Atmospheric Optical Thickness Research Articles

Photosynthetically active radiation separation model for high-latitude regions in agrivoltaic systems modeling

Photosynthetically active radiation is a key parameter for determining crop yield. Separating photosynthetically active radiation into direct and diffuse components is significant to agrivoltaic systems. The varying shading conditions caused by the solar panels produce a higher contribution of diffuse irradiance reaching the crops. This study introduces a new separation model capable of accurately estimating the diffuse component from the global photosynthetically active radiation and conveniently retrievable meteorological parameters. The model modifies one of the highest-performing separation models for broadband irradiance, namely, the Yang2 model. Four new predictors are added: atmospheric optical thickness, vapor pressure deficit, aerosol optical depth, and surface albedo. The proposed model has been calibrated, tested, and validated at three sites in Sweden with latitudes above 58 °N, outperforming four other models in all examined locations, with R2 values greater than 0.90. The applicability of the developed model is demonstrated using data retrieved from Sweden's first agrivoltaic system. A variety of data availability cases representative of current and future agrivoltaic systems is tested. If on-site measurements of diffuse photosynthetically active radiation are not available, the model calibrated based on nearby stations can be a suitable first approximation, obtaining an R2 of 0.89. Utilizing predictor values derived from satellite data is an alternative method, but the spatial resolution must be considered cautiously as the R2 dropped to 0.73.

Insights on the distribution and environmental implications of the radio-isotope 235U in surface soils and glaciers of the Tibetan Plateau

Atom ratio between 235U and 238U is often used as an indicator of U contamination as the isotopic signature of products generated by the nuclear and military industry significantly vary from the natural isotopic ratio of U. In this study, surface soils and glaciers samples were collected in the Tibetan Plateau (TP) and its surrounding areas and analyzed for U isotopic composition. Results show that the 235U/238U atom ratios in the surface soils of the TP ranges from 0.007122 to 0.007615, with an average value of 0.007378 ± 0.00011; while in the snow/ice dust from high-altitude glaciers it ranges from 0.007254 to 0.007687, with an average value of 0.007345 ± 0.000128. These ratios are slightly higher than the typical crustal value, indicating that the TP was affected by an anthropogenic input of 235U, especially in its northeast and southwest sectors. The variability of our results suggests that the spatial distribution of this contamination is not uniform, pointing to differences in the potential sources and transmission paths of radioactive particles. Combining the knowledge of past tests and activities conducted in the geographic areas around the TP with the knowledge of prevailing winds, we hypothesize that the observed 235U contamination in the TP surface soils and glaciers may have originated mainly from the previous nuclear related activities in surrounding areas (e.g., north Gobi Desert and South Asia). In addition, the horizontal and vertical wind field around the Tibetan Plateau, as well as the atmospheric aerosol optical thickness data also demonstrated the possible transport paths of the radionuclides, that is, originated from in northern Gobi desert and South Asia and reached the TP crossing the Himalayas.

Development and Testing a Method for Retrieving Atmospheric Aerosol Optical Thickness based on the Solar Intensity from the Sun-photometer Data

The context of atmospheric aerosols is an indispensable aspect in studying the Earth’s radiation budget, climate change, and air quality. Therefore, the quality technique in retrieving aerosol parameters is important for a better understanding their characteristics. The precise calculating of the aerosol physical parameter in the planetary boundary layer will increase the accuracy of evaluation of their impact on environmental conditions. In several atmospheric corrections of optical remote sensing using satellite sensors, the AOT’s values play an important role in arranging a Look Up Table (LUT) for scattering parameters. Therefore, this study aims to develop a method for processing and correcting the sun-photometer data to obtain the original AOT in the planetary boundary layer. In AOT calculation using the sun-photometer data, the solar radiation at the extraterritorial of the atmosphere is determined using the Langley plot. Then, using the target data at the same season as the data for the Langley plot, the temporal change of AOT is estimated by employing the Lambert-Beer Law with some corrections. The major correction for the AOT’s values computation in the measurement target is the contribution of molecule from the local station and Ozone (O3) from the GOME-2 satellite data. The result has been compared with an independent measurement using a sky-radiometer at the same time as the sun-photometer monitoring. From the overall procedure, the AOT’s values have uncertainties at approximately 2-5% compared to the sky-radiometer. Therefore, the procedure will be useful for studying aerosol optical properties in the lower troposphere.

