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Development or Application of Remote Sensing Techniques in Atmospheric Monitoring

A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Atmospheric Remote Sensing".

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 14676

Special Issue Editors

Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada
Interests: optical remote sensing of fugitive emissions; development of methods, instruments, and artificial intelligence approach for air monitoring
Optind Solutions Private Limited, Unit No. 11, Technology Business Incubator, National Institute of Technology Calicut, Calicut 673601, India
Interests: spectroscopy; development of Instrumentation for atmospheric, and environmental monitoring using principles of optics; radiative transfer and aerosol forcing on climate (global and regional)
Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China
Interests: inversion of atmospheric aerosol characteristics; air quality remote sensing; radiative transfer modeling; remote sensing for particle nucleation; air pollution assimilation and forecasting
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Emissions, transport, and reactions of atmospheric pollutants determine the air pollution process that negatively affects air quality, ecosystems, and climate. To understand the process and make an effective remediation, it is essential to detect, identify, and quantify those pollutants. Optical remote sensing (ORS) technologies provide a powerful tool to measure atmospheric pollutants, as the measurements can be instantaneous, in situ, continuous, and have high sensitivity and specificity.

The major challenges of ORS applications involve: a) quantifying fugitive emissions that are highly heterogeneous, highly variable, and with undefined boundaries; b) detecting trace gases that exist at low concentrations; and c) determining the spatial distribution of pollutants in a vertical column through the atmospheric layer and/or over a large surface area.

The aim of the Special Issue is to present the latest advancements in optical remote sensing technologies and their applications in measuring atmospheric pollutants. Suitable subjects include, but are not limited to: a) new or improved ORS instrumentation; b) new methods for ORS technology applications; c) new inversion algorithms or models for emission measurements or species detection; and d) characterization or explanation of air pollution processes from optical remote sensing data.

We are looking for manuscripts of research papers, review papers, and technical notes focusing on technique development, methodology, modeling/algorithm development, and ORS data analysis for gas pollutants, greenhouse gases, atmospheric aerosols, and optical-related indices (such as visibility, optical depth, etc.).

Dr. Ke Du
Dr. Ravi Varma
Dr. Ying Zhang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • optical remote sensing
  • fugitive mission
  • trace pollutant detection
  • air pollutants
  • leak detection
  • environmental optics
  • spectroscopy
  • LiDAR
  • light scattering and absorption
  • open-path

Published Papers (12 papers)

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18 pages, 2573 KiB  
Article
Machine Learning Techniques for Vertical Lidar-Based Detection, Characterization, and Classification of Aerosols and Clouds: A Comprehensive Survey
by Simone Lolli
Remote Sens. 2023, 15(17), 4318; https://doi.org/10.3390/rs15174318 - 1 Sep 2023
Cited by 2 | Viewed by 1623
Abstract
This survey presents an in-depth analysis of machine learning techniques applied to lidar observations for the detection of aerosol and cloud optical, geometrical, and microphysical properties. Lidar technology, with its ability to probe the atmosphere at very high spatial and temporal resolution and [...] Read more.
This survey presents an in-depth analysis of machine learning techniques applied to lidar observations for the detection of aerosol and cloud optical, geometrical, and microphysical properties. Lidar technology, with its ability to probe the atmosphere at very high spatial and temporal resolution and measure backscattered signals, has become an invaluable tool for studying these atmospheric components. However, the complexity and diversity of lidar technology requires advanced data processing and analysis methods, where machine learning has emerged as a powerful approach. This survey focuses on the application of various machine learning techniques, including supervised and unsupervised learning algorithms and deep learning models, to extract meaningful information from lidar observations. These techniques enable the detection, classification, and characterization of aerosols and clouds by leveraging the rich features contained in lidar signals. In this article, an overview of the different machine learning architectures and algorithms employed in the field is provided, highlighting their strengths, limitations, and potential applications. Additionally, this survey examines the impact of machine learning techniques on improving the accuracy, efficiency, and robustness of aerosol and cloud real-time detection from lidar observations. By synthesizing the existing literature and providing critical insights, this survey serves as a valuable resource for researchers, practitioners, and students interested in the application of machine learning techniques to lidar technology. It not only summarizes current state-of-the-art methods but also identifies emerging trends, open challenges, and future research directions, with the aim of fostering advancements in this rapidly evolving field. Full article
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20 pages, 11583 KiB  
Article
Spectral Calibration for SO2 Cameras with Light Dilution Effect Correction
by Kuijun Wu, Jianjun Guo, Zihao Zhang, Huiliang Zhang, Juan Li, Faquan Li and Weiwei He
Remote Sens. 2023, 15(14), 3652; https://doi.org/10.3390/rs15143652 - 21 Jul 2023
Viewed by 803
Abstract
The detection ability of SO2 cameras has been improved effectively, while the calibration is still the main factor that limits their measurement accuracy. This paper presents a nonlinear calibration theory by considering the effect of light dilution due to the path radiance [...] Read more.
