scholarly journals Comparison of MODIS and AERONET derived aerosol optical depth over the Ganga Basin, India

2005 ◽  
Vol 23 (4) ◽  
pp. 1093-1101 ◽  
Author(s):  
S. N. Tripathi ◽  
Sagnik Dey ◽  
A. Chandel ◽  
S. Srivastava ◽  
Ramesh P. Singh ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Time Window ◽  
Absolute Error ◽  
Absolute Difference ◽  
Ganga Basin ◽  
Monsoon Period ◽  
Post Monsoon ◽  
Dust Loading ◽  
The Absolute

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) onboard EOS Terra measures global aerosol optical depth and optical properties since 2000. MODIS aerosol products are freely available and are being used for numerous studies. In this paper, we present a comparison of aerosol optical depth (AOD) retrieved from MODIS with Aerosol Robotic Network (AERONET) data for the year 2004 over Kanpur, an industrial city lying in the Ganga Basin in the northern part of India. AOD retrieved from MODIS (τaMODIS) at 0.55µm wavelength has been compared with the AERONET derived AOD (τaAERONET), within an optimum space-time window. Although the correlation between τaMODIS and τaAERONET during the post-monsoon and winter seasons (R2~0.71) is almost equal to that during the pre-monsoon and monsoon seasons (R2~0.72), MODIS is found to overestimate AOD during the pre-monsoon and monsoon period (characterized by severe dust loading) and underestimate during the post-monsoon and winter seasons. The absolute difference between τaMODIS and τaAERONET is found to be low (0.12±0.11) during the non-dust loading season and much higher (0.4±0.2) during dust-loading seasons. The absolute error in τaMODIS is found to be about ~25% of the absolute values of τaMODIS. Our comparison shows the importance of modifying the existing MODIS algorithm during the dust-loading seasons, especially in the Ganga Basin in northern part of India.

scholarly journals Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory – Pyramid (5079 m a.s.l.)

2010 ◽  
Vol 10 (1) ◽  
pp. 1193-1220 ◽  
Author(s):  
G. P. Gobbi ◽  
F. Angelini ◽  
P. Bonasoni ◽  
G. P. Verza ◽  
A. Marinoni ◽  
...  
Keyword(s):  
High Altitude ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Monsoon Season ◽  
Good Reason ◽  
Single Scattering ◽  
Radiative Properties ◽  
Mountain Range ◽  
Monsoon Period

Abstract. In spite of being located at the heart of the highest mountain range in the world, the Himalayan Nepal Climate Observatory (5079 m a.s.l.) at the Ev-K2-CNR Pyramid is shown to be affected by the advection of pollution aerosols from the populated regions of southern Nepal and the Indo-Gangetic plains. Such an impact is observed along most of the period April 2006–March 2007 addressed here, with a minimum in the monsoon season. Backtrajectory-analysis indicates long-range transport episodes occurring in this period to originate mainly in the West Asian deserts. At this high altitude site, the measured aerosol optical depth is observed to be: 1) about one order of magnitude lower than the one measured at Gandhi College (60 m a.s.l.), in the Indo-Gangetic basin, and 2) maximum during the monsoon period, due to the presence of elevated (cirrus-like) particle layers. Assessment of the aerosol radiative forcing results to be hampered by the persistent presence of these high altitude particle layers, which impede a continuous measurement of both the aerosol optical depth and its radiative properties from sky radiance inversions. Even though the retrieved absorption coefficients of pollution aerosols was rather large (single scattering albedo of the order of 0.6–0.9 were observed in the month of April 2006), the corresponding low optical depths (~0.03 at 500 nm) are expected to limit the relevant radiative forcings. Still, the high specific forcing of this aerosol and its capability of altering snow surface albedo provide good reason for continuous monitoring.

scholarly journals Simulation of trace gases and aerosols over the Indian domain: evaluation of the WRF-Chem Model

2013 ◽  
Vol 13 (5) ◽  
pp. 12287-12336 ◽  
Author(s):  
M. Michael ◽  
A. Yadav ◽  
S. N. Tripathi ◽  
V. P. Kanawade ◽  
A. Gaur ◽  
...  
Keyword(s):  
Sulfur Dioxide ◽  
Black Carbon ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Indian Subcontinent ◽  
Trace Gases ◽  
Atmospheric Composition ◽  
Emission Rates ◽  
Vertical Profiles ◽  
Monsoon Period

