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Tratt, David M.

Publications and source records attributed to Tratt, David M..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

The Multi-Center Airborne Coherent Atmospheric Wind Sensor, MACAWS

In 1992 the atmospheric lidar remote sensing groups of the NASA Marshall Space Flight Center, NOAA Environmental Technology Laboratory, and Jet Propulsion Laboratory began a joint collaboration to develop an airborne high-energy Doppler laser radar (lidar) system for atmospheric research and satellite validation and simulation studies. The result is the Multi-center Airborne Coherent Atmospheric Wind Sensor, MACAWS, which has the capability to remotely sense the distribution of wind and absolute aerosol backscatter in the troposphere and lower stratosphere. A factor critical to the programmatic feasibility and technical success of this collaboration has been the utilization of existing components and expertise which were developed for previous atmospheric research by the respective institutions. The motivation for the MACAWS program Is three-fold: to obtain fundamental measurements of sub-synoptic scale processes and features which may be used as a basis to improve sub-grid scale parameterizations in large-scale models; to obtain similar datasets in order to improve the understanding and predictive capabilities on the mesoscale; and to validate (simulate) the performance of existing (planned) satellite-borne sensors. Examples of the latter include participation in the validation of the NASA Scatterometer and the assessment of prospective satellite Doppler lidar for global tropospheric wind measurement. Initial flight tests were made in September 1995; subsequent flights were made in June 1996 following improvements. This paper describes the MACAWS instrument, principles of operation, examples of measurements over the eastern Pacific Ocean and western United States, and future applications.

Rothermel, Jeffry↗
NASA NTRS1997

Remote Sensing of Multi-Level Wind Fields with High-Energy Airborne Scanning Coherent Doppler Lidar

The atmospheric lidar remote sensing groups of NOAA Environmental Technology Laboratory, NASA Marshall Space Flight Center, and Jet Propulsion Laboratory have developed and flown a scanning, 1 Joule per pulse, CO2 coherent Doppler lidar capable of mapping a three-dimensional volume of atmospheric winds and aerosol backscatter in the troposphere and lower stratosphere. Applications include the study of severe and non-severe atmospheric flows, intercomparisons with other sensors, and the simulation of prospective satellite Doppler lidar wind profilers. Examples of wind measurements are given for the marine boundary layer and near the coastline of the western United States.

Rothermel, Jeffry↗
NASA NTRS1995

Evolution of the Pinatubo volcanic aerosol column above Pasadena, California observed with a mid-infrared backscatter lidar

The evolution of the volcanic debris plume originating from the June 1991 eruption of Mt. Pinatubo has been monitored since its genesis using a ground-based backscatter lidar facility sited at the Jet Propulsion Laboratory (JPL). Both absolute and relative pre- and post-Pinatubo backscatter observations are in accord with Mie scattering projections based on measured aerosol particle size distributions reported in the literature. The post-Pinatubo column-integrated backscatter coefficient peaked approximately 400 days after the eruption, and the observed upper boundary of the aerosol column subsided at a rate of approximately 200 m/mon.

Tratt, David M.↗
NASA NTRS1995

Evidence of seasonally dependent stratosphere-troposphere exchange and purging of lower stratospheric aerosol from a multiyear lidar data set

Tropospheric and lower stratospheric aerosol backscatter data obtained from a calibrated backscatter lidar at Pasadena, California (34 deg N latitude) over the 1984-1993 period clearly indicate tightly coupled aerosol optical properties in the upper troposphere and lower stratosphere in the winter and early spring, due to the active midlatitude stratospheric-tropospheric (ST) exchange processes occurring at this time of year. Lidar data indicate that during pre-Pinaturbo background conditions, the subsequent purging of the aerosol in the upper troposphere caused a significant reduction in the aerosol content throughout the 8 - 18 km altitude region in the early spring period. The post-Pinatubo evidence of intense exchange in the winter and early spring is a significant increase in the upper tropospheric aerosol content, such that the backscatter levels reach values nearly equivalent to the enhanced backscatter levels existing in the lower stratosphere. The calculated stratospheric mass extrusion rate is consistent with a 45-day lifetime of lower stratospheric aerosol during this part of the year, which implies that midlatitude ST exchange is a significant sink for stratospheric aerosol.

Menzies, Robert T.↗
NASA NTRS1994

Airborne CO2 coherent lidar measurements of cloud backscatter and opacity over the ocean surface

The use of an airborne CO2 lidar to obtain cloud backscatter and extinction data at a thermal infrared wavelength is described. The extinction in this spectral region is proportional to the cloud liquid water content. The use of coherent detection results in high sensitivity and narrow field of view, the latter property greatly reducing multiple-scattering effects. Backscatter measurements in absolute units are obtained through a hard target calibration methodology. For clouds of low to moderate optical thickness at the lidar wavelength, both geometric thickness and optical thickness can be measured. The sea surface reflectance signal is used to obtain estimates of the cloud optical thickness. The utility of this technique results from studies that indicate that the spatial scale of variability of the sea surface reflectance is generally large compared with that of cloud optical thickness. Selected results are presented from data taken during flights over the Pacific Ocean.

Menzies, Robert T.↗
NASA NTRS1994

More About Graded-Reflectance Optics For Coherent Lidar

Report presents theoretical study of energy-extraction and power-transmission efficiency of unstable-resonator laser cavity, output mirror of which has graded reflectance. Super-gaussian reflectance profile may optimize performance. Similar study reported in "Comparative Study of Resonator Optics for Lidar Applications" (NPO-17776).

