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By utilizing Level 2A products (particle optical properties and numerical weather prediction data) and Level 2C products (numerical weather prediction wind vector assimilated with observed wind component) provided by the Atmospheric Laser Doppler Instrument (ALADIN) onboard the Aeolus mission, and Level 2 vertical feature mask (VFM) products provided by Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission, three remote ocean areas are selected and the optical properties at 355 nm of marine aerosol are derived. The combined analysis of marine aerosol optical properties at 355 nm and instantaneous co-located wind speeds above the remote ocean areas are conducted. Eventually their relationships are explored and discussed at two sperate vertical atmospheric layers (0–1 km and 1–2 km, correspond to the heights within and above marine atmospheric boundary layer (MABL)), revealing the marine aerosol related atmospheric background states. Pure marine aerosol optical properties at 355 nm are obtained after quality control, cloud screening and backscatter coefficient correction from the ALADIN observations. The spatial distributions of marine aerosol optical properties and wind speed above the study areas are presented and analysed, respectively, at two vertical layers. The statistical results of the marine aerosol optical properties along with the wind speed grids at two vertical layers together with the corresponding regression curves fitted by power law functions are acquired and analysed, for each remote ocean area. The optical properties present increasing trends with wind speed in all cases, implying that the atmosphere of the two vertical layers will both receive the marine aerosol input produced and transported by the wind and the turbulence. The marine aerosol enhancement caused by the wind speed at the lower layer is more intensive than at the higher layer. As derived data from ALADIN, the averaged marine aerosol optical depth (AODmar) and the averaged marine aerosol lidar ratio (LRmar) at 355 nm are acquired and discussed along the wind speed range. The marine aerosol optical properties distributions, wind speed bins, and the marine aerosol variation tendencies along wind speed above the individual study areas are not totally similar, implying that the development and evolution of the marine aerosol above the ocean might not only be dominated by the drive of the wind, but also be impacted by other meteorological and environmental factors, e.g., atmospheric stability, sea and air temperature, or relative humidity. Combined analysis on the aerosol optical properties and wind with additional atmospheric parameters above the ocean might be capable to provide more detailed information of marine aerosol production, entrainment, transport and removal.

Accurate monitoring of atmospheric carbon dioxide (CO2) and its distribution is of great significance for studying the carbon cycle and predicting future climate change. Compared to the ground observational sites, the airborne observations cover a wider area and simultaneously observe a variety of surface types, which helps with effectively monitoring the distribution of CO2 sources and sinks. In this work, an airborne experiment was carried out in March 2019 over the Shanhaiguan area, China (39–41∘ N, 119–121∘ E). An integrated path differential absorption (IPDA) light detection and ranging (lidar) system and a commercial instrument, the ultraportable greenhouse gas analyser (UGGA), were installed on an aircraft to observe the CO2 distribution over various surface types. The pulse integration method (PIM) algorithm was used to calculate the differential absorption optical depth (DAOD) from the lidar data. The CO2 column-averaged dry-air mixing ratio (XCO2) was calculated over different types of surfaces including mountain, ocean, and urban areas. The concentrations of the XCO2 calculated from lidar measurements over ocean, mountain, and urban areas were 421.11 ± 1.24, 427.67 ± 0.58, and 432.04 ± 0.74 ppm, respectively. Moreover, through the detailed analysis of the data obtained from the UGGA, the influence of pollution levels on the CO2 concentration was also studied. During the whole flight campaign, 18 March was the most heavily polluted day with an Air Quality Index (AQI) of 175 and PM2.5 of 131 µg m−3. The aerosol optical depth (AOD) reported by a sun photometer installed at the Funing ground station was 1.28. Compared to the other days, the CO2 concentration measured by UGGA at different heights was the largest on 18 March with an average value of 422.59 ± 6.39 ppm, which was about 10 ppm higher than the measurements recorded on 16 March. Moreover, the vertical profiles of Orbiting Carbon Observatory-2 (OCO-2) and CarbonTracker were also compared with the aircraft measurements. All the datasets showed a similar variation with some differences in their CO2 concentrations, which showing a good agreement among them.

