Hello...I am a postdoctoral researcher at Physical Research Laboratory, India. My work is focused on aerosol-cloud-climate interactions, radiative forcing, radiative transfer, post-launch calibration of optical satellite sensor.
Remote Sensing Applications: Society and Environment, 2016
This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG... more This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchro-nising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year's analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.
Remote Sensing Applications: Society and Environment, 2016
This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG... more This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchro-nising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year's analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.
ABSTRACT Clouds have an important role in the Earth’s radiation budget and global atmospheric cir... more ABSTRACT Clouds have an important role in the Earth’s radiation budget and global atmospheric circulation. Aerosols modify the clouds properties by modifying the cloud droplet size. An increase in aerosol concentration may lead to an increase in cloud condensation nuclei (CCN), with an associated change in cloud properties. In the present study, correlations between aerosol optical depth (AOD) and cloud properties are examined over Arabian Sea (AS), Bay of Bengal (BOB) and Central India (CI) for 2008-2013 from the Moderate Resolution Imaging Spectrometer (MODIS) on Terra and Aqua. The relationships are studied on seasonal basis, between AOD, cloud fraction (CF) and cloud effective radius (CER). Additionally, cloud droplet number concentration (CDNC) is retrieved using MODIS products of cloud optical depth (COD) and CER with the assumption that cloud develop in adiabatic conditions. The seasonal distribution of CDNC and CER are discussed over three regions to find the first aerosol indirect effect (AIE). The negative correlation between AOD and CER are observed for four cases (1) monsoon over AS with AOD > 0.3, (2) monsoon over BOB with AOD > 0.1 (3) pre-monsoon over BOB with AOD > 0.3 and (4) winter over CI, which lead to the first AIE. These four cases are further studied for the investigation of second AIE using change in liquid water path (LWP) with AOD and cloud top pressure (CTP). Further analysis of seven day back-trajectories shows that transportation of aerosols species resulting the AIE.
DESCRIPTION In this thesis, as the universe expands astronomical observables such as brightness a... more DESCRIPTION In this thesis, as the universe expands astronomical observables such as brightness and angular size on the sky change in ways that differ from our simple Cartesian expectation. We show how observed quantities depend on the expansion of space and demonstrate how to calculate such quantities using the Friedmann equations. The general solution to the Friedmann equations requires a numerical solution which is easily coded in any computing language. After that calculate same parameters for some another cosmological models like Low mass density, Mass only, WMAP only and Lambda only. Then compare these five cosmological models and then find some parameters like comoving distance, luminosity distance, angular diameter distance and distance modulus and plot a graph and compare those graphs with each other and find the best suitable model which suite the present scenario of the universe.
Clouds have an important role in the Earth’s radiation budget and global atmospheric circulation.... more Clouds have an important role in the Earth’s radiation budget and global atmospheric circulation. Aerosols modify the clouds properties by modifying the cloud droplet size. An increase in aerosol concentration may lead to an increase in cloud condensation nuclei (CCN), with an associated change in cloud properties. In the present study, correlations between aerosol optical depth (AOD) and cloud properties are examined over Arabian Sea (AS), Bay of Bengal (BOB) and Central India (CI) for 2008-2013 from the Moderate Resolution Imaging Spectrometer (MODIS) on Terra and Aqua. The relationships are studied on seasonal basis, between AOD, cloud fraction (CF) and cloud effective radius (CER). Additionally, cloud droplet number concentration (CDNC) is retrieved using MODIS products of cloud optical depth (COD) and CER with the assumption that cloud develop in adiabatic conditions. The seasonal distribution of CDNC and CER are discussed over three regions to find the first aerosol indirect e...
DESCRIPTION The study undertaken deals with study few optical parameters at one site of sub-Himal... more DESCRIPTION The study undertaken deals with study few optical parameters at one site of sub-Himalayan region. The study also utilizes in explaining the possible sources of the aerosols. Various instruments like sunphotometer, ozonometer and aethalometer were used to measure data on aerosol, black carbon, ozone and water vapour over subHimalayan region of Dehradun (700 meters a.m.s.l.) for the month of April & May, 2012. In these two month, there is different climatology variation and to have different levels of pollution. Results suggests that AOD values in May over Dehradun are slightly higher over all wavelengths as compared to April attributing to the presence of more coarse particles in the atmosphere due to episodic events of dust storm come from western direction. The analysis from Angstrom exponents also signifies the same opinion. The turbidity level of Dehradun is more in May. In May BC concentration is decreasing due to the presence of more dust particles in atmosphere as ...