Abstract. The "online" meteorological and chemical transport Weather Research and Forecasting/Chemistry (WRF-Chem) model has been implemented over the Indian subcontinent for three consecutive summers in 2008, 2009 and 2010 to study the aerosol properties over the domain. The initial and boundary conditions are obtained from NCAR reanalysis data. The emission rates of sulfur dioxide, black carbon, organic carbon and PM2.5, which are developed over India at a grid resolution of 0.25° × 0.25° have been used in the present study. The remaining emissions are obtained from global inventories (RETRO and EDGAR). The model simulated the meteorological parameters, trace gases and particulate matter. Predicted mixing ratios of trace gases (Ozone, carbon monoxide and sulfur dioxide) are compared with ground based observations over Kanpur. Simulated aerosol optical depth are compared with those observed at nine Aerosol Robotic Network stations (AERONET). The simulations show that the aerosol optical depth of the less polluted regions is better simulated compared to that of the locations where the aerosol loading is very high. The vertical profiles of extinction coefficient observed at Kanpur Micropulse Lidar Network (MPLNET) station is in agreement with the simulated values for altitudes greater than 1.5 km and qualitatively simulate the elevated layers of aerosols. The simulated mass concentration of black carbon shows very good correlation with observations, due to the better local emission inventory used. The vertical profiles of black carbon at various locations have also been compared with observations from aircraft campaign held during pre-monsoon period of 2008 and 2009 resulting in good agreement. This study shows that WRF-Chem model captures many important features of the observations and therefore can be used for understanding and predicting regional atmospheric composition over Indian subcontinent.

scholarly journals Contribution of the world's main dust source regions to the global cycle of desert dust

2021 ◽  
Author(s):  
Jasper F. Kok ◽  
Adeyemi A. Adebiyi ◽  
Samuel Albani ◽  
Yves Balkanski ◽  
Ramiro Checa-Garcia ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Biogeochemical Cycles ◽  
Deposition Flux ◽  
Dust Deposition ◽  
North African ◽  
Dust Source ◽  
Desert Dust ◽  
Source Regions ◽  
Dust Loading

Abstract. Even though desert dust is the most abundant aerosol by mass in Earth's atmosphere, the relative contributions of the world’s major dust source regions to the global dust cycle remain poorly constrained. This problem hinders accounting for the potentially large impact of regional differences in dust properties on clouds, the Earth's energy balance, and terrestrial and marine biogeochemical cycles. Here, we constrain the contribution of each of the world’s main dust source regions to the global dust cycle. We use an analytical framework that integrates an ensemble of global model simulations with observationally informed constraints on the dust size distribution, extinction efficiency, and regional dust aerosol optical depth. We obtain a data set that constrains the relative contribution of each of nine major source regions to size-resolved dust emission, atmospheric loading, optical depth, concentration, and deposition flux. We find that the 22–29 Tg (one standard error range) global loading of dust with geometric diameter up to 20 μm is partitioned as follows: North African source regions contribute ~50 % (11–15 Tg), Asian source regions contribute ~40 % (8–13 Tg), and North American and Southern Hemisphere regions contribute ~10 % (1.8–3.2 Tg). Current models might on average be overestimating the contribution of North African sources to atmospheric dust loading at ~65 %, while underestimating the contribution of Asian dust at ~30 %. However, both our results and current models could be affected by unquantified biases, such as due to errors in separating dust aerosol optical depth from that produced by other aerosol species in remote sensing retrievals in poorly observed desert regions. Our results further show that each source region's dust loading peaks in local spring and summer, which is partially driven by increased dust lifetime in those seasons. We also quantify the dust deposition flux to the Amazon rainforest to be ~10 Tg/year, which is a factor of 2–3 less than inferred from satellite data by previous work that likely overestimated dust deposition by underestimating the dust mass extinction efficiency. The data obtained in this paper can be used to obtain improved constraints on dust impacts on clouds, climate, biogeochemical cycles, and other parts of the Earth system.

