Spatiotemporal characteristics of atmospheric CO2 under the influence of different industrial emission sources using lidar remote sensing in Nanping, China.

High-resolution vertical profiling and source apportionment of CO2 using coherent differential absorption lidar in coastal urban atmosphere

Due to the acute toxicity and extreme lethality, yet the non-selective type of activity of CWA’s (chemical weapon agents) toward military targets and the civilian population, timely detection and identification of CWA’s is becoming an important element of modern war conflicts. Spectral analysis is employed in nowadays for the engineering of accurate and selective detection of chemical warfare weapons. An analysis of current trends in the development of remote sensing of CWA’s shows the NATO member states and the russian federation have already mastered and are continuing enhancement and modernization of the latest technologies for the development of weapons based on the laser radiation differential absorption spectroscopy (differential absorption LIDARS), Fouriertransformed infrared (FT-IR) spectroscopy for the detection, identification, determination of concentration ranges for revealed CWA contaminated areas, linking them to corresponding geospatial data. The mentioned type of devices is capable of discrimination of main groups of CWA’s like nerve gases, blister substances, explosives as well as industrial toxic compounds at a range of as far as 6 km. The rich possibilities for detection of various industrial toxic substances using long-range stand-off chemical reconnaissance would contribute to increasing the situational awareness of the Armed Forces of Ukraine units that perform combat (special) missions in the territories, where the main chemical industry objects of Ukraine are located. The effective counteraction to recent potential chemical threats depends on the accelerated research and development of the grounds of advanced analytical methods for detecting CWA’s, as well as the settling and development of cooperation with international professional partner organizations would significantly advance the capabilities of the design, scale up the production, move forward the enhancement and modernization of up-to-date chemical reconnaissance equipment.

Lidar has become an increasingly attractive approach for CO2 monitoring. However, simultaneously achieving long-range detection and high-range resolution remains a fundamental tradeoff. To address this issue, first, a superconducting nanowire single-photon detector is integrated into lidar to significantly enhance long-range sensitivity, enabling detection of backscattered signals up to 10 km. In addition, a new retrieval algorithm is proposed to retrieve range-resolved CO2 concentrations from high-SNR column measurements, effectively improving profile resolution and stability. Three consecutive nights of field tests show that the system achieves 30 m range resolution, 5 min temporal resolution, and a near-8-km range. Compared with the traditional CO2 retrieval algorithm, the proposed method improves the range resolution by more than one order of magnitude while still achieving a 3.8-fold enhancement in retrieval accuracy. Cross-validation with in-situ observations shows that the standard deviation between the two datasets is approximately 10 ppm, further confirming the accuracy and robustness of the method. This work underpins future high-resolution CO2 monitoring networks and supports carbon-cycle studies.

Continuous-wave oxygen differential absorption lidar for remote sensing of atmospheric temperature profiles

The Differential Absorption Lidar (DIAL) technique is one of the most effective methods for detecting atmospheric gases. It is based on the interaction between laser-emitted light and atmospheric molecules. The backscattered optical signal is converted into an electrical signal using photomultiplier tubes or other types of detectors. Two main detection approaches are commonly used: analog detection and photon-counting detection. While the analog mode is widely employed, it suffers from limited sensitivity. The photon-counting mode, although more suitable for detecting extremely weak signals, faces challenges in daytime measurements due to strong solar background noise. The main objective of this study is to evaluate the performance of the photon-counting technique to enable the DIAL system to detect extremely weak optical signals. To this end, modeling and simulation of the parameters influencing system performance have been carried out. Furthermore, the impact of using ultra-narrow band filter (UNBF) has been investigated and compared to that of conventional interference filter, with the aim of reducing background noise in daytime measurements and improving the transmission of the useful signal. The results show that the photon counting acquisition technique for a DIAL system or P-DIAL (Photon-counting DIAL) provides superior performance in terms of signal quality and measurement accuracy compared to analogue detection using an UNBF for noise limitation.