Aerosols are significant contributors to atmospheric extinction and play an important role in atm... more Aerosols are significant contributors to atmospheric extinction and play an important role in atmospheric heating patterns by scattering and absorbing solar radiation.The intergovernmental panel on climate change fourth assessment report (IPCC, 2007) estimate for the global annual radiative forcing of the first indirect effect is -0.7 Wm-2 with an uncertainty range of -1.8 to -0.3 Wm-2.Recent studies indicate that the variations in heating pattern affect the monsoon rainfall patterns by modulating cloud processes (Lau et al., 2006). Dehradun (30 ° 30’ N, 78 °18’ Eand 730 m a.m.s.l.)is situated in the northeast part of Indo-Gangetic plains where significant seasonal variations in AOD, aerosol mass concentration and their optical properties are expected due to increased anthropogenic activities. This region experiences four dominant seasons each year winter (December-March), pre-monsoon (April-June), monsoon (July-September) and post-monsoon (October-November). During pre-monsoon seas...
Looking towards the advancements and popularity of remote sensing and an ever increasing need for... more Looking towards the advancements and popularity of remote sensing and an ever increasing need for the development of a variety of new and complex satellite sensors, it has become even more essential to continually upgrade the ability to provide absolute calibration of sensors. This article describes a simple procedure to implement post-launch calibration for VIS and SWIR channels of INSAT-3D imager over land site (Little Rann of Kutch (ROK), Gujarat) on three different days to account for characterization errors or undetermined post-launch changes in spectral response of the sensor. The measurements of field reflectance of study site (of extent ~ 6km x 6 km) in the wavelength range 325-2500 nm, along with atmospheric parameters (Aerosol Optical Depth, Total Columnar Ozone, Water Vapor) and sensor spectral response functions, were input to the 6S radiative transfer model to simulate radiance at top of the atmosphere (TOA) for VIS and SWIR bands. The uncertainty in vicarious calibrati...
In a previous study of Quaas et al. (2008) the radia-tive forcing by anthropogenic aerosol due to... more In a previous study of Quaas et al. (2008) the radia-tive forcing by anthropogenic aerosol due to aerosol–cloud interactions, RF aci , was obtained by a statistical analysis of satellite retrievals using a multilinear regression. Here we employ a new statistical approach to obtain the fitting parameters , determined using a nonlinear least square statistical approach for the relationship between planetary albedo and cloud properties and, further, for the relationship between cloud properties and aerosol optical depth. In order to verify the performance, the results from both statistical approaches (previous and present) were compared to the results from ra-diative transfer simulations over three regions for different seasons. We find that the results of the new statistical approach agree well with the simulated results both over land and ocean. The new statistical approach increases the correlation by 21–23 % and reduces the error compared to the previous approach.
Aerosol optical properties are analyzed for the first time over Desalpar (23.74°N, 70.69°E, 30 m ... more Aerosol optical properties are analyzed for the first time over Desalpar (23.74°N, 70.69°E, 30 m above mean sea level) a remote site in western India during October 2014 to August 2015. Spectral aerosol optical depth (AOD) measurements were performed using the CIMEL CE-318 automatic Sun/sky radiometer. The annual-averaged AOD500 and Ångström exponent (α440–870) values are found to be 0.43 ± 0.26 and 0.69 ± 0.39, respectively. On the seasonal basis, high AOD500 of 0.45 ± 0.30 and 0.61 ± 0.34 along with low α440–870 of 0.41 ± 0.27 and 0.41 ± 0.35 during spring (March–May) and summer (June–August), respectively, suggest the dominance of coarse-mode aerosols, while significant contribution from anthropogenic sources is observed in autumn (AOD500 = 0.47 ± 0.26, α440–870 = 1.02 ± 0.27). The volume size distribution and the spectral single-scattering albedo also confirm the presence of coarse-mode aerosols during March–August. An overall dominance of a mixed type of aerosols (~56%) mostly from October to February is found via the AOD500 vs α440–870 relationship, while marine aerosols contribute to ~18%. Spectral dependence of α and its second derivative (α′) are also used for studying the aerosol modification processes. The average direct aerosol radiative forcing (DARF) computed via the SBDART model is estimated to range from −27.08 W m−2 to −10.74 W m−2 at the top of the atmosphere, from −52.21 W m−2 to −21.71 W m−2 at the surface and from 10.97 W m−2 to 26.54 W m−2 within the atmosphere. This atmospheric forcing translates into heating rates of 0.31–0.75 K day−1. The aerosol properties and DARF are also examined for different trajectory clusters in order to identify the sources and to assess the influence of long-range transported aerosols over Desalpar.
