Spectral Reflectance and Algal Bloom Monitoring of Lake Victoria Using Remote Sensing Techniques, Winum Gulf of Kenya

Abstract

: The study was aimed at measuring the in situ spectral reflectance of Lake Victoria fresh water which contains algal blooms and different suspended solids. Reflectance spectra of wavelengths 340-1,018 nm were collected from Lake Victoria fresh water using a portable spectroradiometer. The data was collected on a cloud free day between 0912 to 1022 hours. Sunlight was used as a source of illumination while dark surface was applied as control to obtain a near-normal angle of observation at a Pacific Daylight Time (PDT) on 27 th October 2022. Google Earth Engine (GEE) was used in analyzing the satellite images of Lake Victoria, Winam Gulf with NDCI index technique which provides an estimation of the chlorophyll-a concentration. The averaged spectrum of the Lake Victoria water showed reflectance maxima from 580-710 nm and reflectance minima near 430 nm and above 740 nm wavelengths. This study showed that the higher the NDCI value, the higher the concentration of chlorophyll-a , the more sever the algal bloom. On average, the concentration of chlorophyll-a was high at 33-50mg/m 3 and highest values recorded between January and February of every year due to high temperatures during the dry season. The Winum Gulf of Lake Victoria is characterized by increasing eutrophication arising from increased anthropogenic activities on the shores of the lake. Major factors contributing to the increased eutrophication include Urban sprawl, industrial loads and agricultural activities. The study, therefore, presents the algal bloom situation and spectral reflectance of the lake under the influence of human activities surrounding Lake Victoria.