The precision of asset beta estimates

2017 ◽  
Vol 13 (2) ◽  
pp. 213-224 ◽  
Author(s):  
Vance Lesseig ◽  
Janet D. Payne
Keyword(s):  
Academic Research ◽  
Systematic Risk ◽  
Absolute Error ◽  
Equity Capital ◽  
Absolute Difference ◽  
Average Difference ◽  
Content Type ◽  
True Value ◽  
The Absolute ◽  
Matching Criteria

Purpose The capital asset pricing model has fundamentally changed the way finance is taught and practiced since its development in 1964. However, one problem with the use of the model is estimating the systematic risk of untraded assets. Academics and practitioners have dealt with the problem by using traded assets as “proxies” for the untraded asset. Some academic research has attempted to measure the validity of this technique using the average difference in the true beta of a traded firm and the “proxy” beta using a sample of similar firms. The paper aims to discuss these issues. Design/methodology/approach However, the use of the average difference across a number of comparisons is not necessarily useful to a practitioner. This paper examines the absolute difference between a firm’s unlevered beta and a proxy beta calculated using the formula given in Hamada, 1972, and the pure play method. Findings The authors find that the estimates are not reliably close to the true value. Using both deciles of relevant variables and a matching method similar to that used by practitioners, the authors examine a variety of different characteristics to identify similar firms. Originality/value However, the authors do not find any matching criteria that improves the absolute error of the estimate to a level, the authors believe would be acceptable to practitioners attempting to measure cost of equity capital for their untraded firm or asset. The authors conclude that managers should use pure play estimates of asset beta with caution. More research should be done in order to identify a better way for managers of untraded firms or assets to proxy their systematic risk.

scholarly journals Simulation of trace gases and aerosols over the Indian domain: evaluation of the WRF-Chem model

2014 ◽  
Vol 7 (1) ◽  
pp. 431-482 ◽  
Author(s):  
M. Michael ◽  
A. Yadav ◽  
S. N. Tripathi ◽  
V. P. Kanawade ◽  
A. Gaur ◽  
...  
Keyword(s):  
Black Carbon ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Trace Gases ◽  
Atmospheric Composition ◽  
Vertical Profiles ◽  
Monsoon Period ◽  
Mixing Ratios

Abstract. The "online" meteorological and chemical transport Weather Research and Forecasting/Chemistry (WRF-Chem) model has been implemented over the Indian subcontinent for three consecutive summers in 2008, 2009 and 2010 to study the aerosol properties over the domain. The model simulated the meteorological parameters, trace gases and particulate matter. Predicted mixing ratios of trace gases (Ozone, carbon monoxide and sulfur dioxide) are compared with ground based observations over Kanpur. Simulated aerosol optical depth are compared with those observed at nine Aerosol Robotic Network stations (AERONET). The simulations show that the aerosol optical depth of the less polluted regions is better simulated compared to that of the locations where the aerosol loading is very high. The vertical profiles of extinction coefficient observed at the Kanpur Micropulse Lidar Network (MPLNET) station is underpredicted by the model by 10 to 50% for altitudes greater than 1.5 km and qualitatively simulate the elevated layers of aerosols. The simulated mass concentration of black carbon shows a correlation coefficient of 0.4 with observations. Vertical profiles of black carbon at various locations have also been compared with observations from an aircraft campaign held during pre-monsoon period of 2008 and 2009. This study shows that WRF-Chem model captures many important features of the observed atmospheric composition during the pre-monsoon season in India.

scholarly journals Validation of MODIS derived aerosol optical depth and an investigation on aerosol transport over the South East Arabian Sea during ARMEX-II

2009 ◽  
Vol 27 (6) ◽  
pp. 2285-2296 ◽  
Author(s):  
M. Aloysius ◽  
M. Mohan ◽  
S. Suresh Babu ◽  
K. Parameswaran ◽  
K. Krishna Moorthy
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mass Concentration ◽  
Arabian Sea ◽  
Second Phase ◽  
The South ◽  
Monsoon Period ◽  
Lower Altitude ◽  
The North ◽  
Coarse Mode

