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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Pulsed Doppler lidar for the detection of turbulence in clear air

A pulsed C02 Doppler lidar system is described and demonstration tests in ground-based and airborne flight operations are discussed. As a ground-based system, it can detect wind shears in thunderstorm gust fronts to a range of 6 km. When in the airborne configuration, the lidar can detect clear air turbulence in advance of the aircraft encountering clear air turbulence. The data provided by the lidar included turbulence location and intensity with intensity being indicated by the measured spectral width which is proportional to the wind gust velocity.

Weaver, E. A.↗
NASA NTRS1988

Airborne Doppler lidar wind field measurements of waves in the lee of Mount Shasta

Doppler lidar wind data obtained along one leg of a race track traverse around Mount Shasta are presently studied to establish their value and limitations for the study of orographic flows, as well as to evaluate the relative usefulness of a linear model in the analyses of the observed fields-of-motion. The model successfully reproduced the observed downstream lee of positive horizontal divergence which embedded spatially irregular waves, but the amplitudes of the model downstream divergence is smaller than the observations by a factor of two.

Blumen, William↗
NASA NTRS1997

Evaluation of the MV (CAPON) Coherent Doppler Lidar Velocity Estimator

The performance of the CAPON velocity estimator for coherent Doppler lidar is determined for typical space-based and ground-based parameter regimes. Optimal input parameters for the algorithm were determined for each regime. For weak signals, performance is described by the standard deviation of the good estimates and the fraction of outliers. For strong signals, the fraction of outliers is zero. Numerical effort was also determined.

Lottman, B.↗
NASA NTRS1996

Signal Processing and Calibration of Continuous-Wave Focused CO2 Doppler Lidars for Atmospheric Backscatter Measurement

Two continuous-wave(CW)focused C02 Doppler lidars (9.1 and 10.6 micrometers) were developed for airborne in situ aerosol backscatter measurements. The complex path of reliably calibrating these systems, with different signal processors, for accurate derivation of atmospheric backscatter coefficients is documented. Lidar calibration for absolute backscatter measurement for both lidars is based on range response over the lidar sample volume, not solely at focus. Both lidars were calibrated with a new technique using well-characterized aerosols as radiometric standard targets and related to conventional hard-target calibration. A digital signal processor (DSP), a surface acoustic and spectrum analyzer and manually tuned spectrum analyzer signal analyzers were used. The DSP signals were analyzed with an innovative method of correcting for systematic noise fluctuation; the noise statistics exhibit the chi-square distribution predicted by theory. System parametric studies and detailed calibration improved the accuracy of conversion from the measured signal-to-noise ratio to absolute backscatter. The minimum backscatter sensitivity is approximately 3 x 10(exp -12)/m/sr at 9.1 micrometers and approximately 9 x 10(exp -12)/m/sr at 10.6 micrometers. Sample measurements are shown for a flight over the remote Pacific Ocean in 1990 as part of the NASA Global Backscatter Experiment (GLOBE) survey missions, the first time to our knowledge that 9.1-10.6 micrometer lidar intercomparisons were made. Measurements at 9.1 micrometers, a potential wavelength for space-based lidar remote-sensing applications, are to our knowledge the first based on the rare isotope C-12 O(2)-18 gas.

Rothermel, Jeffry↗
NASA NTRS1999

Juneau Airport Doppler Lidar Deployment: Extraction of Accurate Turbulent Wind Statistics

A 2 micrometer pulsed Doppler lidar was deployed to the Juneau Airport in 1998 to measure turbulence and wind shear in and around the departure and arrival corridors. The primary objective of the measurement program was to demonstrate and evaluate the capability of a pulsed coherent lidar to remotely and unambiguously measure wind turbulence. Lidar measurements were coordinated with flights of an instrumented research aircraft operated by representatives of the University of North Dakota (UND) under the direction of the National Center for Atmospheric Research (NCAR). The data collected is expected to aid both turbulence characterization as well as airborne turbulence detection algorithm development activities within NASA and the FAA. This paper presents a summary of the deployment and results of analysis and simulation which address important issues regarding the measurement requirements for accurate turbulent wind statistics extraction.

Hannon, Stephen M.↗
NASA NTRSDate not supplied

Analysis of Navigation Doppler Lidar performance for Moon and Mars Landing

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 measurement error and analyzes the impact of vehicle dynamics on the lidar performance.

