A New Method for Aerosol Retrieval Based on Lidar Observations in Beijing

The impact of human activities on the global climate may lead to large disruptions of the economic, social and political status quo in the middle and long term. Understanding the dynamics of the Earth's climate is thus of paramount importance and one of the major scientific challenges of our time. The estimation of the relative contribution of the many components (interacting each other) of the Earth's climate system requires observation and continuous monitoring of various atmospheric physical and chemical parameters. Temperature, water vapor and greenhouse gases concentration, aerosol and clouds loads, and atmospheric dynamics are parameters of particular importance in this respect. The quantification of the anthropogenic influence on the dynamics of these above-mentioned parameters is of crucial importance nowadays but still affected by significant uncertainties. In the present context of these huge uncertainties in our understanding of how these different atmospheric compounds contribute to the radiative forcing, the research presented in this report is related to the following topics: Development of lidar-based remote sensing techniques for monitoring atmospheric compounds and processes Aerosols – cirrus – contrails optical properties up to the tropopause Water vapor mixing ratio and relative humidity estimation in the upper troposphere Temperature profiling in the upper troposphere-lower stratosphere Characterization of the long-range transported mineral aerosols (i.e. Saharan dust outbreaks) Planetary boundary layer-upper troposphere exchanges (i.e. August 2003 heatwave effect) In the above research frames, the development and application of measurement techniques for the monitoring of climate-change parameters, this work refers to the implementation of a multi-wavelength LIDAR1 system (JFJ - LIDAR)2 at the International Scientific Station of Jungfraujoch (ISSJ, 46°33' N, 7°59' E, at 3580 m ASL- above sea level). The JFJ3 station is situated above the planetary boundary layer (PBL) almost all year long and is located in a mountain pass linking the Swiss plateau to the North with the Rhone Valley to the South through the Aletsch glacier corridor. Measurements with the JFF-LIDAR system provide regular vertical and horizontal remote sensing of water vapor, temperature, and optical properties (backscatter and extinction coefficients) of aerosols, cirrus clouds and contrails in the upper troposphere (UT)4. The lidar system is based on the laser emission at 355, 532 and 1064 nm and on subsequent detection of both elastic (Mie) and inelastic (Raman) atmospheric backscatter light. The backscattering collected radiation is precisely: the elastic at 355, 532 and 1064 nm; the rotational-vibrational Raman radiation from nitrogen at ~ 387 nm, and from water vapor at ~ 407 nm as well as the pure rotational nitrogen/oxygen Raman excited at ~ 532 nm. The depolarization of the initially linearly polarized radiation was also detected at 532 nm and it was use to distinguish between water and ice contents in cirrus clouds, but also it may reveal long-range transported mineral aerosols such as Saharan dust. Profiles of backscatter and extinction coefficients of aerosols-cirrus-contrails, needed for estimation of the radiative balance of the atmosphere, are derived from elastic and Raman light scattering processes, or through a combination of both, using devoted algorithms and software developed within this research. Data gathered from routine measurements are statistically analyzed and interpreted in comparison with similar measurements obtained from colocated techniques. Optical and microphysical properties of a typical contrail were studied. The UT water vapor mixing ratio profiles are estimated from the ratio of ~ 407 nm and ~387 nm Raman radiation excited by 355 nm. Upon appropriate calibration, real time water vapor mixing ratio profiles derived from LIDAR measurements are found in good agreement with the closest radiosounding techniques, and co-located measurements such as the GPS5 and sun photometer based measurements. The water vapor profiles, combined with simultaneous temperature profiles taken from atmospheric models, radiosounding or, more realistically, based on the pure rotational Raman technique, were used for the estimation of relative humidity profiles which allow the identification of UT super-saturation regions. Air temperature profiles were obtained up to the lower stratosphere using the backscatter of pure rotational Raman radiation excited by 532 nm. These first results compare well to simultaneous regional radiosounding measurements, and follow standard atmospheric models. The pure rotational Raman backscatter was also used for determining absolute extinction and the lidar ratio for cirrus clouds. Based on the JFJ-LIDAR measurements, supported by co-located and regional measurements, the research presents also in detail two case studies related to climate problematic: The first concerns the tracking of a Saharan dust outbreak (SDO) and the derivation of its optical properties. The second study refers to the analysis of the evolution and consequences of the high altitudes planetary boundary layer (PBL)6 convection during the August 2003 heat - wave episode. The results presented within this research provide a promising basis for extending these JFJ-LIDAR observations from the upper troposphere into the stratosphere by using the existent astronomic telescope (~15 times increased sensitivity) and a new (~ 3 times more powerful) laser source. Consequently DIAL7 technique for measuring the stratospheric ozone will be developed and implemented in the near future at JFJ. Future challenges include also JFJ-LIDAR remote control operation and the ability of real time obtained atmospheric calibrated profiles (i.e. optical properties of aerosols-cirruscontrails, water vapor, temperature and ozone). --------------------1 LIDAR – LIght Detection And Ranging 2 JFJ-LIDAR is the acronym used here for Jungfraujoch multi-wavelength LIDAR system 3 JFJ is the abbreviation for Jungfraujoch 4 UT will be used as abbreviation for upper troposphere (from ~ 3600 m ASL to the tropopause atmospheric region) 5 GPS is the acronym for Global Positioning System 6 PBL - planetary boundary layer – its top is usually situated under the altitude of the JFJ station (i.e. 3600m ASL) 7 DIAL - is the acronym coming from DIfferential Absorption Lidar

