bluuebunny/crossref_metadata_2025 huggingface dataset:
The Earth Observing System (EOS): Centerpiece of NASA’s Mission-to-Planet Earth Initiative
Authors: Wilson Greg S. , Butler Dixon , Wilson Gregory
Published: February 2023

While NASA has been conducting its highly visible efforts of manned space flight and planetary exploration, it has also pioneered the remote sensing of the Earth from space. It is now time for NASA to expand these efforts and provide revolutionary new capabilities to characterize our home planet and its global environment. The science community has pointed out that Earth is already in a process of global change in which virtually all aspects of the Earth interact as part of an integrated system and the impact of human activity is significant. Today, we lack the ability to adequately foresee the direction of these changes and their effects on the global physical, economic, and social climate. Both our nation and the world now require the understanding to reliably predict the future course of our environment on time scales of decades to centuries in response to both human activities and natural forces. The long-term quantitative measurement of the atmosphere, land surface, oceans, and solid Earth using the global perspective of space is essential as the foundation of this new Earth System science. NASA is committed to pursue this goal through implementation of new Earth observing systems in orbit and information systems on the ground and by stimulating others to contribute to this effort.
Lidar Activities at ESA
Authors: Megie Gerard
Published: February 2023

Summary not available.
Error analysis for total wind vector computations using one component measurements from a space-based Doppler lidar
Authors: Emmitt G. D.
Published: February 2023

This paper is a companion paper to another conference paper entitled "Assessment of error sources for one component wind measurements with a space-based Doppler lidar" by Emmitt and Bilbro. In that paper the proposed lidar system is described and errors associated with the radial component measurement of the winds discussed. In this paper we focus upon the errors that arise out of combining these one-component observations into estimates of the total wind vector. These errors are of a totally different nature and have serious implications to the inclusion of lidar observed winds into numerical models.
Algorithm to Calculate Aerosol Backscatter from Airborne CW Focused CO2 Doppler Lidar Measurements
Authors: Rothermel Jeffry , Vaughan J. Michael , Bowdle David A.
Published: February 2023

Since 1981 the Royal Signals and Radar Establishment (RSRE) and the Royal Aircraft Establishment (RAE), United Kingdom, have made vertical and horizontal sounding measurements of aerosol backscatter cross-section using an airborne continuous-wave (CW) focused CO2 Doppler lidar, the Laser True Airspeed System (LATAS). The LATAS measures both the backscatter cross-section and line-of-sight velocity (with respect to the LATAS) of naturally-occurring micrometer-sized aerosol particles. These measurements are an important part of a data base for the development of a global-scale model of aerosol backscatter at CO2 wavelengths (Bowdle, 1986). In turn, the model is used in the design and simulated operation of NASA’s (National Aeronautics and Space Administration) prospective Lidar Atmospheric Wind Sounder (LAWS) (Baker and Curran, 1985). The performance of LAWS in providing global wind measurements will be critically dependent upon the signal-to-noise ratio (SNR) of the received signal, which is primarily a function of the concentration and backscatter efficiency of aerosols in the sample volume. This report describes the computer algorithm used to convert the LATAS measurements of backscatter signal into estimates of SNR and backscatter coefficient.
Laboratory Measurements of the Performance of a Poly Pulse Pair Signal Processor
Authors: Johnson Steve
Published: February 2023

A signal processor has been developed to perform estimations of the parameters associated with the signal return from a coherent CO2 pulsed Doppler lidar. The processor is based on a variation of the pulse pair technique utilized in conventional Doppler radar signal processing. The variation, termed poly-pulse pair processing, was developed in an attempt to provide an optimized method of estimating the mean frequency, intensity and spectral width associated with the lidar return signal. In order to ascertain the performance of the processor, a test program was undertaken in which simulated lidar returns of known spectral characteristics were input and the signal processor output was evaluated as a function of input signal to noise ratio. These results were then compared to the signal processor performance using actual lidar signals from hard targets and clear air.
Calibration of Laser Radars and Compact Ranges
Authors: Gamble W.L. , Davidson R.B. , McMillan R.C. , Whitmore S.J. , Granone J.F. , Dezenberg G.J.
Published: February 2023

The results of several years of experience at the U.S. Army Missile Command in calibrating laser radar compact ranges is discussed. This experience covers a range of cross-sections covering more than ten orders of magnitude and includes the use of both specular and diffuse calibration targets. A calibration target is one of known cross-section which can be used to obtain a relationship between signal and cross-section for a laser radar or a compact range.
A Global-Scale Model of Aerosol Backscatter at CO2 Wavelengths
Authors: Bowdle David A.
Published: February 2023

A global-scale model of background aerosol backscatter cross-sections at CO2 wavelengths is being developed in support of feasibility studies for NASA’s prospective satellite Doppler Lidar Atmospheric Wind Sounder (LAWS). LAWS is intended to provide global-scale wind profiles in the troposphere and lower stratosphere (Baker and Curran, 1985). The accuracy and the global coverage of the retrieved winds from LAWS will depend critically on the local magnitudes and the global distribution of aerosol backscatter coefficients (Huffaker et al, 1984).
Use of Aerosol Microphysical Measurements to Model IR Backscatter in Support of GLOBE
Authors: Patterson E. M , Bowdle D. A.
Published: February 2023

