While heterodyne laser techniques offer remarkable sensitivity in principle, experimental results are usually seriously compromised by environmental vibration. Accordingly, much attention has been invested on reducing the vibration amplitude experienced by the stable cavity being used for laser frequency control. We have recently shown it is valuable to reduce the intrinsic vibration sensitivity of the cavity itself, which is easily achieved using symmetry suitably in the cavity mounting. At present, sub-Hz optical linewidths are easily demonstrated in an ordinary laboratory, with the present limitation ~0.3 Hz being fixed by thermal noise of the mirror’s coated surface. Frequency drift rates can be <20 milliHz/s.

This paper will review the history and progress and the challenge of global remote sensing of wind with an emphasis on solid state laser transmitter development. We reconsider the long-standing notion that transmitter wavelengths greater than 1.4 microns are necessary for eye-safe operation. We present a design for a satellite based lidar system that meets the NASA specifications for eyesafe global wind sensing and operates using the well developed 1 micron laser technology.

The NOAA Earth System Research Laboratory has two coherent Doppler lidar systems that have been deployed onboard research vessels during several experiments. Those instruments measure the wind velocity relative to the motion of the lidar. The correction for the motion of the platform is is derived and implemented. The analysis is general enough to be applied to Doppler velocity measurements from all monostatic ship- and aircraft-borne lidars and radars, and generalization to bistatic systems is doable. The correction is demonstrated using mini-MOPA Doppler velocity data obtained during the Rain In Cumulus over the Ocean (RICO) experiment.

In the last two years several ground based and airborne wake vortex campaigns have been performed with the DLR coherent Doppler Lidar. The objective of those campaigns was the measurement and description of the wakes generated by the new Airbus A380 aircraft for the ICAO landing separation as well as the influence of different configurations on the vortex life time in the project AWIATOR.

A new 1.5 µm pulsed Lidar using an all fiber laser source has been developed by ONERA in cooperation with Leosphere , for wake vortex and wind field measurements . This paper illustrates the good results obtained with a pulsed lidar based on MOPFA 1.5µm laser, for detection and monitoring of wake vortices on airport fields. Operational ranges larger than 400m have been demonstrated, with a 60µJ, 15kHz, 250ns pulse fiber doped Er laser. Wake profiles, positions and circulations can be derived from recorded data.

Long range all-fiber Coherent Doppler LIDAR (CDL) system has been developed for wind sensing. A newly developed Er3+/Yb3+ fiber MOPA (Master Oscillator Power Amplification) source has enabled transmitting optical pulse to be performed its pulse energy of several tenth micro joule, which was previously limited up to several micro joule because of Stimulated Brillouin Scattering (SBS) in an optical fiber. The new all-fiber CDL has successfully measured maximum range for wind velocities up to 8km which is about 5 times as long as the measurable distance of a few kilometer in a conventional all-fiber CDL.

The “EZ WIND LIDAR”TM is a coherent wind lidar developed by LEOSPHERE taking into account the ONERA’s advance in heterodyne lidar and fiber laser technology. This eye safe non visible and soundless, robust, easily portable, low consumption system is dedicated to horizontal and vertical wind speed and direction profiles measurements at altitudes from 45 to 200m. We describe in this paper the main characteristics of the system, the post processing we have developed, and the first results of an independent validation campaign at the RISOE test bed in Denmark in spring 2007.

This paper discusses the application of 4DVAR technique to analyze the terrain-disrupted airflow at the Hong Kong International Airport based on LIDAR data. The conical scans of the LIDAR are employed in the study. The analyzed wind field is found to reveal many salient features of the terrain-induced disturbances, such as mountain wave and jump-like feature in the gap flow in stable boundary layer. It could be useful in the day-to-day monitoring of the airflow at the airport area.

The Hong Kong Observatory develops the automatic LIDAR-based Windshear Alerting System (LIWAS) for the Hong Kong International Airport. This paper discusses a refinement of the method to better capture windshear in rapidly fluctutaing wind condition, such as terrain-disrupted airflow. The method is found to outperform the original LIWAS algorithm by 10-30% in terms of the hit rate of windshear, with a modest increase of alert duration.

