Uncertainty due to hygrometer sensor in eddy covariance latent heat flux measurements

Half-hour latent heat flux (LE) was measured over an early-maturing peach orchard (Prunus persica L.) by two different hygrometers: (1) infrared gas analyzer (IRGA) (LI-COR, model LI-7500) and (2) ultraviolet hygrometer (Campbell, KH20). A good agreement between LE obtained with the IRGA (LEIRGA) and the KH20 (LEKH20) hygrometers was observed. During rainy periods, LEIRGA and LEKH20 were not reliable due to failure of the instruments caused by water drops standing over the sensors heads. Filtering out rainy periods improved the similarity between LEIRGA and LEKH20: mean estimation error, 6.2 W m−2; root mean square error, 21.3 W m−2; and refined index of agreement, 0.919. Even though the IRGA hygrometer is generally recommended, when economic constraints exist, the KH20 hygrometer can be used with similar confidence.