Experiences from one-year continuous operation of a large aperture scintillometer over a heterogeneous land surface

Many applications in meteorology, climatology, hydrology and agriculture require routine estimates of the turbulent sensible heat flux representative for an area of about 10*10 km^2 in magnitude. Over a homogeneous surface, these data can be obtained from local point measurements using profile or eddy correlation techniques. On the other side, over a heterogeneous land surface, as it is typical for large parts of Central Europe, special techniques are necessary to estimate the area-averaged fluxes. These may be mathematical (aggregation) models or integrating measurement techniques.

A technique able to provide area-averaged estimates of the sensible heat flux and suited to be applied continuously with low costs is the use of scintillometers. A large aperture scintillometer has been operated in the LITFASS area (Germany) in an heterogeneous landscape over a distance of 4.7 km for more than a year starting in May, 1998. For daytime non-stable stratification, the turbulent sensible heat flux has been determined from the scintillometer measurements.

Experiences from the long-term, continuous operation of the scintillometer will be discussed including methods for data quality assessment and the annual cycle of data availability. The estimated heat flux values are compared with local measurements (profile method / eddy correlation method) over a grassland site. The mean daytime evolution of the sensible heat flux for each month of the year is compared with the diurnal heat flux cycle simulated for the LITFASS grid cell with the numerical weather prediction model of DWD.