The spaceborne IPDA LIDAR has the potential to measure the global atmosphere CO

Aerosols and clouds greatly affect the Earth's radiation budget and global climate. Light detection and ranging (lidar) has been recognized as a promising active remote sensing technique for the vertical profiles of aerosols and clouds. China is developing its first space-borne aerosol-cloud high-spectral-resolution lidar (ACHSRL) for global high accuracy observations of aerosols/clouds profiles. This study presents a retrieval algorithm for aerosol and cloud optical properties from ACHSRL which was compared with the end-to-end Monte-Carlo simulations and validated with the data from an airborne flight with the ACHSRL prototype (A2P) instrument. Using imaging denoising, threshold discrimination, and iterative reconstruction methods, this algorithm was developed for calibration, feature detection, and extinction coefficient retrievals. The simulation results show that 95.4% of the backscatter coefficient have an error less than 12% while 95.4% of extinction coefficient have an error less than 24%. Cirrus and marine and urban aerosols were identified based on the airborne measurements over different surface types. Then, comparisons were made with U.S. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) profiles, Moderate-resolution Imaging Spectroradiometer (MODIS), and the ground-based sun photometers. High correlations (R > 0.79) were found between backscatter (extinction) coefficient profiles of A2P and CALIOP over forest and town cover; the aerosol optical depth retrievals have correlation coefficient of 0.71 with MODIS data and show spatial variations consistent with those from the sun photometers. The algorithm developed for ACHSRL in this study can be directly employed for future space-borne high-spectral-resolution lidar (HSRL) and its data products will also supplement CALIOP data coverage for global observations of aerosol and cloud properties.

CO2 column-weighted dry-air mixing ratio (XCO2) products with high precision and spatial resolution are essential for inverting CO2 fluxes and promoting our understanding of global climate change. Compared with passive remote sensing methods, IPDA LIDAR, as an active remote sensing technique, offers many advantages in measuring XCO2. However, a significant random error in IPDA LIDAR measurements causes XCO2 values calculated directly from LIDAR signals to be unqualified as the final XCO2 products. Hence, we propose an efficient particle filter-based inversion of CO2 for single observation (EPICSO) algorithm to precisely retrieve the XCO2 of every LIDAR observation while preserving the high spatial resolution of LIDAR measurements. The EPICSO algorithm adopts the sliding average results as the first estimate of the local XCO2; subsequently, it estimates the difference between two adjacent XCO2 points and calculates the posterior probability of XCO2 based on particle filter theory. To evaluate the performance of the EPICSO algorithm numerically, we perform an EPICSO to process pseudo-observation data. The simulation results show that the results retrieved by the EPICSO algorithm satisfy the required high precision and that the algorithm is robust to a significant amount of random errors. In addition, we utilize LIDAR observation data from actual experiments in Hebei, China, to validate the performance of the EPICSO algorithm. The results retrieved by the EPICSO algorithm are more consistent with the actual local XCO2 than those of the conventional method, indicating that the EPICSO algorithm is efficient and practical for retrieving XCO2 with high precision and spatial resolution.

A nearly transform-limited, single-frequency $2~\mu \text{m}$ laser system with multi-stage of double-pass Tm:Ho:LuLiF4 slab amplifiers was demonstrated. An amplified pulse energy up to 5.6 mJ at central wavelength of 2051.9 nm was achieved successfully with around 429.7 ns pulse width at a repetition rate of 10 Hz. The line-width of the laser spectrum detected by a heterodyne technique was about 1.24 MHz. The M2 factors were less than 1.6 and 1.4 in the x and y directions, respectively.

Boron is widely used as a melting point depressant (MPD) element in filler materials for utilization in transient liquid phase (TLP) bonding. Various kinds of borides will precipitate in the diffusion-affected zone (DAZ) and influence the integral mechanical properties of bonded materials. In this study, we systematically investigate the boride precipitates formed in DAZ in a TLP-bonded Ni-based superalloy using electron diffraction and atomic-scale high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The M3B2- and M5B3-type precipitates are observed, both of which obey definitive crystallographic orientation relationships (ORs) with the matrix. The atomic structures of some interfaces associated with these borides are defined. The dendrite morphological feature comprising M3B2 and M5B3 is examined in detail. The dendrite trunks are always composed of two phases including M3B2 and M5B3 borides. The core of the trunk is always M3B2 phase enclosed by M5B3 boride. The dendrite branches consist of M5B3 phase. The M3B2 in the dendrite trunk keeps a definitive OR with the neighboring M5B3. The interfacial features among M3B2, M5B3, and matrix, and the unique intergrowth of M3B2 and M5B3 are further rationalized by phase transformation crystallography.

