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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Optical materials for space based laser systems

The design features and performance characteristics of a sensitized holmium laser applicable to differential lidar and Doppler windshear measurements are presented, giving attention to the optimal choice of sensitizing/activating dopant ions. This development of a 2-micron region eye-safe laser, where holmium is sensitized by either hulium or erbium, has called for interionic energy transfer processes whose rate will not result in gain-switched pulses that are excessively long for atmospheric lidar and Doppler windshear detection. The application of diamond films for optical component hardening is noted.

Buoncristiani, A. M.↗
NASA NTRS2008

The Selection of Q-Switch for a 350mJ Air-borne 2-micron Wind Lidar

In the process of designing a coherent, high energy 2micron, Doppler wind Lidar, various types of Q-Switch materials and configurations have been investigated for the oscillator. Designing an oscillator with a relatively low gain laser material, presents challenges related to the management high internal circulating fluence due to high reflective output coupler. This problem is compounded by the loss of hold-off. In addition, the selection has to take into account the round trip optical loss in the resonator and the loss of hold-off. For this application, a Brewster cut 5mm aperture, fused silica AO Q-switch is selected. Once the Q-switch is selected various rf frequencies were evaluated. Since the Lidar has to perform in single longitudinal and transverse mode with transform limited line width, in this paper, various seeding configurations are presented in the context of Q-Switch diffraction efficiency. The master oscillator power amplifier has demonstrated over 350mJ output when the amplifier is operated in double pass mode and higher than 250mJ when operated in single pass configuration. The repetition rate of the system is 10Hz and the pulse length 200ns.

Petros, Mulugeta↗
NASA NTRSDate not supplied

TPSAS-NF1676L-18834-DND

This presentation will give an overview of the 20-plus years of pulsed transmit laser development at NASA Langley Research Center (LaRC) to enable a coherent Doppler wind lidar to measure global winds from earth orbit. Our group at LaRC has been developing the pulsed laser and other coherent lidar technologies for the global wind mission since the late 1980s. The causal path followed has been from space mission requirements to coherent lidar requirements to component requirements to technology development and finally to ground and aircraft validation. We will describe the development and deployment of Doppler Aerosols Wind Lidar (DAWN) for airborne measurement of wind velocity and direction. The will also present the status of ongoing fully conductively-cooled 2-micron wind lidar transmitter for NASA 3-D winds mission.

Upendra N Singh↗
NASA NTRS2007

DIAL Measurements of Free-Tropospheric Ozone Profiles in Huntsville, AL

A tropospheric ozone Differential Absorption Lidar (DIAL) system, developed jointly by NASA and the University of Alabama at Huntsville (UAH), measures free-tropospheric ozone profiles between 4-10 km. Located at 192 meters altitude in the Regional Atmospheric Profiling Laboratory for Discovery (RAPCD) on the UAH campus in Huntsville, AL, USA, this tropospheric ozone lidar operates under both daytime and nighttime conditions. Frequent coincident ozonesonde flights and theoretical calculations provide evidence to indicate the retrieval accuracy ranges from better than 8% at 4km to 40%-60% at 10 kin with 750-m vertical resolution and 30-minute integration. With anticipated improvements to allow retrievals at both higher and lower altitudes, this ozone lidar, along with co-located aerosol and Doppler Wind Lidars, will provide a unique 18 dataset for investigations of PBL and free-tropospheric chemical and dynamic processes.

Kuang, Shi↗
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 NTRSDate not supplied

An Overview of the NASA ADM-Aeolus Cal/Val Test Flight Campaign

Lidars are uniquely capable of collecting high precision and high spatio-temporal observations that have been used for atmospheric process studies from the ground, aircraft, and space for over 30 years. The Atmospheric Dynamics Mission Aeolus (ADM-Aeolus), the first-ever spaceborne Doppler wind lidar, was developed by the European Space Agency and launched in August 2018. The ADM-Aeolus Atmospheric Laser Doppler Instrument (ALADIN) observes profiles of the component of the wind vector and aerosol optical properties along the instrument’s line-of-sight direction on a global scale. Two airborne lidar systems have been developed at NASA Langley Research Center in recent years that collect measurements in support of several NASA Earth Science Division focus areas. The Doppler Aerosol WiNd (DAWN) lidar measures vertical profiles of horizontal wind speed and direction. The High Altitude Lidar Observatory (HALO) measure high resolution profiles of atmospheric water vapor (WV) and aerosol and cloud optical properties. Though new space-based missions with advanced capabilities such as Aeolus are continuously being conceived and developed, there are limitations in terms of spatial and vertical detail and measurement precision that can be accomplished from space, thus airborne remote sensing observations like those from DAWN and HALO are required to fill these observational gaps as well as to calibrate and validate space-based measurements. Over a two-week period in April 2019 during their Aeolus Cal/Val Test Flight campaign, NASA conducted five research flights over the Eastern Pacific Ocean with the DC-8 aircraft to 1) demonstrate the DAWN Doppler wind lidar, HALO high spectral resolution lidar aerosol/cloud measurement and differential absorption lidar WV measurement capabilities across a range of atmospheric conditions, 2) demonstrate Aeolus Cal/Val flight strategies and compare DAWN and HALO measurements with Aeolus to gain an initial perspective of Aeolus performance, and 3) demonstrate how atmospheric dynamic processes can be resolved and better understood through simultaneous observations of wind, WV, and aerosol profile observations, coupled with numerical model and other remote sensing observations. This paper provides a brief description of the DAWN and HALO instruments, discusses the synergistic observations collected across a wide range of atmospheric conditions sampled during the DC-8 flights, and a summary of the validation of DAWN, HALO, and Aeolus observations and comparisons.