Planned satellite based doppier LIDAR wind sensors operating in the 10 um region will measure the backscatter from atmospheric aerosols. An evaluation of the performance of these systems requires knowledge of the expected levels of backscatter for a variety of situations that span the range of expected measurement conditions. There is a particular interest in determining the free tropospheric backscatter to be expected under conditions in which the aerosol loadings are near background levels, data which are important in determining the usefulness of the wind data to be expected from these systems.
Aerosol Speckle Effects on Atmospheric Pulsed Lidar Backscattered Signals
Authors: Murty S. R.
Published: February 2023

The atmospheric aerosols which are used as targets are randomly distributed and have random motion. They are of different sizes and have separations much greater than the wavelength of the laser. It is also assumed that there are a sufficient number of them present in the scattering volume to form a diffuse, extended target. The radiation scattered by any aerosol has random phase and amplitude with a Doppler shifted frequency. The signals from the various scatterers which make up the target combine to form a speckle pattern at any point along the backscattered beam. The speckle size is approximately, λL/b, where, b, is the radius of the beam on the diffuse target. Therefore, as the beam size on the diffuse target increases, the speckle size at the receiver decreases. The field across a speckle pattern is produced by the addition of a number of signals of random phase, thus the speckle pattern will change as each particle moves, thereby generating spatial and temporal changes in intensity. Churnside and Yura considered the spatial and temporal properties of the aerosol induced speckle in Reference 1.
Wind Sensing Using a Conical Scanned CO2 Laser Doppler System
Authors: Foord R , Vaughan J M
Published: February 2023

This paper describes low level wind measurements using the ground prototype of the LATAS CO2 laser velocimeter in conjunction with a conical scanner. Measurements of wind speed and direction as a function of altitude up to a few hundred metres are obtained under different weather conditions demonstrating the potential for rapid acquisition and display of local wind field data. A measurement giving clear indication of directional wind shear is shown together with cloud effects.
Aerosol Backscatter at 1.06, 0.53 and 1.54 µM
Authors: Spinhirne James D.
Published: February 2023

The Global Backscatter Experiment (GLOBE) was intended to provide data on prevailing values of atmospheric backscatter cross section. The primary intent was predicting the performance of space borne lidar systems, most notably the Laser Atmospheric Wind Sounder (LAWS) for EOS. A second and related goal was to understand the source and characteristics of atmospheric aerosol particles. For remote ocean locations, and the Southern hemisphere in general, a significant lack of knowledge exists. The major components of the experiment were flight surveys throughout the Pacific region by the NASA DC-8 aircraft. A lidar system was operated on the missions to obtain aerosol backscatter cross section at the fundamental and doubled Nd:YAG laser wavelengths of 1.064 an 0.532 µm and, in addition, at a wavelength of 1.54 µm. The system was the first operational lidar at the one-and-a-half micron wavelength region. Coherent doppler lidar at near IR wavelengths is currently under development. Advantages of one-and-a-half micron lidar is eye safe operation and increased sensitivity to aerosol characteristics. The GLOBE flights were carried out in November 1989 and May-June 1990. In this paper we will discuss measurement techniques and initial results.
Aerosol and Cloud Measurements Using an Airborne CO2 Backscatter Lidar
Authors: Menzies Robert T.
Published: February 2023

An airborne CO2 backscatter lidar instrument was recently flown on the NASA DC-8 research aircraft during two extended missions over the Pacific. These two missions, namely the GLOBE 1989 and GLOBE 1990 Missions, consisted of 15 flights between November 6 and November 30, 1989, and 13 flights between May 12 and June 5, 1990. The objectives during these Pacific circumnavigations were to characterize aerosol backscatter levels at infrared wavelengths in relatively pristine regions of the troposphere, and to observe cloud effects on lidar signals. The 9 µm wavelength of the JPL airborne backscatter lidar (ABL) instrument is of particular importance in support of the NASA LAWS (Laser Atmospheric Wind Sounder) assessment and design studies. These lidar studies, when combined with other lidar instrument data and aerosol in-situ sampler data from the aircraft platform, will elucidate the effects of various aerosol sources and sinks and aerosol transport on large-scale aerosol distributions in the Pacific troposphere. These studies form an important element of the NASA GLOBE (Global Backscatter Experiment) program, which is coordinated by the NASA Marshall Space Flight Center.
Remote Tropospheric Backscatter Measurements at 9.1 and 10.6 Micrometers with Airborne Focused Doppler Lidars
Authors: Rothermel Jeffry , Jones William D. , Srivastava Vandana , Jarzembski Maurice , Hampton Diana
Published: February 2023

Over the past ten years, interest has grown in characterizing atmospheric aerosol backscatter levels in response to escalating interest in several proposed satellite-borne, lidar-based sensors. Measurements of some primary atmospheric parameter will be obtained from signals backscattered from micrometer-size aerosols. An example is the Laser Atmospheric Wind Sounder (LAWS) under development by the National Aeronautics and Space Administration (NASA), Marshall Space Flight Center (MSFC) as part of the NASA Earth Observing System (EOS) earth system science initiative (Curran, 1987). LAWS is intended to provide global tropospheric wind measurements using Doppler-shifted signals from aerosols, which act as passive wind tracers. The accuracy of the wind estimates is a function of the signal strength, which in turn is a function of the aerosol backscatter coefficient. Therefore, LAWS performance will depend in part on the spatial distribution of aerosols, and associated physical, chemical, and optical properties.
Lidar Measurements of Aerosol Backscatter in Regions of the North and South Atlantic
Authors: Alejandro S B , Bedo D , Koenig G , Swirbalus R , Woffinden J , Vaughan J M , Brown D W , Callan R D , Davies P H , Foord R , Nash C , Wilson D J
Published: February 2023

