Atmospheric Extinction Coefficient Research Articles

Insights into global visibility patterns: Spatiotemporal distributions revealed by satellite remote sensing

Accurate measurement of surface visibility is vital for transportation. Satellite remote sensing technology offers the advantage of monitoring vast areas over extended time periods, providing a novel approach to visibility monitoring. However, it currently lacks the capability to directly measure visibility, necessitating further theoretical exploration of visibility remote sensing methods. In this study, we introduced an innovative model for remote retrieval of global surface visibility. It leverages the Extreme Random Forest (ERF) model to optimize the residual components of the physical method. The proposed model comprehensively explores the intricate relationship among surface visibility, aerosol optical depth (AOD), atmospheric extinction coefficient, and aerosol heights. Utilizing surface visibility data collected from global ground-based meteorological stations in 2018, we assessed the performance of the proposed model through 10-fold cross-validation, yielding correlation coefficient (R) of 0.85, root mean square error (RMSE) of 2.7 km, and mean absolute error (MAE) of 1.6 km. Results from temporal and site cross-validation further confirm the model’s strong performance in both time and spatial domains. Additionally, this study has developed a global visibility dataset at a daily resolution of 0.1° × 0.1°. Temporal analysis of this dataset reveals that visibility values are higher from June to October, while values are lower in other months. Regarding the spatial distribution of visibility, oceanic areas exhibit markedly superior visibility compared to land areas. Additionally, Oceania, South Africa, and South America boast notably better visibility than other regions.

Atmospheric extinction coefficients and night sky brightness at ITB-Undana remote telescope site

Abstract A remote telescope system has been established at Universitas Nusa Cendana, Kupang. Bosscha Observatory, Institut Teknologi Bandung (ITB), and the Physics Study Program at Universitas Nusa Cendana (Undana) collaborated to develop the system. The ITB-Undana Telescope system has a QSI 616 CCD camera and BV RI Bessel filter attached to a 20-cm (f/10) Schmidt-Cassegrain reflector. Several research and public outreach activities have been conducted using the ITB-Undana remote telescope throughout 2023. When establishing a new astronomical observation site, it is imperative to conduct sky characterization and quality assessment. This process involves measuring night sky brightness and atmospheric extinction coefficients. In May 2023, we observed photometric standard stars using the absolute photometry technique with BV RI Bessel filters. We also utilized the Sky Quality Meter (SQM) to measure night sky brightness over three nights from May 24th to May 26th, 2023, to compare the sky brightness values obtained through the absolute photometry method. Our initial measurement shows a first-order extinction coefficient value ranging from k b ′ = 0.269 to 0.520, k v ′ = 0.216 to 0.297, k r ′ = 0.019 to 0.206, and k i ′ = 0.127 to 0.163, for B, V, R, and I filter, respectively. Application of extinction coefficient value in the sky field gives a mean sky brightness value in V bandpass, V sky = 19.431 ± 0.022, with color index (B − V )sky = 0.492 ± 0.039. These night sky brightness values are suitable for measurements using the SQM.

The Robotic MAAO 0.7 m Telescope System: Performance and Standard Photometric System

We introduce a 0.7 m telescope system at the Miryang Arirang Astronomical Observatory (MAAO), a public observatory in Miryang, Korea. System integration and a scheduling program enable the 0.7 m telescope system to operate completely robotically during nighttime, eliminating the need for human intervention. Using the 0.7 m telescope system, we obtain atmospheric extinction coefficients and the zero-point magnitudes by observing standard stars. As a result, we find that atmospheric extinctions are moderate but they can sometimes increase depending on the weather conditions. The measured 5σ limiting magnitudes reach down to BVRI = 19.4–19.6 AB mag for a point source with a total integrated time of 10 minutes under clear weather conditions, demonstrating comparable performance with other observational facilities operating under similar specifications and sky conditions. We expect that the newly established MAAO 0.7 m telescope system will contribute significantly to the observational studies of astronomy. Particularly, with its capability for robotic observations, this system, although its primary duty is for public viewing, can be extensively used for the time-series observation of transients.