Abstract. The influence of wind and humidity on aerosol optical depth (AOD) over the Arabian sea is being investigated using MODIS (Moderate Resolution Imaging Spectroradiometer) Level 3 (Collection-5) and NCEP (National Centres for Environmental Prediction) reanalysis data for the second phase of the Arabian Sea Monsoon Experiment (ARMEX-II) over the South East Arabian Sea (SEAS) in the pre-monsoon period (14 March–10 April 2003). In order to qualify MODIS data for this study, MODIS aerosol parameters were first compared with ship borne Microtops measurements. This showed correlations 0.96–0.97 in the case of spectral AODs and a correlation 0.72 for the angstrom exponents. The daily AOD data from MODIS and winds from NCEP reveal that the ship observed episodic enhancement and decay of AOD at the TSL (Time Series Location) during 23 March–6 April 2003 was caused by the southward drift of an aerosol pocket driven by an intensification and reduction of surface pressure in the North Western Arabian Sea with a low altitude convergence prevailing over SEAS. The AOD increase coincided with a decrease in the Angstrom exponent and the fine mode fraction suggesting the pocket being dominated by coarse mode particles. A partial correlation analysis reveals that the lower altitude wind convergence is the most influential atmospheric variable in modulating AOD over the ARMEX-II domain during the TSL period. However, surface winds at a distant zone in the north/north west upwind direction also had a moderate influence, though with a lag of two days. But this effect was minor since the winds were not strong enough to produce marine aerosols matching with the high AODs over the ARMEX-II domain. These findings and the similarity between MODIS column mass concentration and the ship borne QCM (Quartz Crystal Microbalance) measured coarse mode mass concentration, suggest that the aerosol pocket was mostly composed of coarse mode mineral dust in the lower atmospheric altitudes transported from the Arabian deserts.

scholarly journals Retrieval of Urban Aerosol Optical Depth from Landsat 8 OLI in Nanjing, China

2021 ◽  
Vol 13 (3) ◽  
pp. 415
Author(s):  
Yangyang Jin ◽  
Zengzhou Hao ◽  
Jian Chen ◽  
Dong He ◽  
Qingjiu Tian ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Absolute Error ◽  
Meteorological Conditions ◽  
Landsat 8 ◽  
Landsat 8 Oli ◽  
Large Area ◽  
The North ◽  
Deep Blue ◽  
Seasonal Characteristics

Aerosol is an essential parameter for assessing the atmospheric environmental quality, and accurate monitoring of the aerosol optical depth (AOD) is of great significance in climate research and environmental protection. Based on Landsat 8 Operational Land Imager (OLI) images and MODIS09A1 surface reflectance products under clear skies with limited cloud cover, we retrieved the AODs in Nanjing City from 2017 to 2018 using the combined Dark Target (DT) and Deep Blue (DB) methods. The retrieval accuracy was validated by in-situ CE-318 measurements and MOD04_3K aerosol products. Furthermore, we analyzed the spatiotemporal distribution of the AODs and discussed a case of high AOD distribution. The results showed that: (1) Validated by CE-318 and MOD04_3K data, the correlation coefficient (R), root mean square error (RMSE), and mean absolute error (MAE) of the retrieved AODs were 0.874 and 0.802, 0.134 and 0.188, and 0.099 and 0.138, respectively. Hence, the combined DT and DB algorithms used in this study exhibited a higher performance than the MOD04_3K-obtained aerosol products. (2) Under static and stable meteorological conditions, the average annual AOD in Nanjing was 0.47. At the spatial scale, the AODs showed relatively high values in the north and west, low in the south, and the lowest in the center. At the seasonal scale, the AODs were highest in the summer, followed by spring, winter, and autumn. Moreover, changes were significantly higher in the summer than in the other three seasons, with little differences among spring, autumn, and winter. (3) Based on the spatial and seasonal characteristics of the AOD distribution in Nanjing, a case of high AOD distribution caused by a large area of external pollution and local meteorological conditions was discussed, indicating that it could provide extra details of the AOD distribution to analyze air pollution sources using fine spatial resolution like in the Landsat 8 OLI.

scholarly journals Analysis of Aerosol Optical Depth and Angstrom Exponents over an AERONET site at Pokhara, Nepal

BIBECHANA ◽  
2021 ◽  
Vol 18 (1) ◽  
pp. 118-127
Author(s):  
Jeevan Regmi ◽  
Khem N Poudyal ◽  
Amod Pokhrel ◽  
Madhu Gyawali ◽  
Anthony Barinelli ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Monsoon Season ◽  
Anthropogenic Aerosols ◽  
Annual Average ◽  
Average Value ◽  
Monthly Average ◽  
Aerosol Loading ◽  
Post Monsoon ◽  
Post Monsoon Season

