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Volker Wulfmeyer - One of the best experts on this subject based on the ideXlab platform.
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3 d water vapor field in the atmospheric boundary layer observed with scanning Differential Absorption Lidar
2016Co-Authors: Florian Spath, Andreas Behrendt, Andrea Riede, Shravan Kumar Muppa, Simon Metzendorf, Volker WulfmeyerAbstract:Abstract. High-resolution three-dimensional (3-D) water vapor data of the atmospheric boundary layer (ABL) are required to improve our understanding of land–atmosphere exchange processes. For this purpose, the scanning Differential Absorption Lidar (DIAL) of the University of Hohenheim (UHOH) was developed as well as new analysis tools and visualization methods. The instrument determines 3-D fields of the atmospheric water vapor number density with a temporal resolution of a few seconds and a spatial resolution of up to a few tens of meters. We present three case studies from two field campaigns. In spring 2013, the UHOH DIAL was operated within the scope of the HD(CP)2 Observational Prototype Experiment (HOPE) in western Germany. HD(CP)2 stands for High Definition of Clouds and Precipitation for advancing Climate Prediction and is a German research initiative. Range–height indicator (RHI) scans of the UHOH DIAL show the water vapor heterogeneity within a range of a few kilometers up to an altitude of 2 km and its impact on the formation of clouds at the top of the ABL. The uncertainty of the measured data was assessed for the first time by extending a technique to scanning data, which was formerly applied to vertical time series. Typically, the accuracy of the DIAL measurements is between 0.5 and 0.8 g m−3 (or
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investigation of pbl schemes combining the wrf model simulations with scanning water vapor Differential Absorption Lidar measurements
2016Co-Authors: Josipa Milovac, Andreas Behrendt, Florian Spath, Kirsten Warrachsagi, Joachim Ingwersen, Volker WulfmeyerAbstract:Six simulations with the Weather Research and Forecasting (WRF) model differing in planetary boundary layer (PBL) schemes and land surface models (LSMs) are investigated in a case study in western Germany during clear-sky weather conditions. The simulations were performed at 2 km resolution with two local and two nonlocal PBL schemes, combined with two LSMs (NOAH and NOAH-MP). Resulting convective boundary layer (CBL) features are investigated in combination with high-resolution water vapor Differential Absorption Lidar measurements at an experimental area. Further, the simulated soil-vegetation-atmosphere feedback processes are quantified applying a mixing diagram approach. The investigation shows that the nonlocal PBL schemes simulate a deeper and drier CBL than the local schemes. Furthermore, the application of different LSMs reveals that the entrainment of dry air depends on the energy partitioning at the land surface. The study demonstrates that the impact of processes occurring at the land surface is not constrained to the lower CBL but extends up to the interfacial layer and the lower troposphere. With respect to the choice of the LSM, the discrepancies in simulating a diurnal change of the humidity profiles are even more significant at the interfacial layer than close to the land surface. This indicates that the representation of land surface processes has a significant impact on the simulation of mixing properties within the CBL.
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Turbulent Humidity Fluctuations in the Convective Boundary Layer: Case Studies Using Water Vapour Differential Absorption Lidar Measurements
2016Co-Authors: Shravan Kumar Muppa, Volker Wulfmeyer, Andreas Behrendt, Florian Spath, Simon Metzendorf, Andrea RiedeAbstract:Turbulent humidity fluctuations in the convective boundary layer (CBL) under clear-sky conditions were investigated by deriving moments up to fourth-order. High-resolution humidity measurements were collected with a water vapour Differential Absorption Lidar system during the $$\hbox {HD(CP)}^{2}$$ HD(CP) 2 Observational Prototype Experiment (HOPE). Two cases, both representing a well-developed CBL around local noon, are discussed. While the first case (from the intensive observation period (IOP) 5 on 20 April 2013) compares well with what is considered typical CBL behaviour, the second case (from IOP 6 on 24 April 2013) shows a number of non-typical characteristics. Both cases show similar capping inversions and wind shear across the CBL top. However, a major difference between both cases is the advection of a humid layer above the CBL top during IOP 6. While the variance profile of IOP 5 shows a maximum at the interfacial layer, two variance peaks are observed near the CBL top for IOP 6. A marked difference can also be seen in the third-order moment and skewness profiles: while both are negative (positive) below (above) the CBL top for IOP 5, the structure is more complex for IOP 6. Kurtosis is about three for IOP 5, whereas for IOP 6, the distribution is slightly platykurtic. We believe that the entrainment of an elevated moist layer into the CBL is responsible for the unusual findings for IOP 6, which suggests that it is important to consider the structure of residual humidity layers entrained into the CBL.
