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Hi Martin, Peter On 10/24/11 7:04 AM, Martin Raspaud wrote:
On 24/10/11 11:55, Peter Miu wrote:Hi, The EUMETSAT Data Centre Archive has developed a SEVIRI MSG15 data sets to support GSICS. GSICS (Global Space-based Inter-Calibration System) is a WMO and CGMS initiative to improving and harmonise the quality of observations from operational weather and environmental satellites of the Global Observing System (GOS). Examples of these SEVIRI MSG15 "GSICS" data sets can be found under the following EUMETSAT THREDDS server. http://gsics.eumetsat.int/thredds/catalog/msg2-seviri/catalog.html The data sets have been developed using Unidata guidelines for gridded data i.e. the data sets can be loaded into Unidata tools and they will be geo-located correctly. The organisation of these NetCDF files would be relevant for discussion here and we (EUMETSAT& the GSICS partners) are very interested in developing CF conventions applicable for GEO and LEO satellites. Examples of LEO NetCDF data sets can also be found on the above server. We have started preparing some guidelines for NetCDF, see: https://gsics.nesdis.noaa.gov/wiki/Development/NetcdfConvention For more information on GSICS, please take a look at: http://gsics.wmo.int/ http://www.star.nesdis.noaa.gov/smcd/GCC/ http://www.eumetsat.int/Home/Main/AboutEUMETSAT/InternationalRelations/CGMS/SP_1226312587804?l=en?l=en If you have any questions, please don't hesitate in contacting me.Hi, First, I have to say that I am by no means a nedcdf nor cf expert... I also have to say that I am very happy that Eumetsat decided using netcdf4, especially with cf conventions. But here are some things that I was wondering looking at a Seviri file: - - Why are southMostLine, eastMostPixel, northMostLine, westMostPixel, and numberOfChannels dimensions and not attributes ? - - How would you deal with the inclusion of the HRV channel ? - - Are the longitudes and latitudes values different from what a "vertical perspective" with right parameters would provide ? If they do, why ? If they don't, why not include a grid-mapping definition ?
We've defined a netcdf structure for the GOES-R ABI (Advanced Baseline Imager). For navigation, similar to SEVIRI, the ABI defines a fixed grid (FGF) of equal angle spaced view angles from an nominal stationary point in space. The grid can be represented
as a cross product of 2 one dimension arrays of the north-south, east-westviews angles in radians. The VerticalPerspective CF definition won't work here because it's a type of Map Projection which defines the transform x,y (kilometers
for instance) <-> (Lon,Lat). Instead of two 1D arrays of view angles, a 2D array of computed map projection plane values for the FGF views would be required which defeats the purpose of defining the navigationvia a transform algorithm. We didn't want rewrite metadata interpretation and visualization components in the software, so we defined a "grid_mapping_type" for the ABI FGF whose "projection_x,y_coordinate" could be radians instead of km. Effectively a projection (radians, raidians) <-> (lon,lat). We did this by extending, actually some modification were required, classes distributed in the ncIdv.jar.
See attached netcdf header file. Another nice advantage to the FGF is that master lon/lat files don't change, and can be indexed directly if desired. Another issue relates to defining a mechanism to provide a time-stamp fora file, ie. time dimension length = 1. Many data providers will not subscribe
to the notion of a 3D variable (time,x,y) with time=1. I'm not agreeing or disagreeing, but engineers associated with the GOES-R project said they would not do this. So we have a Time(time) variable to hold the nominal time of the image.
- - On the cf-satellite list, we have long been discussing "band"s. Did you consider using those ?
I think at the very least, the concept of band dimension should be accepted as a best practice.
- - Did you consider grouping channels in 3d arrays instead of having them separated ? - - Could you provide in the file calibration coefficients needed to convert radiances to reflectances and brightness temperatures ?