Coherent Doppler lidar derived profiles of wind and turbulence are presented for various scanning and processing techniques and compared with high resolution in situ measurements of small scale turbulence. Simultaneous estimates of the energy dissipation rate, velocity variance, and outer scale of turbulence are produced for the two orthogonal horizontal velocity components (longitudinal and transverse). The impact of filtering the radial velocity data to remove the large scale atmospheric processes from the small scale turbulence is presented. Critical lidar engineering design and scanning issues are identified for the challenging conditions of low turbulence.

NICT is conducting research of coherent Doppler lidars for 'Sensing Network Project' and space based wind profiling. 2micron Q-switched output of 100mJ at 20Hz has been achieved in a Tm,Ho:YLF laser oscillator for ground based wind profiling and CO2 measurement. The experiments show that very good thermal conduction is held between rod and heat sink. Another type of Tm,Ho:YLF laser oscillator with 50-100mJ output at 20-30Hz will be developed for coherent Doppler lidars. The coherent Doppler lidars with moderate output laser will be used in the Sensing Network Project, where wind inforrmation obtained with a group of instruments over the area around Tokyo should be collected through network.

An atmospheric dispersion study was conducted in Oklahoma City, Oklahoma, in July 2003 during the Joint Urban study. On the night of July 4th, the ASU and ARL lidars performed a set of complementary scans in region east of the CBD (Central Business District) to capture the aerial movement and dispersion of smoke puffs from the fireworks display. The ASU lidar was located at the south-east side of the CBD and ARL lidar was located towards the north-east. The purpose of this study was to use the data collected from those scans to capture the puff’s movement, shape, and size development as it advects in the atmosphere. We present a methodology for measuring dispersion parameters based on lidar images, which can be used effectively to monitor the time variations of the puff and to deduce its dispersion parameters downstream. The lidars used by ASU and ARL for performing the corresponding scans and collecting the required data were Coherent Doppler lidar.

The High-Resolution Doppler Lidar has been highly effective in the study of dynamic processes in the atmospheric boundary layer (ABL) because of its temporal and spatial resolution. Recently applications involving wind energy have become important, because accelerated flows occurring at night in the form of low-level jets (LLJs) have proven to be an important resource over the U.S. Great Plains. In this paper we will describe the role of the nocturnal LLJ in generating turbulence and turbulent fluxes, and we show the advantages of lidar data for wind–energy applications

We report on work to develop a pulsed coherent Doppler lidar operating at 1.6 microns using a novel ‘laser pumping a laser’ architecture. This system provides higher average power, roughly half the pulse duration, a higher and adaptable PRF, and significantly smaller size, weight and power consumption as compared with the existing 2 micron WindTracer® system. Additional related developments have enhanced the signal processor and super-hemispherical scanner, plus overall reliability, supportability, and performance have been enhanced. Key features are described and sample performance results are provided.

NASA Langley Research Center has been developing and using coherent lidar systems for many years. The current projects at LaRC are the Global Wind Observing Sounder (GWOS) mission preparation, the Laser Risk Reduction Program (LRRP), the Instrument Incubator Program (IIP) rugged wind lidar project, the Autonomous Landing and Hazard Avoidance Technology (ALHAT) project for lunar landing, and the Skywalker project to find and use thermals to extend UAV flight time. These five projects encompass coherent lidar technology development, characterization/validation/calibration facilities, computer simulation, compact/rugged packaging, trade studies, data acquisition/processing/display, system demonstration, and mission design. This paper will further discuss these activities at LaRC.

First flight test results of the AWIATOR airborne direct detection UV LIDAR for turbulence sensing are presented. The sensor was installed in an Airbus A340 aircraft in a fairing below the aircraft nose and measured in four directions ahead at >= 50m distance in order to determine the 3D wind vector. Good Rayleigh signals could be gathered even in flight altitudes up to 39.00 ft in clear, aerosol depleted air. Line-of-sight standard variations of the measured speed was around 1.6 m/s at that maximum altitude. First results show good follow-up of the LIDAR data to the aircraft onboard TAS sensor.

The Atmospheric Dynamics Mission (ADM-Aeolus) is the second core mission within ESA's Earth Explorer Programme. Planned for launch in 2009 Aeolus will deliver global wind observations throughout a planned lifetime of 3 years, serving both numerical weather prediction and various scientific applications.

Aeolus' payload ALADIN is a direct detection Doppler Lidar operating in the ultraviolet. Equipped with a dual-channel receiver system it will allow independent detection of the aerosol and molecular components of the atmospheric backscatter signal, covering a height range from 0-25 km. An outline will be given on the spacecraft and payload design and on the ground segment concept.

