High Resolution Infrared Sounder Data Research Articles

Enhancement of ERBS data by using data from sounders onboard NPP/NPOESS and METOP satellites

The operational climate monitoring and diagnostic community will continue to favor in using outgoing longwave radiation (OLR) estimates that have long and continuous time series such as those estimated from the High Resolution Infrared Sounder (HIRS). OLR from HIRS data could be generated since these data exist since 1979 and will continue during NPOESS era with Cross-Track Infrared Sounder (CrIS) and HIRS/4 on NPOESS and METOP satellites, respectively. OLR estimated from Earth Radiation Budget Suite (ERBS)/Clouds and the Earth’s Radiant Energy System (CERES) can be used to calibrate the HIRS technique that will be used to generate continuous time series of OLR. This will ensure to have a consistent climate data involving different data sources. OLR generated from CrIS on the afternoon orbit could provide a backup in the event of ERBS’s failure. There will be three evenly spaced sounders (two CrIS and one HIRS/4) that could be used to retrieve OLR allowing therefore a better definition of the diurnal variability of OLR. This paper will present results from GOES sounder data to estimate OLR using an approach similar to that used for HIRS. The instantaneous OLR estimates are compared with collocated OLR products from the CERES instruments onboard TRMM and Terra spacecraft to establish the instantaneous accuracy of the multi-spectral estimation techniques for homogeneous scenes. The hourly GOES sounder OLR estimates are used to study the diurnal cycle of OLR. The time-averaged data are used to estimate the accuracy of the ERBE/CERES and HIRS diurnal cycle models as applied to daily- and monthly-averaged products at different spatial resolutions. The study suggests that the technique can be implemented for NPOESS using the CrIS and HIRS/4 for both augmenting the temporal sampling of OLR estimates and reducing the risk of OLR EDR generation.

Atmospheric Ice and Water Content Derived from Parameterization of Nimbus 6 High-Resolution Infrared Sounder Data

A radiative transfer model of spectral infrared radiation in cloudy atmospheres is applied to the most complete set of radiance observations currently available from the Numbis 6 HIRS instrument. The radiative characteristics of clouds in the High-Resolution Infrared Sounder (HIRS) channels are investigated using the discrete-ordinate method for approximating the solution of the radiative transfer equation as it is applied to non-isothermal, inhomogeneous cloudy atmospheres. A method for the estimate of cloud compositions from multi-spectral HIRS radiances, including both shortwave and longwave CO2 channels, is developed. Theoretical calculations of the upwelling radiance at satellite altitude for a number of thicknesses involving middle level and cirrus clouds are carried out. The resulting theoretical radiances are then parameterized and an empirical method to determine cloud type and ice and water content of the clouds is described. Satellite passes from five days over the western United States are employed to test the empirical parameterizations of the theoretical results. Comparisons of the cloud-type determinations with NOAA 4 mosaic are shown to agree reasonably well. Cloud ice and water content derived from the parameterizations of the HIRS data is compared with that obtained from the Air Force Three Dimensional Neph-analysis (3DNEPH) program. Examples of the application of this technique to global mapping of ice and water content are displayed.

Sensitivity of upwelling radiance in nimbus 6 HIRS channels to multilayered clouds

An infrared radiative transfer model is developed that can simulate the effects of clouds on satellite upwelling radiances at the top of the atmosphere for a range of satellite scan angles. The model allows the calculations of the upwelling radiance for single layers of middle or high clouds and for multilayered clouds. Sensitivity analyses are carried out for the upwelling radiance in the presence of clouds in the Nimbus 6 high-resolution infrared sounder (HIRS) channels. Computational results show that thick cirrus cloud reduces the upwelling radiance most in both single and multicloud cases. Thin cirrus and thin middle clouds show a greater decrease in the upwelling radiance in comparison with thin cirrus and thick middle clouds in CO2 channels where the weighting functions peak in or above the thin middle cloud. More variability is noted between window and water vapor channel upwelling radiances than is present in the CO2 channels. Shortwave CO2 channels are further shown to have a greater sensitivity to changes in cloud scenes than longwave CO2 channels. We show that the effect of the atmospheric temperature profile is minimized by dividing the clear column radiance into the cloudy radiance. By utilizing the actual HIRS data a case study for the determination of the cloud thickness based on the theoretical sensitivity analyses has been carried out. When infrared and visible cloud pictures from the NOAA 4 satellite are compared, the case study shows some promise of cloud parameter determination using the combination of infrared channels.