High Resolution Infrared Radiation Sounder (HIRS)
Clear-sky Data

Summary

This data set consists of cloud-cleared and limb-corrected HIRS data in their original swath resolution from November 1978 to present. This time frame covers the NOAA series of satellites from TIROS-N to NOAA-17.

HIRS is an operational infrared sounder aboard the National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites. It is a discrete stepping, line-scan instrument with 20 spectral channels. The channels are composed of twelve longwave channels, seven shortwave channels, and one visible channel. The pixel resolution is approximately 20km at nadir.

The technique used to compute the clear-sky data is similar to the ISCCP cloud clearing approach (Rossow and Garder, 1993; Jackson and Bates, 2000; Jackson and Bates, 2001; Jackson et al., 2003). Observed window channel brightness temperatures at 11.1 micron are compared spatially and temporally to an estimated clear-sky value and rejected as cloudy if the observation is too cold. For obtaining clear-sky observations, the thresholds are chosen that seek to remove all clouds at the expense of removing some clear-sky pixels. The observations over high terrains and polar regions are included.

Data Description

The data can be obtained through an OpenDAP server or through anonymous ftp.

Each file contains one day of global HIRS data with the following filename format:

                        HIRS.Nss.Yyy.Dddd.nc

In which ss is for 2-digit satellite number (Note one exception: "05" is used to stand for TIROS-N),  yy for 2-digit year,  and ddd for 3-digit Julian Day.

The following header information shows the variables included in each file:

dimensions:
             ch = 19 ;
             time = UNLIMITED ;
variables:
             float bt(time, ch) ;
                        bt:long_name = "brightness temperature" ;
                        bt:units = "Kelvin" ;
             float lc(time, ch) ;
                        lc:long_name = "limb-corrected brightness temperature" ;
                        lc:units = "Kelvin" ;
             float vis(time) ;
                        vis:long_name = "HIRS channel 20" ;
                        vis:units = "%" ;
             float lat(time) ;
                        lat:units = "degrees_north" ;
                        lat:valid_range =  -90.,  90. ;
             float lon(time) ;
                        lon:units = "degrees_east" ;
                        lon:valid_range = 0., 360. ;
             float time(time) ;
                        time:units = "seconds" ;
                        time:long_name = "GMT time" ;
             float zen(time) ;
                        zen:long_name = "zenith" ;
             float alt(time) ;
                        alt:long_name = "altitude" ;
             int line(time) ;
                        line:long_name = "line" ;
             int posi(time) ;
                        posi:long_name = "position" ;

Bibliography

Rossow, W.B. and L.C. Garder, 1993: Cloud detection using satellite measurements of infrared and visible radiances for ISCCP. /J. Climate/, *6*, 2341-2369.

Jackson, D.L., and J.J. Bates, 2000: A 20-yr TOVS Pathfinder data set for climate analysis. /Tenth Conference on Satellite Meteorology and Oceanography/, Long Beach, CA, January 10-14, 2000.

Jackson, D.L. and J.J. Bates, 2001: Climate analysis with the 21-yr HIRS Pathfinder radiance clear-sky data set. /11th Conference on Satellite Meteorology & Oceanography/, Madison, Wisconsin, October 15-18, 2001.

Jackson, D.L., J.J. Bates, and D. Wylie, 2003: The HIRS Pathfinder Radiance data set (1979-2001). /12th Conference on Satellite Meteorology and Oceanography/, Long Beach, California, February 10-13, 2003.

Contact

Dr. Lei Shi
NOAA/NESDIS/National Climatic Data Center
151 Patton Ave
Asheville, NC 28801
USA
E-mail: Lei.Shi@noaa.gov
Phone: 1+828-350-2005
FAX: 1+828-271-4328