Aerosol-cloud interaction is the subject of considerable scientific research, due to the importan... more Aerosol-cloud interaction is the subject of considerable scientific research, due to the importance of clouds in controlling climate. In the present study, three years (2011–2013) satellite observations are used to investigate the aerosol indirect effect (AIE) over Dehradun. The low values of Angstrom exponent (α) during March–July are attributed to the loading of dust-like coarse particles in the atmosphere, whereas the analysis of aerosol type and Spectral Radiation Transport Model for Aerosol species (SPRINTARS) simulated aerosol species variation supports the fact. Moderate Resolution Imaging Spectroradiometer (MODIS) derived AOD data are associated to the cloud product to examine the dust impact on properties of liquid cloud and ice cloud. The positive values of aerosol cloud interaction effect (ACI) for ice cloud during pre-monsoon (March–May) and monsoon (June–August) seasons reveal the significant impact of dust on ice clouds over Dehradun, which is maximum during May (~0.24 ± 0.05). The present study shows that ice cloud effective radius (ICER) decrease with AOD during dust period. The increase in ice water path (IWP) and ice cloud optical depth (ICOD) reveals the impact of dust on heterogeneous ice generation in low level clouds. However, there is no relation between dust and liquid water cloud during dust period. It is difficult to provide definite conclusions that the dust and cloud changes are driven by the same meteorological conditions. Cloud and the Earth's Radiant Energy System (CERES) derived flux data are used to examine the associated changes in TOA cloud radiative forcing. The diminution in effective size of ice crystal due to aerosol first indirect effect traps more longwave radiation and reflects more solar radiation. Both first and second indirect effects enhance cloud cooling, whereas the dust induced cloud warming is mainly the result of the semi-direct effect.
This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG... more This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchro-nising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year's analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.
Dust storm, a natural hazard, has a direct impact on daily life for a short period. Dust storms a... more Dust storm, a natural hazard, has a direct impact on daily life for a short period. Dust storms are periodic events over India, especially in northern regions. This study has been carried out to investigate the dust impacts on the aerosol characteristics over Dehradun (DDN) during pre-monsoon (March–June), 2012 using ground measurements, satellite observations and model simulations. The measurements illustrate the distinct monthly impact on the aerosol properties with maximum dust loading during May (aerosol optical depth at 500 nm (AOD 500) = 0.72 ± 0.18) over DDN, which is confirmed with the Terra-MODIS (AOD 550 = 0.70 ± 0.19) measurements. The major dust loading was recorded in aerosol measurements during May at the station, which permitting to examine the influence of dust transports on the aerosol characteristics. Spectral variation of AOD and Angstrom exponent (α) values displayed day to day variation of aerosol during dust episodes. Analysis of aerosol types and seven-day back-trajectories reveal the transportation of desert dust during May over DDN. The Optical Properties of Aerosols and Clouds (OPAC) model was used to compute the aerosol optical properties (e.g., Single scattering albedo (SSA) and asymmetry parameter (g)) and size distribution. The high values of SSA and g are indicating the dust loading in the atmosphere during May. Aerosol volume concentration at the coarse mode (geometric mean radii (R V) = 2.89 ± 0.027 µm) is found to be increased in the May, whereas decrement has been observed in the finer mode (R V = 0.16 ± 0.006 µm). The aerosol direct radiative forcing (ARF) was computed using Santa Barbara Discrete Ordinate Atmospheric Radiative Transfer (SBDART) model in the shortwave (SW) region (0.25– 4.00 µm). The mean top of the atmosphere (TOA) and surface forcing come out to be –14.49 W m –2 and –53.29 W m –2 respectively in May. The mean net atmospheric radiative forcing (38.79 W m –2 maximum during May) corresponds to heating rate of ~1.06° K d –1 in the atmosphere.
Ground and satellite based measurements of spectral optical properties of aerosols have been carr... more Ground and satellite based measurements of spectral optical properties of aerosols have been carried out at Dehradun (DDN) in the Indo-Gangetic Plain (IGP) and Kavaratti (KVT) at Lakshadweep in southern Arabian Sea during pre-monsoon season (March– May) 2012. The measurements illustrate distinct seasonal impact on aerosol properties with maximum dust loading during May in conjunction with anthro-pogenic aerosols over DDN and marine aerosols over KVT. Aerosol optical depth (AOD) values have been observed maximum in May (0.72 0.03) over DDN and in April (0.77 0.05) over KVT. The high AOD at DDN during May is associated with low and high , means higher loading in May is associated with coarse mode aerosols, may be dust loading as evident from SSA and volume size distribution. Similarly, high AOD at KVT during March and April are associated with high and low , may be due to anthropogenic influence as evident from BT analysis as well as SSA and volume size distribution. However, influence of marine aerosols is also noticeable over KVT during May as indicated by the lower values of with high turbidity coefficient . Comparison between sunpho-tometer and MODIS AOD observations indicates good statistical agreement with the minimal error.
