Measurement of evapotranspiration and precipitation using a single instrument

Introduction

Evapotranspiration and precipitation are the key variables for the exchange of water between the soil and the atmosphere. Therefore they are very important for hydrology as well as meteorology. Dual-wavelength links are in principle able to measure these two variables if the wavelengths are in the optical (or infrared) and microwave ranges. Evapotranspiration is estimated by using these links as scintillometers (focusing on signal fluctuations caused by turbulence), and rainfall can be estimated by using the attenuation (reduction of the signal level) of the signals.

The figures above show (left) evapotranspiration (LvE, black and red lines) and sensible heat flux (Hs, blue and green lines) when the links are used as scintillometers (black andblue lines) compared to eddy-covariance measurements (red and green lines), and (right) precipitation estimated from microwave links (red without correction, red with correction) compared to rain gauge measurements (black lines). These are two examples of event-based analyses. Currently, no method exists to automatically distinguish between dry and wet weather, and hence all past analyses have been on an ad-hoc basis.

Activities

Four months of data from one infrared link and two microwave links (26 and 38 GHz) recorded at the Chilbolton (UK) test range are available. The aim of this project is to devise an automated algorithm to compute both of these fluxes. The main challenge for this is to distinguish between dry weather and rain based on link measurements. The algorithm can be tested by using eddy covariance data (for evapotranspiration) and disdrometer and rain gauge data (for precipitation).