Differential Absorption Lidar Research Articles

A 3.2-μm Wavelength Integrated Path Differential Absorption Lidar for Probing Open-Path Benzene Gas

A 3.2-<i>μ</i>m Wavelength Integrated Path Differential Absorption Lidar for Probing Open-Path Benzene Gas

The effects of warm-air intrusions in the high Arctic on cirrus clouds

Abstract. Warm-air intrusions (WAIs) are responsible for the transportation of warm and moist air masses from the mid-latitudes into the high Arctic (&gt; 70° N). In this work, we study cirrus clouds that form during WAI events (WAI cirrus) and during undisturbed Arctic conditions (AC cirrus) and investigate possible differences between the two cloud types based on their macrophysical and optical properties with a focus on relative humidity over ice (RHi). We use airborne measurements from the combined high-spectral-resolution and differential-absorption lidar, WALES, performed during the HALO-(AC)3 campaign. We classify each research flight and the measured clouds as either AC or WAI, based on the ambient conditions, and study the macrophysical, geometrical and optical characteristics for each cirrus group. As our main parameter we choose the relative humidity over ice (RHi), which we calculate RHi by combining the lidar water vapor measurements with model temperatures. Ice formation occurs at certain RHi values depending on the dominant nucleation process taking place. RHi can thus be used as an indication of the nucleation process and the structure of cirrus clouds. We find that during WAI events the Arctic is warmer and moister and WAI cirrus clouds are both geometrically and optically thicker compared to AC cirrus. WAI cirrus clouds and the layer directly surrounding them are more frequently supersaturated, also at high supersaturations over the threshold for homogeneous ice nucleation (HOM). AC cirrus clouds have a supersaturation-dominated cloud top and a subsaturated cloud base. WAI cirrus clouds also have high supersaturations at cloud top but also at cloud base.

Three-dimensional detection of CO2 and wind using a 1.57 µm coherent differential absorption lidar

A 1.57-µm coherent differential absorption lidar is demonstrated for measuring three-dimensional CO2 and wind fields simultaneously. The maximum detection range of CO2 is up to 6 km with a range resolution of 120 m and a time resolution of 1 min. A preliminary assessment of instrument performance is made with a 1-week continuous observation. The CO2 concentration over a column from 1920 to 2040 m is compared with the one measured by an optical cavity ring-down spectrometer placed on a 2 km-away meteorological tower. The concentration is strongly correlated with the in-situ spectrometer with a correlation coefficient and RMSE of 0.91 and 5.24 ppm. The measurement accuracy of CO2 is specified with a mean and standard deviation of 2.05 ppm and 7.18 ppm, respectively. The regional CO2 concentration and the three-dimensional wind fields are obtained through different scanning modes. Further analysis is conducted on vertical mixing and horizontal transport of CO2 by combining with the measured wind fields.

All-fiber multifunction differential absorption CO2 lidar integrating single-photon and coherent detection

All-fiber multifunction differential absorption CO2 lidar integrating single-photon and coherent detection

Global estimation of range resolved thermodynamic profiles from micropulse differential absorption lidar

We demonstrate thermodynamic profile estimation with data obtained using the MicroPulse DIAL such that the retrieval is entirely self contained. The only external input is surface meteorological variables obtained from a weather station installed on the instrument. The estimator provides products of temperature, absolute humidity and backscatter ratio such that cross dependencies between the lidar data products and raw observations are accounted for and the final products are self consistent. The method described here is applied to a combined oxygen DIAL, potassium HSRL, water vapor DIAL system operating at two pairs of wavelengths (nominally centered at 770 and 828 nm). We perform regularized maximum likelihood estimation through the Poisson Total Variation technique to suppress noise and improve the range of the observations. A comparison to 119 radiosondes indicates that this new processing method produces improved temperature retrievals, reducing total errors to less than 2 K below 3 km altitude and extending the maximum altitude of temperature retrievals to 5 km with less than 3 K error. The results of this work definitively demonstrates the potential for measuring temperature through the oxygen DIAL technique and furthermore that this can be accomplished with low-power semiconductor-based lidar sensors.

Power-modulated integrated path differential absorption lidar for probing benzene concentration.