Ground based measurement of aerosol optical depth (AOD) and black carbon (BC) aerosols were carri... more Ground based measurement of aerosol optical depth (AOD) and black carbon (BC) aerosols were carried out over Dehradun during January to December 2007. The AOD values during winter (December-February) are low and found to be in the range of (0.08-0.38) than during summer (March-June) periods (0.32-0.62). The aerosol loading was observed to be high during summer period due to the long-range transportation of aerosol particles by air mass from the Thar Desert region to the observing site besides the biomass burning and frequent incidents of forest fire at local levels. The annual average BC concentration observed was found to be 4.3 + 0.62 µgm-3. Diurnal variation of BC shows a gradual build up in the morning hours between 0600 to 0900 local time and in evening from 1900 to 2200 hrs local time while low concentration is observed during day and night time. The analysis of traffic density measured in the city shows that it has direct influence on the BC concentration. BC concentration increases more than three times during morning and evening compared to afternoon and night hours. Seasonal variations of BC shows high concentration during winter dry season associated with the air masses predominantly coming from Indo-Gangetic plain rich in carbonaceous aerosols and minimum during monsoon season due to wash out. The BC concentration is found to have relationship with anthropogenic activities, boundary layer dynamics and biomass burning which has been observed by the MODIS fire data in and around the region. BC concentration were positive correlated with diurnal temperature range and negative correlated with rainfall and humidity. The values of aerosol optical depth and black carbon concentration over Dehradun have been compared with those reported from selected locations in India. INTRODUCTION Aerosols are important components of earth–atmosphere–ocean system. They affect climate through three primary mechanisms-direct radiative forcing (absorption and scattering of sun radiation), indirect radiative forcing (modifying the cloud properties thereby affecting albedo of clouds) and have indirect effect in the atmospheric chemistry by modifying the concentration of climate-influencing constituents (Schwartz et al., 1995) (such as GHG's). Aerosols enhances the back scattering of solar radiation and leading to negative radiative forcing while the absorbing black carbon (BC) aerosols leads to the positive effect. Black carbon aerosol, the optically absorbing part of the carbonaceous aerosols is the major anthropogenic component of atmospheric aerosol system. Black carbon is one of the important constituents of ambient particulate matter, which is emitted into the atmosphere as a by-product of combustion processes such as fossil fuels, vegetation burning, industrial effluents, motor vehicle and aircraft exhausts and are generally in the sub-micron region and considered as tracers of anthropogenic impact on environment. The increase in anthropogenic emission would increase in aerosol loading thereby reducing the incoming solar radiation reaching the ground surface. These effects influence regional aerosol radiative forcing (Haywood and Shine, 1997). It has been reported that one of the
Remote Sensing Applications: Society and Environment, 2016
This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG... more This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchro-nising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year's analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.
Remote Sensing Applications: Society and Environment, 2016
This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG... more This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchro-nising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year's analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.
ABSTRACT Clouds have an important role in the Earth’s radiation budget and global atmospheric cir... more ABSTRACT Clouds have an important role in the Earth’s radiation budget and global atmospheric circulation. Aerosols modify the clouds properties by modifying the cloud droplet size. An increase in aerosol concentration may lead to an increase in cloud condensation nuclei (CCN), with an associated change in cloud properties. In the present study, correlations between aerosol optical depth (AOD) and cloud properties are examined over Arabian Sea (AS), Bay of Bengal (BOB) and Central India (CI) for 2008-2013 from the Moderate Resolution Imaging Spectrometer (MODIS) on Terra and Aqua. The relationships are studied on seasonal basis, between AOD, cloud fraction (CF) and cloud effective radius (CER). Additionally, cloud droplet number concentration (CDNC) is retrieved using MODIS products of cloud optical depth (COD) and CER with the assumption that cloud develop in adiabatic conditions. The seasonal distribution of CDNC and CER are discussed over three regions to find the first aerosol indirect effect (AIE). The negative correlation between AOD and CER are observed for four cases (1) monsoon over AS with AOD > 0.3, (2) monsoon over BOB with AOD > 0.1 (3) pre-monsoon over BOB with AOD > 0.3 and (4) winter over CI, which lead to the first AIE. These four cases are further studied for the investigation of second AIE using change in liquid water path (LWP) with AOD and cloud top pressure (CTP). Further analysis of seven day back-trajectories shows that transportation of aerosols species resulting the AIE.
DESCRIPTION In this thesis, as the universe expands astronomical observables such as brightness a... more DESCRIPTION In this thesis, as the universe expands astronomical observables such as brightness and angular size on the sky change in ways that differ from our simple Cartesian expectation. We show how observed quantities depend on the expansion of space and demonstrate how to calculate such quantities using the Friedmann equations. The general solution to the Friedmann equations requires a numerical solution which is easily coded in any computing language. After that calculate same parameters for some another cosmological models like Low mass density, Mass only, WMAP only and Lambda only. Then compare these five cosmological models and then find some parameters like comoving distance, luminosity distance, angular diameter distance and distance modulus and plot a graph and compare those graphs with each other and find the best suitable model which suite the present scenario of the universe.
