Engineering Papers⌕ Search

Engineering topics

Reagan, J. A.

Publications and source records attributed to Reagan, J. A..

25 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Determination of the complex refractive index and size distribution of atmospheric particulates from bistatic-monostatic lidar and solar radiometer measurements

A method is presented for inferring both the size distribution and the complex refractive index of atmospheric particulates from combined bistatic-monostatic lidar and solar radiometer observations. The basic input measurements are spectral optical depths at several visible and near-infrared wavelengths as obtained with a solar radiometer and backscatter and angular scatter coefficients as obtained from a biostatic-monostatic lidar. The spectral optical depth measurements obtained from the radiometer are mathematically inverted to infer a columnar particulate size distribution. Advantage is taken of the fact that the shape of the size distribution obtained by inverting the particulate optical depth is relatively insensitive to the particle refractive index assumed in the inversion. Bistatic-monostatic angular scatter and backscatter lidar data are then processed to extract an optimum value for the particle refractive index subject to the constraint that the shape of the particulate size distribution be the same as that inferred from the solar radiometer data. Specifically, the scattering parameters obtained from the bistatic-monostatic lidar data are compared with corresponding theoretical computations made for various assumed refractive index values. That value which yields best agreement, in a weighted least squares sense, is selected as the optimal refractive index estimate. The results of this procedure applied to a set of simulated measurements as well as to measurements collected on two separate days are presented and discussed.

Reagan, J. A.↗
NASA NTRS1978

Aerosol size distributions obtained by inversion of spectral optical depth measurements

Columnar aerosol size distributions have been inferred by numerically inverting particulate optical depth measurements as a function of wavelength. An inversion formula which explicitly includes the magnitude of the measurement variances is derived and applied to optical depth measurements obtained in Tucson with a solar radiometer. It is found that the individual size distributions of the aerosol particles (assumed spherical), at least for radii greater than or approximately equal to 0.1 micron, fall into one of three distinctly different categories. Approximately 50% of all distributions examined thus far can best be represented as a composite of a Junge distribution plus a distribution of relatively monodispersed larger particles centered at a radius of about 0.5 micron. Scarcely 20% of the distributions yielded Junge size distributions, while 30% yielded relatively monodispersed distributions of the log-normal or gamma distribution types. A representative selection of each of these types will be presented and discussed. The sensitivity of spectral attenuation measurements to the radii limits and refractive index assumed in the numerical inversion will also be addressed.

King, M. D.↗
NASA NTRS1978

Some results of the UA-ARE Program

During the period of May 6-16, 1977, the University of Arizona Aerosol Research Group conducted a cooperative Aerosol and Radiation Experiment (UA-ARE Program) in Tucson, Ariz. The principal objective of the program was to compare how well theoretically computed fluxes at selected visible wavelengths agreed with measured fluxes for the case where the theoretical flux calculations were based on inferred atmospheric aerosol parameters derived exclusively from simultaneous optical remote sensing measurements. A second objective of the experiment was to intercompare the results obtained by different remote sensing techniques. The various measurement techniques employed in the UA-ARE Program are listed along with brief summaries of the information to be derived from the data obtained with each technique.

Reagan, J. A.↗
NASA NTRS1973

Investigations of atmospheric extinction using direct solar radiation measurements made with a multiple wavelength radiometer.

A multiple wavelength solar radiometer designed for the purpose of measuring atmospheric optical depth at discrete wavelengths through the visible region is described. Experimental techniques, including sample observations, are presented for obtaining atmospheric optical depth from radiometer measurements. These techniques apply for conditions where the optical depth is either temporally variant or invariant during the course of a day. The influence of the aerosol size distribution on optical depth is investigated. Theoretical calculations of the wavelength dependency of the aerosol optical depth contribution are presented for several representative aerosol size distributions. Methods are also presented for estimating the aerosol size distribution and aerosol mass loading from multiwavelength optical depth measurements.

Shaw, G. E.↗
NASA NTRS1971

Three optical methods for remotely measuring aerosol size distributions.

Three optical probing methods for remotely measuring atmospheric aerosol size distributions are discussed and contrasted. The particular detection methods which are considered make use of monostatic lidar (laser radar), bistatic lidar, and solar radiometer sensing techniques. The theory of each of these measurement techniques is discussed briefly, and the necessary constraints which must be applied to obtain aerosol size distribution information from such measurements are pointed out. Theoretical and/or experimental results are also presented which demonstrate the utility of the three proposed probing methods.

Reagan, J. A.↗
NASA NTRS1969

Comments on bistatic lidar

The use of bistatic lidar to determine the size and concentration of atmospheric aerosols is discussed. It is shown that bistatic measurements made at several scattering angles coupled with logical assumptions about the size distribution can provide estimates of the aerosol concentration, and by polarization measurements, meteorological parameters that influence the vertical distribution of particulates can be determined.

Reagan, J. A.↗