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  • 1
    Electronic Resource
    Electronic Resource
    Air-surface exchange measurement in heterogeneous regions: extending tower observations with spatial structure observed from small aircraft (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Global change biology 2 (1996), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Strategies to assess long-term atmosphere-ecosystem exchange of CO2 and H2O must deal not only with time trends but also with spatial variability. Flux towers efficiently measure time trends, but only at discrete sites, always limited in number. Representativeness of these sites and the causes of spatial variation between sites are difficult to investigate from tower data alone. Such issues are better addressed with flux measurements from moving vehicles, particularly aircraft. Recent technological advancements in aircraft and instrumentation now allow mobile flux measurement with enhanced precision, greater ease, and lower cost. Results are presented which illustrate the importance of spatial variability, and some suggestions are given for assessment of flux-tower representativeness. Unfortunately, airborne observations of the kind presented here are practical only during a part of the daylight hours in brief intensive field campaigns. Extrapolation of spatial-structure information derived from these measurements to night-time or to long-term averages thus remains problematic. For the foreseeable future this extrapolation will require models that faithfully simulate both space and time characteristics of H2O and CO2 exchange. The development and validation of such models will be greatly enhanced by the increased availability of measurements from moving vehicles, which record spatial as well as temporal structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.1996.tb00079.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    An eddy correlation technique with extended applicability to non-simple terrain (1988)
    Springer
    Boundary layer meteorology 43 (1988), S. 231-245 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A system is described which is intended to calculate vertical fluxes of heat, moisture, momentum, and certain atmospheric pollutants at sites that are less than ideal. Fluxes, along with other turbulence statistics, are computed in real-time and printed at the end of each averaging period. The main elements of the program are (1) ‘detrending’ (by use of running mean removal), (2) calculation of the entire stress tensor (which allows a three-dimensional coordinate rotation to be performed on the covariances), (3) software-adjustable timing delays for each instrument channel, and (4) real-time graphic presentation of the raw data as stripchart images. The first two of these program elements tend to relax the normal site and sensor-leveling requirements. Sample results are presented, and the sensitivities of the calculated quantities to coordinate rotation and to mean removal time are examined for both ideal and non-ideal sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00128405
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Correcting airborne flux measurements for aircraft speed variation (1993)
    Springer
    Boundary layer meteorology 66 (1993), S. 237-245 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Airplane aerodynamic characteristics correlate aircraft speed with vertical wind velocity, making the time average inappropriate for estimating the ensemble average in airborne eddy-correlation flux computations. The space average, the proper form, is implemented as a time integral by a transformation of variables, which can be interpreted as a ground-speed correction to the time average. The mathematical forms are presented, and the importance of the speed correction is illustrated with airborne data. The computed correction is found to be highly variable, depending on both the turbulent flow encountered and the aircraft used. In general, the speed connection becomes more important as airplane size is reduced. For a small, single-engine Long-EZ airplane, used as an example, the straight time average erred, half the time, by 12%, 10%, 20%, and 15%, respectively, for computed fluxes of momentum, heat, moisture, and CO2. For a much heavier Twin Otter airplane, also used as an example, the straight time average erred, half the time by only 1%. These errors increased with decreasing altitude for the Long-EZ and with increasing altitude for the Twin Otter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705476
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    Paper (German National Licenses)
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