The detection ability of SO2 cameras has been improved effectively, while the calibration is still the main factor that limits their measurement accuracy. This paper presents a nonlinear calibration theory by considering the effect of light dilution due to the path radiance as well as the dependence of plume aerosol on scattering wavelength. This new spectral calibration method is used to retrieve the SO2 column density and emission rate of the Etna volcano. Results show that, compared with the DOAS calibration approach, the inversion error can be reduced by 13% if the new spectral calibration is adopted. The superiority of the proposed method will become more obvious for long-distance detection of optically thick plumes. Full article
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10 pages, 2871 KiB  
Communication
Energetic Electron Precipitation via Satellite and Balloon Observations: Their Role in Atmospheric Ionization
by Irina Mironova, Galina Bazilevskaya, Vladimir Makhmutov, Andrey Mironov and Nikita Bobrov
Remote Sens. 2023, 15(13), 3291; https://doi.org/10.3390/rs15133291 - 27 Jun 2023
Cited by 1 | Viewed by 934
Abstract
Information about the energetic electron precipitation (EEP) from the radiation belt into the atmosphere is important for assessing the ozone variability and dynamics of the middle atmosphere during magnetospheric and geomagnetic disturbances. The accurate values of energetic electron fluxes depending on their energy [...] Read more.
Information about the energetic electron precipitation (EEP) from the radiation belt into the atmosphere is important for assessing the ozone variability and dynamics of the middle atmosphere during magnetospheric and geomagnetic disturbances. The accurate values of energetic electron fluxes depending on their energy range are one of the most important problems for calculating atmospheric ionization rates, which, in turn, are taken into account for estimating ozone depletion in chemistry–climate models. Despite the importance of these processes for the high latitudes of middle atmosphere, precipitation of energetic electrons is still insufficiently studied. In order to better understand EEP and related processes in the atmosphere, it is important to have many realistic observations of EEP in order to correctly characterize their spectra. Invading the atmosphere, precipitating energetic electrons, in the range from tens of keV to relativistic energies of more than 1 MeV, generate bremsstrahlung, which penetrates into the stratosphere and is recorded by detectors on balloons. However, these observations can be made only when the balloon is at stratospheric heights. Near-Earth satellites, such as the polar-orbiting operational environmental satellites (POES), are constantly registering precipitating electrons in the loss cone, but are moving too fast in space. Based on a comparison of the results of EEP measurements on balloons and onboard POES satellites in 2003, we propose a criterion that makes it possible to constantly monitor EEP ionization at stratospheric heights using observations on POES satellites. Full article
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21 pages, 100658 KiB  
Article
Deep Convolutional Neural Network for Plume Rise Measurements in Industrial Environments
by Mohammad Koushafar, Gunho Sohn and Mark Gordon
Remote Sens. 2023, 15(12), 3083; https://doi.org/10.3390/rs15123083 - 13 Jun 2023
Viewed by 1335
Abstract
Determining the height of plume clouds is crucial for various applications, including global climate models. Smokestack plume rise refers to the altitude at which the plume cloud travels downwind until its momentum dissipates and the temperatures of the plume cloud and its surroundings [...] Read more.