The frequency-stabilized laser (FSL) is a vital component of differential absorption lidar (DIAL) and can satisfy the requirements for high-precision gas species concentration detection. China's next-generation spaceborne integrated-path differential absorption (IPDA) lidar aims to perform high-precision, multi-species detection of methane and water vapor column concentrations in the atmosphere. The seed laser system requires long-term frequency stability, low power consumption, and a compact size. Here, a 1645 nm triple-wavelength FSL based on silicon-on-insulator (SOI) photonics integrated circuits (PIC) is proposed; its advantages in size, weight, and power consumption (SWaP) are also demonstrated. Over a measurement period of up to 24 hours, the FSL's frequency standard deviation is better than 400 kHz. The peak-to-peak frequency drift is down to 4 MHz under 9 hours of recording. An optical phase-locked loop (OPLL), capable of a frequency difference of up to 28.23 GHz, was constructed, ensuring the long-term stability of the seed laser even under large frequency differences. The FSL is qualified to generate three seed laser pulses and inject them into the 1645-822 nm optical parametric oscillator (OPO). Regarding the 10 MHz wavelength drift requirement of IDPA lidar, the FSL has an environmental temperature tolerance of over 1°C. Furthermore, in the analysis of the PDH frequency stabilization loop based on silicon photonic chips, we have proposed a mathematical analysis for the nonlinear phase modulation.

Abstract. Accurate measurement of the mixed layer height (MLH) is a key observational capability necessary for many studies in weather forecasting, air quality assessment, and surface-atmosphere exchange. However, continuous MLH monitoring with backscatter lidars remains challenging under complex atmospheric conditions, including cloudy conditions and in the presence of residual layers. This study evaluates two complementary MLH retrieval algorithms using a single MicroPulse Differential Absorption Lidar (MPD): an aerosol-based approach that analyzes aerosol backscatter gradients with a wavelet technique and a thermodynamic technique based on the vertical structure of virtual potential temperature profiles. Both techniques were compared against MLH estimates from radiosondes, a Doppler wind lidar, and a high-resolution weather model using data from the M2HATS field campaign in Tonopah, NV, USA, supplemented by a smaller dataset from Boulder, CO, USA. The aerosol method achieved high temporal resolution and agreement with radiosonde MLH estimates under convective conditions (R2= 0.819–0.919), but its MLH estimates deviated from other methods during morning and evening transitions due to residual layer interference. The thermodynamic method avoided these problems but had coarser resolution and degraded instrument performance beneath clouds (R2= 0.661–0.845). Because lidar generally cannot penetrate clouds, conditions with clouds at or below the MLH are not considered, while those with clouds above the MLH are retained. The study highlights the strengths and weaknesses of each method. Together, they offer a path toward more reliable automatic MLH monitoring with a single instrument by capturing when different MLH definitions converge.

We propose an orbital differential absorption lidar operating near 1.84 µm to observe water vapor on Mars. With optimized wavelengths, the system offers high sensitivity to low-altitude water vapor and enables high-resolution, day-and-night observations of potential source regions-helping to close the existing observational gap in the lower atmosphere. Global simulations using feasible lidar parameters and the Mars climate database indicate that differential absorption optical depth can be measured with relative random errors below 1%, using a 1 mJ, 2 kHz laser, a 0.3 m telescope, and 1 km horizontal averaging. The water vapor weighted column mixing ratio can be retrieved to within 1% accuracy using climatological data, except in the southern polar region, where errors can reach 4% during northern winter.

Traditionally, retrieving both temperature and CO2 concentration in atmospheric remote sensing has relied on two independent lidar systems, leading to increased system complexity and limited coordination. To address this challenge, we propose a coordinated retrieval approach using a three-wavelength differential absorption lidar (DIAL) system. A temperature-sensitive wavelength is selected to distinguish strong absorption from weak absorption, forming the tri-wavelength configuration. By exploiting the different sensitivities of absorption cross-sections to thermal and molecular variations, simultaneous retrieval of both parameters is achieved. A standard atmospheric profile under clean-air conditions is constructed. The CO2 absorption spectrum near 1573 nm is generated using Voigt line shapes and data from the HITRAN database. Extinction and backscatter coefficients are retrieved through the Klett method. A layer-by-layer solution of the coupled differential equations is then performed to extract temperature and concentration simultaneously. Results are benchmarked against the atmospheric model, demonstrating the feasibility of the approach. This method provides a promising pathway for high-precision, multi-parameter DIAL sensing.