Conventional lidar methods for deriving particle optical properties suffer from the fact that two unknowns (backscatter and extinction coefficients) need to be determined from only one lidar equation. Thus, additional assumptions (constant lidar ratio or Ångström relationship) have to be introduced to settle this problem. In contrast, a single-line-extracted pure-rotational-Raman (PRR) lidar method allows the strict retrieval of backscatter and extinction coefficients without additional assumptions. Based on the observations of our single-line-extracted PRR lidar from February 2016 to December 2017, the optical properties (backscatter coefficient, extinction coefficient and lidar ratio) of continental polluted aerosols, dust aerosols, and cirrus cloud particles over Wuhan (30.5°N, 114.4°E) are well characterized. The mean values of the measured lidar ratios are respectively 60 ± 7 sr for continental polluted aerosols, 47 ± 4 sr for dust aerosols and 22 ± 4 sr for cirrus cloud particles. The backscatter and extinction coefficients measured by the single-line-extracted PRR lidar deviate as a whole by 7-13% and 13-16%, respectively, from those retrieved by the traditional Fernald method. The optical properties measured by the single-line-extracted PRR lidar can serve as observational standards for particle optical properties (backscatter/extinction coefficient and lidar ratio) at 532 nm wavelength.

The errors in retrieved aerosol backscattering coefficients due to different lidar ratios are analyzed quantitatively in this paper. The actual calculation shows that the inversion error of the aerosol backscattering coefficients using the Fernald backward-integration method increases with increasing inversion distance. The greater the error in the lidar ratio, the faster the error in the aerosol backscattering coefficient increases. For the same error in lidar ratio, the smaller actual aerosol backscattering coefficient will get the larger relative error of the retrieved aerosol backscattering coefficient. The errors in the lidar ratios for dust or the cirrus layer have great impact on the retrievals of backscattering coefficients. The interval between the retrieved height and the reference range is one of the important factors for the derived error in the aerosol backscattering coefficient, which is revealed quantitatively for the first time in this paper. The conclusions of this article can provide a basis for error estimation in retrieved backscattering coefficients of background aerosols, dust and cirrus layer. The errors in the lidar ratio of an aerosol layer influence the retrievals of backscattering coefficients for the aerosol layer below it.