Accurate monitoring of the atmospheric carbon dioxide (CO2) and its distribution is of great significance for studying the carbon cycle and predicting the future climate change. Compared to the ground observational sites, the airborne observations cover a wider area, and simultaneously observe a variety of surface types, which help in effectively monitoring the distribution of CO2 sources and sinks. In this work, an airborne experiment was carried out in March 2019 over Shanhaiguan area, China (39–41N,119–121E). An Integrated Path Differential Absorption (IPDA) Light Detection and Ranging (LIDAR) system and a commercial instrument, the Ultraportable Greenhouse Gas Analyzer (UGGA), were used installed on an aircraft to observe the CO2 distribution over various surface types. The Pulse Integration Method (PIM) algorithm was used to calculate the Differential Absorption Optical Depth (DAOD) from the LIDAR data. The CO2 column-averaged dry-air mixing ratio (XCO2) was calculated over different types of surfaces including mountain, ocean and urban areas. The concentrations of the XCO2 calculated from LIDAR measurements over ocean, mountain, and urban areas were 421.11, 427.67, and 430 ppm, respectively. Moreover, through the detailed analysis of the data obtained from the UGGA, the influence of pollution levels on the CO2 concentration was also studied. During the whole flight campaign, March 18 was heavily polluted with an Air Quality Index (AQI) of 175 and PM2.5 of 131. The Aerosol Optical Depth (AOD) reported by a sun photometer installed at the Funning ground station was 1.28. Compared to the other days, the CO2 concentration measured by UGGA at different heights was the largest on March 18 with an average value of 422.59 ppm, that was about 10 ppm higher than the measurements recorded on March 16. Moreover, the vertical profiles of Orbiting Carbon observatory-2 (OCO-2) OCO-2 and CarbonTracker were also compared with the aircraft measurements. All the datasets showed a similar variation trend with some differences in their CO2 concentrations, which proved the existence of a good agreement among them.

The demand for greenhouse gas measurement has increased dramatically due to global warming. A 1.57-μm airborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system for CO2 concentration measurement was developed. The airborne field experiments of this IPDA LIDAR system were conducted at a flight altitude of approximately 7 km, and the weak echo signal of the ocean area was successfully received. The matched filter algorithm was applied to the retrieval of the weak signals, and the pulse integration method was used to improve the signal-to-noise ratio. The inversion results of the CO2 column-averaged dry-air mixing ratio (XCO2) by the scheme of averaging after log (AVD) and the scheme of averaging signals before log were compared. The AVD method was found more effective for the experiment. The long-term correlation between the changing trends of XCO2 retrieved by the IPDA LIDAR system and CO2 dry-air volume mixing ratio measured by the in-situ instrument reached 92%. In the steady stage of the open area (30 km away from the coast), which is almost unaffected by the residential areas, the mean value of XCO2 retrieved by the IPDA LIDAR system was 414.69 ppm, with the standard deviation being 1.02 ppm. Compared with the CO2 concentration measured by the in-situ instrument in the same period, bias was 1.30 ppm. The flight path passed across the ocean, residential, and mountainous areas, with the mean value of XCO2 of the three areas being 419.35, 429.29, and 422.52 ppm, respectively. The gradient of the residential and ocean areas was 9.94 ppm, with that of the residential and mountainous areas being 6.77 ppm. Obvious gradients were found in different regions.

