J H Chetwynd

Bio: J H Chetwynd is an academic researcher. The author has contributed to research in topics: Atmospheric models & Transmittance. The author has an hindex of 6, co-authored 6 publications receiving 2482 citations.

AFGL atmospheric constituent profiles (0-120km)

Abstract: : An atmospheric data base consisting of volume mixing ratios (o0 to 12okm) for twenty eight (28) minor and trace gases has been assembled for use with spectral radiance transmittance models. Six references atmospheres, each defining temperature, pressure and density as a function of altitude (selected from the U.S. Standard Supplements, 1966 and the U.S. Standard Atmosphere, 1976) provide a range of climatological choices. Analogous zonal-mean descriptions for 2O, O3, N2O, CO, and CH4 have been subsequently adapted from satellite data and/or dynamical-photochemical analyses. The remaining species are defined by single profiles, usually appropriate for U.S. Standard conditions. Because the entire profile set is preferentially based on available measurements, explicit photochemical consistency between the different species has not been maintained. Keywords: ATMOSPHERIC CONSTITUENTS; TEMPERATURE PROFILES; MODEL ATMOSPHERES.

Atmospheric transmittance/radiance: Computer code LOWTRAN 5

Abstract: : This report describes a computer code for predicting atmospheric transmittance and the thermal radiation emitted by the atmosphere and earth from 350 to 40,000 per cm at a spectral resolution of 20 per cm. The program is based on the LOWTRAN 4 (1978) computer code. New altitude and relative-humidity dependent aerosol models and new fog models are included in the code. In addition, the new code structure consists of a main program and 19 subroutines. The computer code contains representative (geographical and seasonal) atmospheric models and representative aerosol models with an option to replace them with user-derived or measured values. The program can be run in one of two modes, namely, to compute only atmospheric transmittance or both atmospheric transmittance and radiance for any given slant path geometry.

Users Guide to LOWTRAN 7

Abstract: : LOWTRAN 7 is a low-resolution propagation model and computer code for predicting atmospheric transmittance and background radiance from 0 to 50,000 cm -1 at a resolution of 20 cm -1. The code is based on the LOWTRAN 6 (1983) model. Multiple scattered radiation has been added to the model as well as new molecular band model parameters and new ozone and molecular oxygen absorption parameters for the UV. Other modifications include a wind dependent desert model, new cirrus cloud models, and new cloud and rain models. The code also includes new representative (geographical and seasonal) atmospheric models and updated aerosol models with options to replace them with user-derived values. An improved extra-terrestrial solar source function is also included. Six modes of program execution are allowed with the new model and computer code for a given slant path geometry. This report contains a description to users for operating the LOWTRAN 7 computer code. It summarizes the capabilities of the new code, provides complete operating instructions as well as input and output from test cases for user validation. Also included are operating instructions for three programs that utilize LOWTRAN 7 output (plot, filter and scanning function programs). Keywords: Computer program documentation, Subroutines, Radiative transfer, Aerosols, Clouds, Attenuation, Lowtran, Computer code, Ultraviolet, Visible, Infrared.

Atmospheric Transmittance/Radiance : Computer Code LOWTRAN 6.

Abstract: : This report describes a computer code for predicting atmospheric transmittance and the thermal radiation emitted by the atmosphere and earth from 350 to 40,000 per cm at a spectral resolution of 20 per cm. The program is based on the LOWTRAN 5 computer code. Solar/lunar scattered radiation has been added to the code, as well as new spherical refractive geometry subroutines and an improved water vapor continuum model. Other modifications to the code include a wind-dependent maritime aerosol model, a vertical structure aerosol model, a cirrus cloud model, and a rain model. The computer code contains representative (geographical and seasonal) atmospheric models and representative aerosol models with an option to replace with user-derived or measured values. The program can be run in one of three modes, namely, to compute only atmospheric transmittance, to compute atmospheric transmittance and radiance, or to compute atmospheric transmittance, atmospheric radiance, and scattered solar/lunar background radiance for a given slant path geometry.

AFGL (Air Force Geophysical Laboratory) atmospheric constituent profiles (0. 120km). Environmental research papers

Abstract: An atmospheric data base consisting of volume-mixing ratios (o0 to 12 okm) for 28 minor and trace gases was assembled for use with spectral-radiance transmittance models. Six reference atmospheres, each defining temperature, pressure and density as a function of altitude (selected from the U.S. Standard Supplements, 1966 and the U.S. Standard Atmosphere, 1976) provide a range of climatological choices. Analogous zonal-mean descriptions for H/sub 2/O, O/sub 3/, N/sub 2/O, CO, and CH/sub 4/ were subsequently adapted from satellite data and/or dynamical-photochemical analyses. The remaining species are defined by single profiles, usually appropriate for U.S. Standard conditions. Because the entire profile set is preferentially based on available measurements, explicit photochemical consistency between the different species has not been maintained.

A generalized split-window algorithm for retrieving land-surface temperature from space

Abstract: Proposes a generalized split-window method for retrieving land-surface temperature (LST) from AVHRR and MODIS data. Accurate radiative transfer simulations show that the coefficients in the split-window algorithm for LST must vary with the viewing angle, if the authors are to achieve a LST accuracy of about 1 K for the whole scan swath range (/spl plusmn/55/spl deg/ from nadir) and for the ranges of surface temperature and atmospheric conditions over land, which are much wider than those over oceans. The authors obtain these coefficients from regression analysis of radiative transfer simulations, and they analyze sensitivity and error over wide ranges of surface temperature and emissivity and atmospheric water vapor abundance and temperature. Simulations show that when atmospheric water vapor increases and viewing angle is larger than 45/spl deg/, it is necessary to optimize the split-window method by separating the ranges of the atmospheric water vapor, lower boundary temperature, and the surface temperature into tractable subranges. The atmospheric lower boundary temperature and (vertical) column water vapor values retrieved from HIRS/2 or MODIS atmospheric sounding channels can be used to determine the range for the optimum coefficients of the split-window method. This new algorithm not only retrieves land-surface temperature more accurately, but is also less sensitive to uncertainty in emissivity and to instrument quantization error.

SBDART: A Research and Teaching Software Tool for Plane-Parallel Radiative Transfer in the Earth's Atmosphere.

Abstract: SBDART is a software tool that computes plane-parallel radiative transfer in clear and cloudy conditions within the earth's atmosphere and at the surface. All important processes that affect the ultraviolet, visible, and infrared radiation fields are included. The code is a marriage of a sophisticated discrete ordinate radiative transfer module, low-resolution atmospheric transmission models, and Mie scattering results for light scattering by water droplets and ice crystals. The code is well suited for a wide variety of atmospheric radiative energy balance and remote sensing studies. It is designed so that it can be used for case studies as well as sensitivity analysis. For small sets of computations or teaching applications it is available on the World Wide Web with a user-friendly interface. For sensitivity studies requiring many computations it is available by anonymous FTP as a well organized and documented FORTRAN 77 source code.