Determining the height of plume clouds is crucial for various applications, including global climate models. Smokestack plume rise refers to the altitude at which the plume cloud travels downwind until its momentum dissipates and the temperatures of the plume cloud and its surroundings become equal. While most air-quality models employ different parameterizations to forecast plume rise, they have not been effective in accurately estimating it. This paper introduces a novel framework that utilizes Deep Convolutional Neural Networks (DCNNs) to monitor smokestack plume clouds and make real-time, long-term measurements of plume rise. The framework comprises three stages. In the first stage, the plume cloud is identified using an enhanced Mask R-CNN, known as the Deep Plume Rise Network (DPRNet). Next, image processing analysis and least squares theory are applied to determine the plume cloud’s boundaries and fit an asymptotic model to its centerlines. The z-coordinate of the critical point of this model represents the plume rise. Finally, a geometric transformation phase converts image measurements into real-world values. This study’s findings indicate that the DPRNet outperforms conventional smoke border detection and recognition networks. In quantitative terms, the proposed approach yielded a 22% enhancement in the F1 score, compared to its closest competitor, DeepLabv3. Full article
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17 pages, 3833 KiB  
Article
Atmospheric CW S-Lidars with Si/InGaAs Arrays: Potentialities in Real Environment
by Ravil Agishev, Zhenzhu Wang and Dong Liu
Remote Sens. 2023, 15(9), 2291; https://doi.org/10.3390/rs15092291 - 26 Apr 2023
Viewed by 1191
Abstract
The article proposes a methodology for analyzing the performance of S-lidars (S comes from Scheimpflug) as a new class of environmental remote sensors operating under conditions of wide variability of optical weather and sky background brightness. The novelty of the problem statement, the [...] Read more.
The article proposes a methodology for analyzing the performance of S-lidars (S comes from Scheimpflug) as a new class of environmental remote sensors operating under conditions of wide variability of optical weather and sky background brightness. The novelty of the problem statement, the methods used and the results obtained are determined by their application to laser sensing systems with unconventional design principles and the consequent need to revise the traditional ways of assessing their potential capabilities. The research method is based on a dimensionless-parametric approach, which allows comparing phenomena and systems of different scales and combining complementary characteristics and parameters. Effects of the dimensionless optical weather factor on lidar potential are shown being investigated under various environmental conditions, from the clear atmosphere through haze and mist to fog when probing in Vis/SWIR spectral bands and using Si/InGaAs detector arrays. It is shown exactly how and to what extent the significant differences in their spectral sensitivity and internal noise parameters are susceptible to the wide spectral and energy variability of the sky background brightness observed at very different angles to the Sun. A detailed analysis of the two most important influencing factors within the system, “S-Lidar instrument + Optical weather + External background source”, taking into account their wide variability, allowed us to describe their joint nonlinear influence and, thus, to anticipate the imposed limitations. The proposed dimensionless-parametric concept for predicting the potential capabilities of S-lidars with Si/InGaAs arrays is aimed at expanding applications of this rapidly developing class of remote sensors in a wide variety of environments. Full article
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17 pages, 4587 KiB  
Article
Intercomparison of NO3 under Humid Conditions with Open-Path and Extractive IBBCEAS in an Atmospheric Reaction Chamber
by Meng Wang, Shengrong Lou, Weiwei Hu, Haichao Wang, Xinming Wang, Fengxian Fan, Ravi Varma, Dean S. Venables and Jun Chen
Remote Sens. 2023, 15(3), 739; https://doi.org/10.3390/rs15030739 - 27 Jan 2023
Viewed by 1498
Abstract
We report an open-path incoherent broadband cavity-enhanced absorption spectroscopy (OP-IBBCEAS) technique for in situ simultaneous optical monitoring of NO2, NO3, and H2O in a reaction chamber. The measurement precision values (1σ) are 2.9 ppbv and [...] Read more.