Space-borne integrated path differential absorption (IPDA) lidar for global observation of methane (CH4) requires a tunable single-longitudinal mode (SLM) pulsed laser source at 1645 nm, which coincides with appropriate absorption line of CH4 molecules. To meet this application, a pulsed injection-seeded optical parametric oscillator (OPO) using potassium titanyle arsenate (KTA) as the nonlinear crystal is developed. The OPO set-up is a four-mirror stable ring cavity with two pieces of 15-mm-long KTA crystal in critical phase-matching cut for wavelengths around 1645 nm. A single frequency Nd:YAG master oscillator power amplifier (MOPA) laser at 1064 nm serves as the pump. A distributed feedback (DFB) fiber laser with a linewidth of 3 MHz is used for injection of the OPO. To insure successful injection seeding process and enough frequency stability, a cavity-length control method based on the optical heterodyne technique is applied on the OPO cavity. Root-mean-square (RMS) of the frequency variation of the signal pulse compared to the seed laser is measured to be 9.9 MHz, and the Allan deviation is less than 0.25 MHz for averaging time of more than 10 s. With 11 mJ pump pulse input at 50 Hz repetition rate, a signal pulse energy of 1.8 mJ is obtained. The pulse width of this OPO is 15 ns and corresponding linewidth is 45 MHz.

Airborne integrated path differential absorption (IPDA) lidar system is an important instrument to verify the performance and data inversion methods of future space-borne lidar systems for atmospheric CO2 measurement. A ground vertical path validation experiment of atmospheric CO2 measurement by an airborne double-pulsed 1.57-μm IPDA lidar has been implemented. The experiment was carried out and temperature, pressure and humidity profiles of Local Meteorological Station at almost the same time are adopted. Backscattering signals from clouds at altitudes of nearly 5 km were received. To avoid the influence of stray light from mirrors, the energy monitoring signal was delayed through the 200 m multimode fiber. But it is interfered by the aerosol scattering echo signals. Inversely, considering the stray light as monitoring signal, the inversion result of XCO2 is pretty good. Six methods are studied and compared to reduce the bias and improve the CO2 column-averaged dry-air mixing ratio (XCO2) accuracy. The “PIM, AVD” and “PIM, AVX” methods are more effective when clouds are acted as hard target. The mean value of lidar measured XCO2 calculated by “PIM, AVD” and “PIM, AVX” methods is 409.63 ppm. The average value of in-situ instrument UGGA is 411.05 ppm over the same period. The bias between IPDA lidar and UGGA is -1.42 ppm. With averaging 148 shots, the standard deviation of XCO2 of the IPDA lidar system is 3.68 ppm.

In this study, a 1.57-µm airborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system was developed for CO

The spaceborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system was found to be helpful in observing atmospheric CO2 and understanding the carbon cycle. The airborne experiments of a scale prototype of China’s planned spaceborne IPDA LIDAR was implemented in 2019. A problem with data inversion caused by the detector module nonlinearity was found. Through many experiments, the amplifier circuit board (ACB) of the detector module was proved to be the main factor causing the nonlinearity. Through amplifier circuit optimization, the original bandwidth of the ACB was changed to 1 MHz by using a fifth-order active filter. Compared with the original version, the linearity of optimized ACB is improved from 42.6% to 0.0747%. The optimized ACB was produced and its linearity was verified by experiments. In addition, the output waveform of the optimized ACB changes significantly, which will affect the random error (RE) of the optimized IPDA LIDAR system. Through the performance simulation, the RE of more than 90% of the global area is less than 0.728 ppm. Finally, the transfer model of the detector module was given, which will be helpful for the further optimization of the CO2 column-averaged dry-air mixing ratio (XCO2) inversion algorithm.

A frequency-stabilized laser system at 1572 nm for space-borne carbon dioxide (CO2) detection LIDAR to realize the precise measurement of the global atmospheric CO2 concentration is presented in this Letter. A distributed-feedback laser diode serves as the master laser (ML) and is wavelength locked to the CO2 line center at 1572.0179 nm using the external frequency modulation technique. The root mean square frequency drift is suppressed to about 50 kHz at an average time of 0.1 s over 8 h. Based on optical phase-locked loops, an online seeder and an offline seeder are offset locked to the reference laser at 1572.024 and 1572.081 nm, respectively, retaining virtually the same frequency stability as the ML.