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high power ti sapphire laser at 820 nm for scanning ground based water vapor Differential Absorption Lidar
2013Co-Authors: Gerd Wagner, Volker Wulfmeyer, Andreas Behrendt, Florian Spath, Max SchillerAbstract:The Ti:sapphire (TISA) laser transmitter of the mobile, three-dimensional-scanning water–vapor Differential Absorption Lidar (DIAL) of the University of Hohenheim is described in detail. The dynamically-stable, unidirectional ring resonator contains a single Brewster-cut TISA crystal, which is pumped from both sides with 250 Hz using a diode-pumped frequency-doubled Nd:YAG laser. The resonator is injection seeded and actively frequency-stabilized using a phase-sensitive technique. The TISA laser is operating near 820 nm, which is optimum for ground-based water–vapor DIAL measurements. An average output power of up to 6.75 W with a beam quality factor of M2<2 is reached. The pointing stability is <13 μrad (rms), the depolarization <1%. The overall optical–optical conversion efficiency is up to 19%. The pulse length is 40 ns with a pulse linewidth of <157 MHz. The short- and long-term frequency stabilities are 10 MHz (rms). A spectral purity of 99.9% was determined by pointing to a stratus cloud in low-elevation scanning mode with a cloud bottom height of ≈2.4 km.
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three dimensional observations of atmospheric humidity with a scanning Differential Absorption Lidar
2009Co-Authors: Andreas Behrendt, Volker Wulfmeyer, Andrea Riede, Gerd Wagner, Sandip Pal, Heinz Bauer, Marcus Radlach, Florian SpathAbstract:A novel scanning water vapor Differential Absorption Lidar (DIAL) system has been developed. This instrument is mobile and was applied successfully in two field campaigns: COPS 2007 (Convective and Orographically-induced Precipitation Study), a research and development project of the World Weather Research Programme, and FLUXPAT2009 within the German Research Foundation project Patterns in Soil-Vegetation-Atmosphere Systems: monitoring, modeling and data assimilation". In this paper, the instrument is described and its capabilities are illustrated with measurements examples. The DIAL provides remote sensing data of the atmospheric water-vapor field with previously unachieved resolution. The data products of the DIAL are profiles of absolute humidity with typical resolutions of 15 to 300 m with a temporal resolution of 1 to 10 s and a maximum range of several kilometers at both day and night. But spatial and temporal resolution can be traded off against each other. Intercomparisons with other instruments confirm high accuracy. Beside humidity, also the backscatter field and thus aerosols and clouds are observed simultaneously. The DIAL transmitter is based on an injection-seeded Titanium:Sapphire laser operated at 820 nm which is end-pumped with a diode-pumped Nd:YAG laser. By use of a scanning transmitter with an 80-cm receiving telescope, the measurements can be performed in any direction of interest and the 3-dimensional structure of the water vapor field can be observed.
Jens Bosenberg - One of the best experts on this subject based on the ideXlab platform.
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ground based Differential Absorption Lidar for water vapor and temperature profiling methodology
1998Co-Authors: Jens BosenbergAbstract:A comprehensive formulation of the Differential Absorption Lidar (DIAL) methodology is presented that explicitly includes details of the spectral distributions of both the transmitted and the backscattered light. The method is important for high-accuracy water-vapor retrievals and in particular for temperature measurements. Probability estimates of the error that is due to Doppler-broadened Rayleigh scattering based on an extended experimental data set are presented, as is an analytical treatment of errors that are due to averaging in the nonlinear retrieval scheme. System performance requirements are derived that show that water-vapor retrievals with an accuracy of better than 5% and temperature retrievals with an accuracy of better than 1 K in the entire troposphere are feasible if the error that results from Rayleigh-Doppler correction can be avoided. A modification of the DIAL technique, high-spectral-resolution DIAL avoids errors that are due to Doppler-broadened Rayleigh backscatter and permits simultaneous water-vapor and wind measurements with the same system.