To establish natural aerosol backscatter coefficients over extended regions of the globe, the Geophysics Laboratory (GL) of the US Air Force Systems Command and the Royal Signals and Radar Establishment (RSRE) of Great Britain have joined in a co-operative program of lidar observations utilizing both ground based and airborne instrumentation. A preliminary account of the measurement programme in the South Atlantic has been given in Reference 1. Aircraft measurements have been made with a CO2 10.6µm coherent lidar mounted in the bomb bay of a Royal Aircraft Establishment Canberra bomber operating throughout complex test flights to above 50,000 feet. At the surface, simultaneously and in the near vicinity of the aircraft flight path, altitude profiles of backscatter were acquired by a coherent CO2 lidar and a doubled and tripled YAG lidar provided by Phillips Laboratory. In addition to the lidar, the aircraft carried particle size probes under the wings. Supporting meteorological data were obtained from local sonde launches, and from the Air Force Air Weather Service and the British Meteorological Office. The airborne system provides essentially an in situ measurement, sampling approximately 100 metres ahead of the aircraft with a sensitivity threshold of 8 × 10-12m-1 - sterad-1. The range gated systems on the ground have altitude resolution of 150 or 300 metre, power levels of the order of 100 millijoule (IR and visible) per pulse, and pulse repetition frequencies of 100 and 10 per second. Field measurements have been completed from Ascension Island in the South Atlantic [Oct-Nov 1988 (aircraft only) and Jun/Jul 1989], from Keflavik, Iceland [May 1990 (aircraft only)], and Terceira, Azores [March 1990 (aircraft only) and Aug 1990]. Two specimen results are shown in Figures 1 and 2. Comparisons of LWIR and visible data, of airborne and ground based data, and results of particle probe measurements will be presented.
The Detection of Aircraft Wake Vortices by Laser Doppler Signatures - An Old Problem Revisited
Authors: Constant G D J , Foord R , Forrester P A , Vaughan J M
Published: February 2023

The presence of wake vortices on airport runways has been a potential hazard for aircraft during takeoff and landing since the introduction of wide-bodied passenger transport aircraft, such as the B 747 and the DC10, in the early nineteen seventies. The problem was quickly recognised by the US Federal Aviation Administration (FAA) and studies were initiated into methods of detecting and tracking the vortices (1) and also into ways of reducing their strength, although the latter only achieved limited success. In particular, a number of studies performed during the mid-nineteen seventies (2) showed that vortices could be detected and tracked using coherent laser systems operating at a wavelength of 10 micrometres by measuring the large Doppler frequency shifts produced at the extremities of the vortex. Extensive measurements were made at J F Kennedy International Airport using a CW system which scanned a focussed beam in a plane transverse to the runway and this system enabled measurements to be made of the vortices produced by a large number of differing aircraft types. Subsequently, operating procedures were introduced, based upon these findings, which provided adequate protection for following aircraft by adjusting the separation distance between landings depending upon the weight classifications of the leading and following aircraft. Little funding has been available since that time to study the wake vortex problem further and the subject has been largely dormant for the past 10 years although Koepp (3) reported some measurements in 1985.
Wind Shear Detection: Pattern Recognition Techniques
Authors: Thomson J. Alex L.
Published: February 2023

Laser radar SNR levels in the lower clear atmosphere are high enough to allow consideration of a multiple-watt on-board coherent laser radar, operating in a 3D imaging mode to sense wind shear patterns in the vicinity of airport terminal glide slopes. Any such Doppler sensor must contend with the fact that detection is limited to velocity components parallel to the viewing direction. Hazardous lateral velocities cannot be seen directly and must be inferred by some type of tracking analysis or model recognition procedure. In this paper an analysis is presented which discusses the use of statistical pattern recognition techniques to sense recognizable and recurrent 3D patterns of line-of-sight velocity. The concept is based on the idea that a historical database can be constructed by a combination of measurement, modeling, and simulation that can be used for assessing hazardous flight situations ahead. A Principle Component Analysis of such a database generates a basis set of observed 'eigen features' against which new observations can be compared in a real-time recognition of hazardous patterns. Numerical simulations are used to demonstrate the concepts for a candidate infrared coherent laser radar detection system flying through various combinations of low altitude turbulence, downbursts, and vortex wake environments.
Parametric Study of Seed Injection into a CO2 Laser with an Unstable Resonator
Authors: Angeley D. , Chou H.P. , Ghoshroy S.
Published: February 2023

It is essential that the transmitting laser of a coherent laser radar operate in single mode. In an unstable resonator, single transverse mode operation is determined by proper choice of physical cavity parameters. Single longitudinal mode operation can be achieved by seed injection and cavity matching. In this paper we present our results from our studies of CO2 laser seed injection using an unstable resonator for our oscillator and a single mode CW CO2 laser as the injection source.
LP-140 Injection Seeding Experiment
Authors: Jaenisch Holger M.
Published: February 2023

