Integrated Path 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

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.

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.

Feasibility study of a total precipitable water IPDA lidar from a solar-powered stratospheric aircraft.

Repetitive, high spatial resolution measurements of water vapor are highly desirable for a range of critical applications, including quantitative forecasts of wildfire risk forecasting, extreme weather, drought implicated in mass refugee dislocation, and air quality. A point design for an integrated path differential absorption (IPDA) light detection and ranging (lidar) for column precipitable water vapor (PWV) intended for high-altitude long-endurance (HALE) uncrewed aerial systems (UASs) is described and analyzed. A novel, to the best of our knowledge, all-semiconductor source utilizing an intensity-modulated continuous wave approach to ranging is proposed, which facilitates reductions in weight, power, and size. Analytic and Monte Carlo calculations suggest that high spatial resolution (<10m) or high precision (<1%) may be obtained.

Quantifying strong point sources emissions of CO2 using spaceborne LiDAR: Method development and potential analysis

Accurate reporting of point source emissions of CO2 is fundamental to addressing climate change. Currently, bottom-up verification methods based on inventory statistics face significant challenges in this area. Satellite remote sensing has emerged as a promising approach for cost-effective global-scale verification of point source emissions, with spaceborne LiDAR offering high spatial resolution ideal for this purpose. However, the inversion of CO2 emissions from spaceborne LiDAR CO2 concentration observations requires urgent attention, as existing methods heavily rely on prior information in diffusion models and the accuracy of meteorological data. In this work, a novel emission inversion method based on genetic algorithms and trust-region techniques is proposed to estimate CO2 emissions from point sources using spaceborne LiDAR observations. A comparison between the CO2 emission rates calculated from actual airborne LiDAR data (as a prototype of spaceborne LiDAR) and emission inventories for the Suizhong power plant showed a deviation of less than 7.0%. Observing system simulation experiment (OSSE) demonstrated that using DQ-1 (spaceborne LiDAR) observation data as input, the relative error of emission rates would be less than 0.6% when the distance between the emission source and the observation footprint is less than 10 km. Furthermore, the developed model mitigates the impact of uncertainties in meteorological data and IPDA (Integrated-Path Differential Absorption) LiDAR measurements on the final emission quantification. The proposed approach is expected to enable DQ-1 to provide affordable and accurate carbon verification services for over 20.0% of the world's strong point source emissions.

Simulation and Error Analysis of Methane Detection Globally Using Spaceborne IPDA Lidar

Methane (CH4) is recognized as the second most important greenhouse gas. An accurate and precise monitoring of methane gas globally has a vital role in studying the carbon cycle and global warming. The spaceborne integrated path differential absorption (IPDA) lidar is one of the most effective payload for methane detection. The simulation and optimization of the lidar system parameters can create an important base for the development of spaceborne payloads. However, previous IPDA lidar simulations have mostly used standard atmospheric models at simulation conditions, and to the best of our knowledge, there is no literature yet which applies a wavelength optimization to the IPDA system. In this study, we have investigated the relationship between the IPDA lidar system, based on wavelength optimization, and error measurement for CH4 column-averaged concentration. By selecting the wavelengths with the lowest comprehensive error as on-line and off-line, the error has been minimized by 10 ppb approximately relative to before optimization. We have proposed an IPDA simulation model at real atmospheric conditions, combining with ERA-5 reanalysis data, to simulate methane concentration globally, and present the distribution of errors. Finally, after the optimization of the lidar system parameters, we have ensured that the maximum inversion error for CH4 measurement is less than 10 ppb, to provide a reference for designing spaceborne IPDA lidar systems for high-precision CH4 column-averaged concentration detection.