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ground based Differential Absorption Lidar for water vapor profiling assessment of accuracy resolution and meteorological applications
1998Co-Authors: Volker Wulfmeyer, Jens BosenbergAbstract:The accuracy and the resolution of water-vapor measurements by use of the ground-based Differential Absorption Lidar (DIAL) system of the Max-Planck-Institute (MPI) are determined. A theoretical analysis, intercomparisons with radiosondes, and measurements in high-altitude clouds allow the conclusion that, with the MPI DIAL system, water-vapor measurements with a systematic error of <5% in the whole troposphere can be performed. Special emphasis is laid on the outstanding daytime and nighttime performance of the DIAL system in the lower troposphere. With a time resolution of 1 min the statistical error varies between 0.05 g/m(3) in the near range using 75 m and-depending on the meteorological conditions-approximately 0.25 g/m(3) at 2 km using 150-m vertical resolution. When the eddy correlation method is applied, this accuracy and resolution are sufficient to determine water-vapor flux profiles in the convective boundary layer with a statistical error of <10% in each data point to approximately 1700 m. The results have contributed to the fact that the DIAL method has finally won recognition as an excellent tool for tropospheric research, in particular for boundary layer research and as a calibration standard for radiosondes and satellites.
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single mode operation of an injection seeded alexandrite ring laser for application in water vapor and temperature Differential Absorption Lidar
1996Co-Authors: Volker Wulfmeyer, Jens BosenbergAbstract:A major improvement of a Differential Absorption Lidar (DIAL) system for measurements of tropospheric water vapor and temperature is introduced. A Q-switched unidirectional alexandrite ring laser is injection seeded by a cw Ti:sapphire ring laser. Using an especially developed single-mode electronic, one starts the Q switch when the slave resonator is in resonance with the frequency of the Ti:sapphire laser. Long-term single-mode operation of the alexandrite laser is achieved. A single-shot spectral linewidth of <40 MHz and a frequency stability of 15 MHz rms can be specified. Thus what is to our knowledge the first single-mode DIAL system in the near infrared is presented.
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injection seeded alexandrite ring laser performance and application in a water vapor Differential Absorption Lidar
1995Co-Authors: Volker Wulfmeyer, Jens Bosenberg, Stefan Lehmann, C Senff, St SchmitzAbstract:A new laser system for use of Differential Absorption Lidar (DIAL) in measurements of tropospheric water vapor and temperature is introduced. This system operates in the 720 – 780-nm region and is configured as an alexandrite ring laser injection seeded by a cw Ti:sapphire ring laser. This combination provides for the necessary narrow-bandwidth, high-frequency stability and excellent spectral purity. A bandwidth of <5.0 × 10−3 cm−1, a frequency stability of 2.1 × 10−3 cm−1 rms, and a spectral purity of 99.995% at 726 nm have been achieved during extended periods of operation. A comparison of a DIAL water-vapor measurement with a radiosonde in the boundary layer between 500 and 2000 m was performed. The maximum deviation between the humidity profiles is 15%, the standard deviation 1.6%, and the difference between the mean values 1%.
Amin R Nehrir - One of the best experts on this subject based on the ideXlab platform.
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field deployable diode laser based Differential Absorption Lidar dial for profiling water vapor
2015Co-Authors: Scott Spuler, Matthew Hayman, Kevin Repasky, Bruce Morley, Drew Moen, Amin R NehrirAbstract:Abstract. A field-deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based Differential Absorption Lidar (DIAL) laboratory prototypes was constructed and tested. Significant advances are discussed, including a unique shared telescope design that allows expansion of the outgoing beam for eye-safe operation with optomechanical and thermal stability; multistage optical filtering enabling measurement during daytime bright-cloud conditions; rapid spectral switching between the online and offline wavelengths enabling measurements during changing atmospheric conditions; and enhanced performance at lower ranges by the introduction of a new filter design and the addition of a wide field-of-view channel. Performance modeling, testing, and intercomparisons are performed and discussed. In general, the instrument has a 150 m range resolution with a 10 min temporal resolution; 1 min temporal resolution in the lowest 2 km of the atmosphere is demonstrated. The instrument is shown capable of autonomous long-term field operation – 50 days with a > 95% uptime – under a broad set of atmospheric conditions and potentially forms the basis for a ground-based network of eye-safe autonomous instruments needed for the atmospheric sciences research and forecasting communities.