Atmospheric CO[formula omitted] retrieval from satellite spectral measurements by a two-step machine learning approach

In the present study, a two-step machine learning approach is proposed and tested based on the Greenhouse gases Observing SATllite (GOSAT) spectral measurements to efficiently retrieve the atmospheric CO2 column density. A simple one-dimensional line-by-line forward radiation model is developed to simulate the GOSAT observed spectra, which is used to generate the training data for the two-step machine learning model. By using the two-step machine learning model, the atmospheric spectral optical thickness can be retrieved first, and then the CO2 column density is retrieved from the optical thickness spectrum later. As a proof-of-concept study, the model has been applied to retrieve CO2 column density in Australia for clear sky conditions from the GOSAT observed 1.6 μm spectra. Results have shown that the accuracy of the proposed method for CO2 column density retrieval is about 3 ppm but the efficiency is found to be excellent. Further improvements for improving the retrieval accuracy are discussed.

Physics interpretation of ISO/CIE sky types

Sky luminance distribution, itself immensely variable solar radiation product, is an indispensable prerequisite for any daylight availability assessment. Currently, prediction-based modeling is a key ingredient of daylight qualification worldwide, while ISO/CIE general sky standard is an essential tool accommodated for simulation purposes. Due to its long term perspective and a number of benefits (e.g. simple mathematics and easy numerical implementation), the model is applied routinely and independent of meteorological conditions prevailing on a regional scale. ISO/CIE classifies sky states into fifteen subtypes on statistical base, however, with no relation to e.g. local sources of pollution. In result, the statistics found for two different territories may accidentally cohere for which there is really no theoretical reason. Here we show that the physics interpretation of sky states is needed for a proper use of the ISO/CIE model in different territories through linking the luminance distributions with atmospheric properties, specifically τ and g. The latter shapes the angular distribution of scattered light, while τ is interpreted in term of atmospheric optical thickness. The new approach we present here not only profits from its theoretical foundation, but both τ and g can be easily derived from the momentary local atmosphere state. This way the characterization of sky states and a use of ISO/CIE skies can be more selective and more systematic.

A Robust Atmospheric Correction Procedure for Determination of Spectral Reflectance of Terrestrial Surfaces from Satellite Spectral Measurements

In this work, we propose simple and robust technique for the retrieval of underlying surface spectral reflectance using spaceborne observations. It can be used to process both multispectral moderate resolution satellite data and also multi-zone high spatial resolution data. The technique can work automatically for different types of land surfaces without using huge databases accumulated in advance. The new cloud discrimination and retrieval of the water vapor content in atmosphere procedures are presented. The key point of the proposed atmospheric correction technique is the suggested single-wavelength method for determining the atmospheric aerosol optical thickness without reference to a specific type of underlying surface spectrum. The retrievals of spectral reflectance for various land surfaces with developed technique, performed using computer simulation and experimental data, have demonstrated a high retrieval accuracy.

Exploiting Tropospheric Measurements From Sun-Tracking Radiometer for Radiopropagation Models at Centimeter and Millimeter Wave

The objective of this paper is to characterize the atmospheric radiometeorological parameters (optical thickness and brightness temperature) at centimeter and millimeter waves. To this aim, we have exploited two radiative transfer models (RTMs): a three-dimensional model (3D-RTM), driven by numerical weather forecasts, and a stochastic one-dimensional (1-D) model (1D-RTM), fed by a synthetic clouds dataset. We have compared the radiative transfer simulations with measurements from two ground-based microwave radiometers: a profiler and a Sun-tracking radiometer. The peculiarity of the latter is the capacity of simultaneously measuring atmospheric optical thickness and brightness temperature in all-weather conditions and at variable elevation angles. The comparisons between simulations and measurements provide satisfactory results that assess the reliability of the 3D-RTM with some biases, in terms of brightness temperature, that should be investigated. 3D-RTM turns out to be able to successfully reproduce correlations between brightness temperature and optical thickness and correlations among the different frequency channels. This confirms the potential of the combined use of weather forecast models and physically-based RTMs. On the other hand, 1D-RTM reveals to be able to reproduce frequency-channel correlation trends, but additional climatological set-up are needed to make the model exploitable for the computation of statistics of atmospheric optical thickness. These comparisons also highlight some possible calibration errors in the Sun-tracking radiometer that must be fixed. Finally, we have exploited measurements from the Sun-tracking radiometer to develop a model to retrieve the probability of atmospheric optical thickness conditioned to a given elevation angle.

