bluuebunny/crossref_metadata_2025 huggingface dataset:
Space-Based Lidar Sampling in Partly Cloudy Regions
Authors: Emmitt G.D. , Flamant P. , Elouragini S. , Dabas A. , Séze S.
Published: February 2023

Unlike most space-based atmospheric sounding instruments, proposed lidar systems are characterized by a very small sampling cross-section (r ~ 10 m). Although lidars may be able to sample through partly cloudy scenes that would be considered "contaminated" for passive systems, there remains the issue of how representative and useful that information might be.
Comparison of Spaceborne Wind Lidars Aladin and Best for Meteorology and Climatology
Authors: Dabas A. , Lieutaud F. , Seze G. , Flamant P. H. , Courtier PH. , Gauthier P. , Rabier F. , Emmitt G. D.
Published: February 2023

Tropospheric wind field is a primary atmospheric variable, the knowledge of which is required at a global scale for operational meteorology and climatology studies. With the present state-of-the-art technology a spaceborne Doppler coherent lidar is foreseen to fullfil the requirements on sampling and wind speed accuracy. An initial feasability study has been conducted at NOAA in the late 70's proposing a viable concept for a laser remote sensor instrument WINDSAT. In the late 80's NASA and ESA started two studies on wind Doppler lidar so-called LAWS and ALADIN respectively to be launched either on a polar or a low inclinaison orbit depending on the scientific objectives and instrument performances dictated by the overall technology : lidar and platform. In these two studies a conical scanning mode provides the horizontal coverage at the earth surface. In a separate way restricting at first the scientific objectives to the climatology of the tropics CNES in France started a feasability study for a low inclinaison mission so-called BEST which includes among others a wind Doppler lidar. A new instrumental concept is proposed for BEST which is a multi-fixed line-of-sight configuration relaxing the constraints on lag-angle compensation and laser technology. So, a comparison of the two scanning modes has to be made keeping in mind the applications in order to show what can be acomplished with an increasing instrumental complexity. The various subjects to be covered by a comparison analysis are : horizontal coverage, cloud obstruction, sampling at various time scales, representativeness and wind speed accuracy, but also the data assimilation methods. Such a study is conducted for BEST and ALADIN by LMD and DMN following a step by step approach with an increasing complexity and completeness.
The Study of Signal Preprocessing on CO2 Coherent Laser Radar
Authors: Haibin Wu , Yongjiang Dai , Xuedong Yang
Published: February 2023

The intelligence signal preprocessing is a important work on CO2 coherent laser radar. The first, it is nimble processing method, it can complete more preprocessing for example acquisition and resyrain noise. The second, some processing of the central host computer can be completed by preprocessor. Each processor is independently and is not disturb, and operating at the same time. So processing of the system is fast.
Two-Frequency Coherent Co2 Laser Ranger
Authors: Vasijenko B.S. , Goldori V.G. , Bernov M.A. , Ishochenko V.N.
Published: February 2023

The operation algorithm of coherent CO2 range finder with tuning two-frequency transmitter is developed and results of laboratory investigations of the system with optical moving target simulator are presented. The system can operate at distances >10 2 km (without atmosphere) and large velocities with space resolution up to 1 m.
A Modulation Polarization Technique to Measure Hard Target Backscatter Reflectance
Authors: Anderson Richard
Published: February 2023

The measurement of the reflectance of hard targets used to calibrate lidar have been complicated by the introduction of polarization effects by Kavaya.1 As a result, some investigators no longer employ hard targets. Haner and Menzies2 presented an excellent paper on the comparison method to calibrate hard targets and the flooded sulfur target appeared to be a good secondary standard for the scattered radiation was nearly depolarized and exhibited reduced retroreflection.
Solid-State Coherent Laser Radar Technology at 2 μm: Current Status and Future Prospects
Authors: Henderson Sammy W. , Hale Charley P. , Suni Paul J.M. , Magee James R.
Published: February 2023

We have recently demonstrated the first working coherent laser radar (CLR) using solid-state Tm,Ho:YAG lasers operating at the eyesafe wavelength of 2.09 μm.1 The system has demonstrated accurate velocity and range measuring capability during preliminary field tests. Results to date include horizontal atmospheric wind measurements to 30 km, vertical atmospheric aerosol returns to 4 km, near-horizontal cloud returns to 100 km, and hard target (mountainside) returns from 145 km. All these returns were obtained with a transmitted pulse energy at 2.09 μm of only ~ 20 mJ. The long range cloud and mountainside returns indicate very high atmospheric transmission at the 2.09 μm wavelength Using diode lasers to pump Tm:YAG laser crystals, we have also recently demonstrated the feasibility for developing very compact, rugged, efficient, and long-lived 2 μm CLR systems.2 These very encouraging early results suggest that many remote sensing applications could benefit by using 2 μm CLR systems.
Atmospheric Effects on 2.09μm Laser Radar Performance
Authors: Richmond Richard , Kavaya Michael J , Henderson Sammy W
Published: February 2023