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progress towards an autonomous field deployable diode laser based Differential Absorption Lidar dial for profiling water vapor in the lower troposphere
2013Co-Authors: Kevin Repasky, Scott Spuler, Amin R Nehrir, Drew Moen, J L CarlstenAbstract:A laser transmitter has been developed and incorporated into a micro-pulse Differential Absorption Lidar (DIAL) for water vapor profiling in the lower troposphere as an important step towards long-term autonomous field operation. The laser transmitter utilizes two distributed Bragg reflector (DBR) diode lasers to injection seed a pulsed tapered semiconductor optical amplifier (TSOA), and is capable of producing up to 10 mJ of pulse energy with a 1 ms pulse duration and a 10 kHz pulse repetition frequency. The on-line wavelength of the laser transmitter can operate anywhere along the water vapor Absorption feature centered at 828.187 nm (in vacuum) depending on the prevailing atmospheric conditions, while the off-line wavelength operates at 828.287 nm. This laser transmitter has been incorporated into a DIAL instrument utilizing a 35.6 cm Schmidt-Cassegrain telescope and fiber coupled avalanche photodiode (APD) operating in the photon counting mode. The performance of the DIAL instrument was demonstrated over a ten-day observation period. During this observation period, data from radiosondes were used to retrieve water vapor number density profiles for comparisons with the number density profiles retrieved from the DIAL data.
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micropulse water vapor Differential Absorption Lidar transmitter design and performance
2012Co-Authors: Amin R Nehrir, Kevin Repasky, J L CarlstenAbstract:An all diode-laser-based micropulse Differential Absorption Lidar (DIAL) laser transmitter for tropospheric water vapor and aerosol profiling is presented. The micropulse DIAL (MPD) transmitter utilizes two continuous wave (cw) external cavity diode lasers (ECDL) to seed an actively pulsed, overdriven tapered semiconductor optical amplifier (TSOA). The MPD laser produces up to 7 watts of peak power over a 1 µs pulse duration (7 µJ) and a 10 kHz pulse repetition frequency. Spectral switching between the online and offline seed lasers is achieved on a 1Hz basis using a fiber optic switch to allow for more accurate sampling of the atmospheric volume between the online and offline laser shots. The high laser spectral purity of greater than 0.9996 coupled with the broad tunability of the laser transmitter will allow for accurate measurements of tropospheric water vapor in a wide range of geographic locations under varying atmospheric conditions. This paper describes the design and performance characteristics of a third generation MPD laser transmitter with enhanced laser performance over the previous generation DIAL system.
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eye safe diode laser based micropulse Differential Absorption Lidar dial for water vapor profiling in the lower troposphere
2011Co-Authors: Amin R Nehrir, Kevin Repasky, J L CarlstenAbstract:Abstract A second-generation diode-laser-based master oscillator power amplifier (MOPA) configured micropulse Differential Absorption Lidar (DIAL) instrument for profiling of lower-tropospheric water vapor is presented. The DIAL transmitter is based on a continuous wave (cw) external cavity diode laser (ECDL) master oscillator that is used to injection seed two cascaded tapered semiconductor optical power amplifiers, which deliver up to 2-μJ pulse energies over a 1-μs pulse duration at 830 nm with an average power of ∼40 mW at a pulse repetition frequency of 20 kHz. The DIAL receiver utilizes a commercial 28-cm-diameter Schmidt–Cassegrain telescope, a 250-pm narrowband optical filter, and a fiber-coupled single-photon-counting Avalanche photodiode (APD) detector, yielding a far-field full-angle field of view of 170 μrad. A detailed description of the second-generation Montana State University (MSU) DIAL instrument is presented. Water vapor number density profiles and time–height cross sections collected w...