Seasonal and interannual changes in optical thickness of the atmosphere in the Yakutsk array region

The analysis of the atmospheric optical thickness is given. Atmospheric optical thickness is obtained from spectral transparency of the atmosphere by CE318 radiometer. In the paper features of seasonal and interannual AOT of the atmosphere in the period 2004-2014 are discussed. It is noted that AOT measured at the Yakutsk sensitive to restructure of the atmosphere from winter to summer, passage of storm fronts in summer and large-scale wildfires.

Comparison of air quality at different altitudes from multi-platform measurements in Beijing

Abstract. The features of upper-air visibility at altitudes of 0.1, 0.3, and 0.5 km and the two-dimensional haze characteristics in the northwest of downtown Beijing were studied by using a multi-platform analysis during haze episodes between 17 December 2016 and 6 January 2017. Through the multi-platform data analysis in hourly and daily variation, the upper-air visibility increased along with the decrease of PM2.5 mass concentration. And the upper-air visibility on non-haze days was about 3–5 times higher than that on haze days with the ground-based Raman–Mie lidar data between 13 December 2016 and 11 January 2017. The vertical transport of pollutants can be inferred from the delayed variation of upper-air visibility between high altitude and low altitude. In addition, the two-dimensional haze characteristics could be studied by analyzing the correlation between vertical haze parameters (atmospheric boundary layer, haze thickness, and aerosol optical thickness) and horizontal haze parameter (upper-air visibility). The characteristics of multi-parameters have been analyzed and concluded for different haze levels.

Comprehensive assessment of four-parameter diurnal land surface temperature cycle models under clear-sky

Diurnal land surface temperature cycle (DTC) models are useful tools for generating continuous diurnal land surface temperature (LST) dynamics from temporally sparse satellite observations. Four-parameter DTC models (FPD) can be applied to tandem polar-orbiting satellite observations that sample the surface at least four times per day and, therefore, they have received especial attention. Different approaches have been proposed to reduce the parameter number of DTC models to only four, but a comprehensive and systematic comparison of the published FPDs and their performance is lacking. In addition, it remains unclear whether there are even better parameter-reduction approaches (PRAs) for DTC modeling when only four observations per day are available. Consequently, we chose three semi-empirical DTC models (GOT01, INA08, and GOT09) and one quasi-physical DTC model (GEM) and obtained nine FPDs with PRAs (e.g., by fixing some of the DTC parameters as constants). Using in-situ thermal observations from the U.S. Climate Reference Network, as well as LSTs from the geostationary MSG and FY-2F satellites under clear sky, we compared the performances of these nine FPDs for 24 and 4 available LST observations per day. We obtained the following results: (1) The GOT09- and GEM-type models generally performed better than the other models with in-situ measurements, while the INA08-ts and GOT09-type models possessed high accuracies for the geostationary LSTs. (2) For the semi-empirical models, the PRA ‘ts = tss − 1’ (where ts and tss are the onsets of nighttime cooling and sunset, respectively) is generally more accurate than the PRA ‘δT = 0’ (where δT is the day-to-day change of residual temperature). The only exception is the GOT09-type model, for which the ‘ts = tss − 1’ strategy is less accurate. (3) GOT09-dT-τ, which fixes δT as zero and the atmospheric optical thickness (τ) as 0.01 for parameter reduction, shows the best performance of the FPDs. The study gives an overview of commonly-used four-parameter DTC models, provides a foundation for generating spatio-temporally continuous LST products, and offers guidance for choosing four-parameter DTC models in various applications.