Optical and Near-infrared Atmospheric Extinction Coefficients at La Silla

We used observations obtained at the Rapid Eye Mount (REM) at the La Silla Observatory between 2016 June 7 UT to determine the extinction coefficients of the REM filters currently in use. The observations were obtain on 6 nights, spanning 2016 June UT through 2016 July 4 UT, over a wide range of airmass values, to determine the mean atmospheric extinction coefficients at the La Silla Observatory site. Coefficients in the REM filter sets—Sloan g′, r′, i′, z′, and J, H and K were determined, where the REM infrared filters closely match those of the J, H, and Ks filters of the 2MASS All-Sky Survey.

Study on the characteristics of actinic radiation and direct aerosol radiation effects in the Pearl River Delta region

Combined air pollution prevails in the Pearl River Delta (PRD) region in recent years; large amounts of aerosols have caused a significant attenuation of actinic radiation. Solar radiation is the driving energy for photochemical reactions and plays an important role in the ozone formation. In this study, characteristics of actinic radiation and atmospheric composition in the PRD region have been analyzed based on long-term observation. The radiation transfer model (SBDART) is used to quantitatively estimate the direct radiation effect and actinic radiation effect of aerosol. Results indicate that PM2.5 concentration and atmospheric extinction coefficient have shown a downward trend. Meanwhile, ozone and Single Scattering Albedo (SSA) have increased. The average value of SSA is 0.914 ± 0.041, attaining the highest level in spring, followed by autumn and summer, and the lowest is found in winter. A linear relationship between UVA/UVB of actinic radiation flux and solar shortwave radiation has been revealed. Through the conversion formula proposed in the article, conventional radiation data can be converted into actinic radiation flux and species photolysis rate. The actinic radiation and radiation attenuation caused by aerosols shows an overall downward trend at the surface. In the ultraviolet to visible wavelength range (280–670 nm), the annual average attenuation of aerosol direct radiation and actinic radiation is 61.6 ± 31.8 W/m2 and 120.1 ± 59.7 W/m2, respectively. The radiation attenuation caused by aerosols is the largest in spring, with little difference in summer, autumn and winter, which are 92.9 ± 42.1 W/m2, 53.7 ± 21.3 W/m2, 48.0 ± 13.7 W/m2 and 52.1 ± 15.8 W/m2, respectively. The attenuation of actinic radiation caused by aerosol is the largest in spring, followed by winter, and there is little difference between summer and autumn, which are 174.8 ± 78.4 W/m2, 111.1 ± 33.1 W/m2, 98.3 ± 38.4 W/m2 and 96.7 ± 26.9 W/m2, respectively. The direct radiation effect of aerosol and the actinic radiation effect have opposite trends with increasing height. Below the aerosol scale height, the larger SSA is corresponding with greater radiant flux, and it is opposite above the aerosol scale height. SSA has the same effect on the actinic radiant flux of the entire layer: The larger SSA is in accordance with greater actinic radiant flux.

Semi-Empirical Satellite-to-Ground Quantum Key Distribution Model for Realistic Receivers

Satellite-based link analysis is valuable for efficient and secure quantum communication, despite seasonal limits and restrictions on transmission times. A semi-empirical quantum key distribution model for satellite-based systems was proposed that simplifies simulations of communication links. Unlike other theoretical models, our approach was based on the experimentally-determined atmospheric extinction coefficient typical for mid-latitude ground stations. The parameter was measured for both clear and foggy conditions, and it was validated using published experimental data from the Micius satellite. Using this model, we simulated secure QKD between the Micius satellite and ground stations with 300 mm and 600 mm aperture telescopes.