Spectral Energy Model-Driven Inversion of XCO2 in IPDA Lidar Remote Sensing

Carbon observation satellites based on passive theory (e.g., OCO-2/3, GOSAT-1/2, and TanSat) have relatively high carbon dioxide column concentration (XCO2) accuracy when the observation conditions are met. Passive satellites have data bias and coverage deficiencies due to cloud cover, low albedo, low-light conditions, and aerosol scattering, resulting in carbon observation satellites based on passive theory that cannot meet the demand for high-precision, all-day, all-weather XCO2 monitoring. Active detection satellites are urgently needed to support global carbon sources, sinks, and carbon neutrality. China intends to launch a sensor satellite with active detection of XCO2 in the coming years. In this work, based on the satellite’s scaled-down airborne experiments, a spectral energy model was developed to optimize the conventional inversion algorithm and achieve a more accurate XCO2 inversion. The 1.572- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> integrated path differential absorption (IPDA) lidar column length is used indirectly to evaluate the accuracy of the spectral energy model for signal extraction. Also, the experimental results show that the accuracy of the signal extracted by the 1.572- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> IPDA lidar column length is 0.74 and 6.20 m at sea and on land based on the indirect evaluation of the length of the 1.572- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> IPDA lidar column length. The optimized XCO2 was evaluated (standard deviation as an evaluation metric) and its XCO2 standard deviation reduced by 31%, 63%, and 66% in the ocean, plains, and mountains, respectively. Our algorithm can obtain the XCO2 with a consistent trend by using XCO2 from the OCO-2 satellite as a reference. The calculated XCO2 is more accurate in areas dominated by anthropogenic factors (plains), due to the accuracy of the IPDA detection mechanism. This algorithm improves the accuracy and robustness of XCO2 inversion and has important reference significance for the IPDA lidar carried by China’s satellites to be launched in this year.

Study on the Impact of the Doppler Shift for CO2 Lidar Remote Sensing

Atmospheric carbon dioxide (CO2) is recognized as the most important component of the greenhouse gases, the concentration of which has increased rapidly since the pre-industrial era due to anthropogenic emissions of greenhouse gases (GHG). The accurate monitoring of carbon dioxide is essential to study the global carbon cycle and radiation budget on Earth. The Aerosol and Carbon Detection Lidar (ACDL) instrument onboard the Atmospheric Environmental Monitoring Satellite (AEMS) was successfully launched in April 2022, which allows a new perspective to quantify the global spatial distribution of atmospheric CO2 with high accuracy. In this work, the impact of the Doppler shift on CO2 measurements for an integrated-path differential absorption (IPDA) light detection and ranging (lidar) system was evaluated to meet the weighted column-averaged mixing ratio of carbon dioxide (XCO2) measurement requirements of less than one part per million (ppm). The measurement uncertainties due to the Doppler shift were first evaluated in airborne IPDA observations. The result shows that most of the Doppler shift is in the range of 6–8 MHz, resulting in 0.26-0.39 ppm deviations in the XCO2 results. The deviations between the XCO2 retrievals and in situ measurements decreased to 0.16 ppm after the correction of the Doppler shift from 11:28:29 to 11:28:49 in the flight campaign. In addition, the online Doppler shift accounts for 98% of the deviations between XCO2 retrievals and in situ measurements. Furthermore, the impact of the Doppler shift on ACDL measurements is also assessed. The differences between the XCO2 retrievals with and without Doppler shift are used to quantify measurement uncertainties due to the Doppler effect. The simulations reveal that a pointing misalignment of 0.067 mrad can lead to a mean bias of about 0.30 ppm (0.072%) in the CO2 column. In addition, CO2 measurements are more sensitive to the Doppler shift at high altitudes for IPDA lidar, so the largest differences in the CO2 columns are found on the Qinghai–Tibet Plateau in China.

Electro-optic frequency comb based IPDA lidar: assessment of speckle issues.

We present a theoretical, numerical and experimental assessment of the impact of speckle on a dual electro-optic frequency comb (EOFC) based system for integrated path differential absorption (IPDA) measurements. The principle of gas concentration measurements in a dual EOFC configuration in the absence of speckle is first briefly reviewed and experimentally illustrated using a C2H2 gas cell. A numerical simulation of the system performance in the presence of speckle is then outlined. The speckle-related error in the concentration estimate is found to be an increasing function of the product between the roughness of the backscattering surface and the EOFC line-spacing. As this product increases, the speckle-induced power fluctuations in the comb lines are no longer correlated to each other. To confirm this, concentration measurements are conducted using backscattered light from two different surfaces. Experiment results are in very good agreement with numerical simulations. Though detrimental for IPDA measurements, it is finally shown that decorrelation of speckle noise can be advantageously exploited for surface characterization in a dual EOFC configuration.

