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.
NCDC Dataset 3648
File storage format conventions
- File storage format:
- NetCDF version 4
- File storage format URL:
- File storage convention:
- Climate and Forecasting (CF) Convention version 1.4
- File storage convention URL:
- File metadata convention:
- Start date:
- 1 January 1980
- End date:
a. Southernmost Latitude: 70S
b. Northernmost Latitude: 70N
c. Westernmost Longitude: 180W
d. Easternmost Longitude: 180E
THREDDS Data Server
TDS provides the following access methods:
- DAP access that allows download of binary and ascii portions of the data.
- Directly download the files in their native format (netCDF4).
- Web Coverage Service for the data.
- Web Map Server to the data.
- Allows download of a portion of the files (by subsetting variables, times and/or spatial)
- 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.
For bulk access to the netCDF4 files, data are available via FTP at:
This is also the URL to use when accessing files directly using DAP-enabled products (e.g., netCDF Operators).
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:
Phone: 828 271-4800
GridSat-B1 production is documented using robodoc version 4.99.8.
In short, the GridSat production is accomplished in 6 steps:
- Convert ISCCP B1 files to ISCCP B1U.
- Determine matchups between ISCCP B1U files and NOAA/HIRS
- Colocate ISCCP-B1U pixels with HIRS footprints.
- Summarize matchups by creating monthly calibration corrections.
- Create the gridded satellite data
- Use netCDF Operators (NCO) to isolate the CDR variables (and those associated with the iinfrared window (irwin) channel channel).
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.
- Number of points in the longitude dimenson.
- Number of points in the latitude dimenson.
- Number of geostationary satellites merged in this time slot.
- Number of characters used in storing text..
- Time dimension (currently unlimited)
- Latitude coordinate variable
- longitude coordinate variable
- Time coordinate variable
- Sub-satellite latitude of each geostationary satellite used in the composite image. (see satname for corresponding satellite)
- Sub-satellite longitude of each geostationary satellite used in the composite image. (see satname for corresponding satellite)
- Sub-satellite radius (Center of earth to satellite) of each geostationary satellite used in the composite image. (see satname for corresponding satellite)
- The common satellite name.
- The source B1U files used for this grid.
- 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
- Offset used in the ISCCP calibration adjustment (see above).
- 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
- 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.
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
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).
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: