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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Assessment of measurement error due to sampling perspective in the space-based Doppler lidar wind profiler

A Multipair Algorithm (MPA) has been developed to minimize the contribution of the sampling error in the simulated Doppler lidar wind profiler measurements (due to angular and spatial separation between shots in a shot pair) to the total measurement uncertainty. Idealized wind fields are used as input to the profiling model, and radial wind estimates are passed through the MPA to yield a wind measurement for 300 x 300 sq km areas. The derived divergence fields illustrate the gradient patterns that are particular to the Doppler lidar sampling strategy and perspective.

Houston, S. H.↗
NASA NTRS1986

Doppler lidar atmospheric wind sensors - A comparative performance evaluation for global measurement applications from earth orbit

A comparison is made of four prominent Doppler lidar systems, ranging in wavelength from the near UV to the middle IR, which are presently being studied for their potential in an earth-orbiting global tropospheric wind field measurement application. The comparison is restricted to relative photon efficiencies, i.e., the required number of transmitted photons per pulse is calculated for each system for midtropospheric velocity estimate uncertainties ranging from + or - 1 to + or - 4 m/s. The results are converted to laser transmitter pulse energy and power requirements. The analysis indicates that a coherent CO2 Doppler lidar operating at 9.11-micron wavelength is the most efficient.

Menzies, R. T.↗
NASA NTRS1998

Interference of Backscatter from Two Droplets in a Focused Continuous Wave CO2 Doppler Lidar Beam

Using a focused continuous wave CO2 Doppler lidar at wavelength 9.1 microns the interference of the superposition of backscatter from two approx. 14.12 microns diameter silicone oil droplets in the lidar beam was observed. This interference results in a single backscatter pulse from the two droplets with a distinct periodic structure. The interference is due to the phase difference in backscatter from the two droplets while they are traversing the lidar beam because they are moving at different speeds and, thus, the droplet separation is not constant. The complete cycle of interference, with periodicity of 2(Pi), gives excellent agreement between measurements and lidar theory.

Jarzembski, Maurice A.↗
NASA NTRS2016

Development of Navigation Doppler Lidar for Future Landing Mission

A coherent Navigation Doppler Lidar (NDL) sensor has been developed under the Autonomous precision Landing and Hazard Avoidance Technology (ALHAT) project to support future NASA missions to planetary bodies. This lidar sensor provides accurate surface-relative altitude and vector velocity data during the descent phase that can be used by an autonomous Guidance, Navigation, and Control (GN&C) system to precisely navigate the vehicle from a few kilometers above the ground to a designated location and execute a controlled soft touchdown. The operation and performance of the NDL was demonstrated through closed-loop flights onboard the rocket-propelled Morpheus vehicle in 2014. In Morpheus flights, conducted at the NASA Kennedy Space Center, the NDL data was used by an autonomous GN&C system to navigate and land the vehicle precisely at the selected location surrounded by hazardous rocks and craters. Since then, development efforts for the NDL have shifted toward enhancing performance, optimizing design, and addressing spaceflight size and mass constraints and environmental and reliability requirements. The next generation NDL, with expanded operational envelope and significantly reduced size, will be demonstrated in 2017 through a new flight test campaign onboard a commercial rocketpropelled test vehicle.

Amzajerdian, Farzin↗
NASA NTRS1999

Measuring Tropospheric Winds from Space Using a Coherent Doppler Lidar Technique

The global measurement of tropospheric wind profiles has been cited by the operational meteorological community as the most important missing element in the present and planned observing system. The most practical and economical method for obtaining this measurement is from low earth orbit, utilizing a Doppler lidar (laser radar) technique. Specifically, this paper will describe the coherent Doppler wind lidar (CDWL) technique, the design and progress of a current space flight project to fly such a system on the Space Shuttle, and plans for future flights of similar instruments. The SPARCLE (SPAce Readiness Coherent Lidar Experiment) is a Shuttle-based instrument whose flight is targeted for March, 2001. The objectives of SPARCLE are three-fold: Confirm that the coherent Doppler lidar technique can measure line-of-sight winds to within 1-2 m/s accuracy; Collect data to permit validation and improvement of instrument performance models to enable better design of future missions; and Collect wind and backscatter data for future mission optimization and for atmospheric studies. These objectives reflect the nature of the experiment and its program sponsor, NASA's New Millennium Program. The experiment is a technology validation mission whose primary purpose is to provide a space flight validation of this particular technology. (It should be noted that the CDWL technique has successfully been implemented from ground-based and aircraft-based platforms for a number of years.) Since the conduct of the SPARCLE mission is tied to future decisions on the choice of technology for free-flying, operational missions, the collection of data is intrinsically tied to the validation and improvement of instrument performance models that predict the sensitivity and accuracy of any particular present or future instrument system. The challenges unique to space flight for an instrument such as SPARCLE and follow-ons include: Obtaining the required lidar sensitivity from the long distance of orbit height to the lower atmosphere; Maintaining optical alignments after launch to orbit, and during operations in "microgravity"; Obtaining pointing knowledge of sufficient accuracy to remove the speed of the spacecraft (and the rotating Earth) from the measurements; Providing sufficient power (not a problem on the Shuttle) and cooling to the instrument. The paper will describe the status and challenges of the SPARCLE project, the value of obtaining wind data from orbit, and will present a roadmap to future instruments for scientific research and operational meteorology.