Aimed at the regional open-path detection of benzene (C 6 H 6) in the atmosphere, a power-modulated integrated path differential absorption (PM-IPDA) lidar is introduced and demonstrated. Two tunable interband cascade lasers (ICLs) with about 3.2µm wavelength are utilized to generate the required PM optical signal. These two operation central wavelengths (CWs) of the PM-IPDA lidar are, respectively, 3236.6 and 3187.1nm, which can mitigate the influence of significant gases such as H 2 O, C H 4, and HCl on the detection performance. In this work, the fast Fourier transform algorithm is used to retrieve the measured values with the time resolution of 0.1s corresponding to 104 sampling bins at the sampling rate of 100kSps/s. The modulated frequency of the PM-IPDA lidar is selected as 10kHz by laboratory experiments. The slow fluctuation characteristic of the benzene absorption spectrum within the vicinity region of 3.2µm reduces the impact of small wavelength fluctuations on the performance of PM-IPDA lidar, although a scheme modulated only the driving current causes wavelength fluctuations of ∼±0.2n m. These laboratory experiments also indicate the PM-IPDA lidar can reduce the error resulting from 1/f noise. Open-path observation experiments show that the detection limit is about 0.60m g⋅m -3 and that the PM-IPDA lidar can be used for the regional open-path real-time detection of benzene.

Airborne atmospheric carbon dioxide measurement using 1.5 µm laser double-pulse IPDA lidar over a desert area.

An integrated path differential absorption (IPDA) lidar can accurately measure regional C O 2 weighted column average concentrations (X C O 2), which are crucial for understanding the carbon cycle in climate change studies. To verify the performance and data inversion methods of space-borne IPDA lidar, in July 2021, we conducted an airborne lidar validation experiment in Dunhuang, Gansu Province, China. An aircraft was equipped with a lidar system developed to measure X C O 2 and an in situ greenhouse gas analyzer (GGA). To minimize measurement errors, energy monitoring was optimized. The system bias error of the DAOD was determined by changing the laser output mode from the off/on to the on/on mode. The X C O 2 inversion results obtained through comparing the schemes of averaging signals before "log (logarithm)" and averaging after "log" indicate that the former performs better. The IPDA lidar measured X C O 2 over the validation site at 405.57ppm, and both the IPDA lidar and GGA measured sudden changes in the C O 2 concentration. The assimilation data showed a similar trend according to the altitude to the data measured by the in situ instrument. A comparison of the mean X C O 2 derived from the GGA results and assimilation data with the IPDA lidar measurements showed biases of 0.80 and 1.12ppm, respectively.

Airborne lidar measurements of atmospheric CO2 column concentrations to cloud tops made during the 2017 ASCENDS/ABoVE campaign

Abstract. We measured the column-averaged atmospheric CO2 mixing ratio (XCO2) to a variety of cloud tops with an airborne pulsed multi-wavelength integrated path differential absorption (IPDA) lidar during NASA's 2017 ASCENDS/ABoVE airborne campaign. Measurements of height-resolved atmospheric backscatter profiles allow this lidar to retrieve XCO2 to cloud tops, as well as to the ground, with accurate knowledge of the photon path length. We validated these measurements with those from an onboard in situ CO2 sensor during spiral-down maneuvers. These lidar measurements were 2–3 times better than those from previous airborne campaigns due to our using a wavelength step-locked laser transmitter and a high-efficiency detector for this campaign. Precisions of 0.6 parts per million (ppm) were achieved for 10 s average measurements to mid-level clouds and 0.9 ppm to low-level clouds at the top of the planetary boundary layer. This study demonstrates the lidar's capability to fill in XCO2 measurement gaps in cloudy regions and to help resolve the vertical and horizontal distributions of atmospheric CO2. Future airborne campaigns and spaceborne missions with this capability can be used to improve atmospheric transport modeling, flux estimation and carbon data assimilation.

Water vapor measurements inside clouds and storms using a differential absorption radar

Abstract. NASA's Vapor In-cloud Profiling Radar (VIPR) is a tunable G-band radar designed for in-cloud and precipitation humidity remote sensing. VIPR estimates humidity using the differential absorption radar (DAR) technique. This technique exploits the difference between atmospheric attenuation at different frequencies (“on” and “off” an absorption line) and combines it with the ranging capabilities of the radar to estimate the absorbing gas concentration along the radar path. We analyze the VIPR humidity measurements during two NASA field campaigns: (1) the Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) campaign, with the objective of studying wintertime snowstorms focusing on east coast cyclones; and (2) the Synergies Of Active optical and Active microwave Remote Sensing Experiment (SOA2RSE) campaign, which studied the synergy between DAR (VIPR) and differential absorption lidar (DIAL, the High altitude Lidar Observatory – HALO) measurements. We discuss a comparison with dropsondes launched during these campaigns as well as an intercomparison against the ERA5 reanalysis fields. Thus, this study serves as an additional evaluation of ERA5 lower tropospheric humidity fields. Overall, in-cloud and in-snowstorm comparisons suggest that ERA5 and VIPR agree within 20 % or better against the dropsondes. The exception is during SOA2RSE (i.e., in fair weather), where ERA5 exhibits up to a 50 % underestimation above 4 km. We also show a smooth transition in water vapor profiles between the in-cloud and clear-sky measurements obtained from VIPR and HALO respectively, which highlights the complementary nature of these two measurement techniques for future airborne and space-based missions.