We report an open-path incoherent broadband cavity-enhanced absorption spectroscopy (OP-IBBCEAS) technique for in situ simultaneous optical monitoring of NO2, NO3, and H2O in a reaction chamber. The measurement precision values (1σ) are 2.9 ppbv and 2.9 pptv for NO2 and NO3 in 2 s, respectively, and the measurement uncertainties are 6% for NO2 and 14% for NO3. Intercomparison of measured concentrations of NO2 and NO3 by open-path and extractive IBBCEAS was carried out in the SAES-ARC reaction chamber during the reaction of NO2 with O3. The measurement accuracy of OP-IBBCEAS is verified by an NO2 intercomparison and the NO3 transmission efficiency of the extractive IBBCEAS is determined by comparison against the in situ NO3 measurement. The relationship between H2O absorption cross section and its mixing ratio at 295 K and 1 atm was analysed. Due to the spectral resolution of IBBCEAS system, the strong and narrow absorption lines of H2O are unresolved and exhibit non-Beer–Lambert Law behaviour. Therefore, a correction method is used to obtain the effective absorption cross section for fitting the H2O structure. An inappropriate H2O absorption cross section can cause an overestimation of NO3 concentration of about 28% in a humid atmosphere (H2O = 1.8%). This spectroscopic correction provides an approach to obtain accurate NO3 concentrations for open-path optical configurations, for example in chamber experiments or field campaigns. The measurement precision values are improved by a factor of 3 to 4 after applying Kalam filtering, achieving sub-ppbv (0.8 ppbv) and sub-pptv (0.9 pptv) performance in 2 s for NO2 and NO3, respectively. Full article
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20 pages, 6374 KiB  
Article
Effect of UV Scattering on Detection Limit of SO2 Cameras
by Kuijun Wu, Zihao Zhang, Jianjun Guo, Xiangrui Hu, Juan Li, Faquan Li and Weiwei He
Remote Sens. 2023, 15(3), 705; https://doi.org/10.3390/rs15030705 - 25 Jan 2023
Cited by 2 | Viewed by 1531
Abstract
SO2 ultraviolet (UV) camera technology has been successfully applied to the accurate imaging detection of pollutant gas concentration; however, the actual detection ability of this technology has not been intensively studied, especially the detection accuracy and limit under the influence of the [...] Read more.
SO2 ultraviolet (UV) camera technology has been successfully applied to the accurate imaging detection of pollutant gas concentration; however, the actual detection ability of this technology has not been intensively studied, especially the detection accuracy and limit under the influence of the light dilution effect. Here, we theoretically and experimentally investigate the UV scattering on SO2 concentration inversion. The radiation transfer model of the light dilution effect is reconstructed, and the concept of the optimized detection limit is discussed. An outfield experiment is conducted on a ship exhaust, and the results are compared with the theoretical calculations, which indicates that the detection limit of the SO2 UV camera is 15 ppm·m at close range and increases to 25 ppm·m when the detection distance is 3.5 km. This study proves that the detection limit of the SO2 UV camera deteriorates with the decreasing atmospheric visibility, the lengthening detection distance, and the increasing aerosol content within the plume. In addition, the hardware indicators of the camera systems also play a key role in the detection limit, and taking reasonable image processing can significantly release the instruments’ performance and extend the applicability of the SO2 UV camera. Full article
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16 pages, 3630 KiB  
Technical Note
Design of a Data Acquisition, Correction and Retrieval of Na Doppler Lidar for Diurnal Measurement of Temperature and Wind in the Mesosphere and Lower Thermosphere Region
by Yuan Xia, Xuewu Cheng, Zelong Wang, Linmei Liu, Yong Yang, Lifang Du, Jing Jiao, Jihong Wang, Haoran Zheng, Yajuan Li, Faquan Li and Guotao Yang
Remote Sens. 2023, 15(21), 5140; https://doi.org/10.3390/rs15215140 - 27 Oct 2023
Cited by 1 | Viewed by 811
Abstract
Based on the resonance fluorescence scattering mechanism, a narrowband sodium (Na) lidar can measure temperature and wind in the mesosphere and lower thermosphere (MLT) region. By using a narrowband spectral filter, background light noise during the day can be suppressed, allowing for continuous [...] Read more.