Miller, Timothy L.↗
NASA NTRS1998

Airborne/Space-Based Doppler Lidar Wind Sounders Sampling the PBL and Other Regions of Significant Beta and U Inhomogeneities

This final report covers the period from April 1994 through March 1998. The proposed research was organized under four main tasks. Those tasks were: (1) Investigate the vertical and horizontal velocity structures within and adjacent to thin and subvisual cirrus; (2) Investigate the lowest 1 km of the PBL and develop algorithms for processing pulsed Doppler lidar data obtained from single shots into regions of significant inhomogeneities in Beta and U; (3) Participate in OSSEs including those designed to establish shot density requirements for meso-gamma scale phenomena with quasi-persistent locations (e.g., jets, leewaves, tropical storms); and (4) Participate in the planning and execution of an airborne mission to measure winds with a pulsed CO2 Doppler lidar. Over the four year period of this research contract, work on all four tasks has yielded significant results which have led to 38 professional presentations (conferences and publications) and have been folded into the science justification for an approved NASA space mission, SPARCLE (SPAce Readiness Coherent Lidar Experiment), in 2001. Also this research has, through Task 4, led to a funded proposal to work directly on a NASA field campaign, CAMEX III, in which an airborne Doppler wind lidar will be used to investigate the cloud-free circulations near tropical storms. Monthly progress reports required under this contract are on file. This final report will highlight major accomplishments, including some that were not foreseen in the original proposal. The presentation of this final report includes this written document as well as material that is better presented via the internet (web pages). There is heavy reference to appended papers and documents. Thus, the main body of the report will serve to summarize the key efforts and findings.

Emmitt, Dave↗
NASA NTRS1992

Ge's Mobile, Coherent Doppler Lidar Test/Ealuation Facilities

The primary objective of this independent research and development (IR and D) program in support of the Laser Atmospheric Wind Sounder (LAWS) program is to develop and evaluate technologies with direct applications to spaceborne laser wind sensing, and to develop system level engineering experience in designing, operating, and modeling a coherent Doppler lidar. GE is developing a mobile, ground based coherent Doppler lidar as an end-to-end system level test facility to evaluate applicable technologies, verify system level performance issues, perform instrument calibration, and validate end-to-end system performance model predictions. Here, the primary focus is on a description of the ground based lidar system and the performance during the initial shakedown operation after system integration.

Sroga, J. T.↗
NASA NTRS1980

First Scientific Working Group Meeting of Airborne Doppler Lidar Wind Velocity Measurement Program

The purpose of the first scientific working group meeting was fourfold: (1) to identify flight test options for engineering verification of the MSFC Doppler Lidar; (2) to identify flight test options for gathering data for scientific/technology applications; (3) to identify additional support equipment needed on the CV 990 aircraft for the flight tests; and (4) to identify postflight data processing and data sets requirements. The working group identified approximately ten flight options for gathering data on atmospheric dynamics processes, including turbulence, valley breezes, and thunderstorm cloud anvil and cold air outflow dynamics. These test options will be used as a basis for planning the fiscal year 1981 tests of the Doppler Lidar system.

Kaufman, J. W.↗
NASA NTRS1984

Overview of mesocale research Doppler lidar activities

In evaluating the performance of the airborne Doppler lidar system, a large number of deficiencies or mistakes were identified in the original system and experiment plans. All of the known problems were addressed and corrected in the planning and engineering for the fall 1984/spring 1985 ADLS flight series. Thus, the most significant result of the data analysis was the input it has provided to the preparations for the new experiment. Attitude measurements are taken together with the streamlined operating procedures, color graphics real time displays of data, and better experiment design, the result is a second-generation system that is considerably better than the one used in 1981.

Fitzjarrald, D. E.↗
NASA NTRS1986

Airborne Doppler lidar measurements

This paper describes recent measurements using coherent Doppler lidars operating at a wavelength of 10.6 microns aboard the NASA Ames Convair 990. The purpose of the measurements was to obtain data on the atmospheric wind fields and the distribution of the backscatter coefficient at 10.6 microns. A decription of the instruments is provided detailing the modifications incorporated following the 1981 test flights of the systems. The measurement program is outlined, and preliminary results are discussed.

Bilbro, James W.↗
NASA NTRS1986

Results from 1984 airborne Doppler lidar wind measurements

Observations made with the revised Airborne Doppler Lidar System (ADLS) during research flights in the summer of 1984 are described. The functioning of the ADLS system is described. The research flights measured the flow around Mt. Shasta about 3 km above the surrounding terrain as well as the flow in the area of the Carquenez Strait in the Sacramento River Valley. The flight tracks are described and the resulting scan radial velocities are shown and discussed. The results demonstrate the success of the modifications made in order to correct major error sources present in the 1981 flights of the ADLS system.