For a coherent laser radar system (CLR), the signal to noise ratio (SNR) from a target at a fixed distance should be a maximum when the focus setting is equal to the target distance. The theoretical shape of a curve of SNR vs focus setting for a target distance of 840 meters and a laser wavelength of 2.09 μm is illustrated in Figure 1. Atmospheric refractive turbulence will distort the phase front of the propagating laser beam. This distortion effectively reduces the heterodyne efficiency of the CLR system and the SNR is correspondingly affected. The curves in Figure 1 are for varying levels of atmospheric refractive turbulence (Cn2). This effect is more pronounced at shorter wavelengths. With the recent advances in 2 μm lasers for CLR, it is important that the prediction of the effect of refractive turbulence be verified. This paper presents the results of an attempt to fit experimental data to theoretical curves of SNR vs. focus and to estimate Cn2 from that fit.
NASA's Program in LIDAR Remote Sensing
Authors: Kakar Ramash K.
Published: February 2023

This paper will describe several major NASA research efforts in lidar remote sensing, including hardware and key sensor issues, along with results and expectations.
1 and 2 μm Laser Radar Transmitter Development
Authors: Durvasula L. N.
Published: February 2023

Compact, efficient, diode-pumped 1 and 2 μm solid-state laser transmitters with wavelength and waveform density will be described for numerous laser radar applications.
SDI Ladar Program
Authors: Dezenberg George J.
Published: February 2023

This paper will describe the laser radar technology program being conducted by the Strategic Defense Initiative (SDI) in support of the Global Protection Against Limited Strikes (GPALS) and follow-on missions. Concomitant efforts are developing laser radar systems, components, and data bases. Developments in agile optical beam steering technology, coherent CO2, and direct detection Nd: YAG laser radar systems will be discussed. Investigative measurements of space deployment phenomenology are being conducted using the MIT/Lincoln Laboratory's FIREPOND Research Facility and specially designed payloads lofted aboard sounding rockets from Wallops Island, Virginia, into suborbital trajectories. Compact ranges are being used to make far-field, mono-, and bistatic target dynamics measurements at 10.6 μm, 1.06 μm and 0.53 μm. Details of these programs will be presented.
Mission profiles for the proposed Doppler lidar WIND
Authors: Werner Ch. , Schwiesow R. , Benesch W.
Published: February 2023

During phase A of the development of the airborne pulsed CO2 laser-Doppler system WIND [1] a lot of scientific objectives were studied. The intension for the airborne system is — to use it for wind field measurements— to use the experience during the development and test phase for further development of a spaccborne lidar.
Performance Optimization for Laser Atmospheric Wind Sounder
Authors: Eberle William R. , Shrider Kenneth R.
Published: February 2023

The Laser Atmospheric Wind Sounder (LAWS) will be designed to measure atmospheric winds over a wide range of atmospheric and backscatter conditions. The LAWS design includes many significant trades because of limited available power and limited available weight. The allocation of available power is a trade between many low energy pulses of low signal-to-noise (S/N) and few high energy pulses high S/N. The power allocation is complicated by range of backscatter conditions over which measurements must be made and by the two sources of measurement variation: measurement error and mesoscale variability of wind velocity. Minimization of measurement error favors a few high energy pulses. Representativeness of wind with mesoscale variability favors many low energy pulses. A second significant trade involves a trade between measurement accuracy and the fraction of the globe covered by the satellite.
Analysis of Vibration Sensing Lidar Performance
Authors: Megaloudis George , Pearson Edwin
Published: February 2023

This paper presents the results of an analysis of the feasibility of measuring vibration signatures with near infrared coherent lidar. Quantitative performance predictions have been obtained through the application of the detailed sensor model and realistic measurement scenarios. Using a rigorous formulation of coherent detection, the output of the photodetector was quantified and shown to have the conventional form of a phase-modulated carrier in the presence of Gaussian additive noise. The phase modulation of the carrier is proportional to the time-dependent vibration signature of the illuminated region of the target surface. The carrier phase was also shown to contain an additive stochastic contribution. This contribution, as well as the carrier amplitude, undergo rapid temporal fluctuations that are due to target surface roughness and the apparent target rotation and tilting motion that result during target illumination from a moving sensor platform.
The Firepond Long Range Imaging CO2 Laser Radar
Authors: Keicher W. E. , Edwards B. E. , Sullivan L. J.
Published: February 2023

The Massachusetts Institute of Technology Lincoln Laboratory has developed and tested the most advanced, high power, coherent CO2 laser radar ever built. The Firepond imaging laser radar is part of a complex of sophisticated radar systems at Millstone Hill, which is located in Westford, Massachusetts. The radar site includes the L band Millstone Hill space surveillance radar and the X band Haystack wideband imaging radar. A photograph of the Millstone Hill radar site is shown in Figure 1. The CO2 laser radar utilizes the 13C16O2 isotope to avoid the effects of atmospheric attenuation and dispersion caused by atmospheric 12C16O2. The laser radar uses linear frequency modulated waveforms to create two dimensional, range-Doppler images using the principles of inverse synthetic aperture radar (ISAR). The waveform agility of the laser radar allows a variety of radar functions to be served including acquisition and tracking.
Present and Future Development of the Lmd's Coherent CO2 Lidar
Authors: Loth C. , Dabas A. , Romand B. , Delume J. , Flamant P.H.
Published: February 2023

The ground-based coherent lidar developped at LMD has been upgraded to make it more practical for atmospheric measurements. One experimental difficulty with our system is the time spent prior any backscatter or wind measurement for optical alignment, frequency offset tuning and stabilization. The overall procedure has to be repeated every time an experiment is to be conducted. The main modifications implemented last year deal with the TE-CO2 transmitter, the local oscillator, and a CCD camera to look at the remote targets we are aiming at for alignment or calibration purposes.
Beam Propagation Analysis of Coherent Lidar Optics
Authors: Noll R.
Published: February 2023