Monitoring the Baric Modulation of Gas Concentration in the Baksan Neutrino Observatory Tunnel in the Elbrus Region Using Differential Absorption Lidar

Monitoring the Baric Modulation of Gas Concentration in the Baksan Neutrino Observatory Tunnel in the Elbrus Region Using Differential Absorption Lidar

Broadband continuous-wave differential absorption lidar for atmospheric remote sensing of water vapor.

What we believe to be a novel low-cost broadband continuous-wave water vapor differential absorption lidar (CW-DIAL) technique has been proposed and implemented by combing the Scheimpflug principle and the differential absorption method. The broadband CW-DIAL technique utilizes an 830-nm high-power multimode laser diode with 3-W output power as a tunable light source and a CMOS image sensor tilted at 45° as the detector. A retrieval algorithm dedicated for the broadband CW-DIAL technique has been developed to obtain range-resolved water vapor concentration from the DIAL signal. Atmospheric remote sensing of water vapor has been carried out on a near-horizontal water vapor path to validate the performance of the broadband CW-DIAL system. The retrieved water vapor concentration showed a good consistency with those measured by an air quality monitoring station, with a correlation coefficient of 0.9669. The fitting error of the water vapor concentration is found to be less than 10%. Numerical simulation studies have revealed that the aerosol-induced error on the water vapor concentration is below 5% with a background water vapor concentration of 5 g/m3 for most atmospheric conditions. The experimental results have successfully demonstrated the feasibility of the present broadband CW-DIAL technique for range-resolved water vapor remote sensing.

A review of atmospheric water vapor lidar calibration methods

AbstractAtmospheric water vapor is a crucial factor in the Earth's water cycle. As an important greenhouse gas, changes in the spatio‐temporal distribution of atmospheric water vapor can contribute to the occurrence of various extreme weather phenomena. Lidar, with its high spatial and temporal resolutions, has great potential for applications in water vapor profile detection. Raman lidar and differential absorption lidar (DIAL) have been successfully used to detect atmospheric water vapor. System calibration is crucial to ensure that the measured profile accurately represents the concentration profile of atmospheric water vapor. Choosing an effective system calibration method can ensure the accuracy of long‐term lidar measurements. This paper reviews the latest progress and applications of atmospheric water vapor lidar calibration in recent years. The basic principles of Raman lidar and DIAL calibration are introduced. Various methods and benefits of system calibration are discussed. Raman lidar has three commonly used calibration methods: external calibration, internal calibration, and hybrid calibration methods. The most commonly used method is external calibration based on radiosondes. DIAL is usually implemented with an advantageous self‐calibration method. Finally, potential development directions for atmospheric water vapor lidar and calibration technology are discussed.This article is categorized under: Science of Water &gt; Methods Engineering Water &gt; Methods Human Water &gt; Value of Water

Multi-Frequency Differential Absorption LIDAR (DIAL) System for Aerosol and Cloud Retrievals of CO2/H2O and CH4/H2O

We discuss a remote sensing system that is used to simultaneously detect range-resolved differential absorption LIDAR (light detection and ranging; DIAL) signals and integrated path differential absorption LIDAR signals (IPDA LIDAR) from aerosol targets for ranges up to 22 km. The DIAL/IPDA LIDAR frequency converter consists of an OPO pumped at 1064 nm to produce light at 1.6 μm and operates at 100 Hz pulse repetition frequency. The probe light is free space coupled to a movable platform that contains one transmitter and two receiver telescopes. Hybrid photon counting/current systems increase the dynamic range for detection by two orders of magnitude. Range resolved and column integrated dry-air CO2 and CH4 mixing ratios are obtained from line shape fits of CO2 and CH4 centered at 1602.2 nm and 1645.5 nm, respectively, and measured at 10 different frequencies over ≈1.3 cm−1 bandwidth. The signal-to-noise ratios (SNRs) of the IPDA LIDAR returns from cloud aerosols approach 1000:1 and the uncertainties in the mixing ratios weighted according to the integrated counts over the cloud segments range from 0.1% to 1%. The range-averaged DIAL mixing ratios are in good agreement with the IPDA LIDAR mixing ratios at the 1% to 2% level for both CO2 and CH4. These results can serve as a validation method for future active and passive satellite observational systems.

