Direct Detection Doppler Lidar Research Articles

Intensity-Modulated Direct-Detection Doppler LiDAR Using Pseudo-Random Code and Optical Direct Down-Conversion of Modulation Frequency for Range and Speed Measurement of a Hard Target

Intensity-modulated direct-detection Doppler LiDAR (IM-DDDL) with pseudo-random code is demonstrated for range and speed measurement of a hard target. This IM-DDDL has key features of (i) long-time coherent signal accumulation without requirement of narrow-linewidth laser source, (ii) high receiving sensitivity with optical direct down-conversion of modulation frequency, (iii) ranging using pseudo-random code, and (iv) Doppler shift detection at baseband frequency. These features are demonstrated in preliminary experiments with fiber-based circuit at 1550 nm wavelength which has eye-safety. The employment of fiber-based configuration contributes to compactness and reliability of the instrument. Ranging function using pseudo-random code is suitable for prevention from interference between multiple LiDARs. The condition for detecting Doppler frequency shift is also shown. A moving stroke of a target within a measurement time needs to be enough larger than the wavelength of modulation frequency. Process for future practical use and application to volumetric target sensing are additionally investigated.

Performance Modeling of a Diode-Laser-Based Direct-Detection Doppler Lidar for Vertical Wind Profiling

Abstract Micropulse differential absorption lidars (MPD) for water vapor, temperature, and aerosol profiling have been developed, demonstrated, and are addressing the needs of the atmospheric science community for low-cost ground-based networkable instruments capable of long-term monitoring of the lower troposphere. The MPD instruments use a diode-laser-based (DLB) architecture that can easily be adapted for a wide range of applications. In this study, a DLB direct-detection Doppler lidar based on the current MPD architecture is modeled to better understand the efficacy of the instrument for vertical wind velocity measurements, with the long-term goal of incorporating these measurements into the current network of MPD instruments. The direct-detection Doppler lidar is based on a double-edge receiver that utilizes two Fabry–Pérot interferometers and a vertical velocity retrieval that requires the ancillary measurement of the backscatter ratio, which is the ratio of the total backscatter coefficient to the molecular backscatter coefficient. The modeling in this paper accounts for the major sources of error. It indicates that the vertical velocity can be retrieved with an error of less than 0.56 m s−1 below 4 km with a 150-m range resolution and an averaging time of 5 min. Significance Statement Monitoring the temperature, relative humidity, and winds in the lower atmosphere is important for improving weather forecasting, particularly for severe weather such as thunderstorms. Cost-effective micropulse differential absorption lidar (MPD) instrumentation for continuous temperature and humidity monitoring has been developed and demonstrated, and its effects on weather forecasting are currently being evaluated. The modeling study described in this paper studies the feasibility of using a similar cost-effective MPD instrument architecture for monitoring vertical wind velocity in the lower atmosphere. Modeling indicates that wind velocities can be measured with less than 0.56 m s−1 accuracy and demonstrates the feasibility of adding vertical wind velocity measurements to the MPD instruments.

Zero Doppler correction for Fabry–Pérot interferometer-based direct-detection Doppler wind LIDAR

Direct-detection Doppler LIDAR has been demonstrated for its high temporal and spatial resolution in atmosphere wind detection from troposphere to stratosphere. As Doppler frequency is a relative value, the zero point drift would lead to wind velocity error. So the zero Doppler correction was necessary for high-accuracy wind measurement. We analyzed the reasons that would cause zero point drift and demonstrated a designed Fabry–Perot interferometer and front optics to measure Rayleigh scatter laser and emitted laser frequency in the meantime. Wind observation experiments were demonstrated in XinJiang, China, and the measured wind profile coincided well with radiosonde results.

Dual-frequency Doppler lidar for wind detection with a superconducting nanowire single-photon detector.

A dual-frequency direct detection Doppler lidar is demonstrated using a superconducting nanowire single-photon detector (SNSPD) at 1.5μm. The so-called double-edge technique is implemented by using a dual-frequency laser pulse, rather than using a double-channel Fabry-Perot interferometer. Such a modification to the reported lidars enhances the frequency stability in the system level. Using the time-division multiplexing method, only one piece of SNSPD is used in the optical receiver, making the system simplified and robust. The SNSPD is adopted to enhance the temporal resolution since it offers merits of high quantum efficiency, low dark count noise, no after-pulsing probability, and a high maximum count rate. Two telescopes that point westward and northward at a zenith angle of 30° are used to detect the line-of-sight wind components, which are used to synthesize the horizontal wind profile. Horizontal wind profiles up to an altitude of about 2.7km are calculated with vertical spatial/temporal resolution of 10m/10s. Wind dynamic evolution and vertical wind shears are observed clearly.