Clouds have an important role in the Earth’s radiation budget and global atmospheric circulation.... more Clouds have an important role in the Earth’s radiation budget and global atmospheric circulation. Aerosols modify the clouds properties by modifying the cloud droplet size. An increase in aerosol concentration may lead to an increase in cloud condensation nuclei (CCN), with an associated change in cloud properties. In the present study, correlations between aerosol optical depth (AOD) and cloud properties are examined over Arabian Sea (AS), Bay of Bengal (BOB) and Central India (CI) for 2008-2013 from the Moderate Resolution Imaging Spectrometer (MODIS) on Terra and Aqua. The relationships are studied on seasonal basis, between AOD, cloud fraction (CF) and cloud effective radius (CER). Additionally, cloud droplet number concentration (CDNC) is retrieved using MODIS products of cloud optical depth (COD) and CER with the assumption that cloud develop in adiabatic conditions. The seasonal distribution of CDNC and CER are discussed over three regions to find the first aerosol indirect e...
DESCRIPTION The study undertaken deals with study few optical parameters at one site of sub-Himal... more DESCRIPTION The study undertaken deals with study few optical parameters at one site of sub-Himalayan region. The study also utilizes in explaining the possible sources of the aerosols. Various instruments like sunphotometer, ozonometer and aethalometer were used to measure data on aerosol, black carbon, ozone and water vapour over subHimalayan region of Dehradun (700 meters a.m.s.l.) for the month of April & May, 2012. In these two month, there is different climatology variation and to have different levels of pollution. Results suggests that AOD values in May over Dehradun are slightly higher over all wavelengths as compared to April attributing to the presence of more coarse particles in the atmosphere due to episodic events of dust storm come from western direction. The analysis from Angstrom exponents also signifies the same opinion. The turbidity level of Dehradun is more in May. In May BC concentration is decreasing due to the presence of more dust particles in atmosphere as ...
Aerosols are significant contributors to atmospheric extinction and play an important role in atm... more Aerosols are significant contributors to atmospheric extinction and play an important role in atmospheric heating patterns by scattering and absorbing solar radiation.The intergovernmental panel on climate change fourth assessment report (IPCC, 2007) estimate for the global annual radiative forcing of the first indirect effect is -0.7 Wm-2 with an uncertainty range of -1.8 to -0.3 Wm-2.Recent studies indicate that the variations in heating pattern affect the monsoon rainfall patterns by modulating cloud processes (Lau et al., 2006). Dehradun (30 ° 30’ N, 78 °18’ Eand 730 m a.m.s.l.)is situated in the northeast part of Indo-Gangetic plains where significant seasonal variations in AOD, aerosol mass concentration and their optical properties are expected due to increased anthropogenic activities. This region experiences four dominant seasons each year winter (December-March), pre-monsoon (April-June), monsoon (July-September) and post-monsoon (October-November). During pre-monsoon seas...
Looking towards the advancements and popularity of remote sensing and an ever increasing need for... more Looking towards the advancements and popularity of remote sensing and an ever increasing need for the development of a variety of new and complex satellite sensors, it has become even more essential to continually upgrade the ability to provide absolute calibration of sensors. This article describes a simple procedure to implement post-launch calibration for VIS and SWIR channels of INSAT-3D imager over land site (Little Rann of Kutch (ROK), Gujarat) on three different days to account for characterization errors or undetermined post-launch changes in spectral response of the sensor. The measurements of field reflectance of study site (of extent ~ 6km x 6 km) in the wavelength range 325-2500 nm, along with atmospheric parameters (Aerosol Optical Depth, Total Columnar Ozone, Water Vapor) and sensor spectral response functions, were input to the 6S radiative transfer model to simulate radiance at top of the atmosphere (TOA) for VIS and SWIR bands. The uncertainty in vicarious calibrati...
In a previous study of Quaas et al. (2008) the radia-tive forcing by anthropogenic aerosol due to... more In a previous study of Quaas et al. (2008) the radia-tive forcing by anthropogenic aerosol due to aerosol–cloud interactions, RF aci , was obtained by a statistical analysis of satellite retrievals using a multilinear regression. Here we employ a new statistical approach to obtain the fitting parameters , determined using a nonlinear least square statistical approach for the relationship between planetary albedo and cloud properties and, further, for the relationship between cloud properties and aerosol optical depth. In order to verify the performance, the results from both statistical approaches (previous and present) were compared to the results from ra-diative transfer simulations over three regions for different seasons. We find that the results of the new statistical approach agree well with the simulated results both over land and ocean. The new statistical approach increases the correlation by 21–23 % and reduces the error compared to the previous approach.