The end-to-end system performance of a coherent lidar system can be expressed in terms of the autocovariance of the signal current in the detector. By following classical beam propagation techniques one can develop expressions for this autocovariance function and thereby isolate many of the various system functions for a clearer total system picture and a more convenient design process.
The truncated Gaussian lidar antenna problem revisited
Authors: Rye Barry J. , Frehlich Rod G.
Published: February 2023

Two papers1,2 have presented inter alia numerical values for the return signal from a coherent lidar having the following properties: Gaussian beam profiles, beam truncation in the antenna plane by circular apertures of equal area, monostatic geometry (common transmitter/receiver axis), incoherent backscatter target of infinite extent lateral to the lidar axis, infinite photodetector area, no refractive turbulence, hard target with no depth, both transmitter and receiver focused on the target, fixed transmitter laser power, and fixed local oscillator (LO) power on a uniform photodetector. The optimal truncation, defined as that giving maximum receiver output subject to these constraints, was computed. The results of the two calculations differ and the reasons for the discrepancy have not previously been resolved. Although the discrepancy is only about 10% in the estimated signal powers, the questions involved are rather fundamental to coherent lidar, and are relevant to future computations for more complex geometries.
Cloud Measurements by Coherent Lidar: Some Examples and Possibilities
Authors: Eberhard Wynn L.
Published: February 2023

Clouds are important to the weather and climate of the earth. The recent increase in concern about climate change has caused a resurgence of interest in cloud research. All lidars can observe bulk structure, e.g., cloud base height and fractional cover. Lidars can also reveal information about the microphysics of clouds. For instance, polarization ruby lidar (0.694μm wavelength) can discriminate whether clouds are composed of ice or water particles1. Each type of lidar can perform some measurements that other types cannot accomplish as well or at all. This paper describes some of the special attributes and measurement capabilities of coherent lidars, including examples from Wave Propagation Laboratory’s (WPL) CO2 system.
A Doppler Rayleigh Lidar for Measuring Winds in the Middle Atmosphere
Authors: Gamier A.
Published: February 2023

A better understanding of the interaction between the waves and the background wind in the altitude range 25 - 65 km, where there is still no possibility to monitor adequately the wind field, led to the development of a new Doppler lidar designed to cover this height range, and therefore it had to rely on Rayleigh scattering from air molecules. The possibility to measure mean winds in the middle atmosphere with this new Doppler lidar has been demonstrated. Its extension down to the tropopause is under study.
Compact Laser Doppler Anemometer
Authors: Werner Ch. , Biselli E. , Herrmann H. , Klier M. , Häring R.
Published: February 2023

A small homodyne-cw-CO2-laser Doppler anemometer was designed, constructed and tested. Wind profiles in the atmospheric boundary layer are a very important parameter also to study atmospheric exchange processes.
Autodyne Coherent Doppler Lidars
Authors: Gorelov E.P.
Published: February 2023

Autodyne coherent lidars, i.e., the lidars with intracavity reception of the echo-signals proved to be of efficient for studying the atmosphere1-3. They possess high sensitivity and high noise immunity. They make it possible to determine few parameters in question simultaneously, namely: the absorption along the path, the distance to the retroreflector and its velocity. The ways for determining the above parameters are described.
Coherent CO2 Laser Imagery
Authors: Martin Vincent
Published: February 2023

Summary No available.
Atmospheric Aerosol Speckle Decorrelation Time Measurements at 10.6 um Wavelength
Authors: Murty S. R. , Johnson S. , Bilbro J. W.
Published: February 2023

In this work we consider the intensity fluctuations caused by speckle effect due to backscatter from diffuse atmospheric aerosol target and its propagation through atmospheric turbulence. The normalized variance of intensity fluctuations due to speckle propagation in weak turbulence was considered by Holmes, Lee and Kerr (1) and they obtained a value of 1.3 for the normalized variance. Churnside and Yura (2) developed the theoretical formulation to analyze decorrelation time, and Murty (3) extended the analysis to include the effects of turbulence along the path. Experimental observations of decorrelation times of 2 to 2.5 usec were reported by Ancellet and Menzies (4) using pulsed CO2 lidar over 1.3 km horizontal range.
Overview of U.S. Air Force Coherent Lidar/Ladar Research Programs
Authors: Alejandro Steven B.
Published: February 2023

The Air Force’s Phillips and Wright Laboratories are engaged in developing and applying coherent lidar/ladar technology from ground and aircraft based platforms with a vision for possible future space based sensors. An overview of current programs in the areas of imaging, wind profiling, DIAL, laser technology, and modeling will be presented.
Wind Profiler for the Atmospheric Boundary L
Authors: Werner Christian , Banakh Victor , Köpp Friedrich , Smalikho Igor
Published: February 2023

The wind field and turbulence of the atmospheric boundary layer are important parameters for various application fields, like meteorology, atmospheric physics, environmental protection, wind-energy utilization, air-traffic control, and-so-on. Their high variability in spatial and temporal scales necessitates a fast remote-sensing method. From the available techniques the Doppler Lidar has proved to be the most promising candidate. Therefore, DLR has combined its well established Laser Doppler Anemometer (LDA) and its laser-based Ceilometer with a Sonic Anemometer. The laser systems are working in the eye-safe wavelength respectively energy region. These subsystems are forming the so-called DLR Windprofiler which is characterized by compact design and half-automatic operation.
Path Resolved Doppler Wind Measurement System Using a Coherent, CW, Pseudo-Random Code Modulated CO2 Lidar
Authors: Holmes J. Fred , Rask B. John
Published: February 2023