Spaceborne lidars have been the subject of extensive investigations by the European Space Agency since the mid 1970’s, resulting in mission and instrument concepts, such as ATLID, the ATmospheric backscatter LIDar payload of the EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer) mission, ALADIN, the Doppler Wind Lidar of the ADM-Aeolus mission (Atmospheric Dynamics Mission), a water vapour Differential Absorption Lidar considered for the WALES mission (Water Vapour Lidar Experiment in Space) and more recently a CO2 Total Column Differential Absorption Lidar considered for the A-SCOPE mission (Advanced Space Carbon and Climate Observation of Planet Earth). These studies have shown the basic scientific and technical feasibility of spaceborne lidars, but they have also demonstrated their instrumental complexity.

As a result, the Agency undertook technology developments in order to strengthen the instrument maturity. The purpose of this paper is to present the technology and instrument developments that are currently running at the ESA in support to EarthCARE, the 6th selected Earth Explorer mission, and to A-SCOPE, a candidate mission for the 7th Earth Explorer mission. The pre-development activities span over a broad range addressing all the critical stages from the transmitter to the receiver and covering both components development and characterisation and sub-systems development

The direct-detection wind lidar mission ADM-Aeolus of the European Space Agency implements two detection channels, one for molecules and one for particles. The molecular channel is based on dual Fabry-Perot. The inversion of the response must be corrected from pressure and temperature effects. The Mie channel is based on a fringe imaging technique using a Fizeau interferometer. The fringe is sampled by a 16-element CCD. The processing of the 16 photocounts aims at estimating the central frequency of the fringe. The algorithm is presented and compared to techniques currently used for heterordyne lidars.

The Atmospheric Dynamic Mission ADM-Aeolus has the objective to measure wind profiles from space using a Lidar operating in the UV. Based on a dual-channel design that allow the detection of molecular and particulate signal, ADM-Aeolus is a High Sprectral Resolution Lidar. It enables the retrieval of cloud and aerosol layers optical properties as spin-off products. This paper presents the basic concept of the L2A processor , responsible for this task. Some solutions are proposed to answer to identified problems due to accumulation of signals in range bins. Some preliminary numerical testing has been conducted and first results are presented.

The idea of deploying a lidar on an Earth-orbiting satellite stems from the need for continuously providing profiles of atmospheric structure with high accuracy, resolution and global coverage independently of the lighting conditions. Interest in this information for climatology, meteorology and the atmospheric sciences in general is huge. Areas of application range from the determination of global warming and greenhouse effects, to monitoring the transport and accumulation of pollutants in different atmospheric regions, to the assessment of the largely unknown microphysical properties and the structural dynamics of the atmosphere itself.

Spaceborne lidar systems have been the subject of extensive investigations by the European Space Agency since the mid 1970’s, resulting in two Earth Explorer missions approved for flight: ADM-Aeolus (Atmospheric Dynamics Mission) and EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer); one mission studied up to Phase A: WALES (Water Vapour Lidar Experiment in Space) and one mission recently selected as a candidate for the 7th Earth Explorer mission: A-SCOPE (Advanced Space Carbon and Climate Observation of Planet Earth). The purpose of this paper is to present both approved and currently studied missions and their related instruments concept, all relying on different use of lidar.

The Optical Autocovariance Wind Lidar (OAWL) direct detection interferometric technique promises to provide the aerosol sensitivity of a coherent system while also measuring winds from molecular backscatter. The OAWL method has the advantages of being insensitive to aerosol to molecular backscatter mixing ratio, requiring no absolute wavelength control, no receiver to transmitter relative frequency control, no injection seeding control loops, and no tuning for spacecraft velocity compensation. OAWL has recently been demonstrated at Ball. This paper discusses the theory, proof of concept test results, and anticipated performance from LEO.

Lidars in space such as LITE, GLAS and more recently CALIPSO provide laser beam scale statistics on cloud penetration and contiguous cloud free scenes. For those lidars (e.g. coherent DWL) probing the lower troposphere through partly cloudy areas, understanding cloud porosity is critical to the design of the sampling pattern. For lidars whose accuracy scales directly to the number of photons detected and whose signal may be compromised by a small cloud in the integration window (e.g. integration on a chip), knowing the probability of cloud free intervals is important in performing system trades.

This paper will summarize a study completed for NASA/ESTO using GLAS data and will also reflect back on an earlier study of the LITE data.