Rothermel, Jeffry↗
NASA NTRS1989

Analysis of airborne Doppler lidar measurements of the extended California sea breeze

Airborne Doppler lidar data obtained by NASA near the top of the PBL in the central valley of California are analyzed. The experimental conditions and quality of the data are described. Wind vectors are produced on a geographic grid divided into 1-km square cells. The resulting wind field has features similar to those seen in ground level wind observations. It is suggested that, although the analysis is labor intensive and cumbersome, it produces a previously unattainable high-resolution depiction of air flow over a broad region.

Carroll, John J.↗
NASA NTRS1999

Interference of Backscatter from Two Droplets in a Focused Continuous-Wave CO2 Doppler Lidar Beam

With a focused continuous-wave CO2 Doppler lidar at 9.1-microns wavelength, the superposition of backscatter from two approximately 14.12-micron-diameter silicone oil droplets in the lidar beam produced interference that resulted in a single backscatter pulse from the two droplets with a distinct periodic structure. This interference is caused by the phase difference in backscatter from the two droplets while they are traversing the lidar beam at different speeds, and thus the droplet separation is not constant. The complete cycle of interference, with periodicity 2(pi), gives excellent agreement between measurements and lidar theory.

Jarzembski, Maurice A.↗
NASA NTRSDate not supplied

Performance of Doppler Lidar Velocity and Range Sensor Operating in Highly Dynamic Environments

The operation of a coherent Doppler lidar, developed by NASA for missions to planetary bodies, is analyzed and its projected performance is described. The lidar transmits three laser beams at different but fixed directions and measures line-of-sight range and velocity along each beam. The three line-of-sight measurements are then combined in order to determine the three components of the vehicle velocity vector and its altitude relative to the ground. Operating from over five kilometers altitude, the NDL provides velocity and range data with a few cm/sec and a few meters precision, respectively, depending on the vehicle dynamics. This paper explains the sources of measurements error and analyzes the impacts of vehicle dynamics on the lidar performance.

Doppler Lidar↗
NASA NTRS1987

Results from 1984 airborne Doppler lidar wind measurement program. Flight 6: Analysis of line-of-sight elevation angle errors and apparent Doppler velocities

During the summer of 1984 the Marshall Space Flight Center's Airborne Doppler Lidar System (ADLS) made a series of wind measurements in the California Central Valley. This study quantifies the lidar beam angle errors and velocity errors through analysis of ground return signals. Line-of-sight elevation (LOSE) angle errors are under 1 deg. Apparent Doppler ground velocities, as large as 2m/s, are considerably less than in a previous flight experiment in 1981. No evidence was found of a Schuler resonance phenomenon common to inertial navigation systems (INS), however the aperiodic nature of the apparent velocities implies an error in the INS-derived ground speeds. Certain features and subtleties in the ground returns are explained in terms of atmospheric structure and characteristics of the ADLS hardware and software. Finally, least squares and low-pass filtering techniques are suggested for eliminating errors during post-processing.

Rothermel, Jeffry↗
NASA NTRS1999

Wind Field Measurements With Airborne Doppler Lidar

In collaboration with lidar atmospheric remote sensing groups at NASA Marshall Space Flight Center and National Oceanic and Atmospheric Administration (NOAA) Environmental Technology Laboratory, we have developed and flown the Multi-center Airborne Coherent Atmospheric Wind Sensor (MACAWS) lidar on the NASA DC-8 research aircraft. The scientific motivations for this effort are: to obtain measurements of subgrid scale (i.e. 2-200 km) processes and features which may be used to improve parameterizations in global/regional-scale models; to improve understanding and predictive capabilities on the mesoscale; and to assess the performance of Earth-orbiting Doppler lidar for global tropospheric wind measurements. MACAWS is a scanning Doppler lidar using a pulsed transmitter and coherent detection; the use of the scanner allows 3-D wind fields to be produced from the data. The instrument can also be radiometrically calibrated and used to study aerosol, cloud, and surface scattering characteristics at the lidar wavelength in the thermal infrared. MACAWS was used to study surface winds off the California coast near Point Arena, with an example depicted in the figure below. The northerly flow here is due to the Pacific subtropical high. The coastal topography interacts with the northerly flow in the marine inversion layer, and when the flow passes a cape or point that juts into the winds, structures called "hydraulic expansion fans" are observed. These are marked by strong variation along the vertical and cross-shore directions. The plots below show three horizontal slices at different heights above sea level (ASL). Bottom plots are enlargements of the area marked by dotted boxes above. The terrain contours are in 200-m increments, with the white spots being above 600-m elevation. Additional information is contained in the original.

Menzies, Robert T.↗