相干光路的直接探测多普勒激光雷达设计

相干光路的直接探测多普勒激光雷达设计

Micro-pulse upconversion Doppler lidar for wind and visibility detection in the atmospheric boundary layer.

For the first time, to the best of our knowledge, a compact, eye-safe, and versatile direct detection Doppler lidar is developed using an upconversion single-photon detection method at 1.5 μm. An all-fiber and polarization maintaining architecture is realized to guarantee the high optical coupling efficiency and the robust stability. Using integrated-optic components, the conservation of etendue of the optical receiver is achieved by manufacturing a fiber-coupled periodically poled lithium niobate waveguide and an all-fiber Fabry-Perot interferometer (FPI). The double-edge technique is implemented by using a convert single-channel FPI and a single upconversion detector, incorporating a time-division multiplexing method. The backscatter photons at 1548.1 nm are converted into 863 nm via mixing with a pump laser at 1950 nm. The relative error of the system is less than 0.1% over nine weeks. In experiments, atmospheric wind and visibility over 48 h are detected in the boundary layer. The lidar shows good agreement with the ultrasonic wind sensor, with a standard deviation of 1.04 m/s in speed and 12.3° in direction.

Velocity spectra and turbulence using direct detection lidar and comparison with thermosonde measurements

[1] Observations of turbulence have been performed in New Hampshire near Mount Washington using two independent instruments: a ground-based direct detection Doppler lidar and a balloon-borne thermosonde. The Doppler lidar measures a time series of the velocity component parallel to the laser beam for each altitude. Spectra of the velocity time series are determined using the Scargle technique. Turbulence levels are estimated from the spectra assuming Kolmogorov behavior. The thermosonde measures the temperature difference between two sensors spaced 1 m apart, computes a running RMS average, and then determines the temperature turbulence parameter, CT2, also assuming Kolmogoroff behavior. The results show that the strongest levels of turbulence exist in a Kelvin-Helmholtz layer in the altitude range of 1.2 < z < 1.9 km. This layer shows a three-tier structure consisting of a well-mixed layer in the center with strong velocity fluctuations bounded on top and bottom by layers with strong temperature fluctuations.

Doppler Rayleigh/Mie/Raman lidar for wind and temperature measurements in the middle atmosphere up to 80 km

Abstract. A direct detection Doppler lidar for measuring wind speed in the middle atmosphere up to 80 km with 2 h resolution was implemented in the ALOMAR Rayleigh/Mie/Raman lidar (69° N, 16° E). The random error of the line of sight wind is about 0.6 m/s and 10 m/s at 49 km and 80 km, respectively. We use a Doppler Rayleigh Iodine Spectrometer (DoRIS) at the iodine line 1109 (~532.260 nm). DoRIS uses two branches of intensity cascaded channels to cover the dynamic range from 10 to 100 km altitude. The wind detection system was designed to extend the existing multi-wavelength observations of aerosol and temperature performed at wavelengths of 355 nm, 532 nm and 1064 nm. The lidar uses two lasers with a mean power of 14 W at 532 nm each and two 1.8 m diameter tiltable telescopes. Below about 49 km altitude the accuracy and time resolution is limited by the maximum count rate of the detectors used and not by the number of photons available. We report about the first simultaneous Rayleigh temperature and wind measurements by lidar in the strato- and mesosphere on 17 and 23 January 2009.

Doppler LIDAR Measurement of Wind in the Stratosphere

A mobile direct detection Doppler LIDAR based on molecular backscattering for measurement of wind in the stratosphere has been developed in Hefei, China. First, the principle of wind measurement with direct detection Doppler LIDAR is presented. Then the configuration of the LIDAR system is described. Finally, the primary experimental results are provided and analyzed. The results indicate that the detection range of the designed Doppler LIDAR reached 50 km altitude, and there is good consistency between the molecular Doppler wind LIDAR(DWL) and the wind profile radar(WPR) in the low troposphere.