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water vapor profiling using a widely tunable amplified diode laser based Differential Absorption Lidar dial
2009Co-Authors: Amin R Nehrir, Kevin Repasky, J L Carlsten, Michael D Obland, Joseph A ShawAbstract:A Differential Absorption Lidar (DIAL) instrument for automated profiling of water vapor in the lower troposphere has been designed, tested, and is in routine operation at Montana State University. The laser transmitter for the DIAL instrument uses a widely tunable external cavity diode laser (ECDL) to injection seed two cascaded semiconductor optical amplifiers (SOAs) to produce a laser transmitter that accesses the 824‐841-nm spectral range. The DIAL receiver utilizes a 28-cm-diameter Schmidt‐Cassegrain telescope; an avalanche photodiode (APD) detector; and a narrowband optical filter to collect, discriminate, and measure the scattered light. A technique of correcting for the wavelength-dependent incident angle upon the narrowband optical filter as a function of range has been developed to allow accurate water vapor profiles to be measured down to 225 m above the surface. Data comparisons using the DIAL instrument and collocated radiosonde measurements are presented demonstrating the capabilities of the DIAL instrument.
Liang Mei - One of the best experts on this subject based on the ideXlab platform.
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evaluation of systematic errors for the continuous wave no2 Differential Absorption Lidar employing a multimode laser diode
2020Co-Authors: Yuan Cheng, Zheng Kong, Zhen Zhang, Chenguang Yang, Zhenfeng Gong, Kun Liu, Liang MeiAbstract:The NO2-Differential Absorption Lidar (NO2-DIAL) technique has been of great interest for atmospheric NO2 profiling. Comprehensive studies on measurement errors in the NO2-DIAL technique are vital for the accurate retrieval of the NO2 concentration. This work investigates the systematic errors of the recently developed continuous-wave (CW) NO2-DIAL technique based on the Scheimpflug principle and a high-power CW multimode laser diode. Systematic errors introduced by various factors, e.g., uncertainty of the NO2 Differential Absorption cross-section, Differential Absorption due to other gases, spectral drifting of the λon and λoff wavelengths, wavelength-dependent extinction and backscattering effect, have been theoretically and experimentally studied for the CW-DIAL technique. By performing real-time spectral monitoring on the emission spectrum of the laser diode, the effect of spectral drifting on the NO2 Differential Absorption cross-section is negligible. The temperature-dependent NO2 Absorption cross-section in the region of 220–294 K can be interpolated by employing a linear fitting method based on high-precision Absorption spectra at 220, 240, and 294 K. The relative error for the retrieval of the NO2 concentration is estimated to be less than 0.34% when employing the interpolated spectrum. The primary interference molecule is found to be the glyoxal (CHOCHO), which should be carefully evaluated according to its relative concentration in respect to NO2. The systematic error introduced by the backscattering effect is subjected to the spatial variation of the aerosol load, while the extinction-induced systematic error is primarily determined by the difference between the aerosol extinction coefficients at λon and λoff wavelengths. A case study has been carried out to demonstrate the evaluation of systematic errors for practical NO2 monitoring. The comprehensive investigation on systematic errors in this work can be of great value for future NO2 monitoring using the DIAL technique.
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remote sensing of atmospheric no 2 by employing the continuous wave Differential Absorption Lidar technique
2017Co-Authors: Liang Mei, Peng Guan, Zheng KongAbstract:Differential Absorption Lidar (DIAL) technique employed for remote sensing has been so far based on the sophisticated narrow-band pulsed laser sources, which require intensive maintenance during operation. In this work, a continuous-wave (CW) NO2 DIAL system based on the Scheimpflug principle has been developed by employing a compact high-power CW multimode 450 nm laser diode as the light source. Laser emissions at the on-line and off-line wavelengths of the NO2 Absorption spectrum are implemented by tuning the injection current of the laser diode. Lidar signals are detected by a 45° tilted area CCD image sensor satisfying the Scheimpflug principle. Range-resolved NO2 concentrations on a near-horizontal path are obtained by the NO2 DIAL system in the range of 0.3-3 km and show good agreement with those measured by a conventional air pollution monitoring station. A detection sensitivity of ± 0.9 ppbv at 95% confidence level in the region of 0.3-1 km is achieved with 15-minute averaging and 700 m range resolution during hours of darkness, which allows accurate concentration measurement of ambient NO2. The low-cost and robust DIAL system demonstrated in this work opens up many possibilities for field NO2 remote sensing applications.