Climate changes and global warming are generally associated with the enhanced greenhouse effect, but aerosols can induce a cooling effect and thus regionally mask this warming effect. Unfortunately, the strong variability both in space and in time of the aerosols and thus the difficulty to characterize their global basic properties induce large uncertainties in the predictions of the numerical models. Those uncertainties are as high as the absolute level of the enhanced greenhouse forcing. To solve this problem it is necessary to improve the set of well-calibrated instruments (both in situ and remote sensing) with the ability to measure the changes in stratospheric and tropospheric aerosols amounts and their radiative properties, changes in atmospheric water vapor and temperature distributions, and changes in clouds cover and cloud radiative properties. The quantity used to assess the importance of one compound (greenhouse gases, aerosols) to the variation of the radiative budget of the Earth is the radiative forcing. One of those forcings is the direct aerosol radiative forcing and it depends on the optical depths and the upscatter fraction of the aerosols. Those two parameters depend on the chemical composition and size distribution of the aerosols. Thus the key parameters of this radiative forcing are the chemical composition through its refractive index and the size distribution of the aerosols. This thesis deals with the design and the implementation of one multi-wavelength lidar system at the Jungfraujoch Alpine Research Station (Alt. 3580m asl). This lidar system is a combination of one standard backscatter lidar and one Raman lidar. Its design have been supported by a ray tracing analysis of the receiver part. The laser transmitter is based on a tripled Nd:YAG laser and the backscattered light is collected by one Newtonian telescope for the tropospheric measurements and by one Cassegrain telescope for the future stratospheric measurements. The received wavelengths for each telescope include three elastically scattered wavelengths (355, 532 and 1064nm), two spontaneous Raman signals from nitrogen (387 and 607nm) and one spontaneous Raman signal from the water vapor (408nm). The optical signals received by each of the telescopes are separated spectrally by two filter polychromators. They are build up around a set of beamsplitters and custom design thin band pass filters with high out-of-band rejection. On the visible channel, the adds of a Wollaston prism separates the parallel polarized backscattered signal (532(p)nm) of the perpendicular polarized one (532(c)nm). Photomultiplier tubes perform the detection of the signals for the UV and visible wavelengths and by Si-avalanche photodiodes for the near-infrared signal. The acquisition of the signals is performed by seven transient recorders in analog and in photon counting modes. Within the frame of the EARLINET (European Aerosol Research Lidar Network), hardware and software intercomparisons have been done. The software intercomparison has been divided into the validation of the elastic algorithm and the Raman algorithm. Those intercomparisons of the inversions of the lidar signals have been performed using synthetic data for a number of situations of different complexity. The hardware intercomparison have been achieved with the mobile micro-lidar of the Observatoire Cantonal de Neuchâtel. The present lidar system provides independent aerosol extinction and backscatter profiles, depolarization ratio and water vapor mixing ratio up to the tropopause. Their uncertainties could be smaller than 20% and thus make possible the retrieval of the microphysical aerosol parameters like the volume concentration distribution and the mean and integral parameters of the particle size distribution, (effective radius, total surface-area concentration, total volume concentration and number concentration of particles). This retrieval is performed by one algorithm of the Institute of Mathematic of the University of Postdam based on the hybrid regularization method. The first results of the retrieval of the volume concentration distribution with three backscatter (355, 532 and 1064nm) and one extinction (355nm) profiles has demonstrated promising results. Future upgrades of the system will add ozone concentration and temperature profile up to the stratopause.

The aerosol optical properties such as depolarization ratio (δ) and aerosol extinction-to-backscatter ratios (S, LIDAR ratio) and Angstrom exponent (A) derived from measurement with AERONET sun/sky radiometer at Gangneung-Wonju National University (GWNU), Gangneung, Korea (37.77°N, 128.87°E) during a winter season (December 2014 - February 2015) are presented. The PM concentration measurements are conducted simultaneously and used to identify the high-PM events. The observation period was divided into three cases according to the PM concentrations. We analysed the δ, S, and A during these high PM-events. These aerosol optical properties are calculated by the sun/sky radiometer data and used to classify a type of aerosols (e.g., dust, anthropogenic pollution). The higher values of δ with lower values of S and A were measured for the dust particles. The mean values of δ, S, and A at 440-870 nm wavelength pair (A440-870) for the Asia dust were 0.19-0.24, 36-56 sr, and 0.48, respectively. The anthropogenic aerosol plumes are distinguished with the lower values of δ and higher values of A. The mean values of spectral δ and A440-870 for this case varied 0.06-0.16 and 1.33-1.39, respectively. We found that aerosol columnar optical properties obtained from the sun/sky radiometer measurement are useful to identify the aerosol type. Moreover, the columnar aerosol optical properties calculated based on sun/sky radiometer measurements such as δ, S, and A will be further used for the validation of aerosol parameters obtained from LIDAR observation as well as for quantification of the air quality.

