Inter-satellite Calibration of HIRS Outgoing Longwave Radiation Data

The narrowband radiance measurements from the High Resolution Infrared Sounder (HIRS) onboard the TIROS-N series of the operational polar orbiting environmental satellites (POES) were used to estimate the broadband outgoing longwave radiation (OLR) at the top of the atmosphere. The entire record of the HIRS radiance observations since 1979 has been reprocessed with the latest NOAA/NESDIS calibration procedures. OLR were retrieved from the HIRS radiances using regression models constructed consistently for each of the POES satellites.

Since the HIRS instruments on each of the POES share similar but not identical spectral characteristics, and since there might be other errors in the instrument implementation and satellite operation, inter-satellite calibration of the measurements is essential for achieving a long, continuous and uniform data record. This is especially important when using these data for trend detection in climate change studies. There are two major factors that can induce artifacts in the HIRS OLR product. One is related to the inter-satellite calibration, and the other is related to the effects of orbital drift in deriving daily/monthly means. This paper discusses in detail the methods of inter-satellite calibration and the investigations of the orbital drift effects for HIRS OLR.