Collision and radiative processes in emission of atmospheric carbon dioxide

The peculiarities of the spectroscopic properties of CO2 molecules in air due to vibration-rotation radiative transitions are analyzed. The absorption coefficient due to atmospheric carbon dioxide and other atmospheric components is constructed within the framework of the standard atmosphere model, on the basis of classical molecular spectroscopy and the regular model for the spectroscopy absorption band. The radiative flux from the atmosphere toward the Earth is represented as that of a blackbody, and the radiative temperature for emission at a given frequency is determined with accounting for the local thermodynamic equilibrium, a small gradient of the tropospheric temperature and a high optical thickness of the troposphere for infrared radiation. The absorption band model with an absorption coefficient averaged over the frequency and line-by-line model are used for evaluating the radiative flux from the atmosphere to the Earth which values are nearby for these models and are equal W m−2 for the contemporary concentration of atmospheric CO2 molecules and W m−2 at its doubled value. The absorption band model is not suitable to calculate the radiative flux change at doubling of carbon dioxide concentration because averaging over oscillations decreases the range where the atmospheric optical thickness is of the order of one, and just this range determines this change. The line-by-line method gives the change of the global temperature K as a result of doubling the carbon dioxide concentration. The contribution to the global temperature change due to anthropogenic injection of carbon dioxide in the atmosphere, i.e. resulted from combustion of fossil fuels, is approximately 0.02 K now.

Study of Saharan dust influence on PM10 measures in Sicily from 2013 to 2015

Nowadays, particulate matter, especially that with small dimension as PM10, PM2.5 and PM1, is the air quality indicator most commonly associated with a number of adverse health effects. In this paper it is analyzed the impact that a natural event, such as the transport of Saharan dust, can have on increasing the particulate matter concentration in Sicily.Consulting the data of daily PM10 concentration, acquired by air quality monitoring network belonging to “Agenzia Regionale Protezionedell’ Ambiente” (Environmental Protection Regional Agency), it was possible to analyze the trend from 2013 to 2015. The days, in which the limit value was exceeded, were subjected to combined analysis. It was based on three models: interpretations of the air masses back-trajectories, using the atmospheric model HYSPLIT (HYbrid Single-Particle Lagrangian Integrated trajectory); on the calculation of the concentration on the ground and at high altitude particulate applying DREAM model (Dust REgional atmospheric model) and on the calculation of the concentration of mineral aerosols according to the atmospheric optical thickness (AOT) applying NAAPS model (Navy Aerosol Analysis and Prediction System).The daily limit value exceedances were attributed to the transport of Saharan dust events exclusively when the three models were in agreement with each other. Identifying the natural events, it was possible to quantify the contribution of the Saharan dust and consequently the reduction of the exceedances number. To quantify the contribution of Saharan dust on daily PM10 concentration, it was calculated the regional background in according to precautionary approach recommended by “Guidance on the quantification of the contribution of natural sources under the EU Air Quality Directive 2008/50/EC”, when the application of the method cannot be validated with chemical analysis, as in this case. In this study is obtained, as the most important quantitative goal, the convergence of the three models to the same result. So, is evident that exceedances of the daily limit value that occurred from 2013 to 2015 in Sicily can be attributed, in most cases, to the Saharan dust intrusion.

Post-launch radiometric calibration of electro-optic sensors for Earth from space observation by differential method with the taking into account atmosphere transmittance coefficient

The developed methodology of the post-launch radiometric calibration of the electro-optic sensors for Earth from space observation is considered. The novelty of this methodology consist in the implementation of the differential method for taking into account the spectral reflection coefficient of test objects from ground-based measurements, and in using of the atmospheric transmittance coefficient obtained from the world AERONET network data. The objective of the radiometric electro-optic sensor post-launch calibration consist in the evaluation of the linear regression dependence of the digital pixel number at sensor output from the spectral radiance at sensor aperture on Top of Atmosphere (TOA). The proposed differential method of the electro-optic sensor radiometric calibration is implemented in each spectral channel in the following stages: 1) determination of the coefficient of the sensor calibration characteristic inclination on the values of the spectral reflectance differences in all possible different pairs of ground measurement points on the surface of the test objects; 2) estimation of the coefficient of the calibration characteristic inclination as a mathematical expectation or as a median or a mod for a set of calculated its differential values; 3) determination on the basis of estimation of the coefficient of the calibration characteristic inclination the radiometric calibration coefficients: gain and offset; 4) recovery using the obtained radiometric calibration coefficients linear dependence of the spectral radiance at sensor aperture from the digital pixel numbers by the space imagery at the ground control points. The differential radiometric calibration method makes possible to avoid of unknown spectral radiance of the atmosphere caused by scattering. The atmospheric characteristics data were obtained from the international network AERONET observations. The nearest station to calibration test site in the area of the National Center for Space Facilities Control and Testing (Vitine, Crimea) (during the method testing procedure – summer 2012) was AERONET station in Sevastopol. The station provided the observational data of the atmosphere optical thickness, by whose values the atmosphere spectral transmittance were calculated based on the Bouguer law. The estimation of the calibration gain factor of the Landsat 5 TM and Landsat 7 ETM+ multispectral sensors on the developed methodology were obtained, which were provided the relative error from 1% to 22% and from –7% to 2% for the corresponding sensors, depending from the spectral channel of the sensor in comparison with etalon data of the calibration gain of these space systems sensors.