The design of an orbiting wind profiling lidar requires selection of dozens of lidar, measurement scenario, and mission geometry parameters. Typical mission designs do not include a thorough trade optimization of all of these parameters. We report here the integration of recently published parameterization of coherent lidar wind velocity estimation with an orbiting coherent wind lidar computer simulation; and the use of these combined tools to perform some preliminary parameter trades. We use the 2006 NASA Global Wind Observing Sounder (GWOS) mission design as the departure point for the trades.

The CALIPSO satellite is providing our first continuous observations of the global three-dimensional distribution of aerosols and clouds. CALIPSO was launched in April 2006 and has been acquiring lidar observations since June 2006. The primary instrument on the CALIPSO satellite is CALIOP, a two-wavelength polarization lidar designed for aerosol and cloud profiling. CALIOP has sensitivity sufficient to detect clouds with optical depth less than 0.01 and aerosol with scattering coefficients less than 1E-3 /km/sr. Ultimate performance limits are still being assessed. This talk will discuss aspects of CALIPSO and aerosol and cloud observations relevant to future Doppler wind lidar missions

A unique, multi-frequency, single-beam, laser absorption spectroscopy instrument has been developed for space-based measurements of carbon dioxide (CO2) in the troposphere. The system utilizes low-power narrow-band modulated-continuous wave all fiber transmitter, with a high gain no excess noise APD detector and narrow-band demodulation system to achieve high signal-to-noise ratios for precision differential CO2 column optical depth measurements. A prototype instrument and high-fidelity, physics-based performance model has been constructed and validated through several years of ground, field and airborne testing. The performance and advantages of this approach will be discussed relative to other systems under consideration for space-based measurements of CO2.

The Global Carbon Cycle has been significantly perturbed by human activities in the last two centuries. The current network is insufficient either to understand the fundamental phenomena or to predict the future rate of increase of atmospheric CO2 density and its impact on climate.

In this context, a 2 µm Heterodyne Differential Absorption Lidar (HDIAL) has been developed and operated at IPSL/LMD to monitor CO2 mixing ratio in the atmospheric boundary layer. In the present paper, we address the comparison of the CO2 HDIAL measurements with in-situ sensors positioned along the path of the laser beam: 1) a 2.064-µm Heterodyne Differential Absorption Lidar 2) a field deployable Laser Diode Spectrometer (LDS) using new commercial diode laser technology at 2.68 µm 3) LICOR NDIR gas analyzer 4) flasks. We present the overall experimental set up i.e. DIAL and in situ measurements conducted at the same location. Moreover, using several sensors of CO2 at different sites, the campaign enables to quantify a gradient of CO2 in a near urban area and to understand the impact of advection on the CO2 variability in the ABL.

The National Institute of Information and Communications Technology (NICT) started a new 5-year program to develop a coherent differential absorption lidar for atmospheric CO2 measurement in April, 2006. Effects of atmospheric temperature and laser wavelength uncertainties were investigated and candidate wavelengths were selected. A high-energy pulsed single-frequency Tm:Ho:YLF laser was developed and the laser operates at a pulse repetition frequency of 10 Hz and emits an output energy of 100 mJ with pulse width of 120 ns (FWHM). The receiver is based on a 10-cm-diameter off-axis telescope, 2-&#956;m waveguide coupler with a 50/50 split ratio, and balanced InGaAs photodiodes. We present the coherent differential absorption lidar developing at the NICT.

A new concept of DIAL (DIfferential Absorption Lidar) system for global CO2 monitoring is introduced. In this system, ON/OFF wavelength laser lights are intensity modulated with CW modulation signal, and received lights of two wavelengths from the ground are discriminated by modulation frequencies in electrical signal domain. Fiber-based optical circuit using wavelength region of 1.6 micron is suitable for the system configuration. After the explanation of this configuration, feasibility study of this system, including the error budget analysis in measurements, is introduced on the application to global CO2 monitoring.