This paper summarizes recent investigations on the PSI LP-140 pulsed CO2 laser. The experiment was performed to enable a comparison between the operational characteristics of the laser in its existing configuration and results obtained earlier when the laser was operating in an extended cavity configuration.
The Effects of CO2 Gain-Switched Spikes on Estimating Lidar Doppler Shifts
Authors: Post Madison J. , Cupp Richard E.
Published: February 2023

We reported earlier1 that, despite having achieved single-mode output from the TEA laser in NOAA’s pulsed Doppler lidar, we could not estimate Doppler shifts to accuracies better than 100 kHz rms, or about 0.6 m s–1 using a complex pulse-pair algorithm. Inaccuracies of this magnitude are acceptable for mesoscale or terrain-induced flows, but they limit the usefulness of the lidar in studying convective flows and turbulent transfers, where accuracies near 0.1 m s–1 are required.
A Compact TEA/CO2 Laser for Wind Lidar Application
Authors: Charasse R. , Pucci P. , Ouhayoun M.
Published: February 2023

In Wind Doppler Lidar, the measurement of the optical frequency shift, related to back scattering on moving particles, requires a high energy and frequency stability pulsed laser.
Broadband Magnetically Tunable Electro-optic Modulators
Authors: Lax B. , Eng R. S. , Harris N. W. , Summers C. L.
Published: February 2023

In coherent CO2 laser radars, it is often desirable to track out the target translational Doppler frequency by shifting the laser LO. A single sideband (SSB) electro–optic (EO) modulator can be used for this purpose. The output from the SSB EO modulator considered here1,2 is high in mode quality and spectral purity. However, the bandwidth is limited by the dispersion of the modulation circuit. The new scheme described here (see Fig. 1) uses a ferrite-loaded waveguide containing an active CdTe EO crystal. A wide tuning range can be achieved by changing the phase velocity of the composite waveguide with an applied magnetic field.
Characterization of CO2 Laser Discharges Using a CCD Camera
Authors: Angeley D. , Faria-e-Maia F. , Stowe H. , Chou H.P. , Ghoshroy S.
Published: February 2023

The gain of the laser medium in a discharge-pumped CO2 laser is directly related to its discharge. Any non-uniformity in the discharge can adversely affect overall laser efficiency and can lead to non-uniformities in the intensity of the output laser beam. It is therefore important to characterize the gain region resulting from the discharge in order to accurately predict the performance of the laser. Such accuracy is especially important for designing light-weight lasers for airborne or space based applications. In this paper, we describe techniques to spatially and temporally characterize the gain region of a pre-ionized self-sustained discharge pumped CO2 laser.
The Laser Radar Sensor for Automatical Rendezvous and Dock of Spacecraft
Authors: Yongjing Dai , Yuan Zhao , Chunfei Li , Mingjia Pi
Published: February 2023

The automatical rendezvous and dock for two spacecrafts are very complex job in aerostro technology. The attitute and range of the target spacecraft relative to active spacecraft must be measure.(1) Becouse of the blind zone of microwave radar the laser radar sensor must be use in short range measuring. In the paper, a method measured attitute angle of the target spacecraft has been introduced. The method is based on "tilted effect" by the narrow interference filter.
HgCdTe Detectors for CO2 Laser Radar Applications
Authors: Shanley J.F. , Weaver F.J. , Caputi S.J. , Reisinger A.R.
Published: February 2023

Infrared heterodyne receivers have been shown to be viable and useful in CO2 laser radar applications. Interaction with space based systems requires frequency response of the order of 2 GHz due to the large Spacecraft Doppler velocities. Current applications are space based wind measurements such as proposed for the Laser Atmospheric Wind Sounder (LAWS) program as well as CO2 laser radar tracking systems (LOWKATER). Wide bandwidth receivers are required since it is not feasible to tune the CO2 laser local oscillator as is done in conventional microwave radar systems. Here we present the results and applications for wide bandwidth MCT detectors developed using the planer mercury diffusion process.
Phasing-up Multiple Aperture Laser Radar Receivers using Extended Soures
Authors: Clark S E , Jones L R , Desandre L F
Published: February 2023

Currently, there is substantial interest in using multiple apterture receiver arrays at laser wavelengths where lightweight structures and high angular resolution (tracking/imaging) are required. In order to achieve image resolution consistent with the overall size of the array, the amplitude and phase at each point in the array must be determined. Determination of the phase can be carried out either by performing heterodyne detection1,2 or by using direct detection combined with phase retrieval3 techniques. Since phase retrieval uses only the incident intensity, it does not suffer as does heterodyne detection from corruption of the incident phase due to errors in detector positioning and phase variations in the reference wavefront.
A Basic Experiment for Development of an Infrared Baseline Interferometer Using Coherent Heterodyne Detection Technique
Authors: Yoshirado Shin , Tarami Hideki , Ishizu Mitsuo , Asai Kazuhiro , Minoh Arimichi , Tsukakoshi Motowo , Aruga Tadashi
Published: February 2023