Study on atmospheric correction approach of Landsat-8 imageries based on 6S model and look-up table

Atmospheric correction is a necessary step for deriving surface geophysical parameters. The aim of this paper is to study the atmospheric correction of Landsat-8 imageries released by the Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences. A look-up table (LUT)-based atmospheric correction method on Landsat-8 OLI is proposed. The LUT is generated with 6S model with inputs including total atmospheric water vapor content, ozone, and aerosol optical thickness (AOT) from MODIS atmospheric level 2 products. The conventional method to build up the atmospheric parameter LUT usually only takes part of the factors (e.g., AOT) into consideration, whereas it is not applicable in the atmospheric correction using per pixel of MODIS products as input atmospheric parameters. Thus, a five-dimensional LUT, which considers most input parameters, is built up and has high universality for the Landsat-8 OLI sensor. Finally, spectral analysis, comparison to U.S. Geological Survey-released surface reflectance (SR) products, and field observations are used to validate the quality of the model-computed SR. The validation results indicate that the proposed method can effectively generate accurate and reliable SR results, although there is an overcorrected problem in the costal blue region when the AOT value is very high.

Assessment of fire emission inventories during the South American Biomass Burning Analysis (SAMBBA) experiment

Abstract. Fires associated with land use and land cover changes release large amounts of aerosols and trace gases into the atmosphere. Although several inventories of biomass burning emissions cover Brazil, there are still considerable uncertainties and differences among them. While most fire emission inventories utilize the parameters of burned area, vegetation fuel load, emission factors, and other parameters to estimate the biomass burned and its associated emissions, several more recent inventories apply an alternative method based on fire radiative power (FRP) observations to estimate the amount of biomass burned and the corresponding emissions of trace gases and aerosols. The Brazilian Biomass Burning Emission Model (3BEM) and the Fire Inventory from NCAR (FINN) are examples of the first, while the Brazilian Biomass Burning Emission Model with FRP assimilation (3BEM_FRP) and the Global Fire Assimilation System (GFAS) are examples of the latter. These four biomass burning emission inventories were used during the South American Biomass Burning Analysis (SAMBBA) field campaign. This paper analyzes and inter-compared them, focusing on eight regions in Brazil and the time period of 1 September–31 October 2012. Aerosol optical thickness (AOT550 nm) derived from measurements made by the Moderate Resolution Imaging Spectroradiometer (MODIS) operating on board the Terra and Aqua satellites is also applied to assess the inventories' consistency. The daily area-averaged pyrogenic carbon monoxide (CO) emission estimates exhibit significant linear correlations (r, p > 0.05 level, Student t test) between 3BEM and FINN and between 3BEM_ FRP and GFAS, with values of 0.86 and 0.85, respectively. These results indicate that emission estimates in this region derived via similar methods tend to agree with one other. However, they differ more from the estimates derived via the alternative approach. The evaluation of MODIS AOT550 nm indicates that model simulation driven by 3BEM and FINN typically underestimate the smoke particle loading in the eastern region of Amazon forest, while 3BEM_FRP estimations to the area tend to overestimate fire emissions. The daily regional CO emission fluxes from 3BEM and FINN have linear correlation coefficients of 0.75–0.92, with typically 20–30 % higher emission fluxes in FINN. The daily regional CO emission fluxes from 3BEM_FRP and GFAS show linear correlation coefficients between 0.82 and 0.90, with a particularly strong correlation near the arc of deforestation in the Amazon rainforest. In this region, GFAS has a tendency to present higher CO emissions than 3BEM_FRP, while 3BEM_FRP yields more emissions in the area of soybean expansion east of the Amazon forest. Atmospheric aerosol optical thickness is simulated by using the emission inventories with two operational atmospheric chemistry transport models: the IFS from Monitoring Atmospheric Composition and Climate (MACC) and the Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modelling System (CCATT-BRAMS). Evaluation against MODIS observations shows a good representation of the general patterns of the AOT550 nm time series. However, the aerosol emissions from fires with particularly high biomass consumption still lead to an underestimation of the atmospheric aerosol load in both models.

