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At least 163 records · Page 9

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NASA NTRS1982

Evaluation of upwelling infrared radiance in a nonequilibrium nonhomogeneous atmosphere

The influence of vibrational nonequilibrium upon upwelling infrared radiance from the earth's atmosphere is investigated. By employing the line-by-line model for spectral absorption, heating rates and upwelling radiances are calculated for equilibrium and nonequilibrium conditions in the spectral range of 4.7 micron CO and 3.3 micron CH4 bands. Heating rates are calculated also for the 15 micron CO2 band and are compared with other available results in the literature. For the spectral range of the CO fundamental band, the influence of different parameters on the upwelling radiance is investigated. It is found that for CO the assumption of local thermodynamic equilibrium (LTE) is not justified at tropospheric temperatures and pressures. If the resonance effects of CO-N2 collisions are considered, then the assumption of LTE is justified up to 60 kilometers. This information is very useful for measurement of atmospheric pollutants, earth radiation budget studies and climate modeling, and infrared signature works.

Tiwari, S. N.↗

NASA NTRS1984

Sensor Radiance for a Midlatitude Atmospheric Model

The Herman radiative transfer code which iteratively traces solar radiance through a discrete number of scattering angles and many atmospheric layers was transferred to a personnal computer to reduce time in recompiling the source code. The code was then used to predict what ground reflectance would saturate the TM sensor output given a standard midlatitude atmospheric model. Output radiance is tabulated for the first four bands. Plots show radiance at the sensor as a function of solar zenith angle from a visibility of 40 km; solar zenith angle as a function of time of year for four latitudes over a typical portion of the descending node of a LANDSAT orbit; and values of ground reflectance required to saturate the TM sensor from three different aerosol loading conditions (corresponding to about 20 km, 40 km. and greater than 100 km visibility).

Source record↗

NASA NTRS1984

The angular distribution of infrared radiances emerging from broken fields of cumulus clouds

Infrared radiances were simultaneously measured from broken cloud fields over the eastern Pacific Ocean by means of the eastern and western geostationary satellites. The measurements were compared with the results of models that characterized the clouds as black circular cylinders disposed randomly on a plane and as black cuboids disposed in regular and in shifted periodic arrays. The data were also compared with the results obtained from a radiative transfer model that considered emission and scattering by a regular array of periodic cuboidal clouds. It was found that the radiances did not depend significantly on the azimuth angle; this suggested that the observed cloud fields were not regular periodic arrays. However, the dependence on zenith angle suggested that the clouds were not disposed randomly either. The implication of these measurements on the understanding of the transfer of infrared radiances through broken cloud fields is considered.

Naber, P. S.↗

NASA NTRS1984

Reflected solar radiances from broken cloud scenes and the interpretation of scanner measurements

If an adequate model of the reflection characteristics of a given scene is available, the reflected solar irradiance from the scene may be determined from radiance measurements made by satellite-borne scanning radiometers. A theoretical analysis of the reflection functions of broken cloud scenes is presented, using Monte Carlo simulations of the radiative transfer in various three-dimensional geometries. It is shown that the reflection functions of horizontally extensive (stratiform) and horizontally limited (cumuliform) clouds are generally quite different. The differences are greatest for nadir and limb views, but tend to vanish for reflected radiances with a zenith angle of 60 deg. Applications to satellite observations suggest potential errors of a factor of 2 in the inferred irradiance are likely due to scene misidentification when the radiances are interpreted indiscriminantly. Selection of preferred satellite viewing directions, however, can significantly reduce this error.

Davies, R.↗

NASA NTRS1985

Electroacoustical imaging technique for encoding incoherent radiance fields as Gabor elementary signals

A technique is presented for directly encoding incoherent radiance fields as Gabor elementary signals. This technique uses an electro-acoustic sensor to modulate the electronic charges induced by the incident radiance field with the electric fields generated by Gaussian modulated sinusoidal acoustic waves. The resultant signal carries the amplitude and phase information required for localizing spatial frequencies of the radiance field. These localized spatial frequency representations provide a link between the either geometric or Fourier transform representations currently used in computer vision and pattern recognition.

Fales, C. L.↗

NASA NTRS1985

Solar radiance models for determination of ERBE scanner filter factor

Shortwave spectral radiance models for use in the spectral correction algorithms for the ERBE Scanner Instrument are provided. The required data base was delivered to the ERBe Data Reduction Group in October 1984. It consisted of two sets of data files: (1) the spectral bidirectional angular models and (2) the spectral flux modes. The bidirectional models employ the angular characteristics of reflection by the Earth-atmosphere system and were derived from detailed radiance calculations using a finite difference model of the radiative transfer process. The spectral flux models were created through the use of a delta-Eddington model to economically simulate the effects of atmospheric variability. By combining these data sets, a wide range of radiances may be approximated for a number of scene types.