The method of buried landmine detection using low-frequency elastic waves in the ground and a laser Doppler vibrometer (LDV) as a vibration sensor has shown excellent performance in field tests. To reduce the time of detection, LDVs with multiple probe beams and parallel signal processing have been developed. A multi-beam LDV with linear array beam configuration can create a vibrational image of the ground surface in a stop-and-stare or a continuously scanning mode. A multi-beam LDV with probe beams configured into 2D-array is capable of creating a vibrational image of the ground surface with a single shot

This paper will review some recent laser sensing activities at FOI. Due to shift of interest from our customer the coherent laser radar activities have been limited so the main part of the paper will be devoted to direct detection laser radars. Hopefully this overview will have some relevance for the CLR community. The presented activities include 3 D imaging, terrain mapping, land mine detection, aerosol lidar, bio detection, remote listening, high resolution range profiling and laser development. We also have some limited activities in retro communication, adaptive optics and beam steering. A recent review gives examples of laser sensing at FOI and elsewhere of relevance for defense and security applications

The Super-resolution Sensor System (S3) program at Lockheed Martin Coherent Technologies (LMCT) is an ambitious effort to exploit the maximum information a laser-based sensor can obtain. We are exploring methods of incorporating multi-function operation (3D imaging, vibrometry, polarimetry, aperture synthesis, agile apertures, etc.) into a single device with waveforms matched to the requirements of both hardware (e.g., optical amplifiers, modulators) and the targets being imaged . The first successful demonstrations of this program have produced high-resolution, 3D images at intermediate stand-off ranges, heavy camouflage penetration, and adaptive techniques for draped multi-layer obscurations.

Ladar based vibrometry has been shown to be a powerful technique in enabling the plant identification of machines. Vibration can be sensed reliably and provide positive identification at ranges beyond the imaging limits of the aperture. However, as the range of observation increases, the diffraction limited beam size on the target increases as well, and may encompass multiple vibrational modes on the target’s surface. As a result, vibration estimates formed from large laser footprints illuminating multiple modes on a vibrating target will experience a degradation. A model to predict this phenomenology is proposed for pulse-pair vibrometry systems.

The limitations of the turbulent atmospheric channel are examined by using the simulation of beam propagation. The aim of this study is to consider how the compensation of atmospheric turbulence wavefront phase distortion by using modal methods improves the performance and reliability of free-space laser systems based on the heterodyne detection scheme. In a process of tracking of the beam wavefront and consequent correction of atmospherically-induced aberrations, the aim of phase compensation would be to restore diffraction-limited resolution. The modal correction of several modes of an expansion of the total phase distortion in a set of basis functions may offer the potential for overcoming some of the restrictions imposed by the atmosphere in practical systems.

Expressions for the bistatic gain of a coherent lidar are reviewed. We show that the fundamental representation of the monostatic gain is in terms of the wander corrected on-axis scintillation index and the wander corrected bistatic gain.

: In this paper, the performance of GAPD based ladar receivers is investigated and a theory for the signal photon detection efficiency (SPDE) is developed as a function of the dead-time; signal, noise and clutter flux; and the GAPD’s photon detection efficiency or PDE. This efficiency theory is valid for arbitrary (short to long) dead-times. With a zero dead-time, GAPDs behave linearly and the efficiency theory converges to the PDE. For long dead-times, compared to the acquisition gate time, the theory converges to previously published works of Fouche and Williams. This SPDE theory is then applied to develop other ladar metrics, e.g. SNR.

This article presents our investigations into the physical and optical properties of canopies and their individual scattering elements in order to develop an improved foliage penetration model. We employed a Monte Carlo algorithm to simulate the propagation of a pencil beam of photons through a canopy of leaves. Simulations were made modeling the individual leaves as several different bidirectional scattering distribution functions (BSDF). The spatial, temporal, and angular point spread functions were measured for each BSDF and compared such that an optimal canopy propagation model was created.

Coherent detection of optical signals offers many benefits for fiber optic communications, but has been regarded as prohibitively complex to implement. Recently a mode of coherent detection has been proposed which overcomes these issues using real time digital signal processing. Experimental results are presented showing how the information is recovered when the signal and local oscillator are combined in a phase diverse hybrid, and good receiver sensitivity is achieved. Fiber propagation impairments can be compensated within the digital processor, and compensation of chromatic dispersion and polarisation mode dispersion is demonstrated. Some of the future possibilities for coherent dection are described.