Based on the resonance fluorescence scattering mechanism, a narrowband sodium (Na) lidar can measure temperature and wind in the mesosphere and lower thermosphere (MLT) region. By using a narrowband spectral filter, background light noise during the day can be suppressed, allowing for continuous observations. To obtain full-diurnal-cycle temperature and wind measurement results, a complex and precise retrieval process is required, along with necessary corrections to minimize measurement errors. This paper introduces the design of a data acquisition unit for three frequencies in three directions of the Na lidar system in the Chinese Meridian Project (Phase II) and investigates the calibration and retrieval methods for obtaining diurnal temperature and horizontal wind in the MLT region, using a Na Doppler lidar with Faraday anomalous dispersion optical filter (FADOF). Furthermore, these methods are applied to observations conducted by a Na lidar in Beijing, China. The wind and temperature results over full diurnal cycles obtained from the all-solid-state Na Doppler lidar are reported for the first time and compared with temperature measurements from satellite, as well as wind observations from a meteor radar. The comparison demonstrates a reasonable agreement between the results, indicating the rationality of the lidar-retrieved results and the feasibility and effectiveness of the data correction and retrieval method. Full article
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14 pages, 5195 KiB  
Technical Note
The All-Solid-State Narrowband Lidar Developed by Optical Parametric Oscillator/Amplifier (OPO/OPA) Technology for Simultaneous Detection of the Ca and Ca+ Layers
by Lifang Du, Haoran Zheng, Chunlei Xiao, Xuewu Cheng, Fang Wu, Jing Jiao, Yuchang Xun, Zhishan Chen, Jiqin Wang and Guotao Yang
Remote Sens. 2023, 15(18), 4566; https://doi.org/10.3390/rs15184566 - 16 Sep 2023
Cited by 3 | Viewed by 1171
Abstract
We report an all-solid-state narrowband lidar system for the simultaneous detection of Ca and Ca+ layers over Yanqing (40.41°N, 116.01°E). The uniqueness of this lidar lies in its transmitter, which is based on optical parametric oscillation (OPO) and optical parametric amplification (OPA) [...] Read more.
We report an all-solid-state narrowband lidar system for the simultaneous detection of Ca and Ca+ layers over Yanqing (40.41°N, 116.01°E). The uniqueness of this lidar lies in its transmitter, which is based on optical parametric oscillation (OPO) and optical parametric amplification (OPA) techniques. The injection seeded OPO and the OPA are pumped by the second harmonic of an injection-seeded Nd:YAG laser, which can generate coherent light at the wavelength of 786 nm or 846 nm lasers, whose second harmonics in turn generate the 393 nm or 423 nm pulses, respectively, for the detection of thermospheric and ionospheric Ca+ and Ca layers. Compared to the conventional dye-based system, this lidar transmitter is a narrowband system (bandwidth < 200 MHz), which has produced a factor of two more output power with higher stability and reliability. The lidar system in Yingqing demonstrated Ca+ detection sensitivity of 0.1 atoms-cm−3 for long-term observation and reached a height of ~300 km. Potential applications and further improvements in this lidar technique are also discussed in this paper. Full article
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13 pages, 5617 KiB  
Technical Note
Gluing Atmospheric Lidar Signals Based on an Improved Gray Wolf Optimizer
by Shijie Li, Tong Wu, Kai Zhong, Xianzhong Zhang, Yue Sun, Yijian Zhang, Yu Wang, Xinqi Li, Degang Xu and Jianquan Yao
Remote Sens. 2023, 15(15), 3812; https://doi.org/10.3390/rs15153812 - 31 Jul 2023
Viewed by 731
Abstract
Lidar is important active remote sensing equipment in the field of atmospheric environment detection. However, the detection range of lidar is severely limited by the dynamic range of photodetectors. To solve this problem, atmospheric lidars are often equipped with two or more channels [...] Read more.