The high spectral resolution lidar (HSRL) technique employs a narrow spectral filter to separate the aerosol and molecular scattering components from the echo signals and therefore can retrieve the aerosol optical properties and lidar ratio (i.e., the extinction-to-backscatter ratio) profiles directly, which is different from the traditional Mie lidar with assumed lidar ratio. Accurate aerosol profiles measurement are useful for air quality monitoring. In this paper, a spaceborne HSRL lidar system simulation model based iodine vapor cell filter was presented. According to three different atmosphere aerosol distribution models and the uncertainties of atmosphere temperature and pressure, the signal to noise ratio (SNR) and the relative errors profiles of the backscattering coefficients of this lidar was simulated theoretically in daytime and nighttime. The result shows that the errors of aerosol backscattering coefficients are smaller in the aerosols dense area than in the sparse area. As altitude increases, the relative error of backscattering coefficient is increased. The relative backscattering coefficient error is within 16.5% below 5 km with 30 m range resolution and 10 km horizontal resolution.

For double-pulsed 1.57 μm integrated path differential absorption lidar, the transmitted pulse energy measurement is an important factor that can influence the uncertainty of CO

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.

Compared with ground-based lidar, airborne lidar has a wider observation area, which is useful for studying aerosol distribution and transportation. A dual-wavelength high spectral resolution Lidar (HSRL) was developed for the validation and calibration of an upcoming satellite payload. The HSRL was installed on an airplane, and field campaigns were conducted in Qinhuangdao, China. Meanwhile, four observation sites were established at different locations on the ground to verify the results of the airborne lidar. This article compares the HSRL measurements with those from ground-based micro-pulse lidar (MPL), Mie-scattering lidar, sun photometer, and spaceborne cloud-aerosol Lidar and infrared pathfinder satellite observations (CALIPSO), and Moderate Resolution Imaging Spectroradiometer (MODIS). The stability and reliability of the HSRL system were fully verified. The flight area covered several surface types, including ocean, town, mountain, and forest, which strongly affect the AOD above them. The boundary layer AOD was analyzed in different regions, based on the impact of human activities. The results demonstrated that the AOD in urban area was the largest, and smallest in marine areas, a result ascribed to the influence of industrial activities.

The characteristics and capability of a homemade all-fiber 1.54-μm pulsed coherent Doppler lidar (CDL) were validated in field experiments by comparing the detection results with a collocated lidar and sounding balloons. With the range gate of 30 m and temporal resolution of 16 s at velocity–azimuth display mode, the detection capability of the CDL ranged from 0.1 to 5 km, and the time sequence and height position of this CDL were calibrated by the collocated lidar. In the intercomparison experiments with sounding balloons, the discrepancy of 30-s averaged measurement results of horizontal wind speed and wind direction was nearly 0.7 m / s and 5.3 deg, respectively. The good agreement achieved in such a short averaged time period was a convincing case of intercomparison experiments between CDL and sounding balloon. The CDL system demonstrated good reliability and operational stability in field experiments.

Coherent Doppler lidar (CDL) has been a powerful instrument to measure atmospheric wind velocity. In this work, an 1.5 μm all-fiber pulsed CDL has been developed and deployed to measure wind profiles in campaign experiment in 2018. The CDL has 0.1-5 km detection range with range resolution of 30 m, temporal resolution of 16 s at Velocity-Azimuth-Display (VAD) mode. Field experiments were implemented and the wind vector profiles were retrieved. As compared with sounding balloon, the discrepancy of wind speed and direction are nearly 0.7 m/s and 5 degrees, respectively. It shows that the CDL is a powerful tool for wind speeds measurement in lower atmospheric troposphere.

Started with needs of the national marine strategy, the necessity of China’s oceanographic lidar developing was analyzed, the characteristics and domestic overseas’ development of the oceanographic lidar were summarized; the oceanographic lidar current construction and planning at home and abroad and the launched spaceborne lidar’s situation were analyzed, the future spaceborne ocean lidar’s development direction was put forward and on-orbit data application product was expected, the key technology of the spaceborne ocean lidar was discussed, the application prospect of developing the oceanographic lidar during the 14th five year plan oceanographic was given.

Spaceborne high spectral resolution lidar (HSRL) provides a wide range of observations, e.g., measurements of aerosol backscattering and extinction coefficients and aerosol depolarization ratio with high accuracy, which are of great significance to the study of air pollution monitoring and climate change. With different cells and finger temperatures, the transmittance of the different absorption lines of the iodine vapor filter at 532 nm wavelength was measured. The 1064 nm fundamental frequency pulse energy and the 532 nm frequency-doubled pulse energy output of different seeder laser wavelengths were measured. Based on the relationship among the laser output power, the absorption line shape of the iodine vapor filter, and the atmospheric model, the echo power was calculated and compared. The 1110 iodine absorption line was selected as the optimized filter for the HSRL, which could increase in 22% and 14% efficiency compared with the traditional 1109 line, and a new proposed 1105 line at the 532 nm HSRL channel at 5 km altitude with an enhanced aerosol model, respectively.