Estimating sea spray volume flux with a laser gauge in a self-consistent system

Sea spray is one of the drivers of heat, mass, and gas exchange between the ocean and the atmosphere, and its volume flux could be estimated by the record of the laser intensity. In the laboratory experiments, the relationship between sea spray and laser intensity could be established since the returned laser intensity of the observing gauge and spray concentration can be observed instantaneously. However, the difficulty to generalize the laboratory result to field observations is that the measurement of sea spray is usually unavailable on the open seas. Recent studies introduced an environment variable (atmospheric extinction coefficient for instance) to relate the laser intensity to spray volume flux for both laboratory and field observations so that the relationship established in the laboratory experiments could be extended to open seas. These studies however gave estimations of great difference since the relationships between each pair of the variables (spray volume flux, laser intensity, and the atmospheric extinction coefficient) are considered separately. This work established a self-consistent system composed of the three variables, in which the relationship between each pair of the variables in the system is consistent with that deduced from their respective relationships with the third variable. Consistency here we means that if Y=f(X), Y=g(Z) and Z=h(X), then Y=g(h(X))=f(X) is expected. The consistency of the relationships ensures that the estimation of the sea spray volume flux from laser intensity is robust. We established self-consistent relationships for the variables in the system composed of laser intensity, environment variable, and sea spray volume flux, for both laboratory and field experiments. Among them, the relationship between wind speed and spray volume flux is a reasonable reflection of the physical properties in two ways: a threshold value of spray volume flux at low wind speeds and the saturation at strong wind speeds. For a uniform regression of wind speed onto spray volume, a dimensionless parameter concerning wind speed is needed.

A new method for calculating average visibility from the relationship between extinction coefficient and visibility

Abstract. Visibility data are fundamental meteorological observation data widely used in many fields. When using visibility data, it is often necessary to calculate the average visibility, which used to be the arithmetic average of the visibility data directly. In this study, we first analyze the relationship between the visibility, the extinction coefficient, and the atmospheric compositions. Then we propose to use the harmonic average of visibility data as the average visibility, which can better reflect changes in atmospheric extinction coefficients and aerosol concentrations. It is recommended to use the harmonic average visibility in the studies of climate change, atmospheric radiation, air pollution, environmental health, etc.

Characterization of Timau National Observatory using limited in situ measurements

ABSTRACT A new astronomical observatory in south-eastern Indonesia is currently under construction. This Timau National Observatory will host a 3.8-m telescope for optical and near-infrared observations. To support the operation and planning, the characterization of the site needs to be appropriately performed. However, limited resources and access to the site hindered the deployment of instruments for comprehensive site testing. Fortunately, in situ sky brightness data from the Sky Quality Meter (SQM) have been available for almost 2 yr. Based on the data acquired in 470 nights, we obtain a background sky brightness of μ0 = 21.86 ± 0.38 mag arcsec−2. Additionally, we evaluate the moonlit sky brightness to estimate the atmospheric extinction coefficient (k) and level of scattering on site. We find an elevated value of k = 0.48 ± 0.04, associated with a high atmospheric aerosol content. It is considered regular for an equatorial area situated at a low altitude (∼1300 masl). By analysing the fluctuation of the sky brightness and infrared images from Himawari-8 satellite, we estimate the available observing time (AOT) of at least 5.3 h/night and the yearly average percentage of usable nights of $66{{\ \rm per\ cent}}$. The monthly average AOT from SQM and satellite data analysis correlate with R = 0.82. In terms of the monthly percentage of usable nights, the correlation coefficient is R = 0.78. During the wet season (November–April), the results from SQM and satellite data analysis deviate more significantly, mainly due to the limited capability of Himawari-8 in detecting fragmented low-altitude clouds. According to these results, we expect Timau to complement other observatories greatly.

Impact of atmospheric extinction coefficient on the solar spectrum at selective wavelengths at Helwan in Egypt

Solar irradiance alterations due to the various atmospheric conditions have received great scientific concern. These alternations can be investigated by both monochromatic extinction coefficient and atmospheric transparency. In this work, continuous measurements of solar spectral irradiation using the Spectroradiometer for six selective wavelengths (350, 368, 500, 615, 780, and 870 nm) are carried out at the Helwan station, (NRIAG) in Egypt. Twelve clear-sky days of continuous observations have been monitored under different atmospheric conditions. The results have shown that using Langley method under cloudless sky for the total atmospheric extinction at the selective wavelengths was correlated. The extinction coefficient at the selected wavelengths shows obvious diurnal variations in each season. The perceptible effect of local climate has been obtained from the comparison of seasonal extinctions. The highest value of extinction coefficient was 0.59 km−1 at 615 nm in summer while the lowest one at 350 nm was 0.07 km−1 in winter. Moreover, it has been found that the afternoon values of transparency have a shift toward the longer wavelengths.

