Aerosol optical depth, ozone and water vapor measurements over Gadanki, a tropical station in peninsular India

This paper reports the results of a study related to the optical and physical characteristics of columnar aerosols and variation in total column ozone (TCO) and precipitable water content (PWC) over Gadanki (13.45°N, 79.18°E), a tropical station in peninsular India, for the first time, using MICROTOPS-II (Microprocessor-based Total Ozone Portable Spectrometer), comprising of both sun photometer and ozonometer. Results show wavelength dependence of AOD, having mean value of �0.4 (± 0.09) at 500 nm optical channel. Daily mean aerosol size spectra shows, most of the time, power-law distribution. However, its diurnal variations show significant changes in aerosol size spectra modulated by a combination of both power-law and bi-modal distributions. To characterize AOD, the Angstrom parameters (i.e., a and β) were used. The day-to-day variations in TCO were found to be in fair agreement with that derived from TOMS satellite data for all the experimental days, having mean observed value of ~253 (± 8) DU over the station. Interestingly, an inverse relationship between TCO and AOD or PWC was observed over the station, on some times of the day, which could be attributed to the mixing of significant fraction of ozone with aerosol and water vapor-rich air mass. However, a significant positive correlation was observed between AOD and PWC

Aerosol characteristics during winter fog at Agra, North India

Simultaneous measurements on physical, chemical and optical properties of aerosols over a tropical semi-arid location, Agra in north India, were undertaken during December 2004. The average concentration of total suspended particulates (TSP) increased by about 1.4 times during intense foggy/hazy days. Concentrations of SO4 2-, NO3 -, NH4 + and Black Carbon (BC) aerosols increased by 4, 2, 3.5 and 1.7 times, respectively during that period. Aerosols were acidic during intense foggy/hazy days but the fog water showed alkaline nature, mainly due to the neutralizing capacity of NH4 aerosols. Trajectory analyses showed that air masses were predominantly from NW direction, which might be responsible for transport of BC from distant and surrounding local sources. Diurnal variation of BC on all days showed a morning and an evening peak that were related to domestic cooking and vehicular emissions, apart from boundary layer changes. OPAC (Optical properties of aerosols and clouds) model was used to compute the optical properties of aerosols. Both OPAC-derived and observed aerosol optical depth (AOD) values showed spectral variation with high loadings in the short wavelengths (<1 μm). AOD value at 0.5 μm wavelength was significantly high during intense foggy/hazy days (1.22) than during clear sky or less foggy/hazy days (0.63). OPAC-derived Single scattering albedo (SSA) was 0.84 during the observational period, indicating significant contribution of absorbing aerosols. However, the BC mass fraction to TSP increased by only 1 during intense foggy/hazy days and thereby did not show any impact on SSA during that period. A large increase was observed in the shortwave (SW) atmospheric (ATM) forcing during intense foggy/hazy days (+75.8 W/m2) than that during clear sky or less foggy/hazy days (+38 W/m2), mainly due to increase in absorbing aerosols. Whereas SW forcing at surface (SUF) increased from -40 W/m2 during clear sky or less foggy/hazy days to -76 W/m2 during intense foggy/hazy days, mainly due to the scattering aerosols like SO4 2-

Correlative measurements of aerosol optical depth and size distribution around INDOEX-FFP 98 from multi-spectral solar radiometry

Spectral aerosol optical depth measurements by means of ground-based solar radiometry have been made at the Indian Institute of Tropical Meteorology, Pune, a continental urban station in India, as part of the INDOEX-FFP 98 during 17 February through 31 March, 1998. The aerosol optical depths and corresponding size distributions observed with both a multi-channel radiometer (sun-photometer) and a spectroradiometer agree well and show marked variations during the experimental period. The day-to-day variation in the aerosol optical depth at 0.50 μm indicates an increasing trend. The results of a comparative study made between the continental urban and coastal aerosol characteristics using the sun-photometric observations carried out around the INDOEX-FFP 98 are also presented

