Search Results
You are looking at 1 - 7 of 7 items for
- Author or Editor: Moustafa T. Chahine x
- Refine by Access: All Content x
Abstract
It is shown that the relaxation method for inverse solution of the full radiative transfer equation leads to unique temperature profiles. Apart from its attractive simplicity, the algorithm is also capable of discriminating between noise and valid information without any need for data smoothing. A set of new inverse problems is formulated for the determination of the concentration of absorbing gases in an atmosphere, the extent and height of clouds, and surface elevations. The proposed methods are illustrated by examples in the earth's atmosphere for the region of the 4.3 μ CO2 band.
Abstract
It is shown that the relaxation method for inverse solution of the full radiative transfer equation leads to unique temperature profiles. Apart from its attractive simplicity, the algorithm is also capable of discriminating between noise and valid information without any need for data smoothing. A set of new inverse problems is formulated for the determination of the concentration of absorbing gases in an atmosphere, the extent and height of clouds, and surface elevations. The proposed methods are illustrated by examples in the earth's atmosphere for the region of the 4.3 μ CO2 band.
Abstract
Day and night mapping of the global distributions of the horizontal cloud covers and the corresponding cloud-top pressure levels are derived from the same set of infrared radiance data used to retrieve clear-column temperature profiles. General formulation of the problem is presented with illustrations for the simple case of a single layer of non-reflecting clouds. Experimental verification is obtained using 15 μm data measured by the NOAA-VTPR infrared sounder. After correcting for water vapor emission, the results show that the effective cloud cover derived from 15 μm data is less than that obtained from visible data.
Abstract
Day and night mapping of the global distributions of the horizontal cloud covers and the corresponding cloud-top pressure levels are derived from the same set of infrared radiance data used to retrieve clear-column temperature profiles. General formulation of the problem is presented with illustrations for the simple case of a single layer of non-reflecting clouds. Experimental verification is obtained using 15 μm data measured by the NOAA-VTPR infrared sounder. After correcting for water vapor emission, the results show that the effective cloud cover derived from 15 μm data is less than that obtained from visible data.
Abstract
The relaxation method for the inverse solution of the radiative transfer equation is applied in a dual frequency scheme for the determination of complete vertical temperature profiles in cloudy atmospheres from radiance observations alone, without any additional information related to the expected solutions.
The dual-frequency principle employs to advantage a property in the Planck function of the dependence of intensity on frequency. This property leads to the formulation of a new convergence criterion for the selection of cloud-sounding frequencies to be used for reconstructing the clear column radiance from observations made in the presence of a broken cloud layer in all fields of view.
The principle is applied to the case of observations in two adjacent or partially overlapping fields of view and to the case of observations in a single field of view. The solutions are illustrated by numerical examples in the dual-frequency ranges of the 4.3 and 15 µm CO2 bands of the terrestrial atmosphere. The resulting profiles can possess the same degree of vertical resolution permitted under cloudless conditions.
Abstract
The relaxation method for the inverse solution of the radiative transfer equation is applied in a dual frequency scheme for the determination of complete vertical temperature profiles in cloudy atmospheres from radiance observations alone, without any additional information related to the expected solutions.
The dual-frequency principle employs to advantage a property in the Planck function of the dependence of intensity on frequency. This property leads to the formulation of a new convergence criterion for the selection of cloud-sounding frequencies to be used for reconstructing the clear column radiance from observations made in the presence of a broken cloud layer in all fields of view.
The principle is applied to the case of observations in two adjacent or partially overlapping fields of view and to the case of observations in a single field of view. The solutions are illustrated by numerical examples in the dual-frequency ranges of the 4.3 and 15 µm CO2 bands of the terrestrial atmosphere. The resulting profiles can possess the same degree of vertical resolution permitted under cloudless conditions.
Abstract
An exact analytical transformation is presented for the remote sensing of atmospheric temperature profiles in the presence of clouds. The transformation permits direct retrieval of clear-column temperature profiles without the need to predetermine the corresponding clear-column radiances. A numerical illustration is given for simulated observations in the 15 µm C02 band in the terrestrial atmosphere. The resulting method is numerically very fast and is especially suitable for handling the massive amount of data needed for numerical weather prediction.
Abstract
An exact analytical transformation is presented for the remote sensing of atmospheric temperature profiles in the presence of clouds. The transformation permits direct retrieval of clear-column temperature profiles without the need to predetermine the corresponding clear-column radiances. A numerical illustration is given for simulated observations in the 15 µm C02 band in the terrestrial atmosphere. The resulting method is numerically very fast and is especially suitable for handling the massive amount of data needed for numerical weather prediction.