The monthly variability of Aerosol Optical Depth at 0.50 μm (AOD0.50) and Ångström exponents (AE) based on spectral AODs over an Aerosol Robotic Network (AERONET) site Pokhara, are analyzed by using aerosol data of the year 2017. The AOD0.50 are characterized by low average values (0.21± 0.12) in monsoon, and highest values in pre-monsoon (0.67± 0.14) followed by winter (0.46± 0.28) and post-monsoon (0.33±.02) with an overall mean of 0.43 ± 0.02. The average AE obtained by using AODs at 0.44 μm and 0.87 μm is 1.20± 0.04 in pre-monsoon, 1.37± 0.05 in monsoon, 1.41±.01 in post-monsoon, and 1.37± 0.07 in winter with an annual average value of 1.35 ± 0.08. These overall variations of AE indicate that the majority of aerosol loading during the study period was mixture of fine and coarse mode aerosols and the influence of anthropogenic aerosols. The monthly average AOD suggests low aerosol loading in the months of the monsoon season (June to September) than other months of pre-monsoon season (March to May) and post-monsoon season (October and November). BIBECHANA 18 (2021) 118-127

Determining the minimum pitch for measuring the spatial position of a pipeline when assessing the stress-strain state from the soil surface

2020 ◽  
Vol 10 (2) ◽  
pp. 138-147
Author(s):  
Ruslan V. Aginey ◽  
◽  
Rustem R. Islamov ◽  
Elmira A. Mamedova ◽  
Alexey A. Firstov ◽  
...  
Keyword(s):  
Strain State ◽  
Soil Surface ◽  
Absolute Error ◽  
Spatial Position ◽  
Absolute Difference ◽  
Stress Strain ◽  
Stress Strain State ◽  
Bending Stresses ◽  
Bending Radius ◽  
The Absolute

In determining the bending radius of an underground pipeline axis from the soil surface, existing methods have some disadvantages associated with a lack of studies on how pipeline depth and equipment errors affect the results of measurement pitch calculations. The purpose of the study is to determine the minimum measuring pitch relative to the spatial position of the pipeline using line locating equipment to assess the stress-strain state from the soil surface. An assumption was made that the pipeline section has a bend in one plane only. Therefore, it is considered as a combination of three axis points that, when interconnected, form a part of a circle. To find the actual values of the bending radii in two borderline cases, some expressions were proposed. Regarding the absolute difference between the maximum bending stresses and the measuring pitch, dependences were obtained for various values of the absolute error attributed to the equipment used with a 1.400 mm diameter pipe. It was established that to limit an error in the absolute difference of the maximum bending stresses to 50 MPa, the minimum measurement pitch should be 20 to 60 meters (this varies depending on the error of the line locating equipment used). Using the MATLAB programming language, a program code was written to construct a three-dimensional graph representing the dependence between the absolute difference of the maximum bending stresses and the measurement pitch for various values of an absolute error attributed to the equipment. It was found that the pipeline bending radius does not affect the value of the minimum pitch for measuring the spatial position of the pipeline.

scholarly journals Retrieval of High Spatial Resolution Aerosol Optical Depth from HJ-1 A/B CCD Data

2019 ◽  
Vol 11 (7) ◽  
pp. 832 ◽  
Author(s):  
Xianlei Fan ◽  
Ying Qu
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Estimation Method ◽  
Absolute Error ◽  
Lookup Table ◽  
Visual Interpretation ◽  
Infrared Band ◽  
Moderate Resolution Imaging Spectroradiometer

A high-spatial resolution aerosol optical depth (AOD) dataset is critically important for regional meteorology and climate studies. Chinese Huanjing-1 (HJ-1) A/B charge-coupled diode (CCD) data are a suitable data source for retrieving AODs. However, AOD cannot be retrieved based on the dark target method due to the absence of a shortwave infrared band. In this study, an AOD estimation method based on the relationships between visible bands of HJ-1 A/B CCDs is proposed. The Polarization and Directionality of the Earth's Reflectances (POLDER) Bidirectional Reflectance Distribution Function (BRDF) dataset was used to construct a lookup table for interband regression coefficients that varied by solar/view angle and land cover type. Finally, high-spatial resolution AODs could be retrieved with the aerosol lookup table and constraints. The results showed that the AODs retrieved from the HJ-1 A/B CCD data had the same range of distribution and trends as a visual interpretation of the images and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products did. The validation results using four sites of the Aerosol Robotic Network (AERONET) in Beijing showed that the value of the correlation coefficient R was 0.866, the root mean square error (RMSE) was 0.167, the mean absolute error (MAE) was 0.131, and the expected error (EE) was 53.9%. If the measurements of an AERONET site were used as prior knowledge, AOD retrieval results could be much more accurately obtained by this method (R is 0.989, RMSE is 0.052, MAE is 0.042, and EE is 96.7%).

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