Since last year, we have been conducting a basic experiment for the development of an infrared baseline interferometer system which can realize coherent imaging of distant objects with extremely high resolution. Through the experiment using a CO2 laser as a trial radiation source, we have confirmed that the system fulfils its fundamental function for such a temporal radiation source with relatively strong power.
High Performance Velocity Estimators for Coherent Laser Radars
Authors: Anderson John R.
Published: February 2023

The use of high performance Doppler velocity estimators to enhance the performance of laser radars has taken on an added importance in the context of space based wind measurement systems such as the Laser Atmospheric Wind Sounder (LAWS) instrument. The LAWS mission is designed to make wind measurements throughout the troposphere using scattering from atmospheric aerosols at CO2 laser wavelengths. The need to make velocity estimates in very clean upper tropospheric conditions coupled with the strict limits imposed on the system power and aperture by the orbital platform require that usable velocity measurements be made at the lowest possible signal-to-noise ratios.
First spectral moment estimates from an adaptative notch filter
Authors: Zarader J.L. , M'Sirdi N.K. , Ancellet G. , Flamant P. , Dabas A.
Published: February 2023

The first spectral moment estimation of a Doppler signal yk can be obtained using an FFT or an autocovariance [1,2] algorithm if the assumption on stationnarity and a slow variation are not met. The FFT algorithm has limited on resolution related to the number of sampled to be used (2N).
Science Advances Anticipated with the Laser Atmospheric Wind Sounder
Authors: Baker Wayman E.
Published: February 2023

Knowledge of the global wind field is widely recognized as fundamental
to advancing our understanding and prediction of the total Earth
system. The motion of the atmosphere directly affects a wide-range of
geophysical processes including: the horizontal transport of momentum,
moisture, chemical constituents and aerosols, the evaporation of water
and heat from the land and oceans, and atmospheric teleconnections,
such as the influence of the tropical Pacific on the circulation of
the northern hemisphere middle latitudes. An accurate depiction of the
atmospheric motion is also a key parameter for improving the skill of
weather forecasts. Yet, because wind profiles are primarily measured
by land-based, balloon-tethered instruments, the oceanic areas
(covering roughly three quarters of the Earth’s surface) and many
regions of the less-developed tropical and southern hemisphere land
areas are poorly observed. The gap between our requirements for global
wind data and their availability continues to widen. For example, as
faster computers become available to model the atmosphere with ever
increasing resolution and sophistication, our ability to do so is
hampered because of the lack of data, particularly wind profiles.
Status of the Laser Atmospheric Wind Sounder
Authors: Bilbro James W. , Jayroe Robert , Baker Wayman
Published: February 2023

The Phase I studies for the LAWS instrument were competitively bid and planned as a parallel effort between two prime contractors. The main purposes of the Phase I studies were to define the LAWS instrument requirements, define the instrument concepts and configurations, and conduct instrument performance analysis. The option to procede to Phase II as a parallel effort with the same contractors was to be exercised based on the recommendation of a Non-Advocacy Review (NAR) panel, which was composed of nationally recognized laser experts. The main purposes of the Phase II studies are for both contractors to optimize their instrument configuration via trades and analyses, perform a preliminary design based upon the optimized configuration, prepare a systems plan for the follow on Phase C/D contract, and define the tasks needed to complete Phase C/D effort. Phase C/D includes building the LAWS flight hardware, delivering and integrating the hardware at the launch area and developing the procedures for mission operations. In addition to the Phase II study effort, there is a parallel LAWS breadboard effort with both contractors to demonstrate the laser technology required for deriving wind fields and retiring as much risk as possible before building the flight hardware. The Phase C/D effort will be open to competitive bidding. LAWS was originally scheduled to fly on the Japanese Polar Orbiting Platform (JPOP) in 1998, but the agreement between Japan and the United States was never formalized and has since been dropped.
Laser Atmospheric Wind Sounder (LAWS) Phase I Study Results
Authors: Wilson D.J. , Eberle W.R. , Jones W.E. , Kurzius S.C. , Schrider K.R. , Speer T.K. , Schwarzenberger P.M. , Buczek C. , Ghoshroy S. , Chou H.P. , Ullathorne C. , DiMarzio C.
Published: February 2023

LAWS, a facility instrument for the Earth Observation System (EOS), is being designed to measure line-of-sight wind velocities throughout the troposphere (see Figure 1). Horizontal winds will then be derived from the line-of-sight measurements of aerosol velocities. Our baseline instrument concept is a coherent lidar operating at an 9.11 mm wavelength with a 1.7 m aperture, conically scanning telescope and 3 μs, 20 J pulses. Radiation from the lidar is backscattered by ambient aerosols, collected by the instrument receiver, and heterodyne detected to resolve the wind velocity. Global grid resolution is 100 × 100 km horizontal and 1 km vertical. A polar orbit of 705 km is the mission profile with a 3 to 5 year life span.
Spectral and Covariance algorithms for Doppler Lidar Signals
Authors: Dabas A. , Flamant P.H.
Published: February 2023