The horizontal and vertical distributions of aerosol optical properties over China in 2013–2015 were investigated using RAMS (Regional Atmospheric Modeling System)-CMAQ (Models-3 Community Multiscale Air Quality) simulations and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) observations. To better understand the performance of the RAMS-CMAQ model over China, comparisons with the ground-based Sun photometers AERONET (Aerosol Robotic Network), MODIS (Moderate Resolution Imaging Spectroradiometers) data and the on-board Lidar CALIOP were used for comprehensive evaluations, which could characterize the abilities of the model to simulate the spatial and vertical distributions of the AOD (Aerosol Optical Depth) as well as the optical properties for four seasons. Several high value areas (e.g., the Sichuan Basin, Taklamakan Desert, North China Plain, and Yangtze River Delta) were found over China during the study period, with the maximum mean AOD (CALIOP: ~0.7; RAMS-CMAQ: >1) in the Sichuan district. Compared with AODs of AERONET, both the CALIOP and RAMS-CMAQ AODs were underestimated, but the RAMS-CMAQ data show a better correlation with AERONET (AERONET vs. RAMS-CMAQ R: 0.69, AERONET vs. CALIOP R: 0.5). The correlation coefficients between RAMS-CMAQ and CALIOP are approximately 0.6 for all four seasons. The AEC (Aerosol Extinction Coefficient) vertical profiles over major cities and their cross sections exhibit two typical features: (1) most of the AEC peaks occurred in the lowest ~0.5 km, decreasing with increasing altitude; and (2) the RAMS-CMAQ AEC underestimated the region with high AODs in the northwest of China and overestimated the region with high AODs in the east–central plain and the central basin regions. The major difference in the AEC values of RAMS-CMAQ and CALIOP is mainly caused by the level of relative humidity and the hygroscopic growth effects of water-soluble aerosols, especially, in the Sichuan district. In general, both the column and vertical RAMS-CMAQ aerosol optical properties could be supplemented efficiently when satellite observations are not available or invalid over China in the applications of climate change and air pollution.

