University of Twente Student Theses


Mapping colored dissolved organic matter (CDOM) of Nashiva Lake (Kenya) from MERIS satellite imagery

Daksa, Bashana Wondimu (2011) Mapping colored dissolved organic matter (CDOM) of Nashiva Lake (Kenya) from MERIS satellite imagery.

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Abstract:Sustainable use of Lake Naivasha water and sustainable protection of its aquatic environment require water quality monitoring which are important factors to offset impacts from future development. Colored dissolved organic matter is one of the components of water quality component along with turbidity and Chlorophyll a. Given its importance for the structure and function of the lake ecosystems, satellite remote sensing that could estimate the concentration of CDOM in Lake Naivasha would be highly desirable to investigate its concentration data. In situ measurements of absorption coefficients of the lake water constituents and optical measurements were carried out at 93 sampling sites in lake Naivasha. Remote sensing reflectance measured by a hyperspectral handheld spectroradiometer was used to retrieve the ratio of CDOM to total absorption coefficients ( CDOM t a /a ) at 412 nm. The coefficient determination ( 2 R ) and RMSE between in situ and retrieved from optical measurements were 0.81 and 0.05 respectively. The ratio between CDOM and total absorption coefficients in the Lake was found to vary from 0.09 (in the main lake) to 0.67 (in the Crater lake) with an average value of 0.24. Remote sensing reflectances retrieved from MERIS satellite imageries of Lake Naivasha that were acquired on 20th, 23rd and 26th September 2010 concurrently with in situ absorption measurements of total CDOM were utilized for cross validation. Values of the ratio at 412 nm retrieved from MERIS imageries correlate ( 0.84; 0.03 2 R  RMSE ) with value of CDOM a /at) at 412 nm measured during field campaign and hence, one can simply retrieve the value of absorption coefficients of CDOM in the lake from MERIS imageries by strategic sampling and improving laboratory measurement of total absorption coefficients of the lake Naivasha by using empirical algorithm proposed for optically complex water. The spatial variability of concentration of CDOM is insignificant with average value of 4.06+-0.63 m-1 where as Absorption of particles in the lake varies between 2.30m-1 and 34.31m-1 with an average value of 14.36 m-1 and a standard deviation of 5.51 which confirms the large variability of suspended particles (phytoplankton and non algal particles) in the lake that influence the quality and quantity of subsurface irradiance in the Lake.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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