The performances in terms of bias and standard deviation of the frequency estimators originally applied to Doppler Radar signals (FFT, Pulse-Pair and Poly-Pulse-Pair), are analysed, when working on Doppler Lidar signals characterized by low Signal to Noise Ratio (down to −10dB). Analytical equations were presented by Berger&Groginsky, and Zrnic, for the statistical error as a function of SNR and signal processor parameters. Those equations are rederived from the basic maths to make more explicit the various assumptions and limitations they imply. Those equations are then systematically compared to numerically derived performances (study made for the franco-german airbone Doppler lidar project WIND), based on simulated Doppler Lidar signals. Examples are presented of the estimator standard deviations when they are applied to signals with wide-band SNR ranging from −10dB to +10dB.
Power estimator bias in filtered incoherent backscatter heterodyne lidar returns
Authors: Rye Barry J. , Hardesty R. Michael
Published: February 2023

We have considered various Kalman filters1 that can recursively filter and smooth, in an optimal way, the observations of a return that is varying in time. A basic problem for any lidar filter is estimation of return power. For coherent lidar, raw power measurements are corrupted by speckle that is characterized by high variance and asymmetrical exponential statistics. Both problems are mitigated if speckle diversity techniques are used, so data taken over a time short compared with the time scale of return power fluctuations can be preprocessed by averaging. Here we consider interfacing small samples of return power data, observed with and without such preprocessing, to the Kalman filter used subsequently.
Multifrequency CO2 Laser Heterodyne Detection
Authors: Xia ZHao
Published: February 2023

The nonlinear four-frequency heterodyne detection has been analysed theoretically in experiment. The nonlinear four-frequency heterodyne detection was realized and the results obtained coincides with expected one in this paper, we suggest multifrequency heterodyne detection systems, which can be used for finding out objectives, imaging contours and other application, etc.
Sequential Detection of Multiple Materials Using Multiwavelength Lidar Time Series Data
Authors: Hannon Stephen M. , Warren Russell E.
Published: February 2023

Previous work1 produced a maximum likelihood (ML) estimator for the path-integrated concentration vector, CL, for a set of N materials measured using topographic or atmospheric backscatter differential absorption lidar (DIAL) with at least N+1 wavelengths. That analysis also showed that a Neyman-Pearson-based detection algorithm for the generalized DIAL measurement could be developed using a fixed-size sample of lidar data. Although adequate for many purposes, the Neyman-Pearson detection approach with fixed sampling does not fully exploit the time series aspect of most DIAL data collection. As a first step toward utilizing this aspect, it was shown2 that an adaptive Kalman filter could significantly improve the estimation of CL using a sequence of lidar measurements with little or no additional processing time. The question naturally arises as to whether a sequential approach could improve detection as well as estimation performance for a DIAL sensor.
A Diode-Pumped 2 μm Tm:YAG Laser Suitable for Short- to Medium-Range Coherent Laser Radar Applications
Authors: Suni Paul J.M. , Gates Greg H.
Published: February 2023

Coherent laser radar systems operating in the 2 μm spectral range have recently been demonstrated to work very well. For example, horizontal wind measurements to > 20 km and hard-target measurements to ranges of about 150 km have been shown with our fielded system. To date 2 μm systems have been based around flashlamp pumped Cr,Tm,Ho:YAG. In this material Cr is used to absorb pump light, energy is transferred to Tm, following which cross-relaxation and energy transfer populates the lasant Ho ions. In recent years it has also been demonstrated that Tm can be pumped by laser diodes and that direct laser action in Tm near 2.0 μm can be extremely efficient.
Enhanced Heterodyne Detection of 1 μm Nd:YAG Coherent Lidar using a 2-Dimensional Detector Array
Authors: Chan Kin Pui , Killinger Dennis K.
Published: February 2023

Recently, there has been increased interest in the development of an all solid-state coherent lidar for remote wind sensing and the detection of windshears in front of aircraft. In the course of the development of a 1 μm Nd:YAG and a 2 μm Ho:YAG coherent Doppler lidar, we have experimentally measured that the effective receiver telescope aperture diameter may be reduced due to atmospheric turbulence effects for a near infrared coherent lidar operating near the ground.1 In addition, our Monte-Carlo computer simulations of the atmospheric turbulence effects have indicated that this limitation could be reduced by the usage of a 2-dimensional (2-D) heterodyne detector array.2 In this paper, we report the first experimental demonstration of enhanced heterodyne detection of a 1 μm Nd:YAG coherent Doppler lidar using a 2-D InGaAs multi-element heterodyne detector array.
DOD Applications of Laser Radar
Authors: McManamon Paul F.
Published: February 2023

DOD applications of laser radar will be discussed. Space-to-space, air-to-air, and air-to-ground laser radar will be discussed.
Space Shuttle Wind Profiler
Authors: Johnson Steven C.
Published: February 2023

Knowledge of winds is required to reduce aerodynamic loads on the Space Shuttle during launch. Knowledge of winds is also required to safely land the unpowered orbiter. Balloons are currently used in both instances to produce the necessary wind profiles. The balloons require an hour to rise through the altitude range, sometimes drifting far from the area where the wind measurement is desired. As a result, the correlation between the actual winds encountered by the vehicle and those measured is reduced. NASA is investigating the potential of alternate wind sensors to produce more local wind measurement in less time to increase this correlation. Lidar is one technique under investigation.
Analytic Solution for the Location and Volume of CW Coherent Lidar Atmospheric Measurements
Authors: Kavaya Michael J. , Suni Paul J. M.
Published: February 2023

