Verifying the BR-DTS method with hand measurements executed with the PT-100 and the Eddy Covariance method

Verifying the BR-DTS method with hand measurements executed with the PT-100 and the Eddy Covariance method

van Iersel, T.A.

Coenders, A.M.J. (mentor)
Schilperoort, B. (mentor)

Civil Engineering and Geosciences

Water Management

2016-12-16

Within hydrology evaporation is one of the most important terms in the water- and land surface energy balance. However evaporation is difficult to estimate accurately. Conventional techniques to measure actual evaporation have their drawbacks. One of the main drawbacks is that multiple sensors need to be used, with all their own bias. One of these techniques, the Eddy Covariance (EC) system has the drawback that it is dependent on weather conditions and is known for its problems with closure of the energy balance (Foken, 2008). A new method called the Bowen Ratio- Distributed Temperature Sensing (BR-DTS) method is introduced by Euser et al. (2014). This method determines the Bowen ratio which is the ratio between the sensible heat flux and the latent heat flux. The BR-DTS method measures temperature using a fiber optic cable. This cable is placed vertically along a tower, the cable going up is dry and the cable going down is wrapped in cotton and kept wet. With the dry and wet temperature of the DTS-cable the air temperature and vapour pressure can be determined. By having a large amount of measurements over the height and measuring it with a single sensor the BR-DTS method does not have the problem of varying biases of sensors (Euser et al. 2014). The aim of this study is at first to verify if the temperature data of the dry and wet cable are correct and second to compare the outcome with the EC data. The temperature of the dry and wet cable measured with the BR-DTS method are really close to the temperatures measured with the relative humidity sensors with a maximum R2 of 0.998 at 4 and 16 meter height for the dry cable and a maximum R2 of 0.988 at 16 meter height for the wet cable. The energy gap found is relatively small, see figure 11, and the latent heat flux measured with the BR-DTS setup is just as in the results from B. Schilperoort (2015) greater than the latent heat flux measured with the EC setup. On the other hand the sensible heat flux measured with the BR-DTS setup is smaller than the sensible heat flux measured with the EC setup which is in contradiction with the results from B. Schilperoort (2015).

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(c) 2016 van Iersel, T.A.