poster - International Conference of Agricultural Engineering

Figure 2. Fully equipped Bowen station
Both compared sensors were installed at a height of 0.55m and 1.19m. Concretely
two E-type fine-wire thermocouples (chrome-constantan) with a diameter of 76 μm and two
CS215 temperature and relative humidity sensors (Campbell Sci. Inst., USA) constituted by a
thermometric probe for measuring air temperature (which integrates a platinum resistance of
1000 Ω) and a capacitive relative humidity sensor, were used. The ET values were
determined in duplicate: on the one hand, by using the ΔT values acquired from
thermocouples in the calculation of the Bowen ratio, and on the other hand, by using the
values obtained from RTDs. Collected data were analysed and filtered, and a regression
analysis of the calculated ET values was performed, discarding those values in which the β
value entered into the exclusion interval (Pérez et al., 1999).
3. Results
The water balance analysis gives evidence of the existence of sensible heat advection,
which was registered almost daily, except for some days. Several days, this phenomenon
was especially severe, reaching this sensible heat advection to contribute up to 64% of the
energy consumed in the evapotranspiration process.
The ET values measured by the lysimeter during all the days of the study, and mainly
in those in which the advection phenomenon was more severe, were underestimated by the
values provided by the BREB method (see figure 3). These results coincide with the ones
obtained by Dunin et al. (1991) and Prueger et al. (1997), who found that Bowen method
tends to underestimate the lysimetric values of ET in advection conditions.