CNRM, INRA and Laboratoire d’Aérologie surface measurements will be installed on an irrigated, agricultural parcel covered by beans. This field is a part of the farmland called “La Cape Sud”, which is a more than 6 km2 cultivated area inside the Landes forest. Individual fields cover an area of 0.30 to 1km2, and the region is completely flat, which allows good fetch conditions for surface flux measurements. In the same farmland, but about 3 km away from this bean field, INRA will install a flux station on a maize field.

The measured parameters are described in the table below. The main meteorological parameters (wind, radiation, temperature and moisture) are measured at 2m height, whereas atmospheric pressure is measured at 0.3m. Rainfall is measured by both a tipping bucket rain gauge and an optical ORG device. Below the surface, temperature and water content are measured at various depths (see table below).

Fluxes of momentum, sensible heat, latent heat and CO2 are computed with conventional eddy-correlation technique, on the basis of 20Hz measurements done by a sonic anemometer and an open-path gas analyser (Li7500).

Emission/deposition of Ozone and nitrogen oxides are also measured on this site: Ozone flux is computed with eddy-correlation technique by INRA, from the measurements performed by their fast-response analyser, calibrated against a slow-response TEI sensor. A relaxed eddy-accumulator (REA), built at CNRM, is set up with a second sonic anemometer, in order to measure the fluxes of CO2 and water vapor (using a Li 6262 closed-path IR gas analyser), and of NOx (using a TEI gas analyser). According to the well-known REA method, the system pumps the air at a constant rate as close as possible to the sonic anemometer sampling volume, and alternatively fills two bags according to the sign of the instantaneous vertical velocity. After the sampling period (20min.), the contents of the bags is analysed and the system is emptied in order to start the next 30 min. cycle. During the sampling phase, the analysers (of CO2, H2O, NO and NO2) are used to measure the ambient mean concentration of these gases. Details on the system can be found in Brut et al. (J. Atmos. Ocean. Tech., 2004). The REA will be installed close to the eddy-correlation station, so the CO2 and latent heat fluxes will be computed with two different techniques and therefore thoroughly compared.

During two or three weeks in the beginning of the campaign, NO soil emission will be measured by the Laboratoire d’Aérologie with the chamber technique. This value will be analysed jointly with the NOx flux measured by the REA, this latter flux being the difference between the NO soil emission and the NO2 deposition at the surface of the soil and the vegetation.

The site coordinates are :

Longitude : 0° 35.85 min. W
Latitude : 44° 24.00 min. N
Altitude : 70m

table VI.5.6-a : measured parameters

(*) Not measured during the REA bag analysis period (10 min. every 30 min.)