Introduction

The SMOS Near real Time (NRT) product is available from ESA in BUFR format. The NRT SMOS BUFR files contain a large volume of data, at all incidence angles ranging from 0 to about 60 degrees. The SMOS NRT BUFR data is currently used for the SMOS data monitoring.

For offline forward modelling and assimilation studies, as well as for bias correction developments, requesting the use of long time series, a light format and a noise filterd product are requested.
To this end, ECMWF developed a convertion software to get SMOS brightness temperature products in GRIB format on a grid compatible with that used for the land surface model and microwave emission model, at all resolutions. In addition the software includes angular binning and observation spatial average which allow to filter out the noise in the data.
The SMOS_BUFR2GRIB converter uses the SMOS BUFR file information content only. Since the BUFRfile contains a lot of information on the altitude, water fraction etc, there is no need to use auxilliary data for the conversion.

Description of the SMOS_BUFR2GRIB software

The SMOS_BUFR2GRIB software is suitable to be used on Linux or Unix platforms. It converts SMOS NRT BUFR files to GRIB files, either on a regular Latitue-longitude (LL) grid or a Gaussian Reduced (GR) grid. The software works in two steps:

  • First a metview programme converts BUFR to GEOPOINT and then GEOPOINT to GRIB on a regular Latitude-Longitude Grid.
  • Second, an interpolation software is used to interpolate the regular Latitude-Longitude (LL) GRIB file on a regular Gaussian grid if requested. It is available at ECMWF, so at the moment users outside ECMWF can not use it. The SMOS_BUFR2GRIB proposes the option to skip the step2 (conveting the BFR files to a regular LL grid only).

 

The control script is smos_bufr2grib.sh ; When editing the script, the user has to define the input file name and the requested incidence angle(s), angular binning angle, as well as the output grid type (regular Latitude-Longitude or Gaussian reduced) and the resolution. The user also has to choose if he would like to converted only the Alias Free Field of View data (AFOV), or the entire FOV. It is recommended to use the alias free field of view to ensure good data quality. The script launches the metview macro smos_bufr2gribLL.met

 

In the default smos_bufr2gribLL.met programme only land data are converted to GRIB. To convert the data over ocean only or on both ocean and land, change the the water fraction custom values, line 82 of smos_bufr2gribLL.met.

 

To run the converter place it in the directory where the smos file is (or give the full path/name of the input file) and type: sh smos_bufr2grib.sh

Requested tools:
- Linux or Unix computer
- Metview
- EC-Regrid: ECMWF New interpolation software. Not yet available outside ECMWF, so skip this part if not at ECMWF by puting grid_resol="regular" in smos_bufr2grib.sh

 

Note on the SMOS NRT BUFR file content and the paramater identification numbers: radiometric accuracy: 012167, snapshot accuracy: 012166 (Corbella), polarization: 002099 (0h, 1V), snapshot overallquality: 033028 (must be =1 but is always=3,so far (Feb 2012)), SMOS info flag: 025174, Faraday angle: 025083, TB: 12080. For more information see the SMOS BUFR specification document.

 

Download the Software

Control script: smos_bufr2grib.sh

Metview programme: smos_bufr2gribLL.met

Readme file: README

 

Examples

In these examples the SMOS BUFR file s converted to GRIB on 07 February 2010 at 06 UTC (+/-3h). The input smosbufr is 1.1 Gb. It contains all the SMOS data.

 

Example1:


Convert SMOS data for incidence angles of 30 (+/-1) degrees, on a regular Lat-Lon grid, at resolution 0.25 degrees x 0.25 degrees. Do do so, select the following options in smos_bufr2grib.sh :
bin_angle="1"
reg_grid_resol="0.25"
grid="regular"
inputfile="smosbufr"
afov="yes"
for AA in 30

The two brightness temperature output 0.25x0.25 GRIB files are each 0.208 Mb. The entire output (ten files) is 2Mb:
smosbufr_Faxx_0.25_angle30.grib: Faraday angle for XX polarised data
smosbufr_Fayy_0.25_angle30.grib: Faraday angle for YY polarised data
smosbufr_flagfov5_xx_0.25_angle30.grib: SMOS information flag, bit5 (AFOV), for XX polarised data
smosbufr_flagfov5_yy_0.25_angle30.grib: SMOS information flag, bit5 (AFOV), for YY polarised data
smosbufr_snpaxx_0.25_angle30.grib: Snapshot accuracy for XX polarised data
smosbufr_snpayy_0.25_angle30.grib: Snapshot accuracy for YY polarised data
smosbufr_snpqxx_0.25_angle30.grib: Snapshot quality for XX polarised data
smosbufr_snpqyy_0.25_angle30.grib: Snapshot quality for YY polarised data
smosbufr_tbxx_0.25_angle30.grib: Brightness Temperature for XX polarised data
smosbufr_tbyy_0.25_angle30.grib: Brightness Temperature for YY polarised data

 

 

 

 

Example2:

Other options can be selected. In particular if the scin software is available on the user's computer, the SMOS data can be converted on a Gaussian Reduced grid (grid="gaussian" in smos_bufr2grib.sh), which is deirectly comparable to the ECMWF models (IFS, HTESSEL, CMEM) outputs.

Convert SMOS BUFR data for incidence angles of 30 (+/-1) degrees, on a Gaussian T511 grid. Do do so, select the following options in smos_bufr2grib.sh :
bin_angle="1"
reg_grid_resol="0.25"
grid="gaussian"
gr_resol="256" # grid N256 corresponds to T511
inputfile="smosbufr"
afov="yes"
for AA in 30

The Gaussian Reduced format output is 0.076 Mb for the TB files, and it is 0.64 Mb for the 10 output files at 30 (+/-1) degrees incidence angle.
GR_N256_smosbufr_Faxx_0.25_angle30.grib: Faraday angle for XX polarised data
GR_N256_smosbufr_Fayy_0.25_angle30.grib: Faraday angle for YY polarised data
GR_N256_smosbufr_flagfov5_xx_0.25_angle30.grib: SMOS information flag, bit5 (AFOV), for XX polarised data
GR_N256_smosbufr_flagfov5_yy_0.25_angle30.grib: SMOS information flag, bit5 (AFOV), for YY polarised data
GR_N256_smosbufr_snpaxx_0.25_angle30.grib: Snapshot accuracy for XX polarised data
GR_N256_smosbufr_snpayy_0.25_angle30.grib: Snapshot accuracy for YY polarised data
GR_N256_smosbufr_snpqxx_0.25_angle30.grib: Snapshot quality for XX polarised data
GR_N256_smosbufr_snpqyy_0.25_angle30.grib: Snapshot quality for YY polarised data
GR_N256_smosbufr_tbxx_0.25_angle30.grib: Brightness Temperature for XX polarised data
GR_N256_smosbufr_tbyy_0.25_angle30.grib: Brightness Temperature for YY polarised data

 

 

 

 

Comments:

The finer the resolution, the larger the grib files are. For example conveted on a regular 0.15x0.15 grid, each TB file is 550 Mb. The map given at the top of this page shows the SMOS data converted on a regular grid at a resolution of 0.15 degrees