Aerosols play a fundamental role in physical and chemical processes affecting regional and global climate, and have adverse effects on human health. Although much progress has been made over the past decade in understanding aerosol-climate interactions, their impact still remains one of the largest sources of uncertainty in climate change assessment. The wide variety of aerosol sources and the short lifetime of aerosol particles cause highly variable aerosol fields in both space and time. Groundbased measurements can provide continuous data with high accuracy, but often they are valid for a limited area and are not available for remote areas. Satellite remote sensing appears therefore to be the most appropriate tool for monitoring the high variability of aerosol properties over large scales. Passive remote sensing of aerosol properties is based on the ability of aerosols to scatter and absorb solar radiation. Algorithms for aerosol retrieval from satellites are used to derive the aerosol optical depth (AOD), which is the aerosol extinction integrated over the entire atmospheric column. The aim of the work described in this thesis was to develop and validate a new algorithm for the retrieval of aerosol optical properties from geostationary observations with the SEVIRI (Spinning Enhanced Visible and Infra-Red Imager) instrument onboard the MSG (Meteorological Second Generation) satellite. Every 15 minutes, MSG-SEVIRI captures a full scan of an Earth disk covering Europe and the whole African continent with a high spatial resolution. With such features MSG-SEVIRI offers the unique opportunity to explore transport of aerosols, and to study their impact on both air quality and climate. The SEVIRI Aerosol Retrieval Algorithm (SARA) presented in this thesis, estimates the AOD over sea and land surfaces using the three visible channels and one near-infrared channel of the instrument. Because only clear sky radiances can be used to derive aerosol information, a stand-alone cloud detection algorithm was developed to remove cloud contaminated pixels. The cloud mask was generated over Europe for different seasons, and it compared favorably with the results from other cloud detection algorithms - namely the cloud mask algorithm of Meteo-France for MSG-SEVIRI, and the MODIS (Moderate Resolution Imaging Spectroradiometer) algorithm. The aerosol information is extracted from cloud-free scenes using a method that minimizes the error between the measured and the simulated radiance. The signal observed at the satellite level results from the complex combination of the surface and the atmosphere contributions. The surface contribution is either parameterized (over sea), or based on a priori values (over land). The effects of atmospheric gases and aerosols on the radiance are simulated with the radiative transfer model DAK (Doubling-Adding-KNMI) for different atmospheric scenarios. The algorithm was applied for various case studies (i.e. forest fires, dust storm, anthropogenic pollution) over Europe, and the results were validated against groundbased measurements from the AERONET database, and evaluated by comparison with aerosol products derived from other space-borne instruments such as the Terra/- Aqua-MODIS sensors. In general, for retrievals over the ocean, AOD values as well as their diurnal variations are in good agreement with the observations made at AERONET coastal sites, and the spatial variations of the AOD obtained with the SARA algorithm are well correlated with the results derived from MODIS. Over land, the results presented should be considered as preliminary. They show reasonable agreement with AERONET and MODIS, however extra work is required to improve the accuracy of the retrievals based on the proposed method

Atmospheric aerosol is defined as a suspension of solid or liquid particles in air. The major concerns about aerosol particles are their adverse health effects and their role in the Earth's climate system. Atmospheric particles influence the Earth's radiation budget in two ways: either directly by scattering and absorbing incoming solar radiation (and to a far less extent longwave radiation emitted from the Earth) or indirectly by their ability to act as cloud condensation nuclei (CCN). With increasing particle concentrations, caused by, e.g., anthropogenic emissions, more CCN are available to form cloud droplets. For a fixed water content in the atmosphere this leads to more but smaller droplets and therefore to enhanced cloud albedos as well as to rain suppression. Both effects have been recognized in recent years to be of great importance for understanding the observed climate change. Nevertheless, they remain poorly understood and quantified. The Jungfraujoch (JFJ, 3580 m asl; 46.548°N, 7.984°E) High Alpine Research Station is equipped with instruments that have for decades performed important Global Climate Observations. A major part of the aerosol instruments perform in-situ measurements. However, due to the harsh weather conditions, they usually cannot be run outdoors. The ambient air has to be inducted into a housing, such that the aerosol is sampled at a temperature (T) and relative humidity (RH) different from the ambient values. Therefore, the measured aerosol properties may considerably differ from the ambient — the climate-relevant — ones. During the first Cloud and Aerosol Characterization Experiment (CLACE) at the JFJ in-situ aerosol size distributions were measured simultaneously indoor at dry conditions (T ≈ 25 °C and RH 1 µm) particles were assumed to be water-insoluble homogeneous spheres. Ambient scattering coefficients σsca(RH) were found to be considerably different from the dry scattering coefficients σsca(RH = 0). The scattering enhancement factors ξ(RH) = σsca(RH)/σsca(RH = 0) strongly depend on the particle size. At RH = 85% they vary for example between ≈ 1.2 and ≈ 3.8. It was possible to establish a parameterization of ξ(RH) with the dry Angstrom exponent a (based on scattering only). Since a follows directly from the dry scattering measurements, the parameterization allows to derive ambient scattering coefficients from the dry scattering coefficients without the need of any additional measurement other than ambient RH. RH also affects the absorption coefficient σabs. Depending on particle size and wavelength (investigated between 370 nm and 950 nm) absorption enhancement factors χ(RH) = σabs(RH)/σabs(RH = 0) were found to range from 0.84 to 1.78. However, it was possible to demonstrate that, even though the humidity effect on absorption is substantial, its contribution to the humidity effect on extinction and the single scattering albedo is negligible at the JFJ. The EPFL Raman lidar installed at the JFJ provides profiles of extinction and backscattering coefficients at the wavelengths 355 nm, 532 nm and 1064 nm for altitudes between typically 4 km and 15 km asl. These measurements are ambient but afflicted with more uncertainties than the dry in-situ measurements. A method was developed to derive microphysical aerosol properties from optical lidar data. This is a so-called ill-posed problem, i.e., small errors in the lidar data lead to huge errors in the inverted microphysical properties, unless special mathematical tools are applied. Therefore the method makes use of regularization techniques. It is shown that microphysical parameters can be inverted with acceptable accuracy from an optical dataset as it is provided by a lidar of e.g. the EPFL type.