We present a tunable diode-laser absorption spectroscopy (TDLAS) system operating at 1.5711 µm for CO2 gas concentration measurements. The system can operate in either a traditional direct-mode (dTDLAS) sawtooth wavelength scan or a recently demonstrated wavelength-toggled single laser differential-absorption lidar (WTSL-DIAL) mode using precompensated current pulses. The use of such precompensated pulses offsets the slow thermal constants of the diode laser, leading to fast toggling between ON and OFF-resonance wavelengths. A short measurement time is indeed pivotal for atmospheric sensing, where ambient factors, such as turbulence or mechanical vibrations, would otherwise deteriorate sensitivity, precision and accuracy. Having a system able to operate in both modes allows us to benchmark the novel experimental procedure against the well-established dTDLAS method. The theory behind the new WTSL-DIAL method is also expanded to include the periodicity of the current modulation, fundamental for the calculation of the OFF-resonance wavelength. A two-detector scheme is chosen to suppress the influence of laser intensity fluctuations in time (1/f noise), and its performance is eventually benchmarked against a one-detector approach. The main difference between dTDLAS and WTSL-DIAL, in terms of signal processing, lies in the fact that while the former requires time-consuming data processing, which limits the maximum update rate of the instrument, the latter allows for computationally simpler and faster concentration readings. To compare other performance metrics, the update rate was kept at 2 kHz for both methods. To analyze the dTDLAS data, a four-parameter Lorentzian fit was performed, where the fitting function comprised the six main neighboring absorption lines centered around 1.5711 µm. Similarly, the spectral overlap between the same lines was considered when analyzing the WTSL-DIAL data in real time. Our investigation shows that, for the studied time intervals, the WTSL-DIAL approach is 3.65 ± 0.04 times more precise; however, the dTDLAS-derived CO2 concentration measurements are less subject to systematic errors, in particular pressure-induced ones. The experimental results are accompanied by a thorough explanation and discussion of the models used, as well as their advantages and limitations.

Abstract. High-resolution measurements of water vapor concentrations and their transport throughout the turbulent planetary boundary layer (PBL) and beyond are key for an enhanced understanding of atmospheric processes. This study presents data from the mobile Atmospheric Monitoring System (ATMONSYS) Differential Absorption Lidar (DIAL), operated with a novel titanium sapphire (Ti:Sa) laser concept, for the first time. The ATMONSYS DIAL aims to resolve turbulence throughout the PBL with a sampling frequency of 10 s and vertical resolutions of less than 200 m. General measuring capabilities during high-noon, clear-sky, summer conditions with a maximum vertical measurement range of >3 km and statistical uncertainties of <5 % are demonstrated. The analysis of turbulence spectra shows good agreement with Kolmogorov's law, demonstrating the system's capability to resolve turbulence. However, deviations from Kolmogorov behavior are observed at certain frequency ranges. By combining the ATMONSYS DIAL with an adjacent high-quality Doppler wind lidar, some of these deviations are mitigated in the co-spectra due to independent noise from both instruments. However, intermediate deviations from Kolmogorov behavior persist, likely due to surrounding surface heterogeneities. The agreement of the co-spectra with Kolmogorov's law at the highest frequencies demonstrates that the ATMONSYS DIAL is capable of resolving turbulent latent energy fluxes down to the measurement's Nyquist frequency of 5×10-2Hz. A system cross-intercomparison of the ATMONSYS DIAL with two adjacent water vapor Raman lidars and radiosondes shows overall good agreement between the sensors, despite minor DIAL deficiencies under certain conditions with broken clouds passing over the lidar. The observed profile-to-profile DIAL fluctuations and sensor-to-sensor deviations, in combination with low statistical uncertainty, highlight the advantage of humidity lidars, such as the ATMONSYS DIAL, in capturing both short-term and small-scale dynamics of the lowermost atmosphere.