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Continuous-wave Differential Absorption Lidar
2015Co-Authors: Liang Mei, Mikkel BrydegaardAbstract:This work proves the feasibility of a novel concept of Differential Absorption Lidar based on the Scheimpflug prin-ciple. The range-resolved atmospheric backscattering signal of a laser beam is retrieved by employing a tilted linear sen-sor with a Newtonian telescope, satisfying the Scheimpflug condition. Infinite focus depth is achieved despite employ-ing a large optical aperture. The concept is demonstrated by measuring the range-resolved atmospheric oxygen con-centration with a tunable continuous-wave narrow-band laser diode emitting around 761 nm over a path of one kilome-ter during night time. Laser power requirements for daytime operation are also investigated and validated with single-band atmospheric aerosol measurements by employing a broad-band 3.2-W laser diode. The results presented in this work show the potential of employing the continuous-wave Differential Absorption Lidar (CW-DIAL) technique for remote profiling of atmospheric gases in daytime if high-power narrow-band continuous-wave light sources were to be employed.
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Differential Absorption Lidar system employed for background atomic mercury vertical profiling in south china
2014Co-Authors: Liang Mei, Sune Svanberg, Guangyu ZhaoAbstract:A Differential Absorption Lidar (DIAL) system based on a Nd:YAG laser pumped narrow-band dye laser is developed and employed to monitor the atmospheric background concentration of atomic mercury in Guangzhou, South China. Atmospheric oxygen is also studied by using neighboring wavelengths to the mercury Absorption line (253.7 nm), and is used to verify the operation of the DIAL system. A 24-hour continuous monitoring of background mercury concentration is performed and the average atomic mercury concentration below 330 m is between 5 ng/m(3) and 12 ng/m(3). (C) 2013 Elsevier Ltd. All rights reserved.
J L Carlsten - One of the best experts on this subject based on the ideXlab platform.
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progress towards an autonomous field deployable diode laser based Differential Absorption Lidar dial for profiling water vapor in the lower troposphere
2013Co-Authors: Kevin Repasky, Scott Spuler, Amin R Nehrir, Drew Moen, J L CarlstenAbstract:A laser transmitter has been developed and incorporated into a micro-pulse Differential Absorption Lidar (DIAL) for water vapor profiling in the lower troposphere as an important step towards long-term autonomous field operation. The laser transmitter utilizes two distributed Bragg reflector (DBR) diode lasers to injection seed a pulsed tapered semiconductor optical amplifier (TSOA), and is capable of producing up to 10 mJ of pulse energy with a 1 ms pulse duration and a 10 kHz pulse repetition frequency. The on-line wavelength of the laser transmitter can operate anywhere along the water vapor Absorption feature centered at 828.187 nm (in vacuum) depending on the prevailing atmospheric conditions, while the off-line wavelength operates at 828.287 nm. This laser transmitter has been incorporated into a DIAL instrument utilizing a 35.6 cm Schmidt-Cassegrain telescope and fiber coupled avalanche photodiode (APD) operating in the photon counting mode. The performance of the DIAL instrument was demonstrated over a ten-day observation period. During this observation period, data from radiosondes were used to retrieve water vapor number density profiles for comparisons with the number density profiles retrieved from the DIAL data.