Aerosol optical properties are analyzed for the first time over Desalpar (23.74°N, 70.69°E, 30 m ... more Aerosol optical properties are analyzed for the first time over Desalpar (23.74°N, 70.69°E, 30 m above mean sea level) a remote site in western India during October 2014 to August 2015. Spectral aerosol optical depth (AOD) measurements were performed using the CIMEL CE-318 automatic Sun/sky radiometer. The annual-averaged AOD500 and Ångström exponent (α440–870) values are found to be 0.43 ± 0.26 and 0.69 ± 0.39, respectively. On the seasonal basis, high AOD500 of 0.45 ± 0.30 and 0.61 ± 0.34 along with low α440–870 of 0.41 ± 0.27 and 0.41 ± 0.35 during spring (March–May) and summer (June–August), respectively, suggest the dominance of coarse-mode aerosols, while significant contribution from anthropogenic sources is observed in autumn (AOD500 = 0.47 ± 0.26, α440–870 = 1.02 ± 0.27). The volume size distribution and the spectral single-scattering albedo also confirm the presence of coarse-mode aerosols during March–August. An overall dominance of a mixed type of aerosols (~56%) mostly from October to February is found via the AOD500 vs α440–870 relationship, while marine aerosols contribute to ~18%. Spectral dependence of α and its second derivative (α′) are also used for studying the aerosol modification processes. The average direct aerosol radiative forcing (DARF) computed via the SBDART model is estimated to range from −27.08 W m−2 to −10.74 W m−2 at the top of the atmosphere, from −52.21 W m−2 to −21.71 W m−2 at the surface and from 10.97 W m−2 to 26.54 W m−2 within the atmosphere. This atmospheric forcing translates into heating rates of 0.31–0.75 K day−1. The aerosol properties and DARF are also examined for different trajectory clusters in order to identify the sources and to assess the influence of long-range transported aerosols over Desalpar.
Aerosol-cloud interaction is the subject of considerable scientific research, due to the importan... more Aerosol-cloud interaction is the subject of considerable scientific research, due to the importance of clouds in controlling climate. In the present study, three years (2011–2013) satellite observations are used to investigate the aerosol indirect effect (AIE) over Dehradun. The low values of Angstrom exponent (α) during March–July are attributed to the loading of dust-like coarse particles in the atmosphere, whereas the analysis of aerosol type and Spectral Radiation Transport Model for Aerosol species (SPRINTARS) simulated aerosol species variation supports the fact. Moderate Resolution Imaging Spectroradiometer (MODIS) derived AOD data are associated to the cloud product to examine the dust impact on properties of liquid cloud and ice cloud. The positive values of aerosol cloud interaction effect (ACI) for ice cloud during pre-monsoon (March–May) and monsoon (June–August) seasons reveal the significant impact of dust on ice clouds over Dehradun, which is maximum during May (~0.24 ± 0.05). The present study shows that ice cloud effective radius (ICER) decrease with AOD during dust period. The increase in ice water path (IWP) and ice cloud optical depth (ICOD) reveals the impact of dust on heterogeneous ice generation in low level clouds. However, there is no relation between dust and liquid water cloud during dust period. It is difficult to provide definite conclusions that the dust and cloud changes are driven by the same meteorological conditions. Cloud and the Earth's Radiant Energy System (CERES) derived flux data are used to examine the associated changes in TOA cloud radiative forcing. The diminution in effective size of ice crystal due to aerosol first indirect effect traps more longwave radiation and reflects more solar radiation. Both first and second indirect effects enhance cloud cooling, whereas the dust induced cloud warming is mainly the result of the semi-direct effect.
This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG... more This study is carried out as the post-launch calibration for visible (IMG-VIS) and shortwave (IMG-SWIR) bands of INSAT-3D imager and visible (SND-VIS) band of Indian National Satellite System (INSAT)-3D sounder over land site (Little Rann of Kutch (ROK), Gujarat) on five clear-sky days. This calibration activity is performed to account for the characterisation errors or undetermined post-launch changes in sensor spectral response. We had measured the surface reflectance and atmospheric variables at the site synchro-nising with the viewing and solar geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer (RT) code with the surface reflectance and atmospheric variables as well as spectral response function (SRF) of each channel. The uncertainties involved due to spatial variability of site and variation in aerosol type in calibration coefficients were also computed. MODIS Bidirectional Reflectance Distribution Function (BRDF) product is used to account the effect of surface anisotropy on TOA spectral radiance. Comparison between 2014 and 2015 vicarious calibration results, indicate that the INSAT-3D measured radiance are stable within 0.38%, 0.18% and 0.13% for IMG-VIS, IMG-SWIR and SND-VIS, respectively. 6SV simulated atmospherically corrected reflectances were found to match much better with the observed surface reflectance in the inverse mode for all three bands. Comparing these results with the previous year's analysis, there is no indication of major change in calibration coefficients for all three bands of INSAT-3D.