In these files scaled radiances are converted to radiances via the scale/offset
variable attributes, and coefficients required to obtain reflectance factor or brightness temperature are included. The former happens automatically through the Java-NetCDF library, though this might not always be desirable. Tom
Thanks a lot for making this data available ! Best regards, Martin Raspaud SMHI, Sweden -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (GNU/Linux) Comment: Using GnuPG with Red Hat -http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJOpVRaAAoJEBdvyODiyJI4G70IANwTM5v+zH5IFZuKgzcBtc/0 DyhJxONvdE2ga60D7dU3WAUzi+bmkmXnCzdZj+vFZclIHthmLZLuVPEqj1JRS9RX jQ8IUUVzM+8nLcfAYarPLnM2dbOXPGJW7gpKDvgYuGBvrNxQ7Ipn1QQdhngjOJrr YuRiFOlPKwMizmVNDGj4CDyphqciU0bHsxztZGwe39Ux0rd+/LlcLh96pGt1cTHt 5boI3ftkG0eEwqBfOdnOBTdFM6Zrwi8cxegVueGnfoKLmYfK4z95/38LcqfpbfIw gGp7FCZtbB5wlvRHWwDvts5OhHPZLY8Hz3QeKPU5+paEaRK3N9n8HKce5rsJra0= =wT2W -----END PGP SIGNATURE----- _______________________________________________ cf-satellite mailing list cf-satellite@xxxxxxxxxxxxxxxx For list information or to unsubscribe, visit:http://www.unidata.ucar.edu/mailing_lists/
ions:
y = 328;
x = 580;
time = 1;
e_sun = 1;
swath_t = 22;
variables:
short ABI_scaledint_b05(y=328, x=580);
:long_name = "ABI scaled radiance band05 (1.61um)";
:units = "milliwatts/m2/steradian/cm-1";
:add_offset = -0.79255992; // double
:scale_factor = 0.0061933864; // double
:grid_mapping = "Projection";
:coordinates = "y x";
double x(x=580);
:standard_name = "projection_x_coordinate";
double y(y=328);
:standard_name = "projection_y_coordinate";
float time(time=1);
:long_name = "Image start time";
:units = "seconds since 2006-07-19 12:00";
float E_sun(e_sun=1);
:long_name = "E_SUN";
:units = "milliwatts/m2/cm-1";
short swathtimes(swath_t=22);
:long_name = "Swath start Time ";
:units = "seconds since 2006-07-19 12:00";
char Projection;
:grid_mapping_name = "FGFProjection";
:_CoordinateTransformType = "Projection";
:_CorrdinateAxes = "y x";
:subpoint_longitude_degrees = "-75.";
:delta_lamda_radians = "5.6e-05";
:TITLE = "PSC ABI-WEST 5-KM FULLDISK ABI DATA REMAPPED TO NEW GOES-R FGF 2-KM
FULLDISK DOMAIN";
:INSTITUTE = "UNIVERSITY OF WISCONSIN-MADISON SSEC/CIMSS";
:HISTORY = "The WRF-CHEM model was simulated on a supercomputer at the
National Center for Supercomputing Applications (NCSA), Pittsburg
Supercomputing Center (PSC). A beta version of the NOAA/NESDIS Community
Radiative Transfer Model (CRTM) was used then used to compute simulated
radiances for each ABI band";
:SOURCE = "Simulated ABI scaled integer data for this dataset were computed
using output from a high-resolution Weather Research and Forecasting model with
Chemistry (WRF-CHEM, version 3.0.1) simulation coupled with the NOAA/NESDIS
CRTM forward radiative transfer model";
:REFERENCE = "Schaack, T., R. B. Pierce, A. Lenzen, G. Grell, S. Peckham, J.
Otkin (2009), High Resolution Coupled RAQMS/WRF-Chem Ozone and Aerosol
Simulations for GOES-R Research, Extended Abstracts for the 10th WRF Users
Workshop, June 23 - 26, 2009, Boulder, CO";
:SOLAR_CONSTANT = "2000 ASTM Standard Extraterrestrial Spectrum Reference
E-490-00 for a solar constant of 1366.1 W/m**2";
:pi = "3.14159265";
:Radiance = "(ABI_scaledint* scale_factor) + add_offset";
:Reflectance_factor = "(Radiance * PI ) / E_sun";
:Conventions = "CF-1.4";
:FM_AUTHOR = "CRTM";
:PROCESSED_DATE = "Wed May 18 21:33:22 2011";
:BIT_DEPTH = 12S; // short
:FM_CVS_VERSION = "Release_Sep09_A";
:NWP_MODEL = "OUTPUT FROM WRF V3.0.1.1 MOD";
:CEN_LAT = 0.0f; // float
:CEN_LON = -75.0f; // float
:Longitude_Subpoint = -75.0f; // float
:OUTPUT_TIME = "2006-07-19 12:00UTC";
:dyKm = 1.0f; // float
:dxKm = 1.0f; // float
:rotation = 0.0f; // float
:Sampling_Method = "Simple Averaged";
}
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