Gridded Satellite (GridSat) - Geostationary

Climate Data Record (CDR)

The NOAA Climate Data Record program flagged the GridSat-B1 infrared window channel as a fundamental CDR for FY2011. To avoid confusion, only the variable - infrared window brightness temperature - identified as a CDR is provided by this dataset.

The following information applies to the CDR data, because it is a subset of the complete GridSat-B1 dataset.


Overview - Access - Source Code - Variables - Notes

GridSat-B1 CDR Data

NCDC Dataset 3648

File storage format conventions

File storage format:
NetCDF version 4
File storage format URL:
http://www.unidata.ucar.edu/software/netcdf/
File storage convention:
Climate and Forecasting (CF) Convention version 1.4
File storage convention URL:
http://cf-pcmdi.llnl.gov/
File metadata convention:
http://www.unidata.ucar.edu/software/netcdf-java/formats/DataDiscoveryAttConvention.html

Temporal Information

Start date:
1 January 1980
End date:
Ongoing.

Spatial Coverage

a. Southernmost Latitude: 70S
b. Northernmost Latitude: 70N
c. Westernmost Longitude: 180W
d. Easternmost Longitude: 180E


GridSat-B1 CDR Data Access

THREDDS Data Server

TDS provides the following access methods:

OPENDAP
DAP access that allows download of binary and ascii portions of the data.
HTTPServer
Directly download the files in their native format (netCDF4).
WCS
Web Coverage Service for the data.
WMS
Web Map Server to the data.
NetcdfSubset
Allows download of a portion of the files (by subsetting variables, times and/or spatial)
netcdf-download
Download the entire file as a netCDF-3 file. These files will be much larger than the netCDF4 files because these files are not compressed.

FTP Access

For bulk access to the netCDF4 files, data are available via FTP at:
ftp://eclipse.ncdc.noaa.gov/pub/gridsat/b1-climate-data-record/
This is also the URL to use when accessing files directly using DAP-enabled products (e.g., netCDF Operators).

Offline Orders

Offline orders are not encouraged because the entire dataset is already provided online via FTP and TDS. Users requiring assistance in obtaining the data are encouraged to contact:
NCDC.SatOrder@noaa.gov
Phone: 828 271-4800
Fax: 828-271-4876


GridSat-B1 Source Code

GridSat-B1 production is documented using robodoc version 4.99.8.

In short, the GridSat production is accomplished in 6 steps:

  1. Convert ISCCP B1 files to ISCCP B1U.
  2. Determine matchups between ISCCP B1U files and NOAA/HIRS
  3. Colocate ISCCP-B1U pixels with HIRS footprints.
  4. Summarize matchups by creating monthly calibration corrections.
  5. Create the gridded satellite data
  6. Use netCDF Operators (NCO) to isolate the CDR variables (and those associated with the iinfrared window (irwin) channel channel).

GridSat-B1 Variables

This description of the variables is a supplament to the documentation available in the netCDF file. A sample CDL file is provided here for your reference.

See Notes for information on how the data was remapped.

Dimensions - Variablies
  • top of page Dimensions
    lon
    Number of points in the longitude dimenson.
    lat
    Number of points in the latitude dimenson.
    Ngeo
    Number of geostationary satellites merged in this time slot.
    StrLen
    Number of characters used in storing text..
    time
    Time dimension (currently unlimited)
  • top of page Variables
    lat
    Latitude coordinate variable
    lon
    longitude coordinate variable
    time
    Time coordinate variable
    satlat
    Sub-satellite latitude of each geostationary satellite used in the composite image. (see satname for corresponding satellite)
    satlon
    Sub-satellite longitude of each geostationary satellite used in the composite image. (see satname for corresponding satellite)
    satrad
    Sub-satellite radius (Center of earth to satellite) of each geostationary satellite used in the composite image. (see satname for corresponding satellite)
    satname
    The common satellite name.
    b1ufile
    The source B1U files used for this grid.
    calslp_irwin
    The irwin was adjusted following (Knapp, 2008). This is the slope used in that correction. The original ISCCP calibration can be backed out from this as: ISCCP_Calibration=(irwin-caloff_irwin)/calslp_irwin
    caloff_irwin
    Offset used in the ISCCP calibration adjustment (see above).
    irwin
    The infrared window (11 um) channel merged from all satellites. Due to the correction following (Knapp 2008), the effective wavelength of this channel matches HIRS channel 8 on NOAA-??.
    This variable is always a 2-dimensional array
    This channel has been adjusted using the calibration of Knapp(2008), the view zenith correction following Joyce et al (2001) and parallax-corrected following Janowiak et al. (2001)
    The values in irwin are the nadir-most values
    satid_ir
    Pixel level flag defining which satellite was used for that satellite. The satellite ID is determined by SateliteNumber=floor(satid_ir/15). (This is notation is a result of the complete dataset that can pack the informationo of two satellites into satid_ir.

GridSat-B1 - Processing Notes

Topics include:

Filename and storing time

Files currently hold one time slice per file. The time coordinate is provided unlimited to allow concatenation of files in time. It is likely that future files will be stored by concatenating time into daily or monthly files.

Filename: GridSat-B1.YYYY.MM.DD.HH.Version.irwin.nc
YYYY = 4-digit year
MM = zero-filled month of year [01-12]
DD = zero-filled day of month [01-31]
HH = zero-filled UTC hour of day [00, 03, ..., 21]
Version = version of the file (currently=v01r01)
irwin = denotes that only 1 channel (irwin data) is stored in the file
nc = denotes that the files is a netCDF file

Remapping Satellite data to the grid

Gridded data are denoted by lat/lon values. Gridded lat/lon values can reference the grid center or a grid corner. GridSat lat/lon values are remapped by determining the closest B1 pixel to the given lat/lon value. Thus, the lat/lon values are considered the center of the grid cell. (In essence, the lat/lon values aren't true cells that contain multiple pixel values, but are simply nearest-neighbor resampling of the B1 data).


Calculating satellite and solar angles

The satellite and solar angles (zenith and azimuth) are not stored in GridSat. Instead, satellite information is provided that allows the saetllite angles to be calculated based on a satellite location and an Earth location. Similarly, the solar information is calculated from the file time and the Earth location.

Determining satellite from the satid variable

To save space, the satellite IDs are combined for the primary and secondary layers of the three channels (which is a holdover from the complete GridSat-B1 file). The satellite ID is determined from the satid_ir variable using:

satellite_id = satid_ir / 15


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