Inter-/intra-pulse dual-wavelength-operated mid-infrared optical parametric oscillator.

We demonstrate a pulsed mid-infrared (MIR) optical parametric oscillator (OPO) with both inter-pulse and intra-pulse dual-wavelength operation capability. A fiber master oscillator power amplifier incorporating an acousto-optic tunable filter (AOTF) was employed as the pump for the OPO. By finely adjusting the drive wave packets for the AOTF, dual-wavelength pump can be realized within each pulse or between two adjacent pulses. These special temporal-spectral behaviors of the pump can be transferred to MIR via an OPO. In the proof-of-principle experiments, two pump wavelengths at ∼1065 and ∼1076 nm were generated and amplified to ∼31.2 W with equivalent spectral intensities for both pulsation modes. At the highest pump power, total idler power of ∼3.5 W was achieved at ∼3.45 and ∼3.55 µm under both pulsation modes. To the best of our knowledge, this is the first demonstration of both inter-pulse and intra-pulse dual-wavelength MIR generation via an OPO with an identical configuration. It is believed that our design may provide a promising solution to many practical applications including differential absorption lidar and tunable terahertz wave generation.

Remote Measurements of Industrial CO2 Emissions Using a Ground-Based Differential Absorption Lidar in the 2 µm Wavelength Region

Carbon dioxide (CO2) is a known greenhouse gas and one of the largest contributors to global warming in the Earth’s atmosphere. The remote detection and measurement of CO2 from industrial emissions are not routinely carried out and are typically calculated from the fuel combusted or measured directly within ducted vents. However, these methods are not applicable for the quantification of fugitive emissions of CO2. This work presents the results of remote measurement of CO2 emissions using the differential absorption lidar (DIAL) technique at a wavelength of ~2 µm. The results from the DIAL measurements compare well with simultaneous in-stack measurements, these datasets were plotted against each other and can be described by a linear regression of y (t/h) = 1.04 x − 0.02, suggesting any bias in the DIAL data is likely small. Moreover, using the definition outlined in EN 15267-3 a lower detection limit of 0.12 t/h was estimated for the 2 µm wavelength DIAL data, this is three orders of magnitude lower than the corresponding CO2 detection limit measured by NPL in the 1.5 µm wavelength region. Thus, this paper demonstrates the feasibility of high-resolution, ground-based DIAL measurements for quantifying industrial CO2 emissions.

Vertical profiles and regional transport of ozone in typical area of Yangtze-Huaihe River Basin during the autumn base on multiple lidars

In recent years, the Yangtze-Huaihe River Basin has become one of the key areas of air pollution control in China, however, there are some differences in the spatial and temporal characteristics of ozone in different cities. In order to explore the vertical structure characteristics of ozone in Yangtze-Huaihe River Basin and its influencing factors, this study analyzed the vertical and horizontal distribution of ozone in typical cities in the Yangtze-Huaihe River Basin in October 2021 by using differential absorption lidar(DIAL), temperature and humidity profile lidar and wind profile radar system, studied two typical ozone pollution processes, and the meteorological factors of ozone pollution at vertical height. The results showed that the ozone pollution was mainly produced locally from October 13 to 14, while the ozone pollution was affected by local production and transport from October 21 to 31, the average ozone concentration reached a maximum of 357.6 μg/m3. There is a significant residual layer at night. The temperature of 272.85–285.88 k and water vapor mixing ratio of 3.22–5.7 g/kg are favorable for ozone generation in Huaibei City. The ozone contribution of Henan, Shandong and Anhui to Huaibei City is above 200 μg/m3. The study on the vertical structure of ozone is helpful to fill the knowledge gap between the evolution of ozone events in Yangtze-Huaihe River Basin.

Results of Remote Monitoring of Methane Concentration in the Air of Western Siberia Using the On-board Infrared Lidar Complex

The description of the developed infrared on-board differential absorption lidar for measuring methane content in the air was presented. The lidar was installed on board of aircraft-laboratory Tu-134 "Optic". Flight tests of the developed lidar and experimental measurements of methane concentration along the vertical routing were carried out in the summer atmosphere of mid-latitudes. Lidar measurements of methane content in the air were analyzed. They were compared with local measurements from the gas analyser installed on board of aircraftlaboratory and the results of preliminary numerical modelling. It was concluded that the on-board lidar can measure methane concentration within background values in the mid-latitude summer atmosphere.

