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LML Downward Longwave Irradiance
Validation

DLI Match to Data Base

The calculated DLI is routinely compared to pyrgeometer measurements over land to estimate its accuracy, using a Match Up Data Base (MDB), which contains coincident pyrgeometer measurements and calculated DLI :

  • calculated DLI : average on a 0.3 degree square box centered on the pyrgeometer station.
  • measured DLI : hourly value centered at the time of the satellite image, obtained by integration of several measures (or interpolation).

    • The MDB is updated in near real time for satellite data and off line for pyrgeometer measurements, with a delay of about 50 days. Non automatic updates may occur in cases of numerous missing measurements.

    The validation is made on a limited set of measurement stations :

  • List of pyrgeometer stations.
  • Map of pyrgeometer stations : An abbreviated name is indicated for each station and different colors are used for the various data networks.

    DLI validation results

    Error statistics (where error means calculated DLI minus measured DLI) are calculated monthly, separately for each satellite, GOES and MSG, and globally on the LML area. The errors are expressed in W/m2 and in percentage of the mean mesure. The last available results are presented :

    A crude filtering is applied to the monthly results, however it can only eliminate the cases where one station is strongly erroneous compared to the others.
    A more careful validation has been made on one year data set, but restricted to the U.S.A. stations, it had been presented in [conference paper].