Abstract
It is shown that high–precision extinction measurements over a spectral interval can he used to infer aerosol optical parameters including the, heretofore elusive, complex index of refraction, if aerosol particles in the atmosphere are assumed to he spherical Mie scatters with a uniform refractive index over this spectral interval and their sizes are distributed according to the modified gamma function. The error analysis shows that the degree of precision required is attainable, thus making it a viable and unique real–time remote sensing device. No assumptions are made on the vertical profile of aerosols and hence, in a satellite application (occultation experiment), the difficulties due to the sphericity of the medium can be avoided.
Abstract
It is shown that high–precision extinction measurements over a spectral interval can he used to infer aerosol optical parameters including the, heretofore elusive, complex index of refraction, if aerosol particles in the atmosphere are assumed to he spherical Mie scatters with a uniform refractive index over this spectral interval and their sizes are distributed according to the modified gamma function. The error analysis shows that the degree of precision required is attainable, thus making it a viable and unique real–time remote sensing device. No assumptions are made on the vertical profile of aerosols and hence, in a satellite application (occultation experiment), the difficulties due to the sphericity of the medium can be avoided.
Abstract
Two meteorological reanalysis datasets are analyzed to determine the mechanical energies of the global atmosphere in the El Niño and La Niña years. The general consistency of the mean energy components between the two datasets reveals ~1%–3% increase and ~2%–3% decrease in the mean energies in the El Niño years and La Niña years, respectively. These analyses further reveal that the tropospheric temperature responds to the sea surface temperature anomaly with a time lag of two months, which leads to the varying mean atmospheric energies in the El Niño and La Niña years.
Abstract
Two meteorological reanalysis datasets are analyzed to determine the mechanical energies of the global atmosphere in the El Niño and La Niña years. The general consistency of the mean energy components between the two datasets reveals ~1%–3% increase and ~2%–3% decrease in the mean energies in the El Niño years and La Niña years, respectively. These analyses further reveal that the tropospheric temperature responds to the sea surface temperature anomaly with a time lag of two months, which leads to the varying mean atmospheric energies in the El Niño and La Niña years.
AIRS
Improving Weather Forecasting and Providing New Data on Greenhouse Gases
The Atmospheric Infrared Sounder (AIRS) and its two companion microwave sounders, AMSU and HSB were launched into polar orbit onboard the NASA Aqua Satellite in May 2002. NASA required the sounding system to provide high-quality research data for climate studies and to meet NOAA's requirements for improving operational weather forecasting. The NOAA requirement translated into global retrieval of temperature and humidity profiles with accuracies approaching those of radiosondes. AIRS also provides new measurements of several greenhouse gases, such as CO2, CO, CH4, O3, SO2, and aerosols.
The assimilation of AIRS data into operational weather forecasting has already demonstrated significant improvements in global forecast skill. At NOAA/NCEP, the improvement in the forecast skill achieved at 6 days is equivalent to gaining an extension of forecast capability of six hours. This improvement is quite significant when compared to other forecast improvements over the last decade. In addition to NCEP, ECMWF and the Met Office have also reported positive forecast impacts due AIRS.
AIRS is a hyperspectral sounder with 2,378 infrared channels between 3.7 and 15.4 μm. NOAA/NESDIS routinely distributes AIRS data within 3 hours to NWP centers around the world. The AIRS design represents a breakthrough in infrared space instrumentation with measurement stability and accuracies far surpassing any current research or operational sounder..The results we describe in this paper are “work in progress,” and although significant accomplishments have already been made much more work remains in order to realize the full potential of this suite of instruments.
The Atmospheric Infrared Sounder (AIRS) and its two companion microwave sounders, AMSU and HSB were launched into polar orbit onboard the NASA Aqua Satellite in May 2002. NASA required the sounding system to provide high-quality research data for climate studies and to meet NOAA's requirements for improving operational weather forecasting. The NOAA requirement translated into global retrieval of temperature and humidity profiles with accuracies approaching those of radiosondes. AIRS also provides new measurements of several greenhouse gases, such as CO2, CO, CH4, O3, SO2, and aerosols.
The assimilation of AIRS data into operational weather forecasting has already demonstrated significant improvements in global forecast skill. At NOAA/NCEP, the improvement in the forecast skill achieved at 6 days is equivalent to gaining an extension of forecast capability of six hours. This improvement is quite significant when compared to other forecast improvements over the last decade. In addition to NCEP, ECMWF and the Met Office have also reported positive forecast impacts due AIRS.
AIRS is a hyperspectral sounder with 2,378 infrared channels between 3.7 and 15.4 μm. NOAA/NESDIS routinely distributes AIRS data within 3 hours to NWP centers around the world. The AIRS design represents a breakthrough in infrared space instrumentation with measurement stability and accuracies far surpassing any current research or operational sounder..The results we describe in this paper are “work in progress,” and although significant accomplishments have already been made much more work remains in order to realize the full potential of this suite of instruments.