Novel Inversion Algorithm for the Atmospheric Aerosol Extinction Coefficient Based on an Improved Genetic Algorithm

As an important atmospheric component, aerosols play a very important role in the radiation budget balance of the earth–atmosphere system. To study the optical characteristics of aerosols, it is necessary to use an inversion algorithm to process the lidar return signal to obtain both the aerosol extinction coefficient and the backscattering coefficient. However, the lidar return power equation is ill-conditioned and contains two unknown parameters, meaning that traditional inversion algorithms must be solved by adopting certain assumptions (e.g., a uniform atmosphere and the lidar ratio), which to a certain extent can seriously affect the inversion accuracy. Here, to improve the accuracy of the aerosol extinction coefficient inversion, an inversion method based on an improved genetic algorithm is proposed. Using the U.S. Standard Atmosphere model and the return power equation, the aerosol extinction coefficient and the backscattering coefficient are independent variables that randomly provide initial values to simulate the theoretical lidar power. Then, the genetic algorithm is used to approximate the theoretical lidar power to the measured lidar return power with height; when the two are infinitely close, the values of the corresponding two independent variables (i.e., the extinction and backscattering coefficients) are inverted. Experiments performed to compare the different effects between a simple genetic algorithm and the improved genetic algorithm showed the proposed method capable of inverting the aerosol extinction coefficient without reliance on traditional inversion methods, representing a novel approach to the inversion of the aerosol extinction coefficient and the backscattering coefficient.

Characterisations of the HinOTORI telescope with a three-color imager at Ali Observatory in Western Tibet

HinOTORI is a new telescope supported by an international collaboration project between China and Japan. It is a 50 centimeter telescope equipped with simultaneous three-color imagers (u', R C, and I C bands). It is located at Ali Observatory at an altitude of 5100m. Thanks to the high altitude and extreme dryness, Ali site is one of the most suitable sites for optical astrometry. HinOTORI telescope aims at detecting optical transients such as the counterparts of gravitational wave (GW) sources, supernovae, gamma-ray bursts (GRB) and so on. This paper describes the site information, design of simultaneous three-color optical layout, system instruments and whole control system. We also report some telescope characterisations for three bands (u'/R C/I C) respectively, such as Hartmann constant (0.49”/0.56”/0.60”), best focus position (3.922/3.920/3.903 mm), PSF FWHM size (3.755/3.328/3.167pixels), total transmittance and limiting magnitude (15.69/17.57/17.05mag, 10 σ 30 seconds exposure time). With different airmass observation data, the atmospheric extinction coefficients of three bands (0.366/0.061/0.026) were also derived.

An Aerosol Extinction Coefficient Retrieval Method and Characteristics Analysis of Landscape Images.

Images based on RGB pixel values were used to measure the extinction coefficient of aerosols suspended in an atmospheric state. The pixel values of the object-image depend on the target-object reflection ratio, reflection direction, object type, distances, illumination intensity, atmospheric particle extinction coefficient, and scattering angle between the sun and the optical axes of the camera, among others. Therefore, the imaged intensity cannot directly provide information on the aerosol concentration or aerosol extinction coefficient. This study proposes simple methods to solve this problem, which yield reasonable extinction coefficients at the three effective RGB wavelengths. Aerosol size information was analogized using the RGB Ångström exponent measured at the three wavelengths for clean, dusty, rainy, Asian dust storm, and foggy days. Additionally, long-term measurements over four months showed reasonable values compared with existing PM2.5 measurements and the proposed method yields useful results.

Current challenges of improving visibility due to increasing nitrate fraction in PM2.5 during the haze days in Beijing, China

The annual mean PM2.5 mass concentration has decreased because of the stringent emission controls implemented in Beijing, China in recent years, whereas the nitrate NO3– mass fraction in PM2.5 increases gradually. Low-visibility events occur frequently even though PM2.5 pollution has been mitigated significantly, with the daily mean PM2.5 mass concentration mostly less than 75 μg/m3. In this study, the non-linear relationship was analyzed between atmospheric visibility and PM2.5 based on chemical composition from a two-year field observation. Our results showed that NO3– became the main constituent of PM2.5, especially during the haze pollution episodes. A localized parameterization scheme was proposed between the atmospheric extinction coefficient (σext) and major chemical constituents of PM2.5 by multiple linear regression (MLR). The contribution of NO3– to σext increased with increasing air pollution, and NO3– became the most important contributor for PM2.5 above 75 μg/m3. The visibility decreased with increasing NO3– mass fraction for the same PM2.5 mass concentration when PM2.5 was above 20 μg/m3. The hygroscopicity of PM2.5 increased with increasing mass fraction of hygroscopic NO3–. These results stressed the importance of reducing particulate NO3– and its precursors (for instance, NH3) through effective emission control measures as well as the tightening of PM2.5 standards to further improve air quality and visibility in Beijing.