In this study, a 1.57-µm airborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system was developed for CO2 measurements. This airborne IPDA LIDAR is integrated with a real-time frequency monitoring system, an integrated sensor for temperature, pressure, and humidity, an inertial navigation system, and a global positioning system. The random errors of the LIDAR system, which are caused by the signal noise, background noise, and detector noise, among other factors, are analyzed for different target reflectivities at a flight altitude of 8 km. After parametric optimization, the signal is unsaturated at high target reflectivity. Further, it can be detected at low target reflectivity by adjusting the detector gain. After the averaging of 148 shots, the relative random error (RRE) was 0.057% for a typical target reflectivity of 0.1 sr-1. Moreover, the systematic errors caused by the laser pulse energy, linewidth, spectral purity, and frequency drift, as well as the atmospheric parameters related to the flight experiments are also investigated. The relative system error (RSE) was 0.214% as determined based on an analysis of the systematic errors, which are primarily caused by the frequency drift. Two methods are proposed to reduce the RSE caused by the frequency drift. The first is the averaging of 148 shots, which can reduce the RSE to 0.096%. The other method involves calculating the integral weight function (IWF) using real-time frequency. However, this is a time-consuming and computationally intensive process. Hence, look-up tables for the absorption cross-section were created to overcome this issue, resulting in a decrease in the RSE to 0.096%. Using actual aircraft attitude angles, velocity, and position data from flight experiments, the relative errors (REs) in the IWF caused by the uncorrected integral path and Doppler shift were determined to be 0.273% and 0.479%, respectively. However, it was found that corrections to the integral path and Doppler shift based on accurate calculations of the IWF cause the airborne platform to turn in such a way that the REs are eliminated. Hence, this study confirms the validity of system parameters and provides a reference for other researchers who study similar IPDA LIDAR systems. Further, the sensitivity analysis of the airborne IPDA LIDAR system can provide a reference to future data inversions. Moreover, the proposed correction algorithms for the integral path and Doppler shift contribute to more accurate inversion results.

Since over 70% of carbon emissions are from urban areas, it is of great importance to develop an effective measurement technique that can accurately monitor atmospheric CO2 in global urban areas. Remote sensing could be an effective way to achieve this goal. However, due to high aerosol loading in urban areas, there are large, inadequately resolved areas in the CO2 products acquired by passive remote sensing. China is planning to launch the Atmospheric Environment Monitoring Satellite (AEMS) equipped with a CO2-light detecting and ranging (LIDAR) system. This work conducted a feasibility study on obtaining city-scale column CO2 volume mixing ratios (XCO2) using the LIDAR measurements. A performance framework consisting of a sensor model, sampling model, and environmental model was proposed to fulfill our demand. We found that both the coverage and the accuracy of the LIDAR-derived city-scale XCO2 values were highly dependent on the orbit height. With an orbit height of 450 km, random errors of less than 0.3% are expected for all four metropolitan areas tested in this work. However, random errors of less than 0.3% were obtained in only two metropolitan areas with an orbit height of 705 km. Our simulations also showed that off-nadir sampling would improve the performance of a CO2-Integrated Path Differential Absorption (IPDA) LIDAR system operating in a 705 km orbit. These results indicate that an active remote sensing mission could help to effectively measure XCO2 values in urban areas. More detailed studies are needed to reveal the potential of such equipment for improving the verification of carbon emissions and the estimation of urban carbon fluxes.

A ground-based double-pulse 1572 nm integrated path differential absorption (IPDA) lidar was developed for carbon dioxide (CO2) column concentrations measurement. The lidar measured the CO2 concentrations continuously by receiving the scattered echo signal from a building about 1300 m away. The other two instruments of TDLAS and in-situ CO2 analyzer measured the CO2 concentrations on the same time. A CO2 concentration measurement of 430 ppm with 1.637 ppm standard error was achieved.