The conventional method for a range resolved lidar is to use a high peak power, pulsed laser source, and either direct or optical heterodyne detection of the radiation scattered from aerosols in the atmosphere. Time of flight is then used to make range resolved measurements. This technique works well and has been in use for quite some time. However, if a continuous wave (cw) laser source could be used, a lighter, smaller, more reliable system would result and the use of laser diodes becomes more feasible. With a cw source, in order to achieve range resolved measurements, some form of modulation must be used. Our approach is to use a pseudo random code (PRC) modulation of the optical phase of the cw laser source.1 The PRC modulation allows path resolved measurements through the use of a correlation-type receiver.
Coherent semiconductor laser radar: design and evaluation
Authors: Karlsson Christer , Letalick Dietmar , Renhom Ingmar
Published: February 2023

Hitherto, the major drawbacks with a semiconductor laser based CLR have been a low power output and a fairly short coherence length. However, with the progress in semiconductor laser development, both these quantities are rapidly increasing and this in turn have made a semiconductor laser based CLR feasible. A CLR of this kind can offer several advantages, some of which are: i) The laser radar can be made physically small which is important in many applications, ii) Along with the smallness follows robustness, i. e. a small system can be less sensitive to external impetus, iii) The cost for a diode-based CLR can be comparatively low. iv) It is possible to achieve eye-safety: the distributed feedback (DFB) laser used in this study operates at the eye-safe wavelength 1.55 μm. v) The laser can be frequency modulated. Therefore, the laser can be run continuously with a relatively low power output and this in turn means low observability, which in some applications is yet another advantage, vi) Compatibility with fibre technology which allows for e. g. distributed measurements.
Atomic line filter based non-coherent Doppler velocimeter using harmonic detection
Authors: Menders J. , Martin Peter , Spivey Brett
Published: February 2023

We demonstrated a new type of cw non-coherent laser Doppler velocimeter based on a variant of a Faraday magneto-optic atomic line filter with a time dependent transmission spectrum. From a detected optical signal of only 10 nW, we measured the velocity of a spinning disk with a resolution of 4 cm/sec, corresponding to a frequency resolution of about 100 kHz. Like harmonic detection, the sensitivity of our technique benefits from ac signal detection at intermediate frequencies, as opposed to the direct detection schemes used in most non-coherent laser Doppler velocimeters. The ac detection is implemented through the use of a dynamic atomic line filter as a Doppler analyzer. Features in the transmission spectrum of the Faraday filter are dithered in frequency by modulating the magnetic field of the filter. To measure the Doppler shift, signal light is passed through the filter, modulating the beam, which is then synchronously detected at the first and second harmonic of the dither frequency using lock-in amplifiers. In the detected waveform, the ratio of the first to the second harmonic of dither frequency are proportional to the Doppler shift. Compared to dc non-coherent Doppler velocimetry techniques, the harmonic detection technique offers significant advantages in noise rejection. At modulation frequencies of a few tens of kHz, the spectral amplitudes are substantially out the low frequency regime where 1/f noise dominates. In addition, lock-in amplifiers are ideally suited to implement harmonic detection, providing very narrow electronic bandpasses and high out-of-band rejection. The utilization of Faraday atomic line filters provide a practical approach to obtaining precise, absolute frequency registration between a diode laser probe and the Doppler analyzer, as well as a fortuitous means to obtain a frequency dithered filter. In this paper, we describe this technique and a proof of principle experiment using a cw diode laser tuned to the stop band of a cesium vapor based Faraday filter near 852 nm.
Aladin: Mission and Instrument Concept for a European Space-borne CO2-Laser Doppler Wind Lidar
Authors: Johann U.A. , Safa F. , Schwarzenberger P. M.
Published: February 2023

The main features of the proposed instrument are a fixed nadir-oriented telescope with an oversized primary mirror and an array of off-axis secondary mirrors, addressing shot azimuth positions on a 30° nadir-angle cone. Step scanning is performed by a small focal plane stepper, avoiding lag-angle and torque compensation problems encountered in scanning telescope concepts. Hence, the concept is insensitive to misalignment and employs a minimum of internal alignment control at full scanning capability.
ALADIN: an Atmospheric Laser Doppler Wind Lidar instrument for wind velocity measurements from space
Authors: Krawczyk R. , Ghibaudo JB. , Labandibar JY. , Willetts D. , Vaughan M. , Pearson G. , Harris M. , Flamant P. H. , Salamitou P. , Dabas A. , Charasse R. , Midavaine T. , Royer M. , Heimel H.
Published: February 2023

