Differential Absorption Lidar Research Articles

Monitoring the baric modulation of gas concentration in the Baksan Neutrino Observatory tunnel in the Elbrus Region using a differential absorption lidar

For the first time, concentrations of gases 12CO2,13CO2, СН4, Н2О and the dynamics of Earth degassing under the changing atmospheric pressure were remotely analyzed using a differential absorption lidar. To reduce the influence of external meteorological factors, the sensing was carried out in a dead-end tunnel of the Baksan Neutrino Observatory of the Institute for Nuclear Research of the Russian Academy of Sciences.

2.7 μm backward wave optical parametric oscillator source for CO2 spectroscopy.

In this work, a novel 2.7 µm source used for CO2 and H2O vapor spectroscopy using the backward propagating wave of a backward wave optical parametric oscillator (BWOPO) is demonstrated for the first time to our knowledge. The unique properties of BWOPOs eliminate the need for additional spectral narrowing or wavelength stabilization, enabling the use of a multi-longitudinal mode Q-switched pump laser centered around 1030 nm. A full characterization of the source is presented, revealing a central output at 2712 nm, showcasing a temperature tuning of -1.77 GHz/K, and achieving an output pulse energy of 2.3 µJ. Novel methods are introduced for measuring the linewidth and wavelength stability using the ambient laboratory air. These approaches demonstrate a narrow output of 43 pm and establish an upper limit of stability at 65 MHz, with no active means of stabilization. These findings underscore the potential of BWOPOs as a robust platform for future differential absorption lidar (DIAL) systems.

An Improved CH4 Profile Retrieving Method for Ground-Based Differential Absorption Lidar

Range-resolved CH4 concentration measurement is important prior data for atmospheric physical and chemical models. Ground-based differential absorption lidar (DIAL) can measure the vertical distribution of CH4 concentration in the atmosphere. The traditional method uses lidar observational data and the lidar equation to calculate profiles, but the inversion accuracy is greatly affected by noise. Although some denoising methods can improve accuracy at low altitudes, the low signal-to-noise ratio caused by the effect of aerosol Mie scattering and lower aerosol concentrations at high altitudes cannot be solved. Here, an improved cubic smoothing spline fitting CH4 concentration profile inversion method is proposed to address this challenge. By adding a penalty term of the second derivative of the conventional cubic spline function to the objective function, this penalty term acts to smooth the fitting, allowing the fitting function to avoid necessarily passing through those noisy sampling points. This avoids the large fluctuations caused by noisy sampling points, effectively suppresses noise, captures signals with lower noise levels, and thereby enhances the inversion accuracy of the profiles. Simulations and case studies demonstrated the superiority of the proposed method. Compared with the traditional method, cubic smoothing spline fitting can reduce the mean error of the whole CH4 profile by 85.54%. The standard deviation of CH4 concentration retrieved is 3.59 ppb–90.29 ppb and 0.01 ppb–6.75 ppb smaller than the traditional method and Chebyshev fitting, respectively. Three real cases also indicate that the CH4 concentration retrieved by cubic smoothing spline fitting is more consistent with in-situ measurements. In addition, long-term DIAL observations have also revealed notable diurnal and seasonal trends in CH4 concentration at observation sites.

Simulation and analysis of the CO2 range-resolved differential absorption lidar system at 2 μm

The range-resolved differential absorption lidar is a high-precision device to measure the concentration of carbon dioxide. This paper provides a system-wide theoretical analysis method for the performance analysis and parameter optimization of the lidar system using the given parameter range. The scattered echo signal, signal-to-noise ratio, and detection sensitivity were simulated by setting assumed parameters with the HITRAN 2020 database and the US 1976 standard atmosphere model to analyze the detection distance and concentration resolution of the lidar system. The effects of the laser energy, repetition frequency, and photodetector noise were also discussed. The wavelength selection near the absorption line is critical because it controls the height region of the highest sensitivity and the demands on frequency stability. Recommendations for the selection of absorption lines are provided in this paper. A quantitative analysis of each error source provided reasonable error ranges.

Evaluating the representation of Arctic cirrus solar radiative effects in the Integrated Forecasting System with airborne measurements

Abstract. In two case studies, airborne measurements of broadband solar irradiances above and below Arctic cirrus are compared to simulations of the Integrated Forecasting System (IFS) operated by the European Centre for Medium-Range Weather Forecasts (ECMWF) using offline runs of ECMWF's operational radiation scheme, “ecRad”. Furthermore, independent of the solar irradiances, cirrus properties are derived from collocated airborne active remote sensing observations to evaluate the optical and microphysical parameterizations in ecRad. The data were collected in the central Arctic over sea ice (81–90° N) with instrumentation installed aboard the High Altitude LOng range research aircraft (HALO) during a campaign in March and April 2022. Among others, the HALO instrumentation included upward- and downward-looking pyranometers to measure broadband solar irradiances, a cloud radar, and a multi-wavelength water vapour differential absorption lidar. Extended horizontal flight legs above and below single-layer cirrus were performed. The solar radiation measurements are used to evaluate ecRad in two case studies of optically thin and thick cirrus, with an average transmissivity of 0.9 and 0.6, respectively. Different ice optics parameterizations optionally available in ecRad are applied to test the match between simulation and measurements. Furthermore, the IFS-predicted ice water content and ice effective radius are replaced by values retrieved with the radar and lidar. The choice of ice optics parameterizations does not significantly improve the model–measurement agreement. However, introducing the retrieved ice microphysical properties brings measured and modelled irradiances in closer agreement for the optically thin cirrus, while the optically thick cirrus case is simulated as too thick. It is concluded that the ice water content simulated by the IFS is realistic and that the mismatch between observed and simulated solar irradiances mostly originates from the assumed or parameterized ice effective radius.