Local comparisons of tropospheric ozone: vertical soundings at two neighbouring stations in southern Bavaria

Abstract. In this study ozone profiles of the differential-absorption lidar at Garmisch-Partenkirchen are compared with those of ozone sondes of the Forschungszentrum Jülich and of the Meteorological Observatory Hohenpeißenberg (German Weather Service). The lidar measurements are quality assured by the highly accurate nearby in situ ozone measurements at the Wank (1780 m a.s.l.) and Zugspitze (2962 m a.s.l.) summits and at the Global Atmosphere Watch station Schneefernerhaus (UFS, 2670 m a.s.l.), at distances of 9 km or less from the lidar. The mixing ratios of the lidar agree with those of the monitoring stations, with a standard deviation (SD) of 1.5 ppb, and feature a slight positive offset of 0.6 ± 0.6 ppb (SD) conforming to the known −1.8 % calibration bias of the in situ instruments. Side-by-side soundings of the lidar and electrochemical (ECC) sonde measurements in February 2019 by a team of the Forschungszentrum Jülich shows small positive ozone offsets for the sonde with respect to the lidar and the mountain stations (0.5 to 3.4 ppb). After applying an altitude-independent bias correction to the sonde data an agreement to within just ±2.5 ppb in the troposphere was found, which we regard as the wintertime uncertainty of the lidar. We conclude that the recently published uncertainties of the lidar in the final configuration since 2012 are realistic and rather small for low to moderate ozone concentrations. Comparisons of the lidar with the Hohenpeißenberg routine measurements with Brewer-Mast sondes are more demanding because of the distance of 38 km between the two sites implying significant ozone differences in some layers, particularly in summer. Our comparisons cover the 3 years September 2000 to August 2001, 2009, and 2018. A slight negative average offset (−3.64 ± 3.72 ppb (SD)) of the sondes with respect to the lidar was found. We conclude that most Hohenpeißenberg sonde data could be improved in the troposphere by recalibration with the Zugspitze station data (1978 to 2011 summit, afterwards UFS). This would not only remove the average offset but also greatly reduce the variability of the individual offsets. The comparison for 2009 suggests a careful partial re-evaluation of the lidar measurements between 2007 and 2011 for altitudes above 6 km, where occasionally a negative bias occurred.

Design Analysis of Mid IR DIAL System for Detection of Hazardous Chemical Species

Nowadays, both military and public agencies are concerned with the remote detection of toxic gases and chemical warfare agents in the atmosphere. A promising method for the remote detection of such harmful chemicals in the atmosphere is Differential Absorption Lidar (DIAL). In the current paper, system design analysis has been carried out to build a DIAL system for the detection of toxic chemical warfare agents, chemical warfare simulants, explosive precursors, and pollutants. The proposed DIAL system comprises an Optical Parametric Oscillator (OPO) based tuneable laser, a 203 mm diameter Cassegrain telescope, a TE-cooled MCT detector, suitable data acquisition hardware, etc. The DIAL output parameters like return signals, SNR, and minimum measurable concentrations have been simulated under different weather conditions such as clear sky, moderately hazy sky, and hazy atmospheric conditions for given system input parameters (pulse energy, detectivity, bandwidth, DAQ resolution, etc.). We have considered chemicals such as Sarin, Thiodiglycol (TDG), acetone, and methane to be detected using the system. Analysis has been carried out for these chemicals present at different locations with varying concentrations. Our analysis reveals that the DIAL system with a laser transmitter of 5 mJ energy and 203 mm receiver telescope is capable of detecting a few ppm concentrations of toxic chemicals present anywhere between the ranges from a few tens of meters to 2 km with topographic target present. The sensitivity of the system in terms of minimum detectable concentrations for the considered chemicals is also estimated for different atmospheric conditions. It is seen that the minimum detectable concentration of TDG is 3.2 ppm in clear weather conditions which increases to 9.2 ppm under a hazy atmosphere. A similar analysis has been carried out for other toxic chemicals and has been discussed in the paper.

Remote Detection and Quantification of Methane Emissions Based on Hyperspectral Data Analysis

Measurement of methane emissions from leaks occurring on the territorially extensive network of transmission gas grid is a topical issue and highly desirable from the point of view of safety and reducing methane emissions into the atmosphere. Remote detection of methane is a problem whose technical solution is based on several types of optoelectronic devices, e.g. thermal imaging cameras with sets of optical filters, spectroradiometers, laser systems of the DIAL (DIfferential Absorption Lidar) type. On the other hand, the quantification of emission magnitudes is in most cases realized by spectoradiometric systems. This paper will present a method for analyzing hyperspectral data from an imaging Fourier infrared spectroradiometer. Measurements will be made on a purpose-built bench simulating methane emissions from a transmission network. Data obtained from ground level under different atmospheric conditions will be presented, together with the results of their analysis for different methane emissions.