ALADIN (standing for Atmospheric Laser Doppler Instrument), as a spaceborne Doppler wind lidar instrument, is intended to respond to the pressing need for an accurate wind field description at global scale for both meteorology and numerical weather prediction and climate applications. Such an active instrument will fulfill the gap existing between the present capability of sophisticated numerical models and the drastic lack of information they do require. It will also bring a full-size demonstration of the potential of spaceborne wind lidar in world meteorological and climate monitoring.
Direct Measurements of Multiphonon Relaxation Rates in YAG, LuAG and YLF laser crystals Doped with Tm and Ho trivalent Ions used for Laser Lidar Systems
Authors: Basiev T.T. , Orlovskii Yu.V. , Sigachev V.B. , Doroshenko M.E. , Pukhov K.K. , Vorob’ev I.N. , Barnes N.P.
Published: February 2023

The 2μm Ho:Tm lasers are primary candidates for several remote sensing missions on NASA Mission to Planet Earth. Such lasers should find other remote sensing missions in terrestrial applications. Furthermore, these lasers have many other potential uses in the field of medicine, communications, and so forth. They can be efficient, even operating at room temperature, by utilizing laser diode pumping. However, the physics associated with their operation is very complicated due to the many manifolds involved and due to the many processes associated with each manifold. To understand the physics of these devices, and thence to optimize their performance, requires parameters describing the properties of these manifolds. One of the important parameters is the nonradiative transition rate. It was the intention of this work to experimentally measure these parameters. Subsequently, these new data were used to verify existing scaling laws which describe the nonradiative transition rate in terms of the properties of the laser material and the specific manifolds of rare- earth ions.
Estimations of turbulent energy dissipation rate from Doppler lidar data
Authors: Banakh Victor A. , Kerkis Natalia N. , Smalikho Igor N. , Köpp Friedrich , Werner Christian
Published: February 2023

Along with measurements of mean wind fields, Doppler lidars are used for estimation of the turbulence parameters.1-4 In particularly, the attempts to use the Doppler lidars for measurement of the dissipation rate of the turbulent kinetic energy ε
T
and the wind field structure constant from estimations of mean spectrum width of Doppler signal are discussed in Refs.2-4. This approach is true for small sizes of lidar sensing volume. If longitudinal size of sensing volume Δz is comparable or exceeds the outer scale of turbulence L
V
this method can not be used. We discuss the feasibility of estimations of dissipation rate from Doppler lidar data at arbitrary size of lidar probe volume.
Tunable Eyesafe Coherent Laser Radar at 1.54-Microns
Authors: Grayson T.P. , Schepler K.L. , Myers L.E. , Nelson M.D. , Duncan B.D. , Dominic V.
Published: February 2023

The incorporation of an OPO as the light source for a laser radar system permits the attainment of strategic wavelengths difficult to reach with existing lasers and enables tunability. Unfortunately, OPO’s are notoriously unstable, emitting multimode radiation over very broad bandwidths, making them impractical as a light source for a coherent system. One way to eliminate this problem is to inject a small amount of light from a single longitudinal mode laser into the OPO cavity. If the cavity is resonant with the injected signal, that single mode dominates over all other modes, forcing the OPO to oscillate on that single wavelength. This is the process known as seeding, and has previously been demonstrated in OPO’s.1
Design and comparative performances of two kinds of transversely excited CO2 lasers
Authors: Fengmei Lui , Lingzhi Li , Chi Zhou , Jingshan Zhao , Yuanqin Xia , Deming Ren , Xinzhi Sheng
Published: February 2023

There is considerable interest in high repetition- rate miniature transversely excited(TE) CO2 lasers for their increasing applications in laser radar, ranging, remote-sensing and other industrial fields. Many of these applications require that the lasers work in a high-repetition-rate state reliably and efficiently, and have long sealed-off lifetime. In the past two decades, intensive efforts were made to improve performances of TEA CO2 lasers.[1]-[3] Here we report the design and performance of two kinds of TE CO2 lasers, one of which was bare spark preionized (BSP) and another surface corona preionized (SCP). It is found that the intrinsic efficiency of the later is four times higher than that of the former under the same condition, and the lifetime of the SCP laser is also longer because some dissociation processes of gas involved in the spark preionization were avoided. A BN ceramic structure was employed as the assembly of resonators to improve the stability, which is similiar to that used in the waveguide CO2 lasers suggested by some of the authors of this paper.[4]
Effects of Special Relativity on the Return Radiation in Space-Based Lidar Experiments
Authors: Rao Gudimetla V. S.
Published: February 2023

Space-based lidar systems are being designed1–3 to measure accurately atmospheric wind profiles. Space-based lidar systems use an orbiting spacecraft with a pulsed laser source and measure the Doppler shift between the transmitted and received frequencies to estimate the atmospheric wind velocities. If a significant return from the ground (sea) is possible, the spacecraft speed and height are estimated from it and these results and the Doppler shift are then used to estimate the wind velocities in the atmosphere. It is expected that at the proposed wavelengths, there will be enough backscatter from the aerosols4 but there may not be significant return from the ground. So a coherent (heterodyne) detection system is being proposed for signal processing because it can make best use of low ground returns. However for a heterodyne detection scheme to provide best results, it is important that the receiving aperture must be aligned properly and for the proposed wind sounder, this amounts to only a few microradians tolerance in alignment. It is suspected5 that the satellite motion relative to the ground may introduce errors in the order of a few microradians in the spherical coordinate angles of the direction of returning radiation because of special relativity. We are interested in addressing this issue and developing analytical expressions for the location and direction for the return radiation, Doppler shift in frequency and the amount of tip for the receiver aperture. Also we are interested in the diffuse scattering direction at the ground, which does not require any tipping of the receiver aperture. All the three cases of retro-reflection, specular reflection and diffuse scattering by the ground should be treated though retro-reflection and diffuse scattering are more important.
On the Deconvolution of Doppler-Lidar Power Profiles with Zero Spectral Components of the Laser Pulses
Authors: Gurdev L.L. , Dreischuh T.N. , Stoyanov D.V.
Published: February 2023