Arduini, R. F.↗

NASA NTRS1984

Dependence of NOAA-AVHRR recorded radiance on scan angle, atmospheric turbidity and unresolved cloud

Experimental evidence on the scan angle and sun angle dependence of radiance recorded by the Advanced Very High Resolution Radiometer (AVHRR) devices on the NOAA-6 and NOAA-7 satellites is presented. The effects of atmospheric turbidity at various scan angles is shown, and simulations of angular anisotropy and recorded radiance are compared with the recorded digital data from the AVHRR obtained over the Great Plains area of the US. Evidence is presented on the effects of unresolved cloud on the recorded radiance and vegetative indices from uniform, vegetative targets.

Piwinski, D. J.↗

NASA NTRS1985

Factors limiting the discrimination and quantification of terrestrial features using remotely sensed radiance

In this paper, factors controlling the radiance incident on a remote-sensing device and the interaction of the sensor with upwelling radiance are considered. Attention is also given to systematic and random radiance variations across an image: while the former may be corrected for (to an extent) the latter may not, so that it is necessary to be aware of the impact of random variations on target identification, discrimination and quantification. Both the optical reflective and the thermal-infrared parts of the spectrum are considered. Equations are presented to concisely illustrate the processes involved.

Duggin, M. J.↗

NASA NTRS1986

A theory for the retrieval of virtual temperature from winds, radiances and the equations of fluid dynamics

A technique to deduce the virtual temperature from the combined use of the equations of fluid dynamics, observed wind and observed radiances is described. The wind information could come from ground-based sensitivity very high frequency (VHF) Doppler radars and/or from space-borne Doppler lidars. The radiometers are also assumed to be either space-borne and/or ground-based. From traditional radiometric techniques the vertical structure of the temperature can be estimated only crudely. While it has been known for quite some time that the virtual temperature could be deduced from wind information only, such techniques had to assume the infallibility of certain diagnostic relations. The proposed technique is an extension of the Gal-Chen technique. It is assumed that due to modeling uncertainties the equations of fluid dynamics are satisfied only in the least square sense. The retrieved temperature, however, is constrained to reproduce the observed radiances. It is shown that the combined use of the three sources of information (wind, radiances and fluid dynamical equations) can result in a unique determination of the vertical temperature structure with spatial and temporal resolution comparable to that of the observed wind.

Tzvi, G. C.↗

NASA NTRS1986

Experimental analysis of the relationship between optical thickness and sky radiance

Data are reported from simultaneous measurements of sky radiance and aerosol optical thickness using a transmissometer tuned to seven bands between 441-872 nm. The measurements were made near Washington, DC in February and November 1985 in generally cloud-free conditions. The data indicated that satellite radiance measurements in one band would be highly correlated with AEC values in other bands, suggesting that transmission and reflection of sunlight in nonabsorbing gaseous bands is highly correlated with path radiance.

Ferrare, R. A.↗

NASA NTRS1987

Use of simulated satellite radiances from a mesoscale numerical model to understand kinematic and dynamic processes

Techniques by which mesoscale numerical weather prediction model output and radiative transfer codes are combined to simulate the radiance fields that a given passive temperature/moisture satellite sensor would see if viewing the evolving model atmosphere are introduced. The goals are to diagnose the dynamical atmospheric processes responsible for recurring patterns in observed satellite radiance fields, and to develop techniques to anticipate the ability of satellite sensor systems to depict atmospheric structures and provide information useful for numerical weather prediction (NWP). The concept of linking radiative transfer and dynamical NWP codes is demonstrated with time sequences of simulated radiance imagery in the 24 TIROS vertical sounder channels derived from model integrations for March 6, 1982.

Kalb, Michael↗

NASA NTRS1988

A semianalytic radiance model of ocean color

A semianalytical radiance model is developed which predicts the upwelled spectral radiance at the sea surface as a function of the phytoplankton pigment concentration for Morel Case 1 waters. The model is in good agreement with experimental measurements carried out in waters which were not included in the data base used to derive it. It suggests that the observed variability in the radiance is due to variations in the backscattering of plankton and the associated detrital material. The model is extended to include other material in the water, such as dissolved organic material, referred to as yellow substances, and detached coccoliths from coccolithophorids, e.g., Emiliana huxleyi. Potential applications include an improved biooptical algorithm for the retrieval of pigment concentrations from satellite imagery in the presence of interference from detached coccoliths and an improved atmospheric correction for satellite imagery. The model also serves to identify and to interpret deviations from Case 1 waters.