Farzin Amzajerdian↗
NASA NTRSDate not supplied

Demonstration of Navigation Doppler Lidar Capabilities Onboard the First Commercial Lunar Lander

Landing on the Moon safely, softly, and precisely is still an extremely difficult task to achieve. Navigation Doppler Lidar (NDL) was designed to provide a solution to spaceflight landing vehicles in achieving this task. NDL is a high-performance, compact, and cost-effective velocity and altitude measurement instrument that has been developed, tested and improved over many years. Testing has now culminated with NDL’s successful operation on two spaceflight vehicles this year: Astrobotic’s Peregrine lunar lander and Intuitive Machines’ Odysseus lunar lander. Odysseus became the first U.S. vehicle to land successfully on the Moon since Apollo 17. The performance data obtained by NDL during the Intuitive Machines mission is exceptional, and this mission fully demonstrated NDL’s ability to produce critical velocity and altitude data for future robotic and human exploration missions to the Moon and other planetary bodies. This paper will give an overview of NDL briefly describing its history, architecture, and theory of operation. NDL’s system checkout on Astrobotic’s Peregrine lunar lander is then discussed followed by NDL’s performance during the Intuitive Machines Odysseus lunar lander mission. A description of how the data acquired by NDL is then used to perform trajectory reconstruction and animation is then provided. Finally, this paper concludes with potential uses of NDL’s acquired mission data to future applications.

Lunar Landing↗
NASA NTRSDate not supplied

Demonstration of Navigation Doppler Lidar Capabilities Onboard the First Commercial Lunar Lander

Landing on the Moon safely, softly, and precisely is still an extremely difficult task to achieve. Navigation Doppler Lidar (NDL) was designed to provide a solution to spaceflight landing vehicles in achieving this task. NDL is a high-performance, compact, and cost-effective velocity and altitude measurement instrument that has been developed, tested and improved over many years. Testing has now culminated with NDL’s successful operation on two spaceflight vehicles this year: Astrobotic’s Peregrine lunar lander and Intuitive Machines’ Odysseus lunar lander. Odysseus became the first U.S. vehicle to land successfully on the Moon since Apollo 17. The performance data obtained by NDL during the Intuitive Machines mission is exceptional, and this mission fully demonstrated NDL’s ability to produce critical velocity and altitude data for future robotic and human exploration missions to the Moon and other planetary bodies. This paper will give an overview of NDL briefly describing its history, architecture, and theory of operation. NDL’s system checkout on Astrobotic’s Peregrine lunar lander is then discussed followed by NDL’s performance during the Intuitive Machines Odysseus lunar lander mission. A description of how the data acquired by NDL is then used to perform trajectory reconstruction and animation is then provided. Finally, this paper concludes with potential uses of NDL’s acquired mission data to future applications.

Lunar Landing↗
NASA NTRS1980

Windfield retrieval from Doppler lidar observations

An approach to the retrieval of a vector wind field from Doppler lidar observations is developed in general terms. The field of radial velocity measurements from each look angle is modeled by a smooth surface, the parameters of the model being determined from the data by least squares techniques. The vector wind field and higher-order fields are obtained from the two modeled surfaces. Estimated measurement errors are taken into account, and error estimates are available for all output data sets.

Lee, R. W.↗
NASA NTRS1980

Windfield retrieval from Doppler lidar observations

An approach to the retrieval of a vector wind field from Doppler lidar observations is developed in general terms. The field of radial velocity measurements from each look angle is modeled by a smooth surface, the parameters of the model being determined from the data by least squares techniques. The vector wind field and higher order fields are obtained from the two modeled surfaces. Estimated measurement errors are taken into account, and error estimates are available for all output data sets.

Lee, R. W.↗
NASA NTRS2016

Coherent Doppler Lidar for Measuring Velocity and Altitude of Space and Aerial Vehicles

A coherent Doppler lidar has been developed to support future NASA missions to planetary bodies. The lidar transmits three laser beams and measures line-of-sight range and velocity along each beam using a frequency modulated continuous wave (FMCW) technique. Accurate altitude and velocity vector data, derived from the line-of-sight measurements, enables the landing vehicle to precisely navigate from several kilometers above the ground to the designated location and execute a gentle touchdown. The same lidar sensor can also benefit terrestrial applications that cannot rely on GPS or require surface-relative altitude and velocity data.