A general form of the lidar equation is given by the convolution where
F(t) is the lidar return signal at
the moment t after the pulse emission,
Φ(z′) is the maximum resolved
(δ-pulse) lidar profile,
S(ϑ) is the pulse power shape
normalized to its peak value, c is the speed of
light. The TE (TEA)
CO2 long pulse lasers used in the coherent
Doppler lidars ensure a satisfactory accuracy in the measurement of
Doppler velocities. At the same time the range resolution is too low
(~ 200-500 m) and an important information about the fine structure of
the lidar power profile is lost. A software way to improve the lidar
resolution is to invert Eq.(1) with respect to
Φ(z′).
Evaluation of Coherent Doppler Lidar Velocity Estimators
Authors: Lottman Brian , Frehlich Rod
Published: February 2023

Coherent Doppler lidar velocity estimators are evaluated using computer simulation to determine the optimal numerical and algorithm parameters that minimize estimation error. The Maximum Likelihood ML and Minimum Variance MV (Capon) algorithms are evaluated using simulated Coherent Doppler lidar data for the typical parameter regime of current 2μm lidar systems used for boundary layer measurements.
An Algorithm for CW Doppler Lidar Wake Vortex Remote Sensing
Authors: Salamitou Philippe , Hansman R. John
Published: February 2023

We propose a new type of algorithm to process aircraft wake vortex data for continuous wave Doppler lidar. This new algorithm is based on geometrical properties that characterized vortex radial windfields.
2 μm Coherent Lidar at CRL/TIT
Authors: Asai Kazuhiro , Oyama Makoto , Ogawa Sigeto , Sato Atushi , Itabe Toshikazu
Published: February 2023

Recent coherent Doppler lidar technologies for measurements of wind vector have been dedicated toward developments of all solid-state system beyond a wavelength of 1.4 μm. The main reasons are the following; eye- safety, reliabilities, long lifetime, high overall electrical efficiencies, good thermal management, etc. Among them, Tm (Thulium) and Ho (Holumium) doped solid-state lasers operating near 2 μm have been and continue to be favored for many of the remote sensing applications.
A New Lidar Calibration Technique Using Aerosols
Authors: Jarzembski Maurice A. , Chambers Diana M. , Srivastava Vandana
Published: February 2023

Atmospheric aerosol backscatter measurements using lidar systems are generally referenced to radiometric calibrations against standard scattering targets with known reflectance. Uncertainty in backscatter measurements is due in part to uncertainty in the calibration measurements and target reflectance. For retrieval of good quality backscatter measurements, it is extremely important to minimize errors/biases that may be present in lidar calibration.
Validation of Radial Velocity Measurements from the NCAR Doppler Lidar
Authors: Mayor S. D. , Schwiesow R. L. , Lenschow D. H. , Frush C. L.
Published: February 2023

The NCAR Doppler lidar, a compact heterodyne CO2 system designed for airborne deployment, underwent extensive ground-based testing in 1994. The lidar uses an injection-seeded TEA laser to transmit 100-200 mJ pulses at 10.6 μm wavelength, usually at a pulse repetition frequency of 10 or 20 s-1. The optically heterodyned signal (5 to 15 MHz) is mixed with a reference oscillator at approximately 10 MHz to produce in-phase and quadrature components of 0 to 5 MHz each in order to use two 107 samples s-1 digitizers. Velocity is calculated using single-lag complex autocovariance processing of the Doppler-shifted backscatter signal from 500 m to 10 km in range every 15 m, with approximately 100 m range resolution for scattering structure. Spatially independent velocity samples are separated by approximately 200 m due to the laser pulse length. Radial velocity precision is ±0.4 m s-1 from 20 laser pulses and the velocity measurement range is ±26 m s-1.
Using a Novel Wideband Doppler Detection Technique in CO2-Lidars with Low Frequency Laser Stability
Authors: Stoyanov D.V. , Marinov V.S. , Bratanov B.M. , Naboko V.N. , Stoykova E.V.
Published: February 2023

Ground-based CO2 Doppler lidars, operating at low frequency laser stability may be created using wideband detection technique as in airborne systems [1,2]. Such approach is one of the effective ways to develop low cost coherent lidars for atmospheric remote technologies. A novel wideband Doppler detection method was developed and tested by us in [3, 4]. Here we describe our ground-based CO2 coherent lidar system for wind and backscattering measurements, based on this new method.
Diode-Pumped Tm:YAG Laser Radar Transceiver
Authors: Kane Thomas J. , Kmetec Jeffrey D.
Published: February 2023

We have built two all-diode-pumped Tm:YAG laser radar transceivers. Figure 1 is a block schematic of the systems.
Frequency Agile Diode Laser-Pumped Tm,Ho:YLiF4 Local Oscillator with 3.6 GHz Tuning Range
Authors: McGuckin B.T. , Menzies R.T. , Esproles C.
Published: February 2023