Temporal Aerosol Optical Depths (AODs) of Phimai district, Nakhon Ratchasima province in Thailand were retrieved from measured Mie lidar data on 17-20 February 2005 using Fernald method. The ground-based station was selected for its high and diverse local agricultural activities contributed to the aerosol content which allows for various parameters such as concentration, size distribution and aerosol optical properties to be investigated by Mie theory. The retrieval algorithm of 24-hour AODs was performed in order to monitor regional impact of biomass burning emission on tropospheric aerosols. Results revealed that open biomass burning was a significant contributor to large carbonaceous aerosols in the vicinity of research site with AOD around 0.6-0.7. Furthermore, the prominence of open burning emission yielded short range aerosol transportation when fine and coarse aerosol particles were accumulated with the minimum and maximum average AODs of 0.2187 and 0.4291, respectively. In addition, the observation provided important insights into the physical and scavenging of aerosols under the influence of regional anthropogenic source and would be great knowledge of aerosol data development. By the lidar technique used in present work, the nocturnal AOD retrieval was advantageously available.

To measure atmospheric temperature, water vapor, and aerosol simultaneously, an efficient multi-function Raman lidar using an ultraviolet-wavelength laser has been developed. A high-performance spectroscopic box that utilizes multicavity interference filters, mounted sequentially at small angles of incidence, is used to separate the lidar return signals at different wavelengths, and to extract the signals with high efficiency. The external experiments are carried out for simultaneous detection of atmospheric temperature, water vapor, and aerosol extinction coefficient in Beijing, under clear and hazy weather conditions. The vertical profiles of temperature, water vapor, and aerosol extinction coefficient are analyzed. The results show that for an integration time of 5 min and laser energy of 200 mJ, the mean deviation between measurements obtained by lidar and radiosonde is small, and the overall trend is similar. The statistical temperature error for nighttime is below 1 K up to a height of 6.2 km under clear weather conditions, and up to a height of 2.5 km under slightly hazy weather conditions, with 5 min of observation time. An effective range for simultaneous detection of temperature and water vapor of up to 10 km is achieved. The temperature-inversion layer is found in the low troposphere. Continuous observations verify the reliability of Raman lidar to achieve real-time measurement of atmospheric parameters in the troposphere.

Satellite remote sensing aerosol monitoring products are readily available but limited to regional and global scales due to low spatial resolutions making them unsuitable for city-level monitoring. Freely available satellite images such as Sentinel -2 at relatively high spatial (10m) and temporal (5 days) resolutions offer the chance to map aerosol distribution at local scales. In this study, we retrieve Aerosol Optical Depth (AOD) from Sentinel -2 imagery for the Munich region and assess the accuracy against ground AOD measurements obtained from two Aerosol Robotic Network (AERONET) stations. Sentinel -2 images with less than 30% cloud cover acquired between January and October 2018 were used in the study and contemporaneous AERONET Level 1.5 AOD data used to validate the AOD retrievals. Since aerosol distribution and properties exhibit high temporal variations, only satellite data and AERONET measurements acquired within 15 minutes were considered for validation and statistical analysis. Sen2Cor, iCOR and MAJA algorithms which retrieve AOD using Look-up-Tables (LUT) pre-calculated using radiative transfer (RT) equations and SARA algorithm that applies RT equations directly to satellite images were used in the study. Sen2Cor, iCOR and MAJA retrieved AOD at 550nm show strong consistency with AERONET measurements with average correlation coefficients of 0.91, 0.89 and 0.73 respectively. However, MAJA algorithm gives better and detailed variations of AOD at 10m spatial resolution which is suitable for identifying varying aerosol conditions over urban environments at a local scale.

