixels representing
reservoir border, containing water with soil and vegetation, are also classified as water pixels,
thereby giving inaccurate estimate of the water-spread area. To compute the water-spread area
accurately, the sub-pixel or linear mixture model (LMM) approach has been adopted in this
study. IRS-1C and 1D satellite image data (24m) of eight optimal dates ranging from minimum
draw down level (MDDL) to full reservoir level (FRL) were used to estimate the water-spread
area of the reservoir. The extracted water-spread areas using sub-pixel approach was in turn
used to quantify the capacity of the Nagarjuna Sagar reservoir for the water year 2002. The
estimated capacity of the reservoir using sub-pixel approach was 8014.49 Mm3.
