Journal article

Publication year: 2005

Pages: 29-37

Journal: Landbauforschung Völkenrode

Volume number: 55

Issue number: 1

ISSN: 0458-6859

URL: https://www.openagrar.de/receive/timport_mods_00030895

Publisher: Forschungsanstalt für Landwirtschaft

Abstract: 
Measurements of meteorological parameters are normally reduced to one set of instruments without replication. If the data are used to generate flux data for the modelling of momentum, heat and matter fluxes between atmosphere and vegetation, the order of magnitude of errors has to be known. Errors arise both from the fact that many instruments are not calibrated individually, as well as from patchiness of vegetation and soil even in ecotopes which are normally considered horizontally homogeneous. In order to quantify the overall errors, experiments were performed with sets of equal or similar instruments whose results were compared under otherwise identical conditions. We concluded that for wind velocities, an overall error a of 0.1 m center dot s(-1) should be assumed for high resolution cup anemometers; 0.2 m center dot s(-1) are adequate for standard instrumentation. Vertical gradients of wind velocities near the canopy can be resolved with a precision of 15 to 20 %. Air temperature measurements are normally performed using instrumentation with a (nominal) resolution of 0.1 K. Air temperature measurements are much more sensitive against spatial inhomogeneities of the canopy than wind velocity measurements. Air temperature gradients require a resolution of 0.01 K which presupposes careful intercalibration of the sensors. The potential to establish air temperature gradients in one location must not lead to the conclusion that these measurements are representative in space; the gradients assessed are in the order of magnitude of the errors, especially at noon. Measurements of relative air humidity are afflicted with an error of 2 %. For precipitation measurements, the overall error is in the order of 0.1 mm per half hour or 5 to 10 for monthly sampling, provided that a flow distortion correction has been performed. Even measurements of entities which are independent of the patchiness of the plant/soil system such as global radiation are not necessarily representative in space if one sensor only is exposed.

Harvard Citation style: Dämmgen, U., Grünhage, L. and Schaaf, S. (2005) The precision and spatial variability of some meteorological parameters needed to determine vertical fluxes of air constituents, Landbauforschung Völkenrode, 55(1), pp. 29-37. https://www.openagrar.de/receive/timport_mods_00030895

APA Citation style: Dämmgen, U., Grünhage, L., & Schaaf, S. (2005). The precision and spatial variability of some meteorological parameters needed to determine vertical fluxes of air constituents. Landbauforschung Völkenrode. 55(1), 29-37. https://www.openagrar.de/receive/timport_mods_00030895