Investigation of Chlorophyll-an in a Small Reservoir by Landsat 7 Imagery

Abstract

Chlorophyll-a (chla) is a source of water pollution. Monitoring the quality of water in reservoirs is necessary to take any action for protecting the water quality. Traditional methods of sampling are usually costly and time consuming. Also they need skillful labors and some areas are out of reach or sampling at those areas is dangerous. Remote sensing technology could solve problems of high cost, time consuming and unavailability of traditional sampling methods. Landsat 7 imagery is a suitable resource of data because it has been using since a long time ago and could be used to analyze past events. This research aims to investigate the possibility of eutrophication assessment in Ecbatan reservoir using remote sensing images. Field data of the study such as chla were collected in 2010. To reach this aim first the Top of Atmosphere (TOA) reflectance of imagery was calculated for each band. Then the relationship between concentration of chla and reflectance values was determined. Different conversions were applied on reflectance values at the next step to find the best regression equation for estimating the concentration of chla. The best model for estimating the concentration of chla was based on the band ratios. The values of R²_Adj and SE are 0.91 and 0.04 respectively for this model. Based on the results of this research Landsat 7 is capable of reflecting the eutrophication problem in a small reservoir as Ecbatan.