Time Series Analysis of Satellie-Measured Vegetation Phenology and Aerosol Optical Thickness over the Korean Peninsula

Abstract. The spatiotemporal influences of climatic factors and atmospheric aerosol on vegetative phenological cycles of the Korean Peninsula was analysed based on four major forest types. High temporal-resolution satellite data can overcome limitations of ground-based phenological studies with reasonable spatial resolution. Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation index (VI) (MOD13Q1 and MYD13Q1) and aerosol (MOD04_D3) data were downloaded from the USGS Earth Observation and Science (EROS) Data Center and NASA Goddard Space Flight Center. Harmonic analysis was used to describe and compare the periodic phenomena of the vegetative phenology and atmospheric aerosol optical thickness (AOT). The method transforms complex timeseries to a sum of various sinusoidal functions, or harmonics. Each harmonic curve, or term (or Fourier series), from time-series data us defined by a unique amplitude and a phase, indicating the half of the height and the peak time of a curve. Therefore, the mean, phase, and amplitude of harmonic terms of the data provided the temporal relationships between AOT and VI time series. The phenological characteristics of evergreen forest, deciduous forest, and grassland were similar to each other, but the inter-annual VI amplitude of mixed forest was differentiated from the other forest types. Overall, forests with high VI amplitude reached their maximum greenness earlier, and the phase of VI, or the peak time of greenness, was significantly influenced by air temperature. AOT time-series showed strong seasonal and inter-annual variations. Generally, aerosol concentrations were peaked during late spring and early summer. However, inter-annual AOT variations did not have significant relationships with those of VI. Weak relationships between inter-annual AOT and VI variations indicate that the impacts of aerosols on vegetation growth may be limited for the temporal scale investigated in the region.

Tracking the Saharan Air Layer with shipborne lidar across the tropical Atlantic

Saharan dust was observed with shipborne lidar from 60° to 20°W along 14.5°N during a 1‐month transatlantic cruise of the research vessel Meteor. About 4500 km off the coast of Africa, mean extinction and backscatter‐related Ångström exponent of 0.1, wavelength‐independent extinction‐to‐backscatter ratios (lidar ratios) of around 45 sr, and particle linear depolarization ratio of 20% were found for aged dust (transport time >10 days). In contrast, dust with a shorter atmospheric residence time of 2–3 days showed Ångström exponents of −0.5 (backscatter coefficient) and 0.1 (extinction coefficient), mean lidar ratios of 64 and 50 sr, and particle linear depolarization ratios of 22 and 26% at 355 and 532 nm wavelength, respectively. Traces of fire smoke were also detected in the observed dust layers. The lidar observations were complemented by Aerosol Robotic Network handheld Sun photometer measurements, which revealed a mean total atmospheric column aerosol optical thickness of 0.05 for pure marine conditions (in the absence of lofted aerosol layers) and roughly 0.9 during a strong Saharan dust outbreak. The achieved data set was compared with first Consortium for Small Scale Modeling‐Multi‐Scale Chemistry Aerosol Transport simulations. The simulated vertical aerosol distribution showed good agreement with the lidar observations.