Eyesafe solid-state laser technology based on the holmium 5I7-5I8 transition is being vigorously developed by NASA in a focussed program directed towards their ultimate use in atmospheric and planetary remote sensing from orbital platforms. Specifically thulium and holmium sensitized yttrium lithium fluoride (Tm,Ho:YLiF4) lasers have benefitted from much recent effort in which improvements in efficiency, Q-switched operation and single frequency oscillation have been demonstrated(1,2,3).
A 2-Micron Power Oscillator for High Pulse Energy Doppler Lidar Transmitter
Authors: Jani Mahendra G. , Barnes Norman P. , Murray Keith E.
Published: February 2023

Two micrometer solid state lasers(1-5) have received considerable attention for detection of wind velocities as well as for remote sensing of carbon dioxide and water vapor in the atmosphere. High-power Q-switched holmium lasers are also useful for generating tunable mid-infrared radiation for optical remote sensing and/or infrared counter measure systems.
Airborne Scanning Pulsed Coherent Doppler Laser Radar for Atmospheric Measurement and Satellite Doppler Lidar Simulation
Authors: Rothermel Jeffry , Hardesty Robert M. , Menzies Robert T.
Published: February 2023

The Multi-center Airborne Coherent Atmospheric Wind Sensor (MACAWS) is an airborne scanning pulsed coherent Doppler lidar jointly developed by the lidar remote sensing groups of NASA Marshall Space Flight Center (MSFC), NOAA Environmental Technology Laboratory (ETL), and Jet Propulsion Laboratory (JPL). MACAWS will be flown initially in summer 1995 on the NASA DC-8 research aircraft. The concept of two-dimensional wind field measurements with airborne scanning Doppler lidar was demonstrated in 1981 (Bilbro et al. 1984). Substantial improvements to scanner control and pointing accuracy were later made and a modified system reflown in 1984 (Bilbro et al. 1986). Subsequent developments in lidar technology have led to significant improvements in lidar remote sensing capabilities. Several of these advancements have been implemented in MACAWS. The resulting measurement capability is envisioned to benefit study of a broad range of issues in atmospheric dynamics, climate, and hydrology, including the role of sub grid scale processes in large-scale atmospheric general circulation models (AGCMs), e.g. WMO (1992), improvement in mesoscale modeling and predictive capabilities, and more realistic simulation of global tropospheric wind measurement with prospective satellite Doppler wind lidar.
Eye Safe Solid State Ladar For Airborne Wind Pofiling
Authors: Richmond R. D. , Woodworth P. D. , Fetner R. , Overbeck J. A. , Salisbury M. , Henderson S. W. , Hannon S. M. , Vetorino S. R.
Published: February 2023

Every airborne operation is affected by the winds. This is particularly true for operations where objects are released from an aircraft to fall to the ground without controls (e.g. cargo parachute deliveries and unguided bomb releases). Aircraft crews have used a variety of techniques (e.g. winds from closest weather station, balloon launch winds, winds at altitude, etc.) in an attempt to determine the intervening winds during such missions so that release points could be adjusted to compensate for these winds. These efforts have had limited success. A desired alternative to these approaches would be to have a sensor on board the aircraft that could directly measure the wind fields in real-time. This project, which is the subject of this paper, is designed to demonstrate exactly that type of airborne sensor using an eye-safe laser radar. We defined this system as an “interim operational capability” (IOC), because the system was not designed nor engineered for this particular application. Rather, we assembled a system using available sub-systems that could be installed on a particular type of aircraft in a short timeframe and thereby provide a wind measuring capability for airdrop missions should the need arise.
Aerosol Sulfate Chemistry Determination from Backscatter Measurements Using Continuous-Wave 9.1 and 10.6 μm Lidars
Authors: Srivastava Vandana , Rothermel Jeffry , Bowdle David A. , Jarzembski Maurice A. , Chambers Diana M. , Clarke Antony D.
Published: February 2023

Aerosols exhibit wide range of size distributions and compositions which affect their scattering properties. Measurement of a scattering parameter, in this case lidar backscatter, can provide information about the aerosol properties. Atmospheric sulfate aerosols, in particular, are of extreme importance to climate and environment (Charlson et al, 1990). Their impact, however, has only been approximately parameterized, emphasizing a need to determine aerosol properties more accurately.
The GLObal Backscatter Experiment (GLOBE): Overview, Results, and Applications
Authors: Bowdle David A. , Srivastava Vandana , Cutten Dean R. , McCaul Eugene W. , Rothermel Jeffry , Jarzembski Maurice A.
Published: February 2023

GLOBE was initiated in 1986 as a cooperative interagency and international research program to develop a model of the spatial, temporal, and spectral variability of atmospheric aerosol backscatter (Bowdle et al., 1995a,b). This research was needed to provide realistic inputs for development studies on NASA’s prospective satellite Doppler lidar (SDL) wind sensor (Baker et al., 1995). SDL concept selection and design optimization studies need threshold backscatter values or typical backscatter profiles for selected global-scale atmospheric targets that are required to meet baseline SDL science objectives. Global SDL Observing System Simulation Experiments (OSSE’s) require detailed backscatter information in a conveniently accessible, computationally friendly, three-dimensional gridded format (Baker et al., 1995). In addition, SDL science planning studies frequently require information on backscatter magnitude and structure for a wide variety of mesoscale to regional scale meteorological features.
Distinguishing Ice and Water Clouds using Dual-Wavelength CO2 Lidar: Theory
Authors: Eberhard Wynn L.
Published: February 2023