Dust storm, a natural hazard, has a direct impact on daily life for a short period. Dust storms a... more Dust storm, a natural hazard, has a direct impact on daily life for a short period. Dust storms are periodic events over India, especially in northern regions. This study has been carried out to investigate the dust impacts on the aerosol characteristics over Dehradun (DDN) during pre-monsoon (March–June), 2012 using ground measurements, satellite observations and model simulations. The measurements illustrate the distinct monthly impact on the aerosol properties with maximum dust loading during May (aerosol optical depth at 500 nm (AOD 500) = 0.72 ± 0.18) over DDN, which is confirmed with the Terra-MODIS (AOD 550 = 0.70 ± 0.19) measurements. The major dust loading was recorded in aerosol measurements during May at the station, which permitting to examine the influence of dust transports on the aerosol characteristics. Spectral variation of AOD and Angstrom exponent (α) values displayed day to day variation of aerosol during dust episodes. Analysis of aerosol types and seven-day back-trajectories reveal the transportation of desert dust during May over DDN. The Optical Properties of Aerosols and Clouds (OPAC) model was used to compute the aerosol optical properties (e.g., Single scattering albedo (SSA) and asymmetry parameter (g)) and size distribution. The high values of SSA and g are indicating the dust loading in the atmosphere during May. Aerosol volume concentration at the coarse mode (geometric mean radii (R V) = 2.89 ± 0.027 µm) is found to be increased in the May, whereas decrement has been observed in the finer mode (R V = 0.16 ± 0.006 µm). The aerosol direct radiative forcing (ARF) was computed using Santa Barbara Discrete Ordinate Atmospheric Radiative Transfer (SBDART) model in the shortwave (SW) region (0.25– 4.00 µm). The mean top of the atmosphere (TOA) and surface forcing come out to be –14.49 W m –2 and –53.29 W m –2 respectively in May. The mean net atmospheric radiative forcing (38.79 W m –2 maximum during May) corresponds to heating rate of ~1.06° K d –1 in the atmosphere.
Ground and satellite based measurements of spectral optical properties of aerosols have been carr... more Ground and satellite based measurements of spectral optical properties of aerosols have been carried out at Dehradun (DDN) in the Indo-Gangetic Plain (IGP) and Kavaratti (KVT) at Lakshadweep in southern Arabian Sea during pre-monsoon season (March– May) 2012. The measurements illustrate distinct seasonal impact on aerosol properties with maximum dust loading during May in conjunction with anthro-pogenic aerosols over DDN and marine aerosols over KVT. Aerosol optical depth (AOD) values have been observed maximum in May (0.72 0.03) over DDN and in April (0.77 0.05) over KVT. The high AOD at DDN during May is associated with low and high , means higher loading in May is associated with coarse mode aerosols, may be dust loading as evident from SSA and volume size distribution. Similarly, high AOD at KVT during March and April are associated with high and low , may be due to anthropogenic influence as evident from BT analysis as well as SSA and volume size distribution. However, influence of marine aerosols is also noticeable over KVT during May as indicated by the lower values of with high turbidity coefficient . Comparison between sunpho-tometer and MODIS AOD observations indicates good statistical agreement with the minimal error.