The Laser Interferometer Gravitational-Wave Observatory (LIGO), consisting of three interferometers at the two LIGO observatory sites (Livingston, LA and Hanford, WA), is operational and the LIGO Scientific Collaboration is embarked on a several-year period of searching for gravitational wave emissions from astrophysical sources. The threshold for measuring gravitational waves as length changes between two test masses is extremely low, requiring extremely high accuracy in the sensitivity to length changes. Each LIGO detector is a power-recycled Michelson Interferometer with Fabry-Perot cavities in the 4 km long arms. All optical elements, and the laser beam between them, operate in UHV. In this talk, I will discuss the operation of the LIGO interferometers, and the techniques that were used to reach a sensitivity of 10^-18 m/sqrt(Hz) for 100 Hz signals.

Supported by the NSF grant PHY-0555453.

Coherent laser communication terminals based on homodyne BPSK (binary phase shift keying) combine highest sensitivity for both, communication and tracking, with immunity against sunlight. We report on a new generation of coherent terminals for a LEO-GEO data relay system to transmit data from TanDEM-X, a German LEO earth observation satellite to a European GEO satellite with a Ka-band downlink. The system will be extended to optical GEO-to-ground links using adaptive optics on ground. All optical inter-satellite links are duplex links with a foreseen data rate of 2.8 Gbps.

Flight demonstrations have proven the feasibility of synthetic aperture LADAR (SAL) imaging and have produced outstanding imagery of vehicles and engineering test targets. These tests were conducted under the Synthetic Aperture LADAR for Tactical Imaging (SALTI) program. SALTI is a Defense Advanced Research Project Agency program executed with the Air Force Research Laboratory, Sensors Directorate which has demonstrated practical SAL architectures. The atmospheric and target phenomenologies were investigated for both short wave infrared (SWIR) and long wave infrared (LWIR) systems and the relevant are compared with some basic SAR parameters. An introduction to the SAL systems is presented, representative simulated images are shown and turbulence driven performance regimes are discussed. Finally, test objectives of a third series of tests and future plans are presented.

With a multi-aperture imaging system, one creates a large imaging aperture by combining the light from a series of distributed telescopes. In doing this, one can construct a fine-resolution imaging system with reduced volume. We present work on multi-aperture, active imaging systems that use coherent detection and digital image formation. In such a system, the image formation process incorporates digital correction of optical and atmospheric phase errors. Here we discuss the principles underlying this method and present results from laboratory experiments and field experiments performed over a 0.5 km outdoor test range. In addition we discuss 3D imaging capability of the method

A primary goal of sparse aperture imaging is to enhance resolution while minimizing the total light collection area, the latter being desirable, in part, because of the cost of large, monolithic apertures. We construct arrays by locating multiple, identical circular sub-apertures and evaluate array performance based on PSF and MTF metrics. We select an optimal array constructed on a compact nonredundant point array first described by Golay. We report experimental results of imaging a resolution target from by masking a large lens with the Golay array noting the loss of image contrast inherent to sparse arrays.

Recently a great deal of work has focused on the use of nonclassical states of light for performing measurements with precision beyond that attainable with the usual coherent laser light. Laser radar poses special challenges for the use of nonclassical states due to the large losses involved in typical laser radar applications. We examine the possibility of employing squeezed states and maximally-entangled (“NOON”) states in laser radar, and find that the presence of loss severely limits their potential utility

This talk will present the first experimental demonstration of coherent detection using an array of photon-counting detectors. These measurements use an array of Geiger-mode avalanche photodiodes with integrated CMOS timing circuitry, and show the potential for shot-noise-limited detection in the single-return-photon regime with comparable local oscillator power. The high-bandwidth timing circuitry and potential to fabricate large arrays enable range-resolved Doppler and angularly-resolved Doppler laser radar measurements. Laboratory results agree well with theory and computer simulations.

Passively mode-locked fiber lasers produce a broad, yet phase-coherent output spectrum. In the frequency domain, this output forms a frequency comb, where each comb line corresponds to an individual laser mode. We will discuss using a frequency comb in a coherent LIDAR system for high resolution range or Doppler measurements. In order to effectively use the broad spectrum, we spectrally resolve the signal into discrete bands, apply any necessary phase compensation, and then Fourier-process the data to produce a range image or Doppler signature. We will discuss both our initial experiments and future efforts using two phase-coherent frequency combs.

Our terahertz-based vibrometer measures at a standoff, vibrations behind optically opaque barriers, such as cardboard, clothing and plastic. Its Michelson-based design gives sub-micron sensitivities, which are limited by the detector. We use commercially available, room temperature components. Measured spectral response compares favorably with optical vibrometry without barriers.