An integrated path differential absorption lidar (IPDA) for remote sensing of flammable and toxic gases is proposed, which is based on a broadband-tunable external-cavity diode laser (ECDL) and InGaAs/InP single-photon detector (SPD). An ECDL can maintain a narrow linewidth of 10 kHz throughout the continuous frequency scanning process in the C + L-band (1520-1620 nm), thus allowing a single laser to satisfy the detection requirements of multiple gases. To eliminate the influence of background light, a programmable frequency- and bandwidth-tunable grating filter is designed to synchronously tune with the output frequency of the ECDL. A homemade multi-channel coupled InGaAs/InP SPD maintains high detection efficiency in the C + L-band, ensuring the remote sensing detection capability of lidar. Four gases-CO, H13CN, C2H2, and NH3-with absorption lines spanning ∼45 nm in wavelength are selected to verify the multi-gas monitoring capability of the lidar. The intensity errors caused by erroneous photon counts and the non-linear frequency caused by the hysteresis effect of piezoelectric ceramic transducer are corrected to enhance the accuracy of absorbance spectra. The standard deviations of residuals between the experiment and single-peak fitting results for CO, H13CN, C2H2 are 0.22%, 0.54%, 0.39%, while the mean deviations are 0.19%, 0.44%, 0.29%, respectively. For the four-peak fitting of NH3, those values are 0.55% and 0.38%, respectively. Continuous 12-hour monitoring of the path-integrated concentrations of the four gases is conducted to verify the stability and accuracy of the system. The mean deviations and standard deviations of CO, H13CN, C2H2, and NH3 are 0.13%, 0.13%, 0.02%, 0.17%, and 1.07%, 1.68%, 1.21%, 0.67%, respectively.

A method is proposed that involves adaptive change of laser power depending on the size of the forest area under study for early detection of forest fires. The proposed method is optimized in relation to finding such a power-distance dependence that minimizes the detectable concentration of the sought substance — the combustion product. Taking into account the limitation of the energy resource allocated for such monitoring, a functional dependence of the optimal power of the probing radiation on the distance to the object is obtained, at which the threshold for recording the concentration of combustion products reaches the lowest value.

Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN), commonly used measures of the instability and inhibition within a vertical column of the atmosphere, serve as a proxy for estimating convection potential and updraft strength for an air parcel. In operational forecasting, CAPE and CIN are typically derived from radiosonde thermodynamic profiles, launched only twice daily, and supplemented by model-simulated equivalent values. This study uses remote sensing observations to derive CAPE and CIN from continuous data, expanding upon previous research by evaluating the performance of both passive and active profiling systems’ CAPE/CIN against in situ radiosonde CAPE/CIN. CAPE and CIN values are calculated from Atmospheric Emitted Radiance Interferometer (AERI), Microwave Radiometer (MWR), Raman LiDAR, and Differential Absorption LiDAR (DIAL) systems. Among passive sensors, results show significantly greater accuracy in CAPE and CIN from AERI than MWR. Incorporating water vapor profiles from active LiDAR systems further improves CAPE values when compared to radiosonde data, although the impact on CIN is less significant. Beyond the direct capability of calculating CAPE, this approach enables evaluation of the various relationships between the water vapor mixing ratio, CAPE, cloud development, and moisture transport.

We present coordinated observations from ozone Differential Absorption lidar (DIAL), aerosol lidar, and Doppler wind lidar at the City College of New York (CCNY) in northern Manhattan during the summer 2023 AGES+ campaigns across the New York City (NYC) region and Long Island Sound (LIS) areas. The results highlight significant ozone formation within the planetary boundary layer (PBL) and the concurrent transport of ozone/aerosol plumes aloft and mixing into the PBL during 26–28 July 2023. Especially, 26 July experienced the highest ozone concentration within the PBL during the three-day ozone episode despite having a lower temperature than the following two days. In addition, the onset of the afternoon sea breeze contributed to increased ozone levels in the PBL. A mobile ozone DIAL was also deployed at Columbia University’s Lamont–Doherty Earth Observatory (LDEO) in Palisades, NY, 29 km north of NYC, from 11 August to 8 September 2023. A notable high-ozone episode was observed by both ozone DIALs at the CCNY and the LDEO site during an unusual heatwave event in early September. On 7 September, the peak ozone concentration at the LDEO reached 120 ppb, exceeding the ozone levels observed in NYC. This enhancement was associated with urban plume transport, as indicated by wind lidar measurements, the HRRR (High-Resolution Rapid Refresh) model, and the Copernicus Sentinel-5 TROPOMI (TROPOspheric Monitoring Instrument) tropospheric column NO2 product. The results also show that, during both heatwave events, those days with slow southeast to southwest winds experienced significantly higher ozone pollution.