The Airborne Demonstrator for the Direct-Detection Doppler Wind Lidar ALADIN on ADM-Aeolus. Part I: Instrument Design and Comparison to Satellite Instrument

Abstract The global observation of profiles of the atmospheric wind speed is the highest-priority unmet need for global numerical weather prediction. Satellite Doppler lidar is the most promising candidate to meet the requirements on global wind profile observations with high vertical resolution, precision, and accuracy. The European Space Agency (ESA) decided to implement a Doppler wind lidar mission called the Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) to demonstrate the potential of the Doppler lidar technology and the expected impact on numerical weather forecasting. An airborne prototype of the instrument on ADM-Aeolus was developed to validate the instrument concept and retrieval algorithms with realistic atmospheric observations before the satellite launch. It is the first airborne direct-detection Doppler lidar for atmospheric observations, and it is operating at an ultraviolet wavelength of 355 nm. The optical design is described in detail, including the single-frequency pulsed laser and the two spectrometers to resolve the Doppler frequency shift from molecular Rayleigh and aerosol Mie backscatter. The airborne prototype is representative of the spaceborne instrument, and their specific differences are discussed.

ALADIN Doppler Wind Lidar and Related Programs at EADS Astrium

ABSTRACTThe Atmospheric Laser Doppler Instrument (ALADIN) is the payload of the ADM-AEOLUS mission, which will make direct measurements of global wind fields. It will determine the wind velocity component normal to the satellite velocity vector. The instrument is a direct detection Doppler Lidar operating in the UV, which will be the first of its kind in space.ALADIN is now in its final construction stage: the integration of the Flight Model is on-going. Most of the subsystems have been integrated; the payload performance and qualification test campaign will commence.This paper describes the ALADIN the development status and the results obtained at this stage. This regards the receiver performance, the telescope development and the challenges of the laser.The paper will also provide insights on the ATLID instrument design which is the backscatter lidar for the EarthCARE mission. This lidar program is starting its detailed design phase.The ALADIN and ATLID instruments are developed by EADS Astrium Satellites for the European Space Agency.

Seed injection and frequency-locked Nd:YAG laser for direct detection wind lidar

The single longitudinal mode operation and frequency stability are essential for the laser transmitter used in the Doppler lidar. We devise a seed injection, frequency tunable and locked Q-switched Nd:YAG laser for the direct detection Doppler lidar. By implementation of the dual-wavelength seed laser and iodine-based PID frequency-locking technique, the frequency-stabilized seed laser is robust to interference and can be locked within 200 kHz for 3 h. The stable output of single longitudinal mode of the frequency-doubled pulsed laser makes it possible to achieve operational wind measurement.

Wind-velocity lidar measurements by use of a Mach-Zehnder interferometer, comparison with a Fabry-Perot interferometer.

We present the first wind-velocity profiles obtained with a direct-detection Doppler lidar that uses a Mach-Zehnder interferometer (MZI) as spectral discriminator. The measurements were performed in the lower stratosphere, between 10 and 40 km in altitude, at the Observatoire de Haute Provence (OHP), France, during nighttime. They are in excellent agreement with those obtained simultaneously and independently with the already validated double Fabry-Perot interferometer (FPI) of the OHP Doppler lidar (mean difference lower than the combined standard deviation). A statistical analysis shows that the random error obtained with this experimental MZI is 1.94 times the Cramer-Rao lower bound and is approximately half of that given by the FPI (both operating in photometric mode). Nevertheless, the present MZI measurements are sensitive to the presence of atmospheric particles and need an additional correction, whereas the OHP FPI is designed to be insensitive to particulate scattering.

Two-channel direct-detection Doppler lidar employing a charge-coupled device as a detector.

A direct-detection Doppler lidar system is demonstrated that uses a CCD as a detector for the first time to our knowledge. The ability to use this linear device with the circular output from a Fabry-Perot etalon comes from use of a circle-to-line converter [Appl. Opt. 29, 1482 (1990)]. In addition to the gains in quantum efficiency obtained through use of this detector, the lidar system described in this paper also has the capability to measure winds from aerosol and molecular backscatter simultaneously in two separate channels by directing the light reflected from one channel into the other. Early measurements with this system are presented; it is shown that, although accurate aerosol wind measurements are easily obtained, molecular measurements require a carefully calibrated inverse model and special hardware to derive accurate wind measurements with this channel.

Criteria for Optimization of Interferometers in the Space-borne Direct-detection Doppler Wind Lidar*

The double-edge technique with different interferometers in the space-borne direct-detection Doppler wind lidar is investigated. Two plane-plate Fabry–Perot (FP) etalons for the double-edge technique have advantages of flexible tuning and a simple structure for space application. Methods of optimizing FP parameters for the molecular double-edge technique are compared. Relevant simulation and analysis are implemented, and similar results are obtained. The method of setting the same sensitivity to both aerosol and molecule obtains better accuracy than that of minimizing the aerosol effect. This study is helpful in designing suitable double FP edge filters for a space-borne direct-detection Doppler lidar.

Fringe-imaging Mach-Zehnder interferometer as a spectral analyzer for molecular Doppler wind lidar.

The theoretical performance of a Mach-Zehnder interferometer used as a spectral analyzer for wind-speed measurement by direct-detection Doppler lidar is presented. The interferometer is optimized for the measurement of wind velocity from the signal that is backscattered by the molecules. In the proposed fringe-imaging Mach-Zehnder (FIMZ) interferometer, a pattern of equally spaced linear fringes is formed and detected by two conventional detector linear arrays. Assuming a pure molecular signal with Gaussian spectral profile, an analytic expression for the standard deviation of the measurement error is obtained and compared with the Cramer-Rao lower bound given by an ideal spectral analyzer (ISA) in the case of shot-noise-limited signal. The FIMZ measurement error is shown to be 2.3 times that of the ISA and is comparable with the error given by previously developed multichannel spectral analyzers that are based on Fabry-Perot interferometers that, in contrast, have the disadvantages of producing unequally spaced circular fringes and requiring dedicated detectors. The optimal path difference for a FIMZ operating at 355 nm is approximately 3 cm. The interferometer is shown to match important lidar beam étendues without significant performance reduction.

Mach–Zehnder interferometer as a spectral analyzer for molecular Doppler wind lidar

The theoretical performance of a Mach-Zehnder interferometer used as a spectral analyzer for wind-speed measurement by direct-detection Doppler lidar is presented. The interferometer is optimized for measurement of wind velocity from the signal backscattered by the molecules. Two arrangements are proposed, involving two detection channels (DMZ) or four detection channels (QMZ). Using the assumption of a pure molecular signal with a Gaussian spectral profile, we derive an analytic expression for the standard deviation of the measurement error for each arrangement. They are then compared with the ideal spectral analyzer (ISA) and with the double-edge Fabry-Perot (DFP) in the case of a shot-noise-limited signal. The DMZ measurement error is shown to be only 1.65 times that of the ISA and is 1.4 times lower than that given by the DFP. The QMZ arrangement provides a measurement that is insensitive to the aerosol scattering contribution but gives a measurement error that is 1.4 times higher than that of the DMZ.

Double-edge molecular measurement of lidar wind profiles at 355 nm

We built a direct-detection Doppler lidar based on the double-edge molecular technique and made the what we believe to be the first molecular-based wind measurements using the eye-safe 355-nm wavelength. Three etalon bandpasses are obtained with step etalons on a single pair of etalon plates. We eliminate long-term frequency drift of the laser and the capacitively stabilized etalon by locking the etalon to the laser frequency. We use a low-angle design to avoid polarization effects. Wind measurements of 1-2-m /s accuracy are obtained to 10-km altitude with 5 mJ of laser energy, a 750-s integration, and a 25-cm telescope. Good agreement is obtained between lidar and rawinsonde measurements.

Modeling the performance of direct-detection Doppler lidar systems including cloud and solar background variability

Previous modeling of the performance of spaceborne direct-detection Doppler lidar systems assumed extremely idealized atmospheric models. Here we develop a technique for modeling the performance of these systems in a more realistic atmosphere, based on actual airborne lidar observations. The resulting atmospheric model contains cloud and aerosol variability that is absent in other simulations of spaceborne Doppler lidar instruments. To produce a realistic simulation of daytime performance, we include solar radiance values that are based on actual measurements and are allowed to vary as the viewing scene changes. Simulations are performed for two types of direct-detection Doppler lidar system: the double-edge and the multichannel techniques. Both systems were optimized to measure winds from Rayleigh backscatter at 355 nm. Simulations show that the measurement uncertainty during daytime is degraded by only approximately 10-20% compared with nighttime performance, provided that a proper solar filter is included in the instrument design.

Rayleigh–Mie Doppler wind lidar for atmospheric measurements II Mie scattering effect, theory, and calibration

A theoretical and experimental study is conducted for the direct-detection Doppler Lidar developed by the Service d'Aéronomie du Centre National de la Recherche Scientifique. Thanks to a specific design, the double-edge technique that applies primarily to Rayleigh scattering can also be employed in presence of aerosols backscatter. We focus on a careful estimate of the particle-induced error on the wind measurements. With a theoretical model for the Fabry-Perot interferometer and two sets of calibration measurements, the true spectral properties of the interferometer and the calibration curves are recovered. Furthermore, the particle-induced error is estimated for varying values of the scattering ratio at 532 nm. When applied to real atmospheric signals, this error is shown to be negligible. A comparison between ancillary data and the wind and backscatter ratio as retrieved from the Doppler lidar signals confirms our estimate.