Dual Laser Indium Phosphide Photonic Integrated Circuit for Integrated Path Differential Absorption Lidar

An indium phosphide photonic integrated circuit (PIC) was demonstrated for integrated path differential absorption lidar of atmospheric carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The PIC consists of two widely tunable sampled grating distributed Bragg reflector (SGDBR) lasers, directional couplers, a phase modulator, a photodiode, and semiconductor optical amplifiers (SOAs). One SGDBR laser, the leader, is locked to the center of an absorption line at 1572.335 nm using the on-chip phase modulator and a bench-top CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Herriott reference cell. The other SGDBR laser, the follower, is stepped in frequency over ±15 GHz around 1572.335 nm to scan the target CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption line. The follower laser is offset locked to the leader laser with an optical phase lock loop. An SOA after the follower laser generates a pulse at each frequency step to create a train of pulses that samples the target CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption line. The PIC components and subsystem are characterized and evaluated based on target performance requirements. The leader laser demonstrated a 236-fold improvement in frequency stability standard deviation when locked compared to free running and the follower laser frequency stability standard deviation compared to the leader laser was 37.6 KHz at a 2 GHz programmed offset.

Integrated path DIAL for standoff detection of acetone vapors under topographic target condition

A mid infrared tunable Differential Absorption Lidar (DIAL) operating in the spectral region of 3000–3450 nm has been developed and its performance has been evaluated by measuring the vapors of diesel and acetone. Diesel, one of the hydrocarbon products has been used for calibration of the DIAL wavelengths. Transmittance spectrum of diesel has been measured in 3360–3390 nm wavelength band using this system. Further, these absorption lines have been validated using Fourier Transform Infrared (FTIR) measured spectra. Acetone, one of the precursors employed in the manufacturing of Improvised Explosive Devices (IED), is used in field experiments. Firstly, the transmittance spectra of acetone vapors in the glass cell is recorded in the spectral band 3250–3365 nm using this setup. Further, the spectra have been compared with the data reported by NIST. Based on the analysis, the wavelengths at 3254 nm and 3362 nm have been chosen as offline and online wavelengths respectively. For open field experiments, a test chamber made of transparent PMMA (polymethyl methacrylate) material with openable windows on both sides placed at standoff distance of 100 m has been used. Standoff measurements have been carried out by keeping the chamber closed as well as open conditions. The average column content of acetone vapors has been measured for closed and open chamber conditions. During open chamber condition, the maximum concentration of about 13180 ppm.m has been measured. The average minimum concentration of about 30 ppm.m was observed during final dispersion stages. The influence of the atmospheric interfering molecules in the measurement wavelengths have also been analyzed and quantified their contribution in the return signals. The total contribution of these molecules in the return signal is about 0.3% at online wavelength whereas this is about 0.13% at offline wavelength.

Airborne Testing of 2-μm Pulsed IPDA Lidar for Active Remote Sensing of Atmospheric Carbon Dioxide

The capability of an airborne 2-μm integrated path differential absorption (IPDA) lidar for high-accuracy and high-precision active remote sensing of weighted-average column dry-air volume mixing ratio of atmospheric carbon dioxide (XCO2) is demonstrated. A test flight was conducted over the costal oceanic region of the USA to assess instrument performance during severe weather. The IPDA targets CO2 R30 absorption line using high-energy 2-μm laser transmitter. HgCdTe avalanche photodiode detection system is used in the receiver. Updated instrument model included range correction factor to account for platform attitude. Error budget for XCO2 retrieval predicts lower random error for longer sensing column length. Systematic error is dominated by water vapor (H2O) through dry-air number density derivation, followed by H2O interference and ranging related uncertainties. IPDA XCO2 retrieval results in 404.43 ± 1.23 ppm, as compared to 405.49 ± 0.01 ppm from prediction models, using consistent reflectivity and steady elevation oceanic surface target. This translates to 0.26% and 0.30% relative accuracy and precision, respectively. During gradual spiral descend, IPDA results in 404.89 ± 1.19 ppm as compared model of 404.75 ± 0.73 ppm indicating 0.04% and 0.23% relative accuracy, respectively. Challenging cloud targets limited retrieval accuracy and precision to 2.56% and 4.78%, respectively, due to H2O and ranging errors.

High-Precision CO2 Column Length Analysis on the Basis of a 1.57-μm Dual-Wavelength IPDA Lidar.

