Engineering topics

Holm, Ronald G.

Publications and source records attributed to Holm, Ronald G..

5 records

NASA NTRS1994

Comparison Of Measurments Of Atmospheric Water Vapor

Report presents experimental intercomparison among measurements by four spectrometric instruments for determining concentration of atmospheric water vapor. Three instruments ground-based and needed to provide independent data to calibrate and validate measurements taken by fourth instrument, which is airborne visible/infrared imaging spectrometer (AVIRIS). Remote down-looking instruments like AVIRIS increases accuracy and coverage of water-vapor measurements.

Bruegge, Carol J.↗

NASA NTRS1992

Water vapor column abundance retrievals during FIFE

A variation of the modified Langley plot algorithm is reported here and applied to the retrieval of atmospheric water column abundance from a filtered sunphotometer. In this new methodology an absorption data base (LOWTRAN 7) is used to compute a water abundance versus transmittance curve of growth, rather than the square-root dependence previously assumed. Validation of the technique is provided from an uncertainty analysis, and plans to further validate using Fourier transform spectrometers are detailed. The new sunphotometer technique is used to report local column water vapor during the First ISLSCP Field Experiment (FIFE), and comparisons are made with abundances retrieved via FIFE radiosonde observations. The sunphotometer data can best be utilized, however, to in turn validate data from airborne or in-orbit measurements of water vapor. With these flight sensors, horizontal and topographic variability within the scene can be viewed. An example of the airborne data set is given using an image from the airborne visible infrared imaging spectrometer, as acquired on August 31, 1990.

Bruegge, Carol J.↗

NASA NTRS1991

Conical Mirrors For Quasi-Retroreflection

Single and multiple-nested conical mirrors assembled and positioned to provide several distinct orders of retroreflection. Design and orientation of "cones" determines positions of, and solid angles subtended by discrete orders of retroreflection. Accommodates larger range of incident angles than corner-cube reflectors. Also provides greater spectral coverage than conventional lens-and mirror retroreflectors. Potential applications include interferometry, metrology, lasers, position and motion sensors, instrument test and calibration, and expanded capability of highway markers and signs.

Dekany, Richard G.↗

NASA NTRS1990

In-situ atmospheric water-vapor retrieval in support of AVIRIS validation

A comparison is made between two ground-based atmospheric water-vapor measurement techniques, each of which uses data from a solar-pointing radiometer. One technique uses visible wavelength channels to retrieve aerosol loading, surface pressure readings for Rayleigh scattering analyses, and the 0.94 micron channel to extract water vapor from the residual of total versus scattering opacity. The other technique requires only the ratio of channels centered at 0.94 and 0.87 micron. Results are given for the April 13, 1989 AVIRIS in-flight calibration.

Bruegge, Carol J.↗

NASA NTRS1989

Surface reflectance factor retrieval from Thematic Mapper data

Based on the absolute radiometric calibration of the TM and the use of a radiative transfer program for atmospheric correction, ground reflectances were retrieved for several fields of crops and bare soil in TM bands 1-4 for six TM scenes acquired over a 12-month period. These reflectances were compared to those measured using ground-based and low-altitude, aircraft-mounted radiometers. When, for four TM acquisitions, the comparison was made between areas that had been carefully selected for their high uniformity, the reflectance factors agreed to + or - 0.01 over the reflectance range 0.02-0.55. When the comparison was made for two of the above acquisitions and two others on different dates, for larger areas not carefully selected to be of uniform reflectance, the reflectance factors agreed to + or - 0.02 (1 sigma RMS), over same reflectance range.

Holm, Ronald G.↗