Gordon, Howard R.↗

NASA NTRS1989

Modeling directional thermal radiance from a forest canopy

The thermal vegetation canopy radiance model of Smith et al. (1981) is extended to account for the geometrically rough structure of a forest canopy. Fourier series expansion of a canopy height profile is used to calculate improved view facts which partially account for directional variations in canopy thermal radiance transfers. Predictions from the Smith model and the modified model are compared with experimental data obtained over a deciduous forest site in Tennessee. The results show that thermal radiance from a forest canopy depends on sensor viewing angle, solar position, and the degree of geometric roughness of the canopy surface. The maximum off-nadir angle variation in the original model was 1.6 deg C, compared with 4.4 C for the modified model.

Mcguire, M. J.↗

NASA NTRS1989

The effects of seasonal and latitudinal earth infrared radiance variations on ERBS attitude control

Analysis performed in the Flight Dynamics Facility by the Earth Radiation Budget Satellite (ERBS) Attitude Determination Support team illustrates the pitch attitude control motion and roll attitude errors induced by Earth infrared (IR) horizon radiance variations. IR scanner and inertial reference unit (IRU) pitch and roll flight data spanning 4 years of the ERBS mission are analyzed to illustrate the changes in the magnitude of the errors on time scales of the orbital period, months, and seasons. The analysis represents a unique opportunity to compare prelaunch estimates of radiance-induced attitude errors with flight measurements. As a consequence of this work the following additional information is obtained: an assessment of an average model of these errors and its standard deviation, a measurement to determine and verify previously proposed corrections to the current Earth IR radiance data base, and the possibility of a mean motion model derived from flight data in place of IRU data for ERBS fine attitude determination.

Phenneger, M. C.↗

NASA NTRS1990

The effects of seasonal and latitudinal earth infrared radiance variations on ERBS attitude control

Phenneger, M.↗

NASA NTRS1990

User's guide: Nimbus-7 Earth radiation budget narrow-field-of-view products. Scene radiance tape products, sorting into angular bins products, and maximum likelihood cloud estimation products

The archived Earth radiation budget (ERB) products produced from the Nimbus-7 ERB narrow field-of-view scanner are described. The principal products are broadband outgoing longwave radiation (4.5 to 50 microns), reflected solar radiation (0.2 to 4.8 microns), and the net radiation. Daily and monthly averages are presented on a fixed global equal area (500 sq km), grid for the period May 1979 to May 1980. Two independent algorithms are used to estimate the outgoing fluxes from the observed radiances. The algorithms are described and the results compared. The products are divided into three subsets: the Scene Radiance Tapes (SRT) contain the calibrated radiances; the Sorting into Angular Bins (SAB) tape contains the SAB produced shortwave, longwave, and net radiation products; and the Maximum Likelihood Cloud Estimation (MLCE) tapes contain the MLCE products. The tape formats are described in detail.

Kyle, H. Lee↗

NASA NTRS1992

Surface roughness considerations for atmospheric correction of ocean color sensors. I - The Rayleigh-scattering component. II - Error in the retrieved water-leaving radiance

The first step in the Coastal Zone Color Scanner (CZCS) atmospheric-correction algorithm is the computation of the Rayleigh-scattering (RS) contribution, L sub r, to the radiance leaving the top of the atmosphere over the ocean. In the present algorithm, L sub r is computed by assuming that the ocean surface is flat. Calculations of the radiance leaving an RS atmosphere overlying a rough Fresnel-reflecting ocean are presented to evaluate the radiance error caused by the flat-ocean assumption. Simulations are carried out to evaluate the error incurred when the CZCS-type algorithm is applied to a realistic ocean in which the surface is roughened by the wind. In situations where there is no direct sun glitter, it is concluded that the error induced by ignoring the Rayleigh-aerosol interaction is usually larger than that caused by ignoring the surface roughness. This suggests that, in refining algorithms for future sensors, more effort should be focused on dealing with the Rayleigh-aerosol interaction than on the roughness of the sea surface.

Gordon, Howard R.↗

NASA NTRS1993

Normalization and calibration of geostationary satellite radiances for the International Satellite Cloud Climatology Project

Procedures are described for normalizing the radiometric calibration of image radiances obtained from geostationary weather satellites that contributed data to the International Satellite Cloud Climatology Project. The key step is comparison of coincident and collocated measurements made by each satellite and the concurrent AVHRR on the 'afternoon' NOAA polar-orbiting weather satellite at the same viewing geometry. The results of this comparison allow transfer of the AVHRR absolute calibration, which has been established over the whole series, to the radiometers on the geostationary satellites. Results are given for Meteosat-2, 3, and 4, for GOES-5, 6, and 7, for GMS-2, 3, and 4 and for Insat-1B. The relative stability of the calibrations of these radiance data is estimated to be within +/- 3 percent; the uncertainty of the absolute calibrations is estimated to be less than 10 percent. The remaining uncertainties are at least two times smaller than for the original radiance data.

Desormeaux, Yves↗