Estimation of path-average evaporation and ...

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XVI International Conference on Computational Methods in Water Resources (CMWR-XVI) Ingeniørhuset

Estimation of path-average evaporation and precipitation using a microwave link
Author:Han Stricker <> (Wageningen University)
Wouter Meijninger <> (Wageningen University)
Hidde Leijnse <> (Wageningen University)
Remko Uijlenhoet <> (Wageningen University)
Presenter:Hidde Leijnse <> (Wageningen University)
Date: 2006-06-18     Track: Special Sessions     Session: Field measurements and simulations of land-atmosphere interaction

The potential of a 27 GHz microwave link for measuring both evaporation and precipitation is investigated. For the estimation of evaporation a combination of the microwave link (radio wave scintillometer) and an energy budget constraint is proposed. This Radio Wave Scintillometry-Energy Budget Method (RWS-EBM) has been tested using data from an experiment with a 27 GHz radio wave scintillometer over 2.2 km and four eddy covariance (EC) systems. Comparing one day of measurements (30- minute intervals) of the evaporation estimated using the RWS-EBM to those measured by eddy covariance systems leads to the conclusion that the method provides consistent estimates under relatively wet conditions. In the case of precipitation, analyses show that the specifc attenuation of an electromagnetic signal at 27 GHz varies nearly linearly with the rainfall intensity, which is ideal for line-integrating instruments. Data from an experiment with a 4.89 km microwave link and a line configuration of seven tipping-bucket raingauges are used to test whether this instrument is indeed suitable for the estimation of path-average rainfall. Results from this experiment show that the attenuation due to wet antennas can have a significant effect on the retrieved rainfall intensity. However, when a two-parameter wet antenna correction function is applied to the link data, comparisons with the raingauge data show that the instrument is indeed well-suited for the measurement of path average rainfall.