Comparison and analysis of two measurement systems of horizontal atmospheric extinction of solar radiation

Direct normal irradiance is the component of solar radiation exploited by concentrating solar power plants. However, solar radiation reflected by heliostats can be partially extinguished on its way to the receivers in solar power tower plants. These energy losses are accentuated with the distance travelled by the light. The growing development of solar power tower plants has highlighted the interest in determining this phenomenon. This paper presents the results of a six-month intercomparison campaign of the two most promising extinction measuring systems. The system developed at Plataforma Solar de Almería (SE Spain) is based on a direct measurement methodology by using two digital cameras. The second system indirectly estimates the extinction from forward-scatter meter (FSM) measurements. Two FSMs were used in this study. Both FSMs provided the same Meteorological Optical Range (MOR) trends, with differences into declared error margins. A selected number of days corresponding to medium to high aerosol loads have been used to assess the performance of both types of systems. Results show that, in these days, the atmospheric extinction coefficient values derived from the two-camera system were on average 2.1 times higher than those determined with the FSMs. Semi-empirical and empirical corrections for the aerosol spectral characteristics and for the content of water vapour in the atmosphere have been applied to the FSM measurements so that both systems provide similar values of horizontal attenuation.

Optimal power of laser beams propagating from the ground through the atmosphere to space orbits

It is shown that, when a high-power laser beam propagates from the ground through the atmosphere to space orbits, there is an optimal beam power that maximizes the target intensity due to self-focusing effect in the atmosphere, even if the atmospheric extinction exists. The B integral is an important parameter to describe self-focusing effect quantitatively. It is found that the value of B integral corresponding to optimal beam power is a constant. Based on this characteristic of the optimal B integral and the concept of the equivalent atmospheric extinction coefficient proposed in this paper, we derive the analytical formula of the optimal beam power, which presents an effective design rule to optimize the target intensity. In addition, it is shown that the optimal beam power increases as the initial beam radius, the wavelength, the atmospheric extinction coefficient, and the aerosol scale height increase.

Ambient Atmospheric Aerosol Extinction Coefficient Reconstruction from PM2.5 Mass Concentrations and Application to Haze Identification in China

ABSTRACT This study developed a method of reconstructing the aerosol extinction coefficient based on hourly observations of the fine-particle (PM2.5) mass concentration, relative humidity (RH), and visibility at 9 stations in China between 2014 and 2015. First, we applied κ-Kӧhler theory to evaluate the number concentration distribution of the fine particles under ambient conditions from the PM2.5 mass and then used Mie theory to calculate the aerosol extinction coefficient. Second, we established the reconstruction model and identified reference values for the relevant parameters. After sensitivity tests confirmed good agreement between the extinction coefficients obtained through combinations of various values and those resulting from the reference values, linear regression was employed to reduce the discrepancy between the reconstructed and the observed coefficients. A closure study enabled us to determine the threshold of the extinction ratio (β/βObs) and identify haze and fog weather phenomena at the stations. Finally, we assessed the bias in the predicted number of hours with haze for 61 stations in China by comparing the estimates derived from different values for the model’s parameters with those derived from the reference values and found a relative bias of less than 15% for approximately 99.8% of the stations, indicating the feasibility of our approach for detecting haze.