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micropulse Differential Absorption Lidar for identification of carbon sequestration site leakage
2013Co-Authors: William Johnson, Kevin Repasky, J L CarlstenAbstract:A scanning Differential Absorption Lidar (DIAL) instrument for identification of carbon dioxide leaks at carbon sequestration sites has been developed and initial data has been collected at Montana State University. The laser transmitter uses two tunable discrete mode laser diodes operating in the continuous-wave mode with one locked to the online Absorption wavelength and the other operating at the offline wavelength. Two in-line fiber optic switches are used to switch between online and offline operation. After the fiber optic switch, an acousto-optic modulator is used to generate a pulse train used to injection seed an erbium-doped fiber amplifier to produce eye-safe laser pulses with maximum pulse energies of 66 μJ, a pulse repetition frequency of 15 kHz, and an operating wavelength of 1.571 μm. The DIAL receiver uses a 28 cm diameter Schmidt–Cassegrain telescope to collect that backscattered light, which is then monitored using a photomultiplier tube module operating in the photon counting mode. The DIAL has measured carbon dioxide profiles from 1 to 2.5 km with 60 min temporal averaging. Comparisons of DIAL measurements with a Licor LI-820 gas analyzer point sensor have been made.
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micropulse water vapor Differential Absorption Lidar transmitter design and performance
2012Co-Authors: Amin R Nehrir, Kevin Repasky, J L CarlstenAbstract:An all diode-laser-based micropulse Differential Absorption Lidar (DIAL) laser transmitter for tropospheric water vapor and aerosol profiling is presented. The micropulse DIAL (MPD) transmitter utilizes two continuous wave (cw) external cavity diode lasers (ECDL) to seed an actively pulsed, overdriven tapered semiconductor optical amplifier (TSOA). The MPD laser produces up to 7 watts of peak power over a 1 µs pulse duration (7 µJ) and a 10 kHz pulse repetition frequency. Spectral switching between the online and offline seed lasers is achieved on a 1Hz basis using a fiber optic switch to allow for more accurate sampling of the atmospheric volume between the online and offline laser shots. The high laser spectral purity of greater than 0.9996 coupled with the broad tunability of the laser transmitter will allow for accurate measurements of tropospheric water vapor in a wide range of geographic locations under varying atmospheric conditions. This paper describes the design and performance characteristics of a third generation MPD laser transmitter with enhanced laser performance over the previous generation DIAL system.
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eye safe diode laser based micropulse Differential Absorption Lidar dial for water vapor profiling in the lower troposphere
2011Co-Authors: Amin R Nehrir, Kevin Repasky, J L CarlstenAbstract:Abstract A second-generation diode-laser-based master oscillator power amplifier (MOPA) configured micropulse Differential Absorption Lidar (DIAL) instrument for profiling of lower-tropospheric water vapor is presented. The DIAL transmitter is based on a continuous wave (cw) external cavity diode laser (ECDL) master oscillator that is used to injection seed two cascaded tapered semiconductor optical power amplifiers, which deliver up to 2-μJ pulse energies over a 1-μs pulse duration at 830 nm with an average power of ∼40 mW at a pulse repetition frequency of 20 kHz. The DIAL receiver utilizes a commercial 28-cm-diameter Schmidt–Cassegrain telescope, a 250-pm narrowband optical filter, and a fiber-coupled single-photon-counting Avalanche photodiode (APD) detector, yielding a far-field full-angle field of view of 170 μrad. A detailed description of the second-generation Montana State University (MSU) DIAL instrument is presented. Water vapor number density profiles and time–height cross sections collected w...
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water vapor profiling using a widely tunable amplified diode laser based Differential Absorption Lidar dial
2009Co-Authors: Amin R Nehrir, Kevin Repasky, J L Carlsten, Michael D Obland, Joseph A ShawAbstract:A Differential Absorption Lidar (DIAL) instrument for automated profiling of water vapor in the lower troposphere has been designed, tested, and is in routine operation at Montana State University. The laser transmitter for the DIAL instrument uses a widely tunable external cavity diode laser (ECDL) to injection seed two cascaded semiconductor optical amplifiers (SOAs) to produce a laser transmitter that accesses the 824‐841-nm spectral range. The DIAL receiver utilizes a 28-cm-diameter Schmidt‐Cassegrain telescope; an avalanche photodiode (APD) detector; and a narrowband optical filter to collect, discriminate, and measure the scattered light. A technique of correcting for the wavelength-dependent incident angle upon the narrowband optical filter as a function of range has been developed to allow accurate water vapor profiles to be measured down to 225 m above the surface. Data comparisons using the DIAL instrument and collocated radiosonde measurements are presented demonstrating the capabilities of the DIAL instrument.