Kristopher M. Bedka↗
NASA NTRS1999

Application of Lidar Winds to Data Assimilation

One of the major applications of space-based doppler wind lidar is to improve atmospheric analyses and numerical weather prediction (NWP). Since the mid 198,0's, Observing System Simulation Experiments (OSSE's) have been conducted in order to evaluate the potential impact of lidar winds on NWP. These experiments have shown tremendous potential for satellite lidar observations to improve atmospheric analyses and forecasts. In addition, the OSSE's are providing an evaluation of trade-offs in lidar design, and are currently being used to define the specific requirements for lidar winds in terms of horizontal and vertical coverage and accuracy. At the meeting the methodology for these experiments and the main results relating to proposed lidars will be presented.

Atlas, Robert↗
NASA NTRS1999

SPARCLE Optical System Design and Operational Characteristics

The SPAce Readiness Coherent Lidar Experiment (SPARCLE) is the first demonstration of a coherent Doppler wind lidar in space. SPARCLE will be flown aboard a space shuttle In the middle part of 2001 as a stepping stone towards the development and deployment of a long-life-time operational instrument in the later part of next decade. SPARCLE is an ambitious project that is intended to evaluate the suitability of coherent lidar for wind measurements, demonstrate the maturity of the technology for space application, and provide a useable data set for model development and validation. This paper describes the SPARCLE's optical system design, fabrication methods, assembly and alignment techniques, and its anticipated operational characteristics. Coherent detection is highly sensitive to aberrations in the signal phase front, and to relative alignment between the signal and the local oscillator beams. Consequently, the performance of coherent lidars is usually limited by the optical quality of the transmitter/receiver optical system. For SPARCLE having a relatively large aperture (25 cm) and a very long operating range (400 km), compared to the previously developed 2-micron coherent lidars, the optical performance requirements are even more stringent. In addition with stringent performance requirements, the physical and environment constraints associated with this instrument further challenge the limit of optical fabrication technologies.

Amzajerdian, Farzin↗
NASA NTRS2008

Solid-State 2-Micron Laser Transmitter Advancement for Wind and Carbon Dioxide Measurements From Ground, Airborne, and Space-Based Lidar Systems

NASA Langley Research Center has been developing 2-micron lidar technologies over a decade for wind measurements, utilizing coherent Doppler wind lidar technique and carbon dioxide measurements, utilizing Differential Absorption Lidar (DIAL) technique. Significant advancements have been made towards developing state-of-the-art technologies towards laser transmitters, detectors, and receiver systems. These efforts have led to the development of solid-state lasers with high pulse energy, tunablility, wavelength-stability, and double-pulsed operation. This paper will present a review of these technological developments along with examples of high resolution wind and high precision CO2 DIAL measurements in the atmosphere. Plans for the development of compact high power lasers for applications in airborne and future space platforms for wind and regional to global scale measurement of atmospheric CO2 will also be discussed.

Singh, Upendra N.↗
NASA NTRS1991

Narrowband lidar technique for sodium temperature and Doppler wind observations of the upper atmosphere

A new two-frequency lidar for measuring mesospheric Na temperature profiles is described that uses a stabilized CW single-mode dye laser oscillator (rms frequency jitter less than 1 MHz) followed by a pulsed dye power amplifier (140 MHz FWHM linewidth) that is pumped by an injection-locked Nd:YAG laser. The laser oscillator is tuned to the two operating freqencies by observing the Doppler-free structure of the Na D2 fluorescence spectrum in a vapor cell. The lidar technique and initial observations of the temperature profile between 82 and 102 km at Ft. Collins, CO are described. Absolute temperature accuracies at the Na layer peak of better than + or - 3 K with a vertical resolution of 1 km and an integration period of approximately 5 min were achieved in this initial experiment. Finally, a multiple frequency technique for the simultaneous measurement of both temperature and Doppler wind profiles is discussed.