Aerosol particles are an important component of the atmosphere. Most of the aerosol mass suspended in the atmosphere resides within the PBL, which is the atmospheric layer directly above the ground. Atmospheric aerosols affect air quality and, in turn, human and ecosystem well-being (WHO, 2013a), and they also play an important role in the Earth’s climate system (IPCC, 2013). In fact, PM (Particles Mater) pollution is probably the most urgent issue in air quality regulation worldwide, and at the same time it represents one of the biggest sources of uncertainty in current climate simulations. Therefore, vertically resolved measurements of physical and optical properties of aerosol particles are of great interest, and height-resolved observations of these parameters can only be carried out with lidar techniques. The lidar technique has proved to be effective to measure the vertical profile of aerosol optical properties with high vertical and temporal resolution. Spaceborne lidars are capable of mapping vertical distributions of aerosol over globe spatial regions in a short amount of time. For existing spaceborne lidars, such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), an assumption of aerosol extinction-to-backscatter ratio is needed to retrieve aerosol optical properties. To measure the vertical profile of aerosol extinction without assumptions of the aerosol extinction-to-backscatter ratio, High Spectral Resolution Lidar (HSRL) technique has been employed due to the advantage of day and night measurements compared to Raman lidar. A spectral analysis system developed for a spaceborne HSRL has been implemented and is presented in this thesis. The spectral analysis system is based on the combination of an interference filter, a planar Fabry-Perot interferometer (PFPI) background filter, and a confocal Fabry-Perot interferometer (CFPI) high spectral resolution filter. By the comparison of a molecular absorption filter and three kinds of interferometer filters, the CFPI has been adopted for the high spectral resolution filter of the spaceborne HSRL. Unlike gas absorption cells, CFPI has no problem of leak and vapor formation, which would make the gas absorption cells useless. Compared to other interferometers, the CFPI can provide high spectral resolution and a large etendue simultaneously, and is much less sensitive to alignment errors and vibrations. A frequency-locking subsystem is used to lock the center transmission wavelength of the spectral analysis system with the wavelength of the emitted laser. The developed two-stage frequency-locking technique is a novel technique and can be used whether the locking laser is a pulsed laser or a continuous laser. The frequency-locking subsystem of the spectral analysis system has been designed and realized. The tests show that it is a robust apparatus, with very good stability. The parameter requirements of the spectral analysis system have been obtained by a simulation of the spaceborne HSRL. All the components of the spectral analysis system have been designed and realized. After being assembled, the spectral analysis system has been tested by using a narrow linewith continuous laser. The test results show that transmission and reflection at the wavelength of 532nm are close to the theoretical value, when the central wavelength of the spectral analysis system is locked to the wavelength of the laser source by the developed frequency-locking system. The error sources that affect the accuracy of aerosol optical properties are analyzed. The results show that the detector noise is the dominant source of error. Further analysis also shows that the relative error of the retrieved aerosol and molecular signals are more sensitive to the error of the CFPI peak transmission than to the error of the CFPI bandwidth.