Tratt, David M.↗
NASA NTRS1992

Optimizing coherent lidar performance with graded-reflectance laser resonator optics

It is demonstrated how the design of graded-reflectance output coupler unstable laser cavities may be tailored to significantly enhance the overall power transmission efficiency of a given laser system relative to that of a conventional diffractively coupled unstable resonator. The importance of these findings in coherent lidar applications is explained with particular emphasis on projected space-based systems.

Tratt, David M.↗
NASA NTRS1992

Multi-wavelength Airborne Lidar Intercomparisons of Aerosol and Cirrus Backscatter over the Pacific Ocean

Airborne CO2 and Nd:YAG lidar instruments were flown on the NASA DC-8 research aircraft during two extended missions over the Pacific. The objectives during these flights were to characterize aerosol backscatter levels at infrared wavelengths in relatively pristine regions of the troposphere, and to observe cloud effects on lidar signals. In addition, the three wavelength Nd:YAG data were processed using independent temperature profile information, in order to deduce the Rayleigh scattering component of the total backscatter at each wavelength. The data can be used to better understand the capabilities of various airborne or Earth-orbiting lidar designs to provide backscatter information from aerosols and clouds, or to provide Doppler or DIAL information from aerosol and cloud backscatter.

Menzies, Robert T.↗
NASA NTRS1992

Comparative Study Of Resonator Optics For Lidar Applications

Report discusses overall transmit/receive performances of laser-radar transceivers. Gaussian case and hard-edged case selected for comparison because of their practical importance. Intercomparison shows that for multi-joule-output pulsed CO2 lasers, Gaussian profiled optics offers little improvement over hard-edged option, while greater hardiness and superior energy extraction capability of latter constitutes strong argument in favor of its application.

Tratt, David M.↗
NASA NTRS1991

Automatic Rejection Of Multimode Laser Pulses

Characteristic modulation detected, enabling rejection of multimode signals. Monitoring circuit senses multiple longitudinal mode oscillation of transversely excited, atmospheric-pressure (TEA) CO2 laser. Facility developed for inclusion into coherent detection laser radar (LIDAR) system. However, circuit described of use in any experiment where desireable to record data only when laser operates in single longitudinal mode.

Tratt, David M.↗
NASA NTRS1991

Aerosol and cloud observations with a CO2 backscatter lidar on the NASA DC-8 GLOBE Pacific Missions

The paper presents an airborne backscatter lidar developed to fly multiple times on the NASA DC-8 research aircraft and measure vertical profiles of aerosol and cloud backscatter throughout the vertical extent of the troposphere, with emphasis on coverage of the range of latitudes. The lidar instrument characteristics are summarized and the calibration procedures are described. Results of aerosol and cloud observations are presented.

Menzies, Robert T.↗
NASA NTRS1990

Design and performance measurements of an airborne aerosol backscatter lidar

The global winds measurement application of coherent Doppler lidar requires intensive study of the global climatology of atmospheric aerosol backscatter at infrared wavelengths. An airborne backscatter lidar is discussed, which has been developed to measure atmospheric backscatter profiles at CO2 laser wavelengths. The instrument characteristics and representative flight measurement results are presented.

Menzies, Robert T.↗
NASA NTRS1989

Altitude and seasonal characteristics of aerosol backscatter at thermal infrared wavelengths using lidar observations from coastal California

A calibrated CO2 lidar has been used to measure boundary layer aerosol backscatter and vertical profiles of tropospheric and lower stratospheric aerosol backscatter over a 1984-1987 time period from a site in Pasadena, California. The lidar data have been taken at two wavelengths, 9.25 and 10.6 microns. Data are presented which show altitude, seasonal, and trend characteristics of backscatter for various air mass histories. Results of trajectory studies indicate the influence of convective activity and other factors on the backscatter profiles.

Menzies, Robert T.↗
NASA NTRS1989

Automated rejection of parasitic frequency sidebands in heterodyne-detection LIDAR applications

A technique is described for the detection of the sporadic onset of multiaxial mode behavior of a normally single-mode TEA CO2 laser. The technique is implemented using primarily commercial circuit modules; it incorporates a peak detector that displays the RF detector output on a digital voltmeter, and a LED bar graph. The technique was successfully demonstrated with an existing coherent atmospheric LIDAR facility utilizing an injection-seeded single-mode TEA CO2 laser. The block schematic diagram is included.

Esproles, Carlos↗
NASA NTRS1988

Atmospheric backscatter vertical profiles at 9.2 and 10.6 microns - A comparative study

The paper reports a series of atmospheric aerosol backscatter measurements at two widely spaced CO2 laser wavelengths: 9.25 and 10.6 microns. Comparisons are made between backscatter coefficient profiles at these two wavelengths up to 20-km altitude. Measurements such as those reported here can be used to assess the feasibility of coherent CO2 lidar for wind measurements, and they also provide a partial test of backscatter model predictions.

Ancellet, Gerard M.↗
NASA NTRS1988

Unstable resonator antenna properties in coherent lidar applications - A comparative study

The antenna parameters of a coherent lidar in the far-field diffraction-limited regime, where the lidar transmitter consists of an unstable resonator with a Gaussian reflectivity profile output coupler, are investigated. A figure-of-merit combining lasr transmitter energy extraction efficiency with the far-field attributes of a given cavity configuration has been used to compare the lidar performance and relative merits of such systems as they relate to those of conventional unstable cavities with diffractive output coupling.

Tratt, David M.↗