월면 디지털 영상 분석을 이용한 대기 광학두께 산출

이 연구에서는 상용 디지털 카메라를 이용하여 야간에 촬영된 월면 영상을 분석하여 야간의 대기 광학두께와 에어로솔 광학두께를 추정하였다. 기본적으로 랑리회귀법을 이용하였으며 구름이 없고 대기의 광학적 특성이 비교적 안정한 날에 관측을 수행하였다. 카메라의 적색(R), 녹색(G), 청색(B) 채널의 파장별 반응함수를 이용하여 월광관측에 대한 유효 중심파장 및 레일리 광학두께를 추정하였으며, 랑리 회귀법에서 유도된 대기광학두께로부터 레일리 광학두께를 제하여 에어로솔 광학 두께를 산출하였다. 야간에는 독립적인 방법으로 산출된 검증자료나 다른 에어로솔 광학두께 자료가 거의 없으므로 월면 관측이 이루어지기 수 시간 전의 주간에 정밀한 태양분광광도계로 측정된 에어로솔 광학두께 자료와 MODIS 위성센서 관측으로부터 산출된 에어로솔 광학두께 자료를 본 연구에서 월면 관측을 통해 산출된 자료와 비교하였다. 비교 결과 R, G, B 채널에서 대략 0.1정도의 오차 범위에서 월면 영상분석을 통해 에어로솔 광학두께의 추정이 가능함을 알 수 있었다. 단, 대기 중의 에어로솔 입자들의 크기를 나타내는 모수인 앙스트롬지수(<TEX>${\AA}$</TEX>ngstr<TEX>$\ddot{o}$</TEX>m Exponent)는 파장별 광학두께의 작은 오차에도 큰 오차를 가질 수 있기 때문에 에어로솔 광학두께의 오차에 비해 비교적 큰 오차를 보일 수 있음이 나타났다. 그럼에도 불구하고, 야간의 에어로솔 광학두께 자료가 많지 않은 현실에서 저비용으로 월면 관측을 통하여 에어로솔 광학두께를 산출할 수 있는 가능성을 찾았다는 점에서 본 연구의 의의가 있으며 앞으로 보다 많은 관측과 분석을 통해 보다 향상된 야간 에어로솔 광학두께 추정이 가능할 것으로 보인다. Atmospheric optical thickness during nighttime was estimated in this study using analysis on the images of the moon taken from commercial digital camera. Basically the Langely Regression method was applied to the observations of the moon for the cloudless and optically stable sky conditions. The spectral response functions for the red(R), green(G), and blue(B) channels were employed to derive effective wavelength centers of each channel for the observations of the moon, and the correspondent Rayleigh optical thickness were also calculated. Aerosol optical thickness (AOT) was calculated by subtracting Rayleigh optical thickness from the atmospheric optical thickness derived from the Langley regression method. As there are only handful of nighttime AOT observations, the AOT from the moon observations was compared with the AOT from sun-photometers and the MODIS satellite sensor, which was taken several hours before the moon observations of this study. As a result, the values of AOT from moon observations agree with those from sun-photometers and MODIS within 0.1 for the R, G, B channels of the digital camera. On the other hand, <TEX>${\AA}$</TEX>ngstr<TEX>$\ddot{o}$</TEX>m Exponent seems to be subject to larger errors due to its sensitiveness to the spectral errors of AOT. Nevertheless, the results of this study indicate that the method reported in this study is promising as it can provide nighttime AOT relatively easily with a low cost instrument like digital camera. More observations and analyses are warranted to attain improved nighttime AOT observations in the future.

Spatial and temporal variations of atmospheric aerosol optical thickness in northwestern Mexico

The purpose of this paper was to study aerosol particles in the Northwestern region of Mexico (NWM) through Aerosol Optical Thickness (AOT) parameter in the atmosphere. This parameter represents one of the extinction coefficients of solar radiation and the rate of suspended particles in the atmosphere. For determination of AOT, we considered the use of remote sensors outside of the atmosphere. In particular, Moderate Resolution Imaging Spectroradiometer (MODIS) which can measure the atmospheric AOT thickness. Data from the MODIS sensor must be validated before they are considered reliable. For this task, we required surface measurements to obtain a correlation with the data acquired with the remote radiometer. The paper describes the validation process performed for data obtained with MODIS through measurements provided by an AErosol RObotic NETwork (AERONET) photometer located in the city of Hermosillo, Sonora, NWM. Additionally, we carried out a temporal analysis based on the behavior of the AOT graphics and spatial analysis supported in maps with sufficient information.

Measuring global solar irradiance and atmospheric optical thickness, using a digital pyranometer under conditions of clear skies and no clouds in Valencia (Venezuela)

The determination of the local solar irradiance and its annual change, well as quantification of atmospheric optical thickness (EOA) is important to assess environmental conditions and air quality in a given region, with multiple practical applications. In this paper we evaluate the performances of irradiance and calculate the atmospheric optical thickness in the city of Valencia (Venezuela). The irradiance measurements are performed by implementing a set of digital pyranometers, simply constructed using LEDs as photosensor elements, and record the solar elevation angle. The average values of irradiance for the city of Valencia (Venezuela) are of 805 W/m² for 620 nm and 249 W/m² at 472 nm with maximum irradiance values at 12:31 and 12:18 respectively HLV, the average EOA sample, a minimum true astronomical midday (12:02 HLV). We conclude that the local variation in irradiance is correlated with the atmospheric optical thickness and irradiance in the blue band of the spectrum is predominantly diffuse, and contribution in the red band is the combination of the direct and diffuse components.