Lidar is important active remote sensing equipment in the field of atmospheric environment detection. However, the detection range of lidar is severely limited by the dynamic range of photodetectors. To solve this problem, atmospheric lidars are often equipped with two or more channels to receive signals from different altitude ranges, where gluing the multi-channel echo signals becomes a key issue for accurate data inversion. In this paper, a multi-channel signal gluing algorithm based on the Improved Gray Wolf Optimizer (IGWO) and Neighborhood Rough Set (NRS), named IGWO-RSD, is proposed. The fitness function F is formed by three objective functions: correlation coefficient R, regression stability coefficient S and mean fit deviation D. All three objective functions are obtained from the data itself and do not rely on prior information. The weights of the objective functions R, S and D are pre-trained by NRS, and IGWO is used to optimize the fitness function F. With ground-based aerosol lidar data, all-day signal gluing experiments are performed, where IGWO-RSD demonstrates obvious advantages in stability, accuracy and applicability in lidar signal processing compared with NRSWNSGA-II. Full article
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16 pages, 8601 KiB  
Technical Note
Uncertainty Evaluation on Temperature Detection of Middle Atmosphere by Rayleigh Lidar
by Xinqi Li, Kai Zhong, Xianzhong Zhang, Tong Wu, Yijian Zhang, Yu Wang, Shijie Li, Zhaoai Yan, Degang Xu and Jianquan Yao
Remote Sens. 2023, 15(14), 3688; https://doi.org/10.3390/rs15143688 - 24 Jul 2023
Cited by 1 | Viewed by 755
Abstract
Measurement uncertainty is an extremely important parameter for characterizing the quality of measurement results. In order to measure the reliability of atmospheric temperature detection, the uncertainty needs to be evaluated. In this paper, based on the measurement models originating from the Chanin-Hauchecorne (CH) [...] Read more.
Measurement uncertainty is an extremely important parameter for characterizing the quality of measurement results. In order to measure the reliability of atmospheric temperature detection, the uncertainty needs to be evaluated. In this paper, based on the measurement models originating from the Chanin-Hauchecorne (CH) method, the atmospheric temperature uncertainty was evaluated using the Guide to the Expression of Uncertainty in Measurement (GUM) and the Monte Carlo Method (MCM) by considering the ancillary temperature uncertainty and the detection noise as the major uncertainty sources. For the first time, the GUM atmospheric temperature uncertainty framework was comprehensively and quantitatively validated by MCM following the instructions of JCGM 101: 2008 GUM Supplement 1. The results show that the GUM method is reliable when discarding the data in the range of 10–15 km below the reference altitude. Compared with MCM, the GUM method is recommended to evaluate the atmospheric temperature uncertainty of Rayleigh lidar detection in terms of operability, reliability, and calculation efficiency. Full article
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16 pages, 3136 KiB  
Technical Note
Quantifying Emissions from Fugitive Area Sources Using a Hybrid Method of Multi-Path Optical Remote Sensing and Tomographic Inverse-Dispersion Techniques
by Sheng Li, Yanna Liu and Ke Du
Remote Sens. 2023, 15(4), 1043; https://doi.org/10.3390/rs15041043 - 14 Feb 2023
Cited by 1 | Viewed by 1207
Abstract
Reducing methane (CH4) emissions from anthropogenic activities is critical to climate change mitigation efforts. However, there is still considerable uncertainty over the amount of fugitive CH4 emissions due to large-scale area sources and heterogeneous emission distributions. To reduce the uncertainty [...] Read more.
Reducing methane (CH4) emissions from anthropogenic activities is critical to climate change mitigation efforts. However, there is still considerable uncertainty over the amount of fugitive CH4 emissions due to large-scale area sources and heterogeneous emission distributions. To reduce the uncertainty and improve the spatial and temporal resolutions, a new hybrid method was developed combining optical remote sensing (ORS), computed tomography (CT), and inverse-dispersion modeling techniques on the basis of which a multi-path scanning system was developed. It uses a horizontal radial plume mapping path configuration and adapts a Lagrangian stochastic dispersion mode into CT reconstruction. The emission map is finally calculated by using a minimal curvature tomographic reconstruction algorithm, which introduces smooth constraints at each pixel. Two controlled-release experiments of CH4 were conducted with different configurations, showing relative errors of only 2% and 3%. Compared with results from the single-path inverse-dispersion method (5–175%), the new method can not only derive the emission distribution but also obtain a more accurate emission rate. The outcome of this research would bring broad application of the ORS-CT and inverse-dispersion techniques to other gases and sources. Full article
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