The measurement of various atmospheric parameters is of great importance to understand physics, chemistry and dynamics. The Lidar has proved to be an important tool for atmospheric probing. Various types of Lidar systems have been used for atmospheric monitoring since the invention of laser by Maiman in early 1960s to measure various atmospheric parameters such as aerosols, minor constituents, wind, temperature etc. Keeping above in view we at National Physical Laboratory, New Delhi have designed and developed a high resolution Laser Heterodyne system with 1 GHz acousto-optical spectrometer as backend for vertical profiles of various trace species including ozone profiles at Maitri, Antarctica during normal as well as ozone hole conditions, Differential Absorption LIDAR (DIAL) for monitoring of surface ozone, water vapour, ammonia, ethylene etc and Micro Pulse lidar for vertical profiles of aerosol and their characterization using depolarization ratio measurements.!

Also appropriate inversion technique has been developed for retrieval of ozone profiles. In the present communications the salient features of the systems developed at NPL and results obtained will be discussed in detail.

We describe and demonstrate a sensitive room-temperature detection of terahertz radiation by nonlinearly upconverting terahertz to the optical near-infrared regime, relying on telecomm components. Terahertz radiation at 700 GHz is mixed with pump light at 1550 nm in a bulk GaAs crystal to generate an idler wave at 1555.6 nm which is separated and detected using a commercial PIN diode. The THz detector operates at room temperature and has terahertz-to-optical photon conversion efficiency of 0.001%.

The 2-micron thulium and holmium-based lasers being considered as the transmitter source for space-based coherent Doppler lidar require high power laser diode pump arrays operating in long pulse regime of about 1 msec. Operating laser diode arrays over such long pulse duration drastically impact their useful lifetime due to the excessive localized heating and substantial pulse-to-pulse thermal cycling of their active regions. This paper describes the long pulse mode performance of laser diode arrays and their critical thermal characteristics. A viable approach is then offered that allows for determining the optimum operational parameters leading to the maximum attainable lifetime

Three-dimensional imaging ladar sensors can be used for terrain mapping missions. Photon counting receiver arrays provide the systems engineer with the ability to make important system trades of range capability, receiver aperture, laser size and ladar FOV. MIT/LL has pioneered Geiger mode APD array receivers for ladar systems that provide photon counting sensitivity in a 32x32 array with good range resolution capabilities.

Boeing SVS, Boeing Spectrolab and MIT/LL have entered into a tech transfer relationship to bring MIT/LL Geiger Mode APD arrays out to industry. The tech transfer project for the 32x32 InGaAsP arrays can be broken down into 5 components, each being handled and funded by different parties. 1. Material growth; 2. Material Characterization; 3. Detector array fabrication; 4. Packaging; 5. Electronics and Real Time Processor. This presentation will provide progress and performance details for all 5 areas and give data examples from a terrain mapping field collection.

The use of lidars in ground, airborne, and space-based missions can provide earth and planetary science measurements that were previously unavailable. Our approach to the laser transmitters needed for such systems focuses on developing environmentally hardened prototypes whose designs can be validated with extensive testing. We applied this approach to the laser transmitter for the CALIPSO aerosol lidar mission by designing and testing the Risk Reduction Laser. We are in the process of a similar development effort for the injection seeded single frequency lasers that will be needed for the next generation of airborne and space-based lidar systems

Photoacoustic technique is introduced as a convenient and accurate method for the control of laser spectral shift. A non resonant photoacoustic cell (PAC) is investigated to monitor a pulsed laser spectral shift on a CO2 absorption line in the 2-µm domain. A minimum ~ 1 % of accuracy on CO2 Heterodyne Differential Absorption Lidar (HDIAL) measurement is estimated when the laser is tuned to the centre of the absorption line.

Tesat Spacecom has build and tested the flight models of the Reference Laser Head (RLH) for the ESA AEOLUS mission, a space borne UV LIDAR system. The RLH provides frequency stable (4 Hz / sec absolute long time frequency drift) and tunable (8.333 GHz in 8.333 MHz steps) single frequency light at 1064n. It is used as seeder input for the pulsed laser system. The design and flight model performance results for the RLH are shown.

subtitle: Eyesafe 1.6 &#956;m Er:YAG transmitters for coherent laser radar

Reconstruction of wind profile based on the turbulent spatio-temporal statistics of reflected optical wave focused by the receiving telescope is considered. Both the expression for the spatial temporal correlation function and spectrum and the algorithm of wind profiling based on the spatio-temporal spectrum of weak intensity fluctuations of a wave scattered off diffuse target are presented. Computer simulations performed under conditions of weak optical turbulence show wind profiles reconstruction by the developed algorithm

