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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Improved solution of the lidar equation utilizing particle counter measurements

The extraction of particle backscattering from incoherent lidar measurements poses some problems. In the case of measurements of the stratospheric aerosol layer the solution of the lidar equation is based on two assumptions which are necessary to normalize the measured signal and to correct it with the two-way transmission of the laser pulse. Normalization and transmission are tackled by adding the information contained in aerosol particle counter measurements of the University of Wyoming to the ruby lidar measurements at Garmisch-Partenkirchen. Calculated backscattering from height levels above 25 km for the El Chichon period will be compared with lidar measurements and necessary corrections. The calculated backscatter-to-extinction ratios are compared to those, which were derived from a comparison of published extinction values to measured lidar backscattering at Garmisch. These ratios were used to calculate the Garmisch lidar returns. For the period 4 to 12 months after the El Chichon eruption a backscater-to-extinction ratio of 0.026 1/sr was applied with smaller values before and after that time.

Jaeger, H.↗
NASA NTRS1990

The new FIRE cloud lidar at Langley Research Center

Using the Langley Aircraft Lidar for cirrus cloud observations at Langley Research Center in Hampton, Virginia is overkill both in terms of the actual lidar and the people required to run the system. A small lidar system to be used specifically for cloud probing was designed and constructed at Langley in 1987. This lidar is presently being used to collect the FIRE ETO (Extended Time Observation) data at Langley. A description of the new FIRE Cloud Lidar System is presented. The data collected by this lidar is discussed as well as some of the cloud statistics emerging from the data. A brief synopsis of system performance is also given.

Alvarez, Jose M.↗
NASA NTRS1991

Differential absorption and Raman lidar for water vapor profile measurements - A review

Differential absorption lidar and Raman lidar have been applied to the range-resolved measurements of water vapor density for more than 20 years. Results have been obtained using both lidar techniques that have led to improved understanding of water vapor distributions in the atmosphere. This paper reviews the theory of the measurements, including the sources of systematic and random error; the progress in lidar technology and techniques during that period, including a brief look at some of the lidar systems in development or proposed; and the steps being taken to improve such lidar systems.

Grant, William B.↗
NASA NTRS1992

Measurements of Stratospheric Pinatubo Aerosol Extinction Profiles by a Raman Lidar

The Raman lidar has been used for remote measurements of water vapor, ozone and atmospheric temperature in the lower troposphere because the Raman cross section is three orders smaller than the Rayleigh cross section. We estimated the extinction coefficients of the Pinatubo volcanic aerosol in the stratosphere using a Raman lidar. If the precise aerosol extinction coefficients are derived, the backscatter coefficient of a Mie scattering lidar will be more accurately estimated. The Raman lidar has performed to measure density profiles of some species using Raman scattering. Here we used a frequency-doubled Nd:YAG laser for transmitter and received nitrogen vibrational Q-branch Raman scattering signal. Ansmann et al. (1990) derived tropospherical aerosol extinction profiles with a Raman lidar. We think that this method can apply to dense stratospheric aerosols such as Pinatubo volcanic aerosols. As dense aerosols are now accumulated in the stratosphere by Pinatubo volcanic eruption, the error of Ramen lidar signal regarding the fluctuation of air density can be ignored.

Abo, Makoto↗
NASA NTRS1992

Observation of Stratospheric Ozone with NIES Lidar System in Tsukuba, Japan

Lidars are expected to play important roles in an international monitoring network of the stratosphere such as the Network for the Detection of Stratospheric Change (NDSC). The National Institute for Environmental Studies (NIES) in Tsukuba constructed an ozone lidar system in March 1988 and started observation in August 1988. The lidar system has a 2-m telescope and injection locked XeCl and XeF excimer lasers which can measure ozone profiles (15-45 km) and temperature profiles (30-80 km). From December 1991, lidar observations have been carried out in which the second Stokes line of the stimulated Raman scattering of a KrF laser has been used. Ozone profiles obtained with the NIES lidar system are compared with the data provided by the SAGE II satellite sensor. Results showed good agreement for the individual and the zonal mean profiles. Variations of ozone with various time scales at each altitude can be studied using the data obtained with the NIES ozone lidar system. Seasonal variations are easily found at 20 km, 30 km, and 35 km, which are qualitatively understood as a result of dynamical and photochemical effects. Systematic errors of ozone profiles due to the Pinatubo stratospheric aerosols have been detected using multi-wavelength observation.

Nakane, H.↗
NASA NTRS1992

Sampling and Representativeness for a Spaceborne Wind Lidar

The capability of an Earth-orbiting lidar to produce a reliable windfield sampling with an error of 1-3 ms(exp -1) and that is relevant to numerical forecasting and climate studies is discussed. The spatial and temporal resolutions range from 100 km to 1000 km and 3 hr to 1 month respectively. In this respect cloud obstruction is of great concern, as it can prevent the lidar probing whole parts of the atmosphere, for both short and long periods of time. A worldwide analysis of cloudiness from either visual observations made from the ground or else from the Stratospheric Aerosol and Gas Experiment (SAGE) instrument, has shown that the average cloud cover is 60 percent. This analysis is only valid at large scales (time and space) compatible with the currently operating satellites. However, a lidar footprint is only about a hundred meters or less, and it was observed from ground based lidars that, even when the cloudiness is 100 percent, some lidar shots get through. A complete analysis of the probability of probing through clouds by a spaceborne lidar is presently beyond our capacities. Hence, no small scale cloudiness data set is yet available representing all kinds of meteorological situations at all latitudes.

Lieutaud, F.↗
NASA NTRS1992

Phase noise in pulsed Doppler lidar and limitations on achievable single-shot velocity accuracy

The smaller sampling volumes afforded by Doppler lidars compared to radars allows for spatial resolutions at and below some sheer and turbulence wind structure scale sizes. This has brought new emphasis on achieving the optimum product of wind velocity and range resolutions. Several recent studies have considered the effects of amplitude noise, reduction algorithms, and possible hardware related signal artifacts on obtainable velocity accuracy. We discuss here the limitation on this accuracy resulting from the incoherent nature and finite temporal extent of backscatter from aerosols. For a lidar return from a hard (or slab) target, the phase of the intermediate frequency (IF) signal is random and the total return energy fluctuates from shot to shot due to speckle; however, the offset from the transmitted frequency is determinable with an accuracy subject only to instrumental effects and the signal to noise ratio (SNR), the noise being determined by the LO power in the shot noise limited regime. This is not the case for a return from a media extending over a range on the order of or greater than the spatial extent of the transmitted pulse, such as from atmospheric aerosols. In this case, the phase of the IF signal will exhibit a temporal random walk like behavior. It will be uncorrelated over times greater than the pulse duration as the transmitted pulse samples non-overlapping volumes of scattering centers. Frequency analysis of the IF signal in a window similar to the transmitted pulse envelope will therefore show shot-to-shot frequency deviations on the order of the inverse pulse duration reflecting the random phase rate variations. Like speckle, these deviations arise from the incoherent nature of the scattering process and diminish if the IF signal is averaged over times greater than a single range resolution cell (here the pulse duration). Apart from limiting the high SNR performance of a Doppler lidar, this shot-to-shot variance in velocity estimates has a practical impact on lidar design parameters. In high SNR operation, for example, a lidar's efficiency in obtaining mean wind measurements is determined by its repetition rate and not pulse energy or average power. In addition, this variance puts a practical limit on the shot-to-shot hard target performance required of a lidar.

Mcnicholl, P.↗
NASA NTRS1992

Determining water cloud particle sizes from lidar depolarization measurements and time dependent multiple scattering coefficients

We present a technique of extracting water cloud particle size information from lidar measurements in conjunction with double scattering calculations. In this presentation, we describe the technique and give examples using data taken with the Air Force Phillips Laboratory's (Geophysics Directorate) low altitude Nd:YAG, elastic backscatter lidar. In a related presentation we describe the double scattering lidar model which we developed for this work. The technique uses simultaneous measurements of two orthogonal linear polarization components of lidar returns from water clouds or other media composed of spherical particles. Any depolarization of the incident lidar radiation backscattered by such a media can only be due to multiple scattering. The amount of depolarization is dependent on the extinction coefficient and the single scatter phase matrix, both of which are functions of position in the medium. The phase matrix is dependent on the index of refraction of the particles and the particle size distribution. Our technique is a modification of a procedure presented in Reference 1. There, particle sizes of water clouds are determined from double scattering calculations together with measurements of radiation scattered from volumes outside the lidar receiver's field of view (which can only be multiply scattered radiation). The methodology of our technique is similar but our 'probe' of the scattering phase function (and thus the particle size distribution) is different.

Garner, R. C.↗
NASA NTRS1992

Lidar analysis techniques for use in the atmospheric boundary layer

There is a growing body of observational and theoretical evidence which suggests that local climate characteristics are associated with variations in the earth's surface. The link between surface variability and local-scale processes must be made if we are to improve our understanding of the feedback mechanisms involved in surface-atmosphere dynamics. However, to understand these interactions, the surface-atmosphere interface must be studied as a large-scale spatial system. Lidars are ideal tools to study the spatial properties of the atmosphere. The described techniques were developed for use with the Los Alamos Water Raman-Lidar, but are applicable to many other types of lidar. The methodology of the analysis of lidar data is summarized in order to determine meteorological parameters in the atmospheric boundary layer. The techniques are not exhaustive but are intended to show the depth and breadth of the information which can be obtained from lidars. Two methods for the computation of water-vapor fluxes were developed. The first uses the fact that the water vapor concentration in the vertical direction follows a logarithmic profile when corrected for atmospheric stability. The second method involves using inertial dissipation techniques in which lidar-derived spatial and temporal power spectra are used to determine the flux.

Eichinger, William E.↗
NASA NTRS1992

Development of a Raman lidar simulation tool

Raman Lidar is a useful and powerful tool for remote probing of the atmosphere. With Raman Lidars, one can accurately determine the identity and concentration of a particular molecular specie present in the atmosphere. We present the results from a program to develop a simulation capability of Raman Lidar systems for the remote detection of atmospheric gases and/or air polluting hydrocarbons. Our model, which integrates remote Raman spectroscopy with SPARTA's BACKSCAT atmospheric lidar simulation package, permits accurate determination of the performance of a Raman Lidar system. The accuracy with which our model operates is due to the accurate calculation, at any given excitation wavelength, of the differential scattering cross section for the molecular specie under investigation. We show excellent correlation of our calculated cross section data with experimental data from the published literature. In addition, the use of our BACKSCAT package, which provides a user friendly environment to define the operating conditions, provides an accurate calculation of the atmospheric extinction at both the excitation and Raman shifted wavelengths. Our code can be used to accurately predict the performance of a Raman Lidar system, the concentration and identification of a specie in the atmosphere, or the feasibility of making Raman measurements.

Grasso, R. J.↗
NASA NTRS1993

Development of a 100 mJ, 5 Hz, flashlamp-pumped, Cr,Tm:YAG coherent lidar transmitter

A contract to develop a 100 mJ, 5 Hz, flashlamp-pumped Cr,Tm:YAG coherent lidar transmitter has been awarded to Coherent Technologies, Inc. (CTI). The lidar transmitter will operate at an eyesafe wavelength of 2.01 microns. The development complements work being performed under an SBIR Phase II with Electro-Optics Technology (EOT). EOT is developing continuous wave, low and medium power Tm:YAG oscillators of a unique design. One of the low power oscillators will be used as the injection seeder/local oscillator in the CIT lidar transmitter. The lidar transmitter will require the addition of a receiver section. Once completed, the lidar will be used in atmospheric performance studies, allowing comparison with that of the more mature CO2 lidar technology. The focus of current research and plans for next year are presented.

Henderson, S.↗
NASA NTRS1985

Doppler lidar sampling strategies and accuracies: Regional scale

It has been proposed that a Doppler lidar be placed in a polar orbit and scanned to provide estimates of lower tropospheric winds twice per day and with a spatial resolution of 300 km. Initial feasibility studies conducted primarily by NOAA and NASA presented an optimistic outlook for a space based lidar. The technology appeared within reach and initial computer simulations suggested that acceptable accuracies could be obtained. Those early studies exposed, however, several potential problem areas which included: (1) the algorithms for computing the wind vectors did not perform well when there were coherent gradients in the wind fields; and (2) the lifetime and power requirements of the lidar put severe restrictions on the pulse repetition frequency (PRF). These two basic problems are currently being addressed by a Doppler lidar simulation study focussed upon three primary objectives: (1) to develop optimum scan parameters and shot patterns for a satellite-based Doppler lidar; (2) to develop robust algorithms for computing wind vectors from lidar returns; and (3) to evaluate the impact of coherent mesoscale structures (wind gradients, clouds, aerosols) on up-scale wind estimates. An overview is provided of the simulation efforts with particular emphasis upon rationale and methodology. Since this research is currently underway, any results shown are meant only as evidence of progress.

Emmitt, G. D.↗
NASA NTRS1995

NDSC and JPL stratospheric lidars

The Network for the Detection of Stratospheric Change is an international cooperation providing a set of high-quality, remote-sensing instruments at observing stations around the globe. A brief description of the NDSC and its goals is presented. Lidar has been selected as the NDSC instrument for measurements of stratospheric profiles of ozone, temperature, and aerosol. The Jet Propulsion Laboratory has developed and implemented two stratospheric lidar systems for NDSC. These are located at Table Mountain, California, and at Mauna Loa, Hawaii. These systems, which utilize differential absorption lidar, Rayleigh lidar, raman lidar, and backscatter lidar, to measure ozone, temperature, and aerosol profiles in the stratosphere are briefly described. Examples of results obtained for both long-term and individual profiles are presented.

McDermid, I. Stuart↗
NASA NTRS1995

New generation lidar systems for eye safe full time observations

The traditional lidar over the last thirty years has typically been a big pulse low repetition rate system. Pulse energies are in the 0.1 to 1.0 J range and repetition rates from 0.1 to 10 Hz. While such systems have proven to be good research tools, they have a number of limitations that prevent them from moving beyond lidar research to operational, application oriented instruments. These problems include a lack of eye safety, very low efficiency, poor reliability, lack of ruggedness and high development and operating costs. Recent advances in solid state laser, detectors and data systems have enabled the development of a new generation of lidar technology that meets the need for routine, application oriented instruments. In this paper the new approaches to operational lidar systems will be discussed. Micro pulse lidar (MPL) systems are currently in use, and their technology is highlighted. The basis and current development of continuous wave (CW) lidar and potential of other technical approaches is presented.

Spinhirne, James D.↗
NASA NTRS1995

Lidar measurements at Lauder, NZ

In March of 1994, the GSFC Stratospheric Ozone Lidar was deployed to the Network for the Detection of Stratospheric Change (NDSC) site at Lauder, NZ. This was in conjunction with a series of NASA ER-2 flights from Christchurch, NZ south to the Antarctic Circle. These flights were organized to study the chemistry of the stratosphere before, during and after the formation of the well-known 'ozone hole'. Lidar measurements were made at four different time periods corresponding to the times of the ER-2 flights. Lauder is situated nearly along the flight path as the aircraft flew south and so the lidar measurements provide a checkpoint for the ozone, aerosol and temperature instruments onboard the aircraft. Whenever the weather permitted, lidar measurements were made as near to dawn, prior to the flight, and as near to sunset, after the flight. This provided data as close to the aircraft transit time as possible. More than 70 individual lidar measurements were made, each consisting of a vertical profile of ozone, temperature, and aerosol. These were made over three different seasons and show seasonal variation. Of particular interest in the lidar data base is the wintertime stratospheric - mesospheric temperature profiles, which show large variations at the stratopause and also some significant wave activity.

McGee, Thomas J.↗
NASA NTRS1998

CART and GSFC raman lidar measurements of atmospheric aerosol backscattering and extinction profiles for EOS validation and ARM radiation studies

The aerosol retrieval algorithms used by the Moderate-Resolution Imaging Spectroradiometer (MODIS) and Multi-Angle Imaging SpectroRadiometer (MISR) sensors on the Earth Observing Satellite (EOS) AM-1 platform operate by comparing measured radiances with tabulated radiances that have been computed for specific aerosol models. These aerosol models are based almost entirely on surface and/or column averaged measurements and so may not accurately represent the ambient aerosol properties. Therefore, to validate these EOS algorithms and to determine the effects of aerosols on the clear-sky radiative flux, we have begun to evaluate the vertical variability of ambient aerosol properties using the aerosol backscattering and extinction profiles measured by the Cloud and Radiation Testbed (CART) and NASA Goddard Space Flight Center (GSFC) Raman Lidars. Using the procedures developed for the GSFC Scanning Raman Lidar (SRL), we have developed and have begun to implement algorithms for the CART Raman Lidar to routinely provide profiles of aerosol extinction and backscattering during both nighttime and ,daytime operations. Aerosol backscattering and extinction profiles are computed for both lidar systems using data acquired during the 1996 and 1997 Water Vapor Intensive Operating Periods (IOPs). By integrating these aerosol extinction profiles, we derive measurements of aerosol optical thickness and compare these with coincident sun photometer measurements. We also use these measurements to measure the aerosol extinction/backscatter ratio S(sub a) (i.e. 'lidar ratio'). Furthermore, we use the simultaneous water vapor measurements acquired by these Raman lidars to investigate the effects of water vapor on aerosol optical properties.

Ferrare, R. A.↗
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 NTRS1998

Tropospheric Wind Profile Measurements with a Direct Detection Doppler Lidar

Research has established the importance of global tropospheric wind measurements for large scale improvements in numerical weather prediction. In addition, global wind measurements provide data that are fundamental to the understanding and prediction of global climate change. These tasks are closely linked with the goals of the NASA Earth Science Enterprise and Global Climate Change programs. NASA Goddard has been actively involved in the development of direct detection Doppler lidar methods and technologies to meet the wind observing needs of the atmospheric science community. In this paper we describe a recently developed prototype wind lidar system using a direct detection Doppler technique for measuring wind profiles from the surface through the troposphere. This system uses a pulsed ND:YAG laser operating at 1064 nm as the transmitter. The laser pulse is directed to the atmosphere using a 40 cm diameter scan mirror. The portion of the laser energy backscattered from aerosols and molecules is collected by a 40 cm diameter telescope and coupled via fiber optics into the Doppler receiver. Single photon counting APD's are used to detect the atmospheric backscattered signal. The principle element of the receiver is a dual bandpass tunable Fabry Perot etalon which analyzes the Doppler shift of the incoming laser signal using the double edge technique. The double edge technique uses two high resolution optical filters having bandpasses offset relative to one another such that the 'edge' of the first filter's transmission function crosses that of the second at the half power point. The outgoing laser frequency is located approximately at the crossover point. Due to the opposite going slopes of the edges, a Doppler shift in the atmospheric backscattered laser frequency produces a positive change in signal for one filter and a negative change in the second filter. Taking the ratio of the two edge channel signals yields a result which is directly proportional to the component of the wind along the line-of-sight of the laser. Measuring the radial wind in several directions provides sufficient information to determine the true wind speed and direction. The lidar has operated from our laboratory at Goddard since June, 1997. Wind profiles have been obtained to altitudes of 12 km with a vertical resolution of 330 in. Vector wind data are obtained by rotating the scan mirror to measure line-of-sight wind profiles for at least two azimuth angles at an elevation angle of 45 degrees. The precision of the data as determined from the standard deviation of multiple independent lidar profiles is in the range of 1 to 3 m/sec up to 10 km. Good agreement is obtained when the lidar data are compared with the upper air rawinsonde soundings taken at Dulles airport. Examples of the wind lidar data will be presented along with a description of the instrument and future developments.

Gentry, Bruce M.↗