Ground based measurement of aerosol optical depth (AOD) and black carbon (BC) aerosols were carri... more Ground based measurement of aerosol optical depth (AOD) and black carbon (BC) aerosols were carried out over Dehradun during January to December 2007. The AOD values during winter (December-February) are low and found to be in the range of (0.08-0.38) than during summer (March-June) periods (0.32-0.62). The aerosol loading was observed to be high during summer period due to the long-range transportation of aerosol particles by air mass from the Thar Desert region to the observing site besides the biomass burning and frequent incidents of forest fire at local levels. The annual average BC concentration observed was found to be 4.3 + 0.62 µgm-3. Diurnal variation of BC shows a gradual build up in the morning hours between 0600 to 0900 local time and in evening from 1900 to 2200 hrs local time while low concentration is observed during day and night time. The analysis of traffic density measured in the city shows that it has direct influence on the BC concentration. BC concentration increases more than three times during morning and evening compared to afternoon and night hours. Seasonal variations of BC shows high concentration during winter dry season associated with the air masses predominantly coming from Indo-Gangetic plain rich in carbonaceous aerosols and minimum during monsoon season due to wash out. The BC concentration is found to have relationship with anthropogenic activities, boundary layer dynamics and biomass burning which has been observed by the MODIS fire data in and around the region. BC concentration were positive correlated with diurnal temperature range and negative correlated with rainfall and humidity. The values of aerosol optical depth and black carbon concentration over Dehradun have been compared with those reported from selected locations in India. INTRODUCTION Aerosols are important components of earth–atmosphere–ocean system. They affect climate through three primary mechanisms-direct radiative forcing (absorption and scattering of sun radiation), indirect radiative forcing (modifying the cloud properties thereby affecting albedo of clouds) and have indirect effect in the atmospheric chemistry by modifying the concentration of climate-influencing constituents (Schwartz et al., 1995) (such as GHG's). Aerosols enhances the back scattering of solar radiation and leading to negative radiative forcing while the absorbing black carbon (BC) aerosols leads to the positive effect. Black carbon aerosol, the optically absorbing part of the carbonaceous aerosols is the major anthropogenic component of atmospheric aerosol system. Black carbon is one of the important constituents of ambient particulate matter, which is emitted into the atmosphere as a by-product of combustion processes such as fossil fuels, vegetation burning, industrial effluents, motor vehicle and aircraft exhausts and are generally in the sub-micron region and considered as tracers of anthropogenic impact on environment. The increase in anthropogenic emission would increase in aerosol loading thereby reducing the incoming solar radiation reaching the ground surface. These effects influence regional aerosol radiative forcing (Haywood and Shine, 1997). It has been reported that one of the
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Papers by Piyushkumar N Patel
level) a remote site in western India during October 2014 to August 2015. Spectral aerosol optical depth (AOD)
measurements were performed using the CIMEL CE-318 automatic Sun/sky radiometer. The annual-averaged
AOD500 and Ångström exponent (α440–870) values are found to be 0.43 ± 0.26 and 0.69 ± 0.39, respectively.
On the seasonal basis, high AOD500 of 0.45 ± 0.30 and 0.61 ± 0.34 along with low α440–870 of 0.41 ± 0.27 and
0.41 ± 0.35 during spring (March–May) and summer (June–August), respectively, suggest the dominance of
coarse-mode aerosols, while significant contribution from anthropogenic sources is observed in autumn
(AOD500 = 0.47 ± 0.26, α440–870 = 1.02 ± 0.27). The volume size distribution and the spectral single-scattering
albedo also confirm the presence of coarse-mode aerosols during March–August. An overall dominance of a
mixed type of aerosols (~56%) mostly from October to February is found via the AOD500 vs α440–870 relationship,
while marine aerosols contribute to ~18%. Spectral dependence of α and its second derivative (α′) are also used
for studying the aerosol modification processes. The average direct aerosol radiative forcing (DARF) computed
via the SBDART model is estimated to range from −27.08 W m−2 to −10.74 W m−2 at the top of the atmosphere, from −52.21 W m−2 to −21.71 W m−2 at the surface and from 10.97 W m−2 to 26.54 W m−2 within the atmosphere. This atmospheric forcing translates into heating rates of 0.31–0.75 K day−1. The aerosol properties and DARF are also examined for different trajectory clusters in order to identify the sources and to assess the influence of long-range transported aerosols over Desalpar.
level) a remote site in western India during October 2014 to August 2015. Spectral aerosol optical depth (AOD)
measurements were performed using the CIMEL CE-318 automatic Sun/sky radiometer. The annual-averaged
AOD500 and Ångström exponent (α440–870) values are found to be 0.43 ± 0.26 and 0.69 ± 0.39, respectively.
On the seasonal basis, high AOD500 of 0.45 ± 0.30 and 0.61 ± 0.34 along with low α440–870 of 0.41 ± 0.27 and
0.41 ± 0.35 during spring (March–May) and summer (June–August), respectively, suggest the dominance of
coarse-mode aerosols, while significant contribution from anthropogenic sources is observed in autumn
(AOD500 = 0.47 ± 0.26, α440–870 = 1.02 ± 0.27). The volume size distribution and the spectral single-scattering
albedo also confirm the presence of coarse-mode aerosols during March–August. An overall dominance of a
mixed type of aerosols (~56%) mostly from October to February is found via the AOD500 vs α440–870 relationship,
while marine aerosols contribute to ~18%. Spectral dependence of α and its second derivative (α′) are also used
for studying the aerosol modification processes. The average direct aerosol radiative forcing (DARF) computed
via the SBDART model is estimated to range from −27.08 W m−2 to −10.74 W m−2 at the top of the atmosphere, from −52.21 W m−2 to −21.71 W m−2 at the surface and from 10.97 W m−2 to 26.54 W m−2 within the atmosphere. This atmospheric forcing translates into heating rates of 0.31–0.75 K day−1. The aerosol properties and DARF are also examined for different trajectory clusters in order to identify the sources and to assess the influence of long-range transported aerosols over Desalpar.