Guidelines for Validating Bowen Ratio Data

For a variety of reasons, the measurement of latent heat flux using the Bowen ratio method can sometimes resultin erroneous data. This study provides guidelines for detecting erroneous Bowen ratio data and illustrates the applicationof these guidelines by comparing Bowen ratio and lysimeter data collected over grass and alfalfa in southern Idaho. Errorsin net radiation were detected by comparing measured with theoretical values. However, it was found that good theoreticalprocedures to validate soil heat flux data are lacking. Only empirical equations mainly used for remote sensing applicationsto obtain estimates close to noontime are available. Extremely inaccurate latent heat fluxes were easily filtered out byrejecting data when the calculated Bowen ratio (.) values were close to 1. A simplified procedure was proposed to rejectfluxes with the wrong sign, and three different equations were used successfully to detect the occurrence of condensation insidethe type of measurement system used in the study. Guidelines to assure adequate fetch are provided. Fetch did not affect themeasured fluxes in this study, which may have been due to the similarity in surface properties between the crops under studyand those in the surrounding fields.