Data coverage

Supported by

Uniwersytet Wrocławski

System

The objective of the EvapProg system is to determine the real-time forecasts of evapotranspiration using the Penman-Monteith method, abbreviated hereinafter as ETPM, and to limit the calculations to a user-defined basin for a purpose of hydrological models. The approach is based on current meteorological forecasts from the Weather Research and Forecasting (WRF) model and the current values of Leaf Area Index (LAI) obtained from observations conducted by AQUA and TERRA satellites in the infrastructure of MODIS (Moderate Resolution Imaging Spectroradiometer). The ETPM calculations are constrained by the snow masks obtained from the Snow Extent (SE) products provided by DMSP (Defense Meteorological Satellite Program) platform.

    The EvapProg system consists of two parts: (1) a module for the real-time computation of the ETPM forecasts for the entire Poland and (2) a user-oriented module for extracting ETPM forecasts for a purpose of hydrological modelling (maps limited to basins, basin-scale averages, adjustable time resolution, adjustable time span of forecasts). The second module is run on user demand, however utilizes the up-to-date information produced in real time by the first module.

    The figure presented below shows the data processing procedures carried out in real time during a single day by the first module. There are highly independent two groups of procedures, called INPUT DATA and PROCESSING.



    The procedures that fall into the INPUT DATA group aim to produce the most up-to-data input data required to compute ETPM. The Leaf Area Index (LAI) data are downloaded from the MODIS infrastructure (Knyazikhin et al., 1999), however the time of their availability varies and data are often of low quality, for instance due to clouds. The system waits for new data and, when they are available, runs interpolation based on the TIMESAT processing (Jönsson and Eklundh, 2002, 2004). This may cause that new data may occur at any time, and if no data is available, the previous observation is treated as the up-to-date information. The SE data are downloaded from the DMSP system (Chang et al., 1987), and snow masks are produced. If no current SE data is available, the previous observation is assumed as the most up-to-date. The WRF model (Skamarock et al., 2008) is run externally by the “Meteorology” grid and provides updates for starting prediction epochs at 00:00, 06:00, 12:00 and 18:00 UTC which are available with time delay of approximately four hours. We extract predictions of eight meteorological parameters from WRF, namely: pressure (on surface), temperature (2 m), relative humidity (2 m), wind velocity (10 m), albedo, short wavelength incoming radiation, long wavelength incoming radiation, long wavelength outgoing radiation. We also use the gridded resistance maps, i.e. the aerodynamic resistance (ra) is expressed by a set of seven maps valid for various periods of the year (they do not differ from year to year) and the canopy resistance (rc) is represented by a single map valid for all periods and years.

    The procedures of the PROCESSING scripts are run at specific times – i.e. 04:00, 10:00, 16:00 and 22:00 CEST – and take the most up-to-date set (LAI, SE, WRFp, ra, rc) produced by procedures of INPUT DATA in order to calculate ETPM for the entire Poland, with the limitation to areas without snow cover.

    The ETPM predictions for the entire Poland are available in the external service meteo.plgrid.pl, but hydrologists are provided with yet another tool – the Application Programming Interface (API) which extracts the ETPM forecasts limited to the user-defined spatial (specific basin) and temporal (time span, time resolution) characteristics.


References


Chang A.T.C., Foster J.L., Hall D.K., 1987. Nimbus-7 SMMR Derived Global Snow Cover Parameters. Annals of Glaciology 9, 39-44.

Jönsson P., Eklundh L., 2002. Seasonality extraction by function fitting to time-series of satellite sensor data. IEEE Transactions on Geoscience and Remote Sensing 40 (8), 1824-1832.

Jönsson P., Eklundh L., 2004. TIMESAT - a program for analysing time-series of satellite sensor data. Computers & Geosciences 30, 833-845.

Knyazikhin Y., Glassy J., Privette J.L., Tian Y., Lotsch A., Zhang Y., Wang Y., Morisette J.T., Votava P., Myneni R.B., Nemani R.R., Running S.W., 1999. MODIS Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation Absorbed by Vegetation (FPAR) Product (MOD15) Algorithm Theoretical Basis Document. NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.

Skamarock W.C., Klemp J.B., Dudhia J., Gill D.O., Barker D.M., Duda M.G., Huang X.-Y., Wang W., Powers J.G., 2008. A description of the advanced research WRF Version 3. NCAR Technical Note, NCAR/TN-475+STR. Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, CO, USA.

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