Characteristics of Aerosol during a Severe Haze-Fog Episode in the Yangtze River Delta: Particle Size Distribution, Chemical Composition, and Optical Properties

Particle size distribution, water soluble ions, and black carbon (BC) concentration in a long-term haze-fog episode were measured using a wide-range particle spectrometer (WPS), a monitor for aerosols and gases (MARGA), and an aethalometer (AE33) in Nanjing from 16 to 27 November, 2018. The observation included five processes of clean, mist, mix, haze, and fog. Combined with meteorological elements, the HYSPLIT model, and the IMPROVE model, we analyzed the particle size distribution, chemical composition, and optical properties of aerosols in different processes. The particle number size distribution (PNSD) in five processes differed: It was bimodal in mist and fog and unimodal in clean, mix, and haze. The particle surface area size distribution (PSSD) in different processes showed a bimodal distribution, and the second peak of the mix and fog processes shifted to a larger particle size at 480 nm. The dominant air masses in five processes differed and primarily originated in the northeast direction in the clean process and the southeast direction in the haze process. In the mist, mix, and fog processes local air masses dominated. NO3− was the primary component of water soluble ions, with the lowest proportion of 45.6% in the clean process and the highest proportion of 53.0% in the mix process. The ratio of NH4+ in the different processes was stable at approximately 23%. The ratio of SO42− in the clean process was 26.2%, and the ratio of other processes was approximately 20%. The average concentration of BC in the fog processes was 10,119 ng·m−3, which was 3.55, 1.80, 1.60, and 1.46 times that in the processes of clean, mist, mix, and haze, respectively. In the different processes, BC was primarily based on liquid fuel combustion. NO3−, SO42−, and BC were the main contributors to the atmospheric extinction coefficient and contributed more than 90% in different processes. NO3− contributed 398.43 Mm−1 in the mix process, and SO42− and BC contributed 167.90 Mm−1 and 101.19 Mm−1, respectively, during the fog process.

Urban air pollution monitoring using scanning Lidar

We have developed a scanning Lidar system in this work to detect urban air pollution changes in real time and locate the sources of urban air pollution. We first proposed an algorithm to retrieve atmospheric extinction coefficients, which we used to create Lidar maps. Using Lidar map of the average extinction coefficients, we identified the locations of the local maximum values, and hence, the positions of the urban air pollution sources. Experimental results indicate that this method is effective for urban air pollution monitoring.

Monsoon Season Quantitative Assessment of Biomass Burning Clear-Sky Aerosol Radiative Effect at Surface by Ground-Based Lidar Observations in Pulau Pinang, Malaysia in 2014

Direct and indirect aerosol effects are still one of the largest uncertainties related to the Earth energy budget, especially in a wild and remote region like South-East Asia, where ground-based measurements are still difficult and scarce, while endemic cloudy skies make difficult active and passive satellite observations. In this preliminary study, we analyzed and quantitatively assessed the differences between monsoon and inter-monsoon seasons, in terms of radiative effects at surface and columnar heating rate, of clear-sky biomass burning aerosols (no clouds) using ground-based lidar observations obtained with a 355 nm elastic lidar instrument, deployed since 2012 at the Physics Department of Universiti Sains Malaysia (USM). The model-based back-trajectory analysis put in evidence that, during the monsoon seasons (November–March and June–September), the air masses advected towards the observational site transit over active fire hotspot regions, in contrast with the inter-monsoon season. In between the monsoon seasons (April–May, October), the atmosphere over Penang is constituted by local background urban aerosols that originate from road traffic emissions, domestic cooking, and industrial plants emissions. The analysis was carried out using the vertically-resolved profiles of the seasonal averaged aerosol optical properties (monsoon vs. inter-monsoon seasons), e.g., the atmospheric extinction coefficient, to evaluate the seasonal surface aerosol radiative effect and column heating rate differences through the Fu–Liou–Gu (FLG) radiative transfer model. The results put in evidence that the biomass burning advection during the monsoon season (especially during the South West monsoon from June to September) lowers the noon daytime incoming solar shortwave solar radiation reaching the Earth surface with respect to the local background conditions by 91.5 W/m2 (114–69 W/m2). The aerosols also lead to an averaged heating in the first kilometer of the atmosphere of about 4.9 K/day (6.4–3.4 W/m2). The two combined effects, i.e., less absorbed energy by Earth surface and warming of the first kilometer of the boundary layer, increase the low-level stability during monsoon seasons, with a possible reduction in cloud formation and precipitation. The net effect is to exacerbate the haze episodes, as the pollutants rest trapped into the boundary layer. Besides these considerations, the lidar measurements are of great interest in this particular world region and might be used for cal/val of the future space missions, e. g., Earthcare.