Remote sensing of spectral signatures of tropospheric aerosols

With the launch of the German Aerospace Agency's (DLR) Modular Opto-electronic Scanner (MOS) sensor on board the Indian Remote Sensing satellite (IRS-P3) launched by the Indian Space Research Organization (ISRO) in March 1996, 13 channel multi-spectral data in the range of 408 to 1010nm at high radiometric resolution, precision, and with narrow spectral bands have been available for a variety of land, atmospheric and oceanic studies. We found that these data are best for validation of radiative transfer model and the corresponding code developed by one of the authors at Space Applications Centre, and called ATMRAD (abbreviated for ATMospheric RADiation). Once this model/code is validated, it can be used for retrieving information on tropospheric aerosols over ocean or land. This paper deals with two clear objectives, viz., (1) Validation of ATMRAD model/code using MOS data and synchronously measured atmospheric data, and if found performing well, then to (2) derive relationship between MOS radiances and Aerosol Optical Thickness (AOT). The data validation procedure essentially involves near-synchronous measurements of columnar aerosol optical thickness and altitude profiles of aerosol concentration using ground-based multi-filter solar radiometers and Argon-ion Lidar, respectively and computation of the top-of-the-atmosphere (TOA) radiances from a low reflecting target (near clear water reservoir in the present study) using the ATMRAD model. The results show that the model performance is satisfactory and a relationship between the spectral parameters of MOS radiances and aerosol optical thickness can be established. In this communication, we present the details of the experiments conducted, database, validation of the ATMRAD model and development of the relationship between AOT and MOS radiance

On-demand fuzzy clustering and ant-colony optimisation based mobile data collection in wireless sensor network

In a wireless sensor network (WSN), sensor nodes collect data from the environment and transfer this data to an end user through multi-hop communication. This results in high energy dissipation of the devices. Thus, balancing of energy consumption is a major concern in such kind of network. Appropriate cluster head (CH) selection may provide to be an efficient way to reduce the energy dissipation and prolonging the network lifetime in WSN. This paper has adopted the concept of fuzzy if-then rules to choose the cluster head based on certain fuzzy descriptors. To optimise the fuzzy membership functions, Particle Swarm Optimisation (PSO) has been used to improve their ranges. Moreover, recent study has confirmed that the introduction of a mobile collector in a network which collects data through short-range communications also aids in high energy conservation. In this work, the network is divided into clusters and a mobile collector starts from the static sink or base station and moves through each of these clusters and collect data from the chosen cluster heads in a single-hop fashion. Mobility based on Ant-Colony Optimisation (ACO) has already proven to be an efficient method which is utilised in this work. Additionally, instead of performing clustering in every round, CH is selected on demand. The performance of the proposed algorithm has been compared with some existing clustering algorithms. Simulation results show that the proposed protocol is more energy-efficient and provides better packet delivery ratio as compared to the existing protocols for data collection obtained through Matlab Simulations

Mitigating risk in ecommerce transactions: perceptions of information credibility and the role of user-generated ratings in product quality and purchase intention

Although extremely popular, electronic commerce environments often lack information that has traditionally served to ensure trust among exchange partners. Digital technologies, however, have created new forms of "electronic word-of-mouth," which offer new potential for gathering credible information that guides consumer behaviors. We conducted a nationally representative survey and a focused experiment to assess how individuals perceive the credibility of online commercial information, particularly as compared to information available through more traditional channels, and to evaluate the specific aspects of ratings information that affect people's attitudes toward ecommerce. Survey results show that consumers rely heavily on web-based information as compared to other channels, and that ratings information is critical in the evaluation of the credibility of online commercial information. Experimental results indicate that ratings are positively associated with perceptions of product quality and purchase intention, but that people attend to average product ratings, but not to the number of ratings or to the combination of the average and the number of ratings together. Thus suggests that in spite of valuing the web and ratings as sources of commercial information, people use ratings information suboptimally by potentially privileging small numbers of ratings that could be idiosyncratic. In addition, product quality is shown to mediate the relationship between user ratings and purchase intention. The practical and theoretical implications of these findings are considered for ecommerce scholars, consumers, and vendors. © 2014 Springer Science+Business Media New York

Echo duration and diffusion coefficient measurements using meteor wind radar

The Meteor Wind Radar at Waltair (17°43′N, 83°18′E), India, was operated during June–July 1979 to study the echo durations and diffusion coefficients of underdense meteor trails. These measurements have also been used to evaluate the elevation angles of the specular reflection points. The most probable echo duration and elevation angle for the present system are found to be 60 ms and 23°, respectively. The values of measured diffusion coefficients (log10 D) are found to vary between 4.6 and 5.5 cm2 s−1. The diurnal variation of the diffusion coefficient showed a broad maximum during morning hours and a broad minimum during evening hours. The results are compared with the measurements at other station