Version 04.01 of the SMOS L2SM Processor is now available!

Category : L2, Tools

Version 04.01 of the SMOS L2SM Processor is now available from Array’s web site

Compared to v04.00, this version addresses two bugs:

  1. When retrieval fails with “poorly conditioned matrix”, segmentation fault can occur as the processor tries to access an empty RSTD vector. This bug has been fixed.
  2. The DSR_Size in the HDR file of the UDP has been corrected from 200 to 220

Also note that v04.01 will NOT work with the current AUX_ECMWF_ products. Hence ECMWF pre-processor must be updated before L2SM can become operational.

How to find your DGG ?

Category : L1, L2, Tools

SMOS products (i.e. L1C brightness temperatures in X and Y pol., and L2 soil moisture) are defined on the ISEA 4H9 grid with a spatial resolution of 15 km. Each point (or node) of this grid is known as a DGG (Discrete Global Grid)  that has fixed coordinates (i.e. Latitude, Longitude) and is assigned an identificator the “DGG Id”.

Some of the routine provided to extract data from the products are based on this DGG Id (i.e. XY2HV.m).
But, how to find a DGG Id that is of interest for the user ?
find_nearestDGG.m is the solution !

All the grid point informations (DGG Id, Latitude, Longitude) has been gathered in an ascii file isea4h9.txt.gz. Using the matlab function find_nearestDGG.m allows the user to extract the nearest DGG node to a given latitude/longitude. We also provide the ascii file isea4h9_land.txt.gz which contains the index of the DGG over land (of interest for L2 soil moisture).
See the files and the readme that comes with them.
You will find the matlab routine together with the grids in the software page.

Be careful not to mixed up the spatial resolution ! The grid of SMOS products is 15 km of spatial resolution and the radiometric resolution of the instrument is ~40 km.


SMOS Polarisations: From antenna frame to surface frame –> the tool you wanted to have!

Category : Tools

As you know there is a significant difference between the polarisations as seen at antenna level and those at surface level.

To go from one to the other it is a very straightforward rotation… But a bit tricky though. As we have developed several such tools for our own purposes we though that to avoid duplication of efforts (and reduce aspirin consumption) many might appreciate having a ready made tool!

So Delphine Leroux looked at what we had in store, selected the most generic and did what was necessary to have a rather robust and hopefully exact matlab tool, directly interfaced with the RWAPI code developped by Array for SMOS. This tools has been tested by several hand picked users and seems now ok. So here it is!

You will find the matlab routine together with a small example (read me file) in the software page. Because of the uncertainty on rotation angle, we can not asssure the results will be correct for L1C product before the 344 prototype version  (July 6th, 2010).
Feel free to use and abuse but remember it is given as it is… and not hot line help please. But if you find a bug, a probelm etc, please tell us so that we can improve.


Delphine Leroux and the CESBIO Smos Team

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