For over 20 years researchers have demonstrated and published many successful remote sensing tasks using continuous-wave (CW), monostatic, coherent laser radar (CLR) systems. With atmospheric aerosol particles serving as the distributed target, the applications have included radial wind velocity, transverse wind velocity, aircraft trailing vortices, aircraft true airspeed (TAS), and atmospheric aerosol backscatter coefficients. Calibration issues of the wind and backscatter data have been investigated, and intercomparisons of the CW CLR measurements with both similar and different sensors have been performed.
Multimode Feed for Optical Monopulse LIDAR
Authors: Kahn W. K. , DeLorenzo J. D. , Heintz R. E. , Ciccarelli S. , German T. , Kulp G. , Raghavan V. P.
Published: February 2023

This paper describes an experimental integrated optic multimode monopulse feed for a future optical tracking LIDAR. A precision monopulse tracker senses angle deviations of the order of a small fraction of the antenna beamwidth. Currently trackers utilize feeds comprised of two (or four) sectoral sensor heads. For proper operation the characteristics of the individual heads must be accurately matched to one another; moreover the septum dividing the sectors causes loss of sensitivity near boresight. These limitations are circumvented by the multimode feed.
Italian CO2 lidar work and laser development
Authors: Barbini R.
Published: February 2023

There is a persuasive evidence that the human existence and economic development is causing effective changes in our world, m particular on the quality of the atmosphere, water and soil.
A Rapidly-Tunable Coherent LIDAR for Chemical Sensing
Authors: Fox Jay A. , Gautier Cynthia R. , Ahl Jeffrey L.
Published: February 2023

Recent world developments have underscored the need for remote sensing of chemical and nerve agents in the modem battlefield. One method of doing this may be to use LIDAR technology. Fortunately, since most of the known threats have prominent spectral features in the 9-11 μm band, the CO2 laser can be utilized. However, in a realistic environment, the identification task can prove to be quite challenging due to the presence of interferents that have similar spectral features. For example, common vapors such as gasoline and ordinary obscurants such as battlefield smoke and even dust can greatly complicate the identification of a typical agent. This means that typically more than two wavelengths are needed to unambiguously identify the agent. Our current requirement is to utilize as many as 16 CO2 lasing lines to perform the task. However, this presents a significant engineering problem.
Study on Homogeneity of Photosensitive Surface of The HgCdTe Photovoltaic Detector
Authors: Yuan Zhao , Yongjiang Dai , Haipeng Yu
Published: February 2023

The injected ion model Hg0.2Cd0.2Te photovoltaic deteotion is important element on CO2 coherent laser radar. The heterodyne quatum efficiency η(x,y) is important parameter for photovoltaic detection. The distribution function of the heterodyne quatum efficiency η(x,y) expreses homogemeity of photo-surface.
The Importance of a Small-Sat Wind Lidar for Weather Prediction and Climate Studies
Authors: Baker Wayman E.
Published: February 2023

Knowledge of the global wind field is widely recognized as fundamental to advancing our understanding and prediction of weather and climate. A small-satellite wind lidar development effort has been proposed beginning in FY 1997 with launch in FY 2001. Preliminary analyses indicate that significant science advances can be expected.
Coherent Doppler Lidar for Boundary Layer Wind Measurement Employing a Diode-Pumped Tm:Lu,YAG Laser
Authors: Grund Christian J.
Published: February 2023

Boundary layer research has been increasingly hampered by the lack of sensors that can economically provide accurate high spatial and temporal resolution wind measurements covering large atmospheric volumes. In particular, measurements of the turbulent fluctuations of the wind with better than 50 m spatial resolution covering volumes of a few km3/sec to distances of 10 km are needed to estimate weakly correlated turbulent quantities (e.g. momentum fluxes , ). These measurements are also needed to test model parameterizations and to initialize model runs for Large Eddy Simulation (LES) models. These models have recently been used to provide detailed insights into fundamental boundary layer processes, particularly non-steady-state, transitional, and intermittent processes. Of particular interest to NOAA are the improvement of vertical resolution in the boundary layer entrainment zone, higher resolution observations of the nocturnal and baroclinic (neutral or shear-driven) boundary layers, day/night boundary layer transition processes, and observation of the ocean-atmosphere boundary layer. Other interests requiring new instrument capabilities are: the development of techniques for the direct measurement of fluxes of moisture, momentum, and chemical species, the measurement of vertical velocities and ice crystal fall speeds in cirrus clouds and the impact of shear on cloud morphology, the measurement of synoptic scale divergence and vorticity, and the behavior of complex terrain flows.
Design of a Doppler Lidar for Global Profiling of Tropospheric Winds
Authors: Kavaya Michael J.
Published: February 2023

During the years 1989 to 1992 NASA/MSFC managed the Laser Atmospheric Wind Sounder (LAWS) project and selected two contractor teams to perform parallel Phase I and II studies, and parallel CO2 laser breadboard demonstrations. The contractor teams were headed by GE Astro Space [1,2] and Lock-heed Missiles & Space Company [3,4]. At that time LAWS was part of NASA’s Earth Observing System (EOS) component of the Mission To Planet Earth (MTPE) program; and LAWS was required to fully profile the tropospheric wind velocity from the ground to 20 km altitude with accuracies near 1 m/s and vertical resolutions better than 1 km. The recommendations of both studies were similar and consisted of a coherent laser radar (lidar) employing an ~20 J, ~5 Hz, rare isotope CO2 pulsed laser with an ~1.6 m diameter conically scanning telescope. The orbit was sun-synchronous at 525 km. During this time the paradigm shift to “faster, better, cheaper” and “smallsats” was occurring; and both the estimated costs and spacecraft accommodations for LAWS precluded mission approval. In Dec. 1993, LAWS was deselected from EOS.
Design Considerations for a Receiver for a Space Based Coherent Doppler Lidar Operating in the Two Micron Wavelength Region
Authors: Spiers Gary D. , Amzajerdian Farzin , Johnson Steve C.
Published: February 2023

