How to read and plot SM-DAS-2 and SM-DAS-3 Grib files

The SM-DAS-2 and SM-DAS-3 products are provided in GRIB-1 format, on a Gaussian grid at the resolution T799, corresponding to N400 (~25 km).

There are several tools available to read and plot grib files. Three applications and examples are provided to read grib files and extract data on specific location (e.g. on validation test sites).

1- Use GRIB API to extract time series over specific sites

We recommend to use the GRIB API software to read grib files. GRIB API can be downloaded from the ECMWF GRIB API web page. It needs to be used under Linux or UNIX systems.

For example if your SM-DAS-2 grib file is named SM-DAS-2_2009122700.grib, the command to extract data from the four nearest grid points from latitude YLAT and longitude XLON is:
grib_ls -p step,shortName -l XLAT,XLON SM-DAS-2_2009122700.grib

A more comprehensive script (and readme file) is given here with GRIB API to extract time series over four test sites. The example contains 3 directories:
- grib contains grib files of SM-DAS-2 31 for December 2009 (31 files).
- prog contains the script that needs to be used to extract SM-DAS-2 in acsii over 4 test sites.
- ascii_sites contains the times series extracted in ascii for the four test sites.
The readme file explains how to use and to modify the script. For any further questions concerning this example please contact Patricia.Rosnay@ecmwf.int.

2- Use Metview-python and other python libraries for reading and plotting

• Metview-python is recommended to extract and plot SM-DAS-2 and SM-DAS-3 grib data.This is essentially a python interface to the ECMWF Metview library.
• The software requirements, documentation and examples for metview-python can be found on the github page and ECMWF confluence page
• The following examples require this software, which is freely available on github: python 3.6, metview, pandas, pylab, matplotlib, numpy and cartopy.
• If you need to install this software, the following scripts will install it in a local conda environment on linux or macOs:
  
  • conda_env_setup_linux.sh
  • conda_env_setup_macOS.sh
• Examples:
  • jupyter-notebook examples
  • Plotting and saving a root-zone SWI time series of local data
  • Global plot of root-zone soil wetness index with metview-python
  • Conversion to regular grid and plot with cartopy

For any further information about using metview-python to read and plot SM-DAS-2/SM-DAS-3, please contact David.Fairbairn@ecmwf.int.

3- Converting grib to netCDF with CDO:

is also recommended to be used to extract data from grib files, to plot and map data as well as to compute statistics. Metview can be downloaded and installed on Linux and Unix systems from the ECMWF Metview web page.

2.1 Extract time series with Metview:
Metview script is given together with a readme file here to read SM-DAS-2 with Metview and to extract time series over four test sites (provides ascii files).

2.2 Map SM-DAS-2 with Metview:
Metview script is given together with a readme file here to map SM-DAS-2 with Metview (provides png files).

For any further question concerning this example or on how to read or map SM-DAS-2 using Metview, please contact Patricia.Rosnay@ecmwf.int.

3. Using Matlab

It is also possible to read GRIB files using Matlab, which can be used on Unix, Linux and Windows systems. Library can be downloaded from ftp://polar.ncep.noaa.gov/pub/ofs/reference/ (also available in read_grib_1.5.tar.gz) .

In the framework of the H-SAF Visiting Scientist programme, tool to read SM-DAS-2 with Matlab has been developed by Luca Brocca (Research Institute for Geo-Hydrological Protection National Research Council, Iyaly). It is freely available (example_readgrib.rar).

For any further question on how to read SM-DAS-2 using Matlab, please contact luca.brocca@irpi.cnr.it