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Menzies, R. T.

Publications and source records attributed to Menzies, R. T..

100 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Measurements of air pollutants over a Los Angeles freeway with a bistatic laser system

Nitric oxide, ozone, and ethylene were monitored over roads during periods of heavy traffic by transmitting several known laser wavelengths over an atmospheric path and measuring the differential absorption of the wavelengths. Heavy afternoon traffic between four and five o'clock over a 3.75 km path produced a noticeable increase in ethylene and a decrease in ozone. The changes occurred on a short time scale and correlated with the sudden traffic density increase. The ozone decrease occurs because of the sudden presence of large quantities of nitric oxide. Although the laboratory laser equipment used is rather cumbersome, the measurements did point out the potential of the laser absorption technique for monitoring large areas from one location.-

Menzies, R. T.↗
NASA NTRS1976

Laser heterodyne detection techniques

The principles of heterodyne radiometry are examined, taking into account thermal radiation, the Dicke microwave radiometer, photomixing in the infrared, and signal-to-noise considerations. The passive heterodyne radiometer is considered and a description is presented of heterodyne techniques in active monitoring systems. Attention is given to gas emissivities in the infrared, component requirements, experimental heterodyne detection of gases, a comparison of the passive heterodyne radiometer with the Michelson interferometer-spectrometer, airborne monitoring applications, turbulence effects on passive heterodyne radiometry, sensitivity improvements with heterodyning, atmosphere-induced degradation of bistatic system performance, pollutant detection experiments with a bistatic system, and the airborne laser absorption spectrometer. Future improvements in spectral flexibility are also discussed.

Menzies, R. T.↗
NASA NTRS1975

Laser-excited fluorescence for measuring atmospheric pollution

System measures amount of given pollutant at specific location. Infrared laser aimed at location has wavelength that will cause molecules of pollutant to fluoresce. Detector separates fluorescence from other radiation and measures its intensity to indicate concentration of pollutant.

Menzies, R. T.↗
NASA NTRS1974

Remote atmospheric sensing with an airborne laser absorption spectrometer

A laser absorption spectrometer, using an IR laser transmitter and a heterodyne radiometer, can be used from an aircraft or spacecraft to measure altitude profiles of air pollutants and other atmospheric constituents. The technique involves measurement of differential absorption at several wavelengths, using the diffusely reflecting earth's surface to provide a return signal. The pressure broadening of absorption lines allows one to discriminate between high and low altitude absorbers. Application of the technique to measurements of ozone, nitric oxide, and water vapor are presented. CO2 and CO lasers are considered as transmitters. The discussion includes altitude resolution limitations, atmospheric temperature dependence, and frequency stability requirements of the instrument.

Menzies, R. T.↗
NASA NTRS1974

Air pollution - Remote detection of several pollutant gases with a laser heterodyne radiometer

An infrared heterodyne radiometer with a spectral resolution of 0.04 reciprocal centimeters has been used to remotely detect samples of ozone, sulfur dioxide, ammonia, and ethylene at room temperature, and samples of nitric oxide at 390 K. Each gas was observed in a background of nitrogen or oxygen at atmospheric pressure. Sensitivities to some of these gases are adequate for detection of ambient concentrations as low as a few parts per billion.

Menzies, R. T.↗
NASA NTRS1974

The effect of centrifugal distortion on CO2-laser frequencies

Values of the coefficient H for the appropriate carbon-dioxide laser levels are estimated on the basis of theoretical considerations. The values are compared with data obtained by Petersen et al. (1973). It is found that very small perturbations become important as the accuracy of the CO2-laser frequencies increases, especially for lines far away from the band center. Careful experimental frequency measurements are mandatory in the high J region if an accuracy of the order of 10 kHz is desired.

Menzies, R. T.↗
NASA NTRS1974

Remote atmospheric sensing with an airborne laser absorption spectrometer

A laser absorption spectrometer, using an infrared laser transmitter and a heterodyne radiometer, can be used from an aircraft or spacecraft to measure altitude profiles of air pollutants and other atmospheric constituents. The technique involves measurement of differential absorption at several wavelengths, using the diffusely reflecting earth's surface to provide a return signal. The pressure broadening of absorption lines allows one to discriminate between high and low altitude absorbers. Application of the technique to measurements of ozone, nitric oxide, and water vapor are presented. CO2 and CO lasers are considered as transmitters. The discussion includes altitude resolution limitations, atmospheric temperature dependence, and frequency stability requirements of the instrument.

Menzies, R. T.↗
NASA NTRS1973

Monitoring atmospheric pollutants with a heterodyne radiometer transmitter-receiver

The presence of selected atmospheric pollutants can be determined by transmitting an infrared beam of proper wavelength through the atmosphere, and detecting the reflections of the transmitted beam with a heterodyne radiometer transmitter-receiver using part of the laser beam as a local oscillator. The particular pollutant and its absorption line strength to be measured are selected by the laser beam wave length. When the round-trip path for the light is known or measured, concentration can be determined. Since pressure (altitude) will affect the shape of the molecular absorption line of a pollutant, tuning the laser through a range of frequencies, which includes a part of the absorption line of the pollutant of interest, yields pollutant altitude data from which the altitude and altitude profile is determined.

Menzies, R. T.↗
NASA NTRS1971

Usefulness of the infrared heterodyne radiometer in remote sensing of atmospheric pollutants.

The application of narrow-band optical receivers to the problem of sensing atmospheric pollution is discussed. The emission/absorption lines of many major atmospheric pollutant molecules overlap the operating frequency bands of CO2 laser and CO laser heterodyne receivers. Several remote pollution sensing systems which are based upon utilization of these spectral overlaps are described, and an analysis of their potential is presented. The possibility of using other lasers (e.g.: the PbSnTe tunable diode laser) as local oscillators is also considered. Results of laboratory experiments with a CO2 laser heterodyne radiometer are presented.

Menzies, R. T.↗