A space-based coherent Doppler lidar, such as the AEOLUS[1] instrument under investigation at NASA, will probably employ some form of scan geometry and will consequently see an azimuth angle dependent Doppler shift due to components of the spacecraft velocity and earth rotational velocity. The two micron wavelength region currently being considered for this instrument means that this varying Doppler shift will be large. Figure (1) shows this Doppler shift as a function of azimuth angle for an instrument with a 30 deg. nadir angle and a 350 km high orbit.
A Pseudo-Random Frequency Modulation CW Coherent Lidar Using an Optical Field Correlation Detection
Authors: Asaka Kimio , Hirano Yoshihito , Tatsumi Kenji
Published: February 2023

Coherent Doppler Lidar is an attractive sensor for remote measurment of target velocity, wind speed and windshear.1 A pulsed laser is usually used for coherent Doppler Lidar.2 Pulsed coherent Lidar needs high peak power, good frequency stability and good spatial characteristics so as to produce a diffraction-limited spot in the far field. The wavelength of 1.5 μ m is highest from the view point of eye-safety, and high quality photo detectors or optical components are easily aveilable at this wavelength for use in optical communication. But it is difficult to get a stable pulsed laser at the wavelength of 1.5 μ m.
The estimate of the measurement accuracy of the average Doppler frequency using the autocorrelation function method
Authors: Afanas'ev Alexei L. , Shelekhov Alexander P.
Published: February 2023

The measurement error depends on a great deal of factors when measuring the average frequency of the Doppler Lidar. One of the main factors is the turbulent wind velocity fluctuations. The existence of these fluctuations is the cause that the particles occurring in a scattering volume have different fluctuation velocities. Moreover, the positions of the particles within the scattering volume are random. Therefore, the photocurrent statistical characteristics of the Doppler Lidar and, consequently, the measurement error depend on the state of the turbulent atmosphere and dimensions of the scattering volume. For example, the statistical characteristics of the photocurrent signal part are the non-Gaussian ones in the case of small value of the dimensions of the scattering volume and the statistical characteristics can be considered the Gaussian ones in the case of large value of the dimensions of the scattering volume. Thus the usual methods of the estimate of the measurement accuracy of the average Doppler frequency based on the assumption of the Gaussian statistics of the photocurrent signal part (see Ref. 1) have a limited application area. The behavior of the measurement error of the average frequency of the pulsed and cw- Doppler Lidar as a function of parameters of the turbulent atmosphere and the dimensions of the scattering volume is studied for the autocorrelation function method. The consideration is based on the results of Ref. 2 in which the non-Gaussian random process is analyzed.
Sensitivity of two-frequency autodyne detection
Authors: Tieliang Shang , Xiuzeng Bao , Yihuang Ye , Chi Zhou , Mingjia Pi
Published: February 2023

Heterodyne detection of laser radar signals is much more sensitive than other non-coherent method. The theory and technology of heterodyne detection are being well developed. In 1985, R. J. Keyes proposed the autodyne detection in a transmission-reception coherent laser radar system with a single-frequency laser.[1] Furhter theoretical and experimenatl efforts were made by D.U. Flukiger et al in visible region in 1987.[2] In 1989, Pi Mingjia proposed a new method of coherent laser radar detect ion, the two-frequency autodyne(TFAD) detection.[3]
Precision Pointing and Tracking through Atmospheric Turbulence for Hard Target Imaging and Ladar Applications
Authors: Harvey James E. , Reddy Stephen P. , Phillips Ronald L.
Published: February 2023

Interferometric sensitivity in pointing and tracking accuracy through atmospheric turbulence is achieved by measuring asymmetries in the Young's interference pattern produced by reciprocal scattering paths between a dual illuminating aperture and a hard target.
Performance of coherent and direct detection laser radars for hard target applications
Authors: Steinvall Ove
Published: February 2023

The first laser range finder (1961) used direct detection and since then a great number of direct detection system have become operational. Work on coherent laser radars began after the discovery of the CO2 laser by Patel in 1964. Since then coherent laser radars have been developed for range finding, wind measurements, vibration sensing, obstacle avoidance and advanced imaging. There are however very few operational coherent laser radars probably due to complexity and high costs. The main advantages of coherent detection over direct detection systems are instantaneous Doppler and shot noise limited detection. Many of laser radar functions can also be realized with direct detection. The direct detection systems are in general simpler. Recent development of efficient short wavelength laser sources might change this in favor of coherent systems but it might also lead to efficient direct detection systems. In this talk we will investigate performance for hard target laser radars using either type of detection. System examples for range finding, target imaging and obstacle avoidance/terrain following will be analyzed. Important parameter variations beside the system parameters include target/background characteristics, atmospheric attenuation and turbulence.