Bills, Richard E.↗
DOE OSTI2024

Tilted lidar profiling: Development and testing of a novel scanning strategy for inhomogeneous flows

The most common profiling techniques for the atmospheric boundary layer based on a monostatic Doppler wind lidar rely on the assumption of horizontal homogeneity of the flow. This assumption breaks down in the presence of either natural or human-made obstructions that can generate significant flow distortions. The need to deploy ground-based lidars near operating wind turbines for the American WAKE experimeNt (AWAKEN) spurred a search for novel profiling techniques that could avoid the influence of the flow modifications caused by the wind farms. With this goal in mind, two well-established profiling scanning strategies have been retrofitted to scan in a tilted fashion and steer the beams away from the more severely inhomogeneous region of the flow. Results from a field test at the National Renewable Energy Laboratory's 135-m meteorological tower show that the accuracy of the horizontal mean flow reconstruction is insensitive to the tilt of the scan, although higher-order wind statistics are severely deteriorated at extreme tilts mainly due to geometrical error amplification. A numerical study of the AWAKEN domain based on the Weather Research and Forecasting Model and large-eddy simulation are also conducted to test the effectiveness of tilted profiling. It is shown that a threefold reduction of the error on inflow mean wind speed can be achieved for a lidar placed at the base of the turbine using tilted profiling.

17 WIND ENERGY↗
NASA NTRS1992

DIAL simulations for satellite water vapor profile measurements within the BEST project

The project BEST has been proposed by several laboratories of the French Space Agency (CNES) as part of the GEWEX program. Its objective is the study of the energy budget of the tropical system, and aims at measuring different components of the water cycle by coupling several observing systems. As part of this, Service d'Aeronomie (SA) proposed to study a Differential Absorption Lidar (DIAL) system to measure tropical water vapor profiles and to determine humidity convergence fields, when coupled with the Doppler wind lidar. We have performed simulation analyses for water vapor measurement from the selected orbit of 400 km. For these simulations, we have adopted an atmospheric model developed at SA. We have optimized, by a Monte Carlo statistical method, the system parameters and evaluated bias and standard deviation of the retrieved water vapor mixing ratio.

Chazette, P.↗
NASA NTRS1999

SPARCLE: A Mission Overview

The SPAce Readiness Coherent Lidar Experiment (SPARCLE) is a NASA mission to demonstrate for the first time the measurement of tropospheric winds from a space platform using coherent Doppler Wind Lidar (DWL). SPARCLE is scheduled for launch in early 2001 on board one of the shuttle orbiters. While primarily a demonstration of the technology's performance at ranges of 300-350 km, the mission will also address sampling issues critical to the design and operation of follow-on missions. In this paper we provide a brief overview of the SPARCLE instrument and the experiments being planned.

Emmitt, G. D.↗
NASA NTRS2010

Lidar Wind Profiler Comparison to Weather Balloon for Support of Orion Crew Exploration Vehicle Landings

A comparison study by the National Aeronautics and Space Administration Dryden Flight Research Center, Edwards, CA and the Naval Post Graduate School Center for Interdisciplinary Remotely-Piloted Aircraft Studies, Marina, CA was conducted to show the advantages of an airborne wind profiling lidar system in reducing drift uncertainty along a reentry vehicle descent trajectory. This effort was in support of the once planned Orion Crew Exploration Vehicle ground landing. A Twin Otter Doppler Wind Lidar was flown on multiple flights along the approximate ground track of an ascending weather balloons launched from the Marina Municipal Airport. The airborne lidar used was a 5-milli-Joules, 2-micron infrared laser with a 10-centimeter telescope and a two-axis scanner. Each lidar wind profile contains data for an altitude range between the surface and flight altitude of 2,700 meters, processed on board every 20 seconds. In comparison, a typical weather balloon would traverse that same altitude range with a similar data set available in approximately 15-20 minutes. These tests were conducted on November 15 & 16, 2007. Results comparing the balloon and a 10 minute multiple lidar profile averages show a best case absolute difference of 0.18 m/s (0.35 knots) in speed and 1 degree in direction during light and variable (less than 5 knots, without constant direction) wind conditions. These limited test results indicated a standard deviation wind velocity and direction differences of 0.71 m/s (1.3 knots) and 7.17 degrees for 1800Z, and 0.70 m/s (1.3 knots) and 6.79 degrees, outside of cloud layer.

Houtas, Franzeska↗
NASA NTRS2010

Lidar Wind Profiler Comparison to Weather Balloon for Support of Orion Crew Exploration Vehicle Landings

A comparison study by the National Aeronautics and Space Administration Dryden Flight Research Center (Edwards, California) and the Naval Post Graduate School Center for Interdisciplinary Remotely-Piloted Aircraft Studies (Marina, California) was conducted to show the advantages of an airborne wind profiling light detection and ranging (lidar) system in reducing drift uncertainty along a reentry vehicle descent trajectory. This effort was in support of the once planned Orion Crew Exploration Vehicle ground landing. A Twin Otter Doppler Wind Lidar was flown on multiple flights along the approximate ground track of each ascending weather balloon launched from the Marina Municipal Airport (Marina, California). The airborne lidar used was a 5-mJ, 2-micron infrared laser with a 10-cm telescope and a two-axis scanner. Each lidar wind profile contains data for an altitude range between the surface and flight altitude of 2.7 km, processed on board every 20 s. In comparison, a typical weather balloon would traverse that same altitude range with a similar data set available in approximately 15 to 20 min. These tests were conducted on November 15 and 16, 2007. Results show a best-case absolute difference of 0.18 m/s (0.35 knots) in speed and 1 degree in direct

Houtas, Franzeska F.↗