Abstract. The Atmospheric Environment Monitoring Satellite (AEMS), also called Daqi-1 or DQ-1, was launched in April 2022; one of its main payloads is a high-spectral-resolution lidar (HSRL) system. This new system enables the accurate measurements of global aerosol optical properties, which can be used in the geoscientific community after the retirement of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Developing a suitable retrieval algorithm and validating retrieved results are necessary. This research demonstrates a retrieval algorithm for aerosol optical properties using the DQ-1 HSRL system. This method has retrieved the aerosol linear depolarization ratio, backscatter coefficient, extinction coefficient, and optical depth. For validation purposes, we compared retrieved results with those obtained through CALIPSO. The results indicate that the profiles of the two datasets are in good agreement, with DQ-1 showing an improved signal-to-noise ratio (SNR). Optical property profiles from National Aeronautics and Space Administration (NASA) Micro-Pulse Lidar Network (MPLNET) stations were selected for validation with the DQ-1 measurements, resulting in a relative error of 25 %. Between June 2022 and December 2022, aerosol optical depth measurements using the DQ-1 satellite and the AErosol RObotic NETwork (AERONET) were correlated and yielded a value of R2 equal to 0.803. We use the DQ-1 dataset to initially investigate the transport processes of the Saharan dust and the South Atlantic volcanic aerosols. These validations and applications show that the DQ-1 HSRL system can accurately measure global aerosols and has significant potential for Earth scientific applications.

Ceilometers are originally designed for cloud base height monitoring. Since a few years, the number of ceilometers available worldwide is rapidly increasing, and these simple backscatter lidars are investigated to be used for aerosol research. This study presents an assessment of the potential of CYY-2B ceilometer for the quantitative retrieval of aerosol properties. The signal-to-noise ratio of the ceilometer is calculated, and the effective height of inversion is determined. It is shown that the effective height of the ceilometer for backscatter coefficient profile inversion is 3-4 km at night and about 1.5–2 km during the day, which is lower than that of the micropulse lidar (MPL) system. The accuracy of the backscatter coefficient profiles derived from the CYY-2B ceilometer is analyzed by using the Vaisala CL51 ceilometer, MPL, forward scatter visibility instrument, and aerosol optical depth (AOD) dataset from aerosol robotic network (AERONET). Spectral conversions of the ceilometer’s and lidar’s data are performed using the Ångström exponent estimated by AERONET measurements. A good agreement is found between two ceilometers and the MPL lidar in backscatter coefficient profiles inversion. The AODs agree well with the AERONET AODs during the observation period of small AODs. However, for the period of large AODs, the results are approximately 50%–60% of AERONET AODs. The limited range of extinction integration is the main cause of this problem.

In this paper, multi-source observation, such as aircraft, ground-based remote sensing, and satellite-retrieved data, has been utilized to compare and analyze the vertical characteristics of aerosol optical properties and the planetary boundary layer height (HPBL) over the North China Plain (NCP) region during May–June 2016. Aircraft observations show the vertical profiles of aerosol absorption coefficients (σabs), scattering coefficients (σsca), and extinction coefficients (σext) gradually decrease with altitude, with their maximum values near HPBL. The vertical profiles of σext depended most on the vertical distribution of measured σsca, indicating a significant contribution of scattering aerosols. In addition, the prominent characteristic of the inverse relationship between σext and moisture profile could serve as a reference for predicting air quality in the NCP region. The lower layer pollution during the field experiment was likely caused by the accumulation of fine-mode aerosols, characterized by the vertical distribution of the Ångström exponent and the Aerosol Robotic Network (AERONET) products. Typically, HPBL derived from aircraft and surface Micro Pulse Lidar (MPL) was approximate, while the predicted HPBL by meteorological data indicates an underestimation of ~192 m. Aerosol optical depth (AOD) calculated from aircraft and ground-based remote sensing (such as MPL and AERONET) experienced a strong correlation, and both of them exhibited a similar tendency. However, the AOD retrieved from satellites was significantly larger than that from aircraft and ground-based remote sensing. Overall, the inversion algorithm, cloud identification algorithm, representativeness of the space, and time of the observation may lead to an overestimation or underestimation of AOD under certain circumstances. This study may serve as a re-evaluation of AOD retrieved from multi-source observations and provide a reference to uncover the actual atmospheric environment in the NCP regions.