Abstract. Coal-fired power plants are a major source of global carbon emissions, and accurately accounting for these significant emission sources is crucial in addressing global warming. Many previous studies have used Gaussian plume models to estimate power plant emissions, but there is a gap in observation capabilities for high-latitude regions and nighttime emissions. However, large emitting power plants exist in high-latitude areas. The DQ-1 satellite is equipped with the world's first active remote sensing lidar for detecting CO2 column concentrations, which, compared to passive remote sensing satellites, enables observations in these regions. This paper applies a two-dimensional Gaussian plume model to the XCO2 results from the DQ-1 satellite and analyses the instantaneous CO2 emissions of 10 power plants globally. Among these, 15 cases of data are from nighttime observations, and 3 cases are from power plants located above 60° N latitude. The estimation results show good consistency when compared with emission inventories such as Climate TRACE and Carbon Brief, with a correlation coefficient R = 0.97. The correlation coefficient between the model fits and satellite observations ranges from 0.49 to 0.88, and the overall relative random error in the estimates is 15.11 %. This paper also analyses the diurnal differences in CO2 emissions from power plants and finds emission fluctuations directly correlated with regional electricity demand dynamics. This method is very effective for monitoring emissions from strong point sources such as power plants.

Abstract The first field campaign of a network of water vapor lidars, called the MicroPulse Differential absorption lidar (MPD) Network Demonstration Project, combined the observational capabilities of the water vapor MPD, the Atmospheric Emitted Radiance Interferometer (AERI), and the Doppler wind lidar (DWL) at five sites at the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) field observatory from 22 April – 19 July 2019. During the field campaign, water vapor profiles from the MPD were collected to complement the ARM/SGP temperature and water vapor profiles from the AERI, wind profiles from the DWL and supplementary radiosondes, along with operational weather radar and surface station data. The impacts of assimilating AERI, MPD, and DWL are evaluated for a mesoscale convection initiation (CI) and precipitation event on 14 June 2019. Short-term forecasts of CI and precipitation are improved by assimilating all MPD and AERI profiling data in comparison to assimilating conventional observations and DWL. While AERI shows marginal impact on the forecasts of CI near the sites, assimilating the MPD water vapor profiles contributes the most to improving forecast skill over almost all forecast times and reflectivity thresholds. The data assimilation (DA) experiments shows the development of moist absolutely unstable layers near the observing sites and MPD DA improved the vertical moisture profile, leading to an improvement of the southern CI forecasts for the MPD DA experiment. Furthermore, MPD DA additionally leads to improved CI forecasts north of the sites due to enhanced thermodynamic instability and modified wind field leading to convergence in the lower atmosphere.

We present a thermal-driven, orthogonally polarized, eye-safe dual-wavelength microchip laser based on an a-cut Er,Yb:YAl3(BO3)4 (Er,Yb:YAB) crystal, operating without the need for additional intracavity elements. Two thermal management schemes were investigated, revealing that additional end-face cooling effectively reduces internal temperature gradients within the crystal. As a result, the laser achieved a total output power of 1.04 W at the polarization intersection point (PIP) and an extended polarization coexistence range (PCR) of up to 11 W, with dual-wavelength emission at 1551.9 nm and 1556.5 nm, corresponding to a frequency difference of 0.57 THz. Furthermore, by adjusting the cooling temperature, both the PIP output power and PCR exhibited an approximately linear dependence, offering a practical means of thermally controlling polarization dynamics. Theoretical simulations showed good agreement with experimental results, confirming the validity of the thermal-driving mechanism. This compact, alignment-free laser architecture holds strong potential for applications in laser interferometry, precision metrology, coherent THz radiation, and eye-safe differential absorption lidar.

Ground-based Stationary Differential Absorption Lidars for Monitoring Greenhouse Gases in the Atmosphere