Determining whether a cloud is in water or ice phase is important in studies of radiative transfer, microphysics, and formation/dissipation mechanisms.
Airborne lidar wind detection at 2 µm*
Authors: Targ R. , Hawley J. G. , Steakley B. C. , Ames L. L. , Robinson P.
Published: February 2023

Wind shear, the sudden and violent change of wind direction near the ground has been a contributing factor in at least 28 aviation accidents and incidents involving commercial aircraft since 1964, including more than 600 fatalities. The hazard due to wind shear on a flying aircraft is characterized by the F-factor hazard index.1 As part of the NASA/FAA Integrated Wind Shear Program, and NASA'S Terminal Area Productivity Program Lockheed designed and built in cooperation with NASA Langley Research Center (along with subcontractors United Technology Optical Systems, Coherent Technologies, Inc., and Lassen Research) two Coherent Lidar Airborne Shear Sensors. These systems have the capability to look ahead of an aircraft 2 to 4 km in clear weather and measure the line-of-sight wind velocity with an accuracy of 1 m/s.
Recent 2 µm Doppler Lidar Measurement Results
Authors: Hannon Stephen M. , Henderson Sammy W. , Thomson J. Alex
Published: February 2023

In 1992, Coherent Technologies, Inc. (CTI) developed a mobile coherent laser radar (Doppler lidar) testbed for the U.S. Air Force Wright Laboratory. Since that time, the mobile unit has been deployed on a number of remote measurement programs in the U.S. and abroad. The Doppler lidar is a flashlamp-pumped system operating at the eyesafe wavelength of 2.09 µm and has been described in detail elsewhere [1]. The system transmits 28 mJ, 175 nsec full width at half maximum (FWHM) pulses at a pulse repetition frequency (PRF) of ~5 Hz with a transmit/receive aperture size of 10 cm. Measurement applications to date include wake vortex detection and tracking for both civilian and military aircraft [2], windshear and turbulence quantification in and around airport terminals [3], volume backscatter coefficient profiling [4], wind profiling for improved ballistic and parachute drop accuracy, and hard target imaging and reflectivity characterization. This manuscript briefly summarizes sample results from a recent deployment at the site of the new Hong Kong airport. The Doppler lidar was used to characterize terrain-induced windshear and turbulence (TIWT) in the vicinity of the airport.
Return power estimation for targets spread in range
Authors: Rye Barry J.
Published: February 2023

Return power is perhaps the most fundamental measurement available to radar after round-trip time delay. For coherent lidars using aerosol targets that are spread in range, there are two approaches. In the more straightforward, an estimate is formed by squaring the heterodyne output of the photodetector and subtracting the mean noise level.1,2,3 This method is often analyzed in the context of heterodyne detection of static hard targets where no account need be taken of Doppler shift in the return. The alternative is, in effect, to reduce noise by filtering the return and using only data within the filter passband for power estimation. Estimation of the frequency shift is then in principle the first step, but it can be combined with estimation of return power by, e.g., forming maximum likelihood (ML) estimates of both parameters simultaneously. For Doppler radar, Zrnic4 analyzed this approach as applied to monochromatic returns and appropriately commented that the need for a filter to optimize the power estimate is 'intuitively satisfying'. The goal of this note is to compare the two approaches.
Coherent Doppler Lidar Performance in the Weak Signal Regime
Authors: Frehlich Rod , Hannon Stephen M. , Henderson Sammy W.
Published: February 2023

Coherent Doppler lidar has become a mature method of remote measurements of wind fields[l, 2, 3]. The development of the eyesafe 2µm coherent Doppler lidar has permitted regular observations of boundary layer winds. Coherent Doppler lidar permits measurements of the radial component of the velocity v as a function of range for every transmitted pulse. As the target range increases, the signal level decreases until the quality of the estimates degrade due to many random outliers. The quality of the velocity estimates can be improved by accumulating the signal from many consecutive pulses[4, 5, 6] provided the wind field is not changing over the accumulation time. Rye and Hardesty investigated the effects of pulse accumulation by comparing the standard deviation of the velocity estimates to Levin’s approximation to the Cramer Rao Bound (CRB), the theoretical best performance. It has been shown that Levin’s approximation to the exact CRB is a good approximation[7]. For very weak signals, the pulse accumulation is insufficient and the standard deviation is dominated by the random outliers. As the number of accumulated pulses increases, the random outliers decrease and the standard deviation approaches the CRB. Rye and Hardesty defined n
CR
as the number of accumulated pulses that were required to first approach the CRB. An approximate expression for n
CR
was produced, i.e., n
CR
M = 64/SNR3/4 where M is the number of complex data points per estimate and SNR is the wide band Signal to Noise Ratio for one shot.
Nanofabrication on Silicon Surfaces by STM
Authors: Shen T.-C.
Published: February 2023

The three basic ingredients of our nanofabrication scheme on silicon surfaces are: (a) utilizing silicon hydride as the initial resist, (b) employing a scanning tunneling microscope (STM) as the e-beam source to desorb H-atoms of the resist to create patterns in an ultrahigh vacuum (UHV) environment, and (c) using either the original H-resist or an oxide-mask generated from (a) and (b) for further pattern transfer. Each of these ideas has been investigated independently by different research groups for different purposes. A brief summary seems appropriate to show how basic research may lead to the development of new technology and vice versa.