For high-precision measurements of the CO2 column concentration in the atmosphere with airborne integrated path differential absorption (IPDA) Lidar, the exact distance of the Lidar beam to the scattering surface, that is, the length of the column, must be measured accurately. For the high-precision inversion of the column length, we propose a set of methods on the basis of the actual conditions, including autocorrelation detection, adaptive filtering, Gaussian decomposition, and optimized Levenberg–Marquardt fitting based on the generalized Gaussian distribution. Then, based on the information of a pair of laser pulses, we use the direct adjustment method of unequal precision to eliminate the error in the distance measurement. Further, the effect of atmospheric delay on distance measurements is considered, leading to further correction of the inversion results. At last, an airborne experiment was carried out in a sea area near Qinhuangdao, China on 14 March 2019. The results showed that the ranging accuracy can reach 0.9066 m, which achieved an excellent ranging accuracy on 1.57-μm IPDA Lidar and met the requirement for high-precision CO2 column length inversion.

Performance Evaluation of Spaceborne Integrated Path Differential Absorption Lidar for Carbon Dioxide Detection at 1572 nm

As one of the most influential greenhouse gases, carbon dioxide (CO2) has a profound impact on the global climate. The spaceborne integrated path differential absorption (IPDA) lidar will be a great sensor to obtain the columnar concentration of CO2 with high precision. This paper analyzes the performance of a spaceborne IPDA lidar, which is part of the Aerosol and Carbon Detection Lidar (ACDL) developed in China. The line-by-bine radiative transfer model was used to calculate the absorption spectra of CO2 and H2O. The laser transmission process was simulated and analyzed. The sources of random and systematic errors of IPDA lidar were quantitatively analyzed. The total systematic errors are 0.589 ppm. Monthly mean global distribution of relative random errors (RREs) was mapped based on the dataset in September 2016. Afterwards, the seasonal variations of the global distribution of RREs were studied. The global distribution of pseudo satellite measurements for a 16-day orbit repeat cycle showed relatively uniform distribution over the land of the northern hemisphere. The results demonstrated that 61.24% of the global RREs were smaller than 0.25%, or about 1 ppm, while 2.76% of the results were larger than 0.75%. The statistics reveal the future performance of the spaceborne IPDA lidar.

Obtaining Gradients of XCO2 in Atmosphere Using the Constrained Linear Least-Squares Technique and Multi-Wavelength IPDA LiDAR

Integrated-path differential absorption (IPDA) LiDAR is a promising means of measuring the global distributions of the column weighted xCO2 (dry-air mixing ratio of CO2) with adequate accuracy and precision. Most IPDA LiDARs are incapable of discerning the vertical information of CO2 diffusion, which is of great significance for studies on the carbon cycle and climate change. Hence, we developed an inversion method using the constrained linear least-squares technique for a pulsed direct-detection multi-wavelength IPDA LiDAR to obtain sliced xCO2. In the proposed inversion method, the atmosphere is sliced into three different layers, and the xCO2 of those layers is then retrieved using the constrained linear least-squares technique. Assuming complete knowledge of the water vapor content, the accuracy of the retrieved sliced xCO2 could be as high as 99.85% when the signal-to-noise ratio of central wavelength retrievals is higher than 25 (with a log scale). Further experiments demonstrated that different carbon characteristics can be identified by the sign of the carbon gradient of the retrieved xCO2 between the ABL (atmospheric boundary layer) and FT (free troposphere). These results highlight the potential applications of multiple wavelength IPDA LiDAR.

Calibration and Improved Speckle Statistics of IM-CW Lidar for Atmospheric CO2 Measurements

An intensity modulated, continuous-wave (IM-CW) integrated path differential absorption (IPDA) fiber-based lidar is developed herein for measuring atmospheric carbon dioxide (CO2). There are two main challenges in improving measurement accuracy, which have not been given enough attention in the previous research: one is that temperature sensitivity in optical components causes biases, due to the drift of component characteristic, and the other is that speckle noise deteriorates the signal-to-noise ratio. With the components thermally controlled, a target calibration accuracy of 0.003 dB is realized, corresponding to a CO2 concentration precision of better than 1 ppm for a 1 km path. A moving diffuser can reduce speckle noise by time averaging. In this paper, movement of the diffuser is substituted by the perturbation of the emitted laser beam by using a vibrating motor mounted on the optical antenna. Selecting on and off wavelengths with a small wavelength separation can improve the correlation between two laser speckle fields. These improvements result in the improved accuracy of the IPDA lidar system. Finally, the lidar performance was analyzed after the improvements described above were implemented. The diurnal variations of the atmospheric CO2 concentration using a topographic target were performed, and the results showed good agreement with the data measured by an in situ sensor. The root mean square (rms) of the deviation between the IPDA lidar and the in situ sensor was less than 1.4%.

