NOPR Collection:

Retrieval of water vapour profiles from radio occultation refractivity using artificial neural network

2014-01-02T16:50:49Z

Title: Retrieval of water vapour profiles from radio occultation refractivity using artificial neural network Authors: Shyam, Abhineet; Gohil, B S; Basu, Sujit Abstract: Artificial neural network (ANN) technique has been used to derive water vapour pressure profiles in the troposphere from radio occultation data over India and adjoining region. A fully connected three-layer network, with one hidden layer, has been constructed and standard back propagation algorithm has been used to train the network. While month, latitude and vertical profile of refractivity/bending angle constitute the input vector, the water vapour partial pressure profile forms the output vector. Only the moisture-laden summer monsoon months of June, July, August and September of 2010 have been considered for developing the retrieval algorithm. There are 2120 input and output pairs, out of which 1696 pairs form the training set while the remaining pairs constitute the validation set. The retrieved profiles of water vapour pressures in the validation set have been compared with the corresponding COSMIC operational products of water vapour pressure profiles. The effectiveness of the algorithm is apparent from this comparison and also from the vertical profiles of bias and root mean square error (RMSE). The statistics show better performance of the algorithm with refractivity as one of the inputs than with bending angle. The RMSE in water vapour retrieval from refractivity is within 1.5-2 hPa compared to markedly higher values of 6 hPa when derived from bending angle. Additionally, the algorithm has also been tested in an independent year 2009 and the performance of the refractivity based retrieval has been found to be highly consistent in the year 2010, with RMSE within 1.5 hPa. Page(s): 411-419

Assessment of electromagnetic radiation for second and third generation frequency spectrum on human body

2013-12-23T16:46:12Z

Title: Assessment of electromagnetic radiation for second and third generation frequency spectrum on human body Authors: Sharma, Pragati; Gautam, A K; Kumar, Sandeep Abstract: The rapid diffusion of wireless communication systems such as mobile phones has caused an increased concern for the potential effects on human health deriving from exposure to electromagnetic fields emitted by antennas and base stations of these systems. A number of studies have been conducted on the topic of electromagnetic field effects over human body. All earlier studies were centered on the second generation (2G) global system for mobile communication (GSM). Now, third generation (3G) mobiles and towers have been launched in the market, therefore, it is high time to calculate the radiation effect of increased frequency of 3G system over human body. In this paper, the specific absorption rate (SAR) value for skin (dry and wet) tissues of human body have been evaluated at 900, 1800 and 2140 MHz frequency bands. The first two frequencies represent the second generation (2G) and the third frequency represents the third generation (3G), respectively. The skin exposure due to base transceiver station (BTS) is calculated through SAR up to a distance of 3.5 mm inside skin for these frequencies. It has been found that values of SAR for electromagnetic radiation due to 2G and 3G frequency spectrums are very highly distributed near the source of radiation (BTS) and SAR have more effect on skin as one moves towards higher frequency band. Page(s): 425-428

Comparison of SMOS soil moisture/brightness temperatures for morning and evening passes

2013-12-23T16:46:04Z

Title: Comparison of SMOS soil moisture/brightness temperatures for morning and evening passes Authors: Calla, O P N; Sharma, Rahul; Gadri, Kishan Lal; Kalla, Abhishek; Agrahari, Sunil Kumar; Rathore, Gaurav Abstract: Soil moisture is an essential element, which controls the land-atmospheric system and thus, its continuous monitoring is extremely important. Regular monitoring of spatio-temporal variability of surface soil moisture can be done using microwave remote sensing techniques, as there is high contrast in dielectric properties of pure dry soil (2-3) and pure water (80) at microwave frequencies. Variation in surface soil moisture is not only affected by precipitation, evaporation and transpiration, but often groundwater and root zone moisture also play an important role. In the present paper, surface soil moisture data from Soil Moisture and Ocean Salinity (SMOS) satellite is used to analyse the changes in surface soil moisture from evening to next or following morning (6.00 PM and 6.00 AM) in an arid region of Rajasthan, India. An increase in surface soil moisture is observed for maximum data from evening to following morning. The same trends were also verified using polarization index values. Page(s): 420-424

Effects of backscattering enhancement considering multiple scattering in rain on MMW radar performance

2013-12-23T16:45:58Z

Title: Effects of backscattering enhancement considering multiple scattering in rain on MMW radar performance Authors: Yang, Rui-Ke; Li, Li; Ma, Hui-Hui Abstract: The theory of the second order backscattering enhancement in discrete random medium is discussed in this paper. The effects of rainfall on millimeter wave (MMW) radar performance are analysed based on Mie theory, Monte Carlo (MC) simulation and backscattering enhancement theory, at 35 and 95 GHz, respectively. The rain attenuation considering the raindrops multiple scattering is introduced into the estimation of the signal to clutter ratios (S/C) and the clutter to noise ratios (C/N) for MMW radar. The S/C and C/N are calculated by means of the backscattering enhancement, Mie theory and MC simulation method, respectively under the condition of rain environment. The results show that the S/C obtained by backscattering enhancement theory is smaller than the results by Mie and MC. The C/N by backscattering enhancement is greater than the results by other. The Mie and MC methods do not consider backscatter enhancement, underestimate the effect of raindrops scattering on radar performance. Hence, it is shown that the attenuation and backscattering enhancement induced by raindrops multiple scattering are necessarily taken into account for the performance estimation of MMW radar operating in heavy rainfall environment. Page(s): 404-410