Amzajerdian, Farzin↗
NASA NTRSDate not supplied

Navigation Doppler Lidar Performance at High Speed and Long Range

NASA is developing a Navigational Doppler LiDAR (NDL) for use in missions involving robotic and human landing scenarios on solar system bodies. The NDL provides unprecedented accuracy in position and velocity measurement for the guidance, navigation and control (GNC) subsystem of a spacecraft. NDL performance has been characterized over different phases of its development through ground tests, helicopter flight tests, and onboard rocket-powered test vehicles, however, none of these tests provided measurements over its full performance envelope. For this reason, a high speed rocket sled test was recently conducted to resolve both range and velocity up to the maximum limits of the NDL. This test campaign was performed at the Supersonic Naval Ordnance Research Tracks (SNORT) facility, Naval Air Weapons Station China Lake, as part of the Safe & Precise Landing and Integrated Capabilities Evolution (SPLICE) project.

Aram Gragossian↗
NASA NTRS2006

IIP Update: A Packaged Coherent Doppler Wind Lidar Transceiver. Doppler Aerosol WiNd Lidar (DAWN)

The state-of-the-art 2-micron coherent Doppler wind lidar breadboard at NASA/LaRC will be engineered and compactly packaged consistent with future aircraft flights. The packaged transceiver will be integrated into a coherent Doppler wind lidar system test bed at LaRC. Atmospheric wind measurements will be made to validate the packaged technology. This will greatly advance the coherent part of the hybrid Doppler wind lidar solution to the need for global tropospheric wind measurements.

Kavaya, Michael J.↗
NASA NTRS1982

NASA airborne Doppler lidar program: Data characteristics of 1981

The first flights of the NASA/Marshall airborne CO2 Doppler lidar wind measuring system were made during the summer of 1981. Successful measurements of two-dimensional flow fields were made to ranges of 15 km from the aircraft track. The characteristics of the data obtained are examined. A study of various artifacts introduced into the data set by incomplete compensation for aircraft dynamics is summarized. Most of these artifacts can be corrected by post processing, which reduces velocity errors in the reconstructed flow field to remarkably low levels.

Lee, R. W.↗
NASA NTRS1989

Doppler lidar measurement of profiles of turbulence and momentum flux

A short-pulse CO2 Doppler lidar with 150-m range resolution measured vertical profiles of turbulence and momentum flux. Example measurements are reported of a daytime mixed layer with strong mechanical mixing caused by a wind speed of 15 m/sec, which exceeded the speed above the capping inversion. The lidar adapted an azimuth scanning technique previously demonstrated by radar. Scans alternating between two elevation angles allow determination of mean U-squared, V-squared, and W-squared. Expressions were derived to estimate the uncertainty in the turbulence parameters. A new processing method, partial Fourier decomposition, has less uncertainty than the filtering used earlier.

Eberhard, Wynn L.↗
NASA NTRS1992

A pulsed CO2 Doppler lidar for boundary layer monitoring

A monostatic, master oscillator power amplifier (MOPA), CO2 pulsed Doppler lidar was constructed and tested. The system is compact (120 x 60 cm), operates at high pulse repetition rates (greater than 1 kHz) and is intended for simultaneous Doppler/Differential Absorption Lidar (DIAL) monitoring of the planetary boundary layer. Details of the system design, hard target calibrations, and aerosol returns are presented.

Pearson, Guy N.↗
NASA NTRS1985

A comparison of Doppler lidar wind sensors for Earth-orbit global measurement applications

Now, there are four Doppler lidar configurations which are being promoted for the measurement of tropospheric winds: (1) the coherent CO2 Lidar, operating in the 9 micrometer region using a pulsed, atmospheric pressure CO2 gas discharge laser transmitter, and heterodyne detection; (2) the coherent Neodymium doped YAG or Glass Lidar, operating at 1.06 micrometers, using flashlamp or diode laser optical pumping of the solid state laser medium, and heterodyne detection; (3) the Neodymium doped YAG/Glass Lidar, operating at the doubled frequency (at 530 nm wavelength), again using flashlamp or diode laser pumping of the laser transmitter, and using a high resolution tandem Fabry-Perot filter and direct detection; and (4) the Raman shifted Xenon Chloride Lidar, operating at 350 nm wavelength, using a pulsed, atmospheric pressure XeCl gas discharge laser transmitter at 308 nm, Raman shifted in a high pressure hydrogen cell to 350 nm in order to avoid strong stratospheric ozone absorption, also using a high resolution tandem Fabry-Perot filter and direct detection. Comparisons of these four systems can include many factors and tradeoffs. The major portion of this comparison is devoted to efficiency. Efficiency comparisons are made by estimating the number of transmitted photons required for a single pulse wind velocity estimate of + or - 1 m/s accuracy in the middle troposphere, from an altitude of 800 km, which is assured to be reasonable for a polar orbiting platform.

Menzies, Robert T.↗