High-Precision and High-Accuracy Column Dry-Air Mixing Ratio Measurement of Carbon Dioxide Using Pulsed 2-$\mu$ m IPDA Lidar

NASA has been conducting several studies for quantifying and monitoring atmospheric CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> including the Orbiting Carbon Observatory space-based missions. To complement CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> passive sensing, the National Research Council recommended active remote sensing techniques, which are valuable for validating current space-based measurements and potential future missions. Recently, a 2-μm triple-pulse integrated path differential absorption (IPDA) lidar was developed for simultaneous and independent measurements of atmospheric CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O. This instrument was operated at fixed wavelengths, precisely selected to avoid mutual interferences. Focusing on optimized CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> measurements, this instrument has been updated to operate in double-pulse mode. The objective is to demonstrate high-precision and high-accuracy column CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> measurements using tunable on-line wavelength suitable for adaptive targeting. Statistical analysis of long record CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> field measurement and retrieval results in 1.92-ppm accuracy, equivalent to 0.44% systematic error, and 1.66-ppm precision, equivalent to 0.39% random error. Referring to the R30 CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption line, this was achieved using an on-line laser frequency offset of 1 GHz, a 5.2% target reflectivity, and 10-s average. The record indicated a better than 99% data success rate. Tuning the on-line frequency offset to 0.5 GHz results in 1.11- and 0.33-ppm measurement accuracy and precision, equivalent to 0.26% and 0.08% systematic and random errors, respectively, obtained using 13.6% target reflectivity. Range measurements indicate 0.7-m precision and 0.2-m accuracy. These results demonstrate the reliability of atmospheric CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> measurements with high precision and high accuracy, using the pulsed 2-μm IPDA lidar.

Flight Demonstration of a 2-Micron, Double Plused CO2 IPDA Lidar Instrument

NASA Langley Research Center (LaRC) developed a double pulsed, high energy 2-micron Integrated Path Differential Absorption (IPDA) lidar instrument to measure atmospheric CO2 column density. The 2-μm double pulsed IPDA lidar was flown ten times in March and April of 2014. It was determined that the IPDA lidar measurement is in good agreement with an in-situ CO2 measurement by a collocated NOAA flight. The average column CO2 density difference between the IPDA lidar measurements and the NOAA air samples is 1.48ppm in the flight altitudes of 3 to 6.1 km.

CH4 and CO2 IPDA Lidar Measurements During the Comet 2018 Airborne Field Campaign

Installed onboard the German research aircraft HALO, the integrated-path differential-absorption (IPDA) lidar CHARM-F measures weighted vertical columns of both greenhouse gases (GHG) below the aircraft and along its flight track, aiming at high accuracy and precision. Results will be shown from the deployment during the CoMet field campaign that was carried out in spring 2018, with its main focus on one of the major European hot spots in methane emissions: the Upper Silesian Coal Basin (USCB) in Poland. First analyses reveal a measurement precision of below 0.5% for 20-km averages and also low bias, which was assessed by comparison with in-situ instruments. The measurements flights were designed to capture individual CH4 and CO2 plumes from e.g. coal mine venting and coal-fired power plants, respectively, but also to measure large and regional scale GHG gradients and to provide comparisons with the Total Carbon Column Observing Network (TCCON). Many other different instruments, both airborne and ground-based, complemented the lidar measurements to provide a comprehensive dataset for model analyses. CHARM-F also acts as the airborne demonstrator for MERLIN, the “Methane Remote Lidar Mission”, conducted by the German and French space agencies, DLR and CNES, with launch foreseen in ~ 2024. In this context, the airborne lidar data are likewise important for mission support such as for e.g. algorithm development and improvement and, moreover, the CoMet mission was also an important step for MERLIN validation preparation.