University of Twente Student Theses


Remote sensing of open water evaporation: A case study of Lake Tana, Ethiopia

Yitateku, Biserat Assegid (2012) Remote sensing of open water evaporation: A case study of Lake Tana, Ethiopia.

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Abstract:The diurnal cycle of Lake Tana evaporation is not well understood and requires further study. The main objective of this study is to assess the diurnal cycle of open water evaporation of the Lake Tana using ground measurement and remote sensing data. Remote sensing is used to fill the gap in the data that is created due to the lack of meteorological stations over the water surface and it also improves spatial coverage. Lake Tana is located in the North-western highlands of Ethiopia at 12000' N and 37015' E. The lake has an altitude of 1786m.a.s.l. with a surface area of 3000 km2, comprising about 20% of the 15000km2 drainage area. The estimation of evaporation from open water is a difficult process in that the necessary meteorological parameters are rarely measured over the water surface and the land based measurements are rendered by the thermal lag between the land and the water surface. By the use of remote sensing data the problem can be solved by obtaining data which covers the area spatially as well as temporally. In this study four methods are applied to estimate open water evaporation using the components of the energy balance: the latent heat, the net radiation, sensible heat and water heat flux. Firstly, a complete set of in situ data are used to estimate the evaporation and secondly, remote sensing data are used in combination with the in situ data. In both cases the methods are applied and estimates of the hourly evaporation from the lake are computed and assessment on the diurnal cycle of evaporation is made. The result showed that the net radiation and the water heat flux have large effects on the estimate of the hourly evaporation. In the diurnal cycle of evaporation the estimated value ranges from -0.09mm/hour at the night time to a maximum of 1.15mm/hour at the middle of the day. A daily estimate of 3.88mm/day from in situ data and 5.49mm/day for the remote sensing combined with the in situ data is found. The net radiation flux showed a stable negative value during the night and it increases steadily form the morning to the mid- day and then decreases. The hourly estimate of the open water evaporation from the Lake Tana shows the same trend. Key words: Lake Tana, net radiation, latent heat flux, water heat flux, diurnal cycle of evaporation
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:38 earth sciences
Programme:Geoinformation Science and Earth Observation MSc (75014)
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