RESUMEN
An evaluation of two different atmospheric transmittance models is performed by using radiance data from the high-resolution infraRed Sounder (HIRS) instrument onboard the National Oceanic and Atmospheric Administration's NOAA-9 satellite and the airborne high-resolution interferometer sounder (HIS) instrument. Synthetic radiances have been derived from collocated radiosondes by using the television infrared observation satellite (TIROS) operational vertical sounder (TOVS) operational transmittance model and the fast atmospheric signature code (FASCOD2) line-by-line transmittance model for comparison with the two independent instrument observations. Radiance observations in various spectral channels from the HIRS and HIS instruments along with the synthetic radiances derived from the FASCOD2 and operational TOVS transmittance models are used for the performance evaluation. The results of the comparison reveal a significant discrepancy between 707 and 717 cm(-l) in the radiance calculation for both models. Exce llent agreement is observed between observation and calculation for the lower tropospheric long-wave temperature sounding channels. Serious problems are noted with the modeling of water vapor in the operational TOVS transmittance model. In addition, poor performance by FASCOD2 is revealed for the short-wavelength N(2)O-CO(2) HIRS spectral channels. In general the operational TOVS transmittance model is found to be only slightly inferior to the FASCOD2 model. Regarding the performance of the instruments, observations from the NOAA-9 HIRS and the aircraft HIS are comparable in terms of their agreement with theoretical computations.
RESUMEN
A linear form of the radiative transfer equation (RTE) is formulated for the direct and simultaneous estimation of temperature and absorbing constituent profiles (e.g., water vapor, ozone, methane) from observations of spectral radiances. This unique linear form of the RTE results from a definition for the deviation of the true gas concentration profiles from an initial specification in terms of the deviation of their effective temperature profiles from the true atmospheric temperature profile. The effective temperature profile for any absorbing constituent is that temperature profile which satisfies the observed radiance spectra under the assumption that the initial absorber concentration profile is correct. Differences between the effective temperature, derived for each absorbing constituent, and the true atmospheric temperature are proportional to the error of the initial specification of the gas concentration profiles. The gas concentration profiles are thus specified after inversion of the linearized RTE from the retrieved effective temperature profiles assuming that one of the assumed concentration profiles is known (e.g., CO(2)). Because the solution is linear and simultaneous, the solution is computationally efficient. This efficiency is important for dealing with radiance spectra containing several thousand radiance observations as obtained from current airborne and planned future spaceborne interferometer spectrometer sounders. Here the solution is applied to spectral radiance observations simulated for current filter radiometers and planned spectrometers to demonstrate the anticipated improvement in future satellite sounding performance as a result of improved instrumentation and associated sounding retrieval methodology.
RESUMEN
A simple and computationally efficient model is developed for calculation of slant path atmospheric transmittances in the microwave and millimeter spectral regions. The model deals simultaneously with absorption by oxygen and water vapor. Its accuracy is assessed for a range of atmospheric conditions for spectral intervals corresponding to the channels of the Advanced Microwave Sounding Unit. The model is found to be very accurate (
RESUMEN
The Nimbus-5 infrared temperature profile radiometer (ITPR) experiment was designed to measure upwelling infrared radiation in appropriate spectral intervals and with sufficient geographical resolution for sounding the atmosphere's temperature distribution down to the earth's surface even under partly cloudy sky conditions. A primary scientific goal of the experiment was the specification of the mesoscale features of surface and atmospheric temperature and water vapor that are associated with intense weather systems. In this paper the ITPR instrument is described and some initial spacecraft results are given that demonstrate the success of the experiment in achieving its scientific goals.