Numerous treatments in the literature over the years have concluded that heterodyne efficiency, and thus heterodyne signals from diffuse targets, decrease as detection apertures increase, based on the mistaken assumption that signals decrease as phase and intensity correlations decrease. Random walk models for laser speckle phenomena suggest that signal strength (carrier-to-noise ratio) always increases (on the average) with aperture, however care must be taken to match the divergence and intensity of the local oscillator to optimally achieve the increased CNR. Theory and examples will be given to justify the conclusions.

Low-level turbulence is an aviation hazard. This paper discusses the use of glide-path scan of the LIDAR at the Hong Kong International Airport to calculate turbulence intensity. Structure function approach based on the radial velocity data of the LIDAR is adopted. The turbulence intensity so determined is compared with pilot reports to illustrate the potential application of the method for turbulence alerting.

Looking ahead of the aircraft in search of vertical motions has usually been done with conical scans of small cone angles. Recent experiments have been performed using raster scans ahead of the aircraft to collect Line-of-Sight velocity data from which the nearly orthogonal vertical motion can be inferred.

The raster scan approach was tested in cloud free conditions over Monterey Bay (CA), the Salinas Valley and the nearby mountain ranges. The experiments revealed useful relationships between aerosol returns and LOS velocity convergence.

This presentation will present results of those flights and discuss implications to aircraft flight control and turbulence avoidance.

Multipixel coherent receivers are not yet commonplace. However, these types of receivers are gaining popularity and it is important to understand their measurement limits. In particular, the angle estimates (from a centroiding technique) produced by a coherent array are intimately tied to the LO pattern on the receiver. This work examines the angle estimation error from one example arrangement. This theory is then shown to compare favorably to Monte Carlo simulation results.

Lidar measurement of oceanic temperature and sound speed by measuring the spectral shift of the backscattered Brillouin doublet has been proposed in previous studies. Technical limitations on both transmitter and receiver have until now prevented experimental demonstration at 1 m/sec accuracy. Receiver requirements are met by utilizing an edge technique based on absorption lines of an iodine isotope. With edge filtering, small changes in frequency shift of the Brillouin doublet produce significant change in the transmission through the iodine vapor. The resulting filter transmission signal has a one-to-one correspondence with water temperature (hence sound speed). Our laboratory measurements demonstrate this.

Coherent imaging provides a means to do multi-aperture imaging without the need for complex sensors, actuators, and control systems that a passive multi-aperture imaging system requires. However, this mechanical complexity is traded for the processing complexity involved in producing the synthetic image. In this paper, the development of a multi-aperture coherent imaging testbed which aims to implement high speed processing is described, and some preliminary tests in both multi-aperture and three-dimensional imaging are documented.

We generally accept the experimentally observed criteria for heterodyne detections that the two waves that are mixed must (i) be collinear, (ii) have matched wave fronts and (iii) cannot be orthogonally polarized. We find that there are a number of unresolved paradoxes in classical and quantum optics regarding the definitions and understanding of the “interference” and “coherence” properties of light, which are attributed as essentially due to inherent properties of the EM waves. The purpose of this paper is to find deeper physical understanding of the heterodyne detection processes that could lead to better laser radar system design.

Averaging is often used in processing coherent lidar data to reduce noise fluctuations and improve the ability to detect the presence of a target. There are many choices of averaging techniques, and this work examines two types of averaging filters. The first is an FIR filter that has often been used in the past and is well understood. The second is an IIR filter that is also common in practice, but has not been carefully analyzed. This work compares the detection performance between these two types of filters and points out the advantages and disadvantages of each.

We explain Level-2B/Level-2C products from the ADM-Aeolus mission. These products aim at providing meteorologically representative wind profiles, meeting neos of user communities in operational numerical weather prediction and more general atmospheric science. Whereas Level-2B profiles report single wind components (along the horizontal line-of-sight), Level-2C profiles report wind vectors (two horizontal components).
We cover a) the theoretical basis of the retrieval algorithms, and b) details of how to obtain the Level-2B processor portable source code - designed for use as either 1) a standalone executable in a general scientific environment, or 2) a callable subroutine integrated within a data assimilation system.