Geostationary IR Channel Brightness Temperature - GridSat B1

Making use of the information in the netCDF file

Calculating brightness temperatures

NetCDF values are stored as integers and can be converted to floats following the CF convention and the variables attributes:

Value = Integer * scale_factor + add_offset

Many of the available netCDF access tools perform this adjustment automatically. More information on data storage is provided in documentation of the non-gonvernment domain netCDF Climate and Forecasting (CF) convention.

Removing the view zenith angle correction

The infrared window channel data have a view zenith angle correction applied, that was defined by Joyce et. al (2001). However, users have the ability to remove this correction. The variable irwin_vza_adj contains the level of correction. As documented in the attributes, the variable can be used to un-correct the irwin_cdr data via:

      Original_temperature_observed = variable(irwin_cdr) - variable(irwin_vza_adj)

Note: Users need to convert the irwin_cdr (stored as short) and irwin_vza_adj (stored as byte) to floats using the scale_factor and add_offsets prior to applying the above equation.

Joyce, R., J. Janowiak, and G. Huffman, 2001: Latitudinally and Seasonally Dependent Zenith-Angle Corrections for Geostationary Satellite IR Brightness Temperatures. Journal of Applied Meteorology, 40, 689-703.

Calculating solar and satellite angles

The solar and satellite angles (zenith and azimuth) are not stored in GridSat-B1 since they can be calculated directly from the data provided in the file. An appendix from the GridSat-B1 C-ATBD provides information on how these parameters can be calculated.

Identifying the satellite that observed each pixel

Each pixel derives from a specific satellite. That satellite is identified by the satid_* variables in the netCDF file. The method to determine the source satellite for each pixel is described in: using_satid.pdf

Mapping the sparse array data

Data for secondary and tertiary views (or layers) can be stored as sparse arrays. This compression technique is also called compression by gathering by the CF convention and is described there.

non-gonvernment domain indicates a link which will lead you out of the Federal Government webspace