ONEVU

MICRO-CLIMATOLOGY PART

Nantes Observatory for Urban Environments (ONEVU) has been operational since 2008 for the long-term study of the hydrology, micro-meteorology, climatology, water, air and soils quality of the urban environments. It has been designed and set up in the framework of the Research Institute for Sciences and Techniques of the City (IRSTV, FR CNRS 2488) and its instrumentation (flux measurements, wind speed, temperature, moisture) has been developed and maintained by the DAUC group with the objective of analysing the micro-climatology of the urban fabric and developing and validating models for micro-climatology in heterogeneous urban sites.

Located at the fringe of the Pin Sec neighborhood in Nantes, a 30-meters high mast has been deployed and equipped for the measurement of heat and C02 fluxes. The main instrumentation, set up at 26 m, consists in a sonic thermometer/anemometer (Metek USA-1) combined with an infrared absorption gas analyser (Licor, Li7500 unitl May 2012, Licor 7200 after). Data acquisition is performed at a 20Hz time-rate and fluxes are estimated over 30 min periods using the Eddy Covariance method. Five humidity and temperature sensors (E+E, EE21) mounted along the mast (26m, 21m, 16m, 11m, 6m and 2m), an energy balance sensors (Kipp&Zonen, CNR4) and thermocouples mounted on surfaces representative of urban materials are also mounted on the site. They allow for the estimation of the fluxes via the gradient method and to estimate the energy budget of surfaces. Meteorological measurements are sampled every 6 seconds and 30 min statistics are then computed.

A network of humidity and temperature sensors (Rotronic, Hydroclip) has also been deployed since 2010 in the Nantes conglomeration to obtain the long-term spatial distribution of these quantities. This network has been augmented in the framework of the project URBIO (2013-2016) for the evaluation of the climatologic characteristics along a city-countryside gradient.

Specific field campaigns have also been performed in order to detail exchanges processes :
 

• FluxSAP (2010) : evaluation of the spatial distribution of turbulent fluxes in heterogeneous sites ;
• FluxSAP (2012) : evalution of the contribution of artificial or vegetated surfaces to the sensible and latent heat flux.

ONEVU has been funded by the contract CPER (2007-2013) MEIGVille2, and by FEDER (Fonds Européen de Développement Régional)