Imaging of Atmospheric Dispersion Processes with Differential Absorption Lidar

Imaging of Atmospheric Dispersion Processes with Differential Absorption Lidar

Sensitivity analysis of space-based water vapor differential absorption lidar at 823 nm

Measurements of water vapor are important for understanding the hydrological cycle, the thermodynamic structure of the lower troposphere, and broader atmospheric circulation. Subsequently, many scientific communities have emphasized a need for high-accuracy and spatial resolution profiles of water vapor within and above the planetary boundary layer (PBL). Advancements in lidar technologies at the NASA Langley Research Center are ongoing to enable the first space-based water vapor differential absorption lidar (DIAL) that can provide high-accuracy and vertical resolution retrievals of moisture in the PBL and through the mid-troposphere. The performance of this space-based DIAL is assessed here for sensitivity throughout the troposphere and globally with representative canonical cases of water vapor and aerosol loading. The specific humidity retrieval sensitivity to systematic and random errors is assessed, and measurement resolutions and capabilities are provided. We show that tunable operation along the side of the 823-nm absorption line allows for the optimization of the lower-tropospheric water vapor retrievals across different meteorological regimes and latitudes and provides the operational flexibility needed to dynamically optimize random errors for different scientific applications. The analysis presented here suggests that baseline and threshold systematic error requirements of <1.5% and <2.5%, respectively, are achievable. Random error is shown to dominate the retrieval, with errors on the order of 5% within the PBL being achievable with 300-m vertical 50-km horizontal resolutions over open ocean and on the order of 10%–15% over high-albedo surfaces. The flexibility of the DIAL method to trade retrieval precision for spatial resolution is shown, highlighting its strengths over passive techniques to tailor retrievals to different scientific applications. Combined, the total error budget demonstrated here indicates a high impact for space-based DIAL, with technologies being advanced for space missions within the next 5–10 years.

Accuracy Evaluation of Differential Absorption Lidar for Ozone Detection and Intercomparisons with Other Instruments

Accuracy Evaluation of Differential Absorption Lidar for Ozone Detection and Intercomparisons with Other Instruments

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

Research on the Correction Algorithm for Ozone Inversion in Differential Absorption Lidar

Due to the complex and variable nature of the atmospheric conditions, traditional multi-wavelength differential absorption lidar (DIAL) methods often suffer from significant errors when inverting ozone concentrations. As the detection range increases, there is a higher demand for Signal to Noise Ratio (SNR) in lidar signals. Based on this, the paper discusses the impact of different atmospheric factors on the accuracy of ozone concentration inversion. It also compares the advantages and disadvantages of the two-wavelength differential method and the three-wavelength dual-differential method under both noisy and noise-free conditions. Firstly, the errors caused by air molecular extinction, aerosol extinction, and backscatter terms in the inversion using the two-wavelength differential method were simulated. Secondly, the corrected inversion errors were obtained through direct correction and the introduction of a three-wavelength dual differential correction. Finally, addressing the issue of insufficient SNR in practical inversions, the inversion errors of the two correction methods were simulated by constructing lidar parameters and incorporating appropriate noise. The results indicate that the traditional two-wavelength differential algorithm is significantly affected by aerosols, making it more sensitive to aerosol concentration and structural changes. On the other hand, the three-wavelength dual differential algorithm requires a higher SNR in lidar signals. Therefore, we propose a novel strategy for inverting atmospheric ozone concentration, which prioritizes the use of the three-wavelength dual-differential method in regions with high SNR and high aerosol concentration. Conversely, the direct correction method utilizing the two-wavelength differential approach is used. This approach holds the potential for high-precision ozone concentration profile inversion under different atmospheric conditions.

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

This study demonstrates a differential absorption lidar (DIAL) for CO2 that integrates both single-photon direct detection and coherent detection. Based on all-fiber 1572 nm wavelength devices, this compact lidar achieves detection of CO2 concentration, wind field, and single photon aerosol backscattering signal. First, by comparing DIAL with VAISALA-GMP343, the concentration deviation between the two devices is less than 5 ppm, proving the accuracy of the DIAL. Second, through the scanning detection experiment in Chaohu Lake, Hefei, not only the CO2 concentration between single-photon detection and coherent detection but also the wind field was obtained, proving the multifunctionality and stability of the DIAL. Benefiting from the advantages of combined the two detection methods, single photon detection offers 3-km CO2 and aerosol backscattering signals; coherent detection offers a 360-m shorter blind zone and wind field. This DIAL can achieve monitoring of CO2 flux and sudden emissions, which can effectively compensate for the shortages of in-situ sensors and spaceborne systems.

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.