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

The SM-DAS-2 product is and SM-DAS-3 products are provided in GRIB-1 format, on a reduced Gaussian grid at the resolution T799 and T1279, corresponding to N400 (~25 km)25 km and 16 km respectively.

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).and plot data from grib files:

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

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 exctracted extracted in ascii for the four test sites.
The readme file explains how to use and to modify the script. For any further question questions concerning this example or on how to read SM-DAS-2, please contact DavidPatricia.Fairbairn@ecmwfRosnay@ecmwf.int.

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

• 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.Cartopy is a good alternative to metview for plotting data on a regular lat/lon grid
• The following examples require the following librariesbelow require this software, which is freely available on github: python 3.6, metview, pandas, pylab, matplotlib, numpy and cartopy . The metview software requires a recent operating system (macOS Mojave or later, Ubuntu 16 or later)
• Metview and cartopy examples:
  • Global plot of SM-DAS-2 grib data - python code and png image
  • Conversion of grib data to regular lat lon and plot with cartopy
• This miniconda script will download and install the libraries to a local repository

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).

• and jupyter.
• 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:
  
  • Plotting and saving a root-zone SWI time series of local data
  • Plot map of root-zone soil wetness index with metview-python
  • Conversion to regular grid and plot map with cartopy
  • jupyter-notebook examples

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. Using Matlab

Matlab is no longer supported at ECMWF. However, it is possible to read GRIB files using Matlab, which can be used on Unix, Linux and Windows systems.

The library can be downloaded from

read_grib_1.5.tar.gz

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In the framework of the H-SAF Visiting Scientist programme, tool Tools 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 (from matlab are available at example_readgrib.rar).

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