NOPR Collection:

Estimation of scattering coefficient of dry and wet soil with different moisture content at microwave frequencies

2016-07-20T04:38:07Z

Title: Estimation of scattering coefficient of dry and wet soil with different moisture content at microwave frequencies Authors: Calla, O P N; Hannan, I Abstract: Microwave backscattering of the soil depends on its dielectric constant, which varies with change in the moisture content of the soil. The knowledge of the variability of the soil moisture is important for agriculture. With the database of the dielectric constant of a typical soil of Rajasthan, the computation of the scattering coefficients has been carried out using the perturbation model. The database of the estimated scattering coefficient at microwave frequencies (2-20 GHz) for dry and wet soil with different moisture contents has been generated. This will be useful for microwave remote sensing of soil, which will provide additional input for agriculture. Page(s): 106-111

An interlaced phased array antenna for atmospheric radars

2016-07-20T04:37:25Z

Title: An interlaced phased array antenna for atmospheric radars Authors: Janardhanan, K V; Mukundan, K K; Shenoy, K S V; Reddy, C A Abstract: The paper describes the design, construction details and test results of a 4×15 phased array Yagi antenna capable of producing three switchable beam orientations in a single plane. The antenna operates at a fixed frequency of 54.95 MHz and is useful for atmospheric studies. The array makes use of the 'interlaced phased array (IPA)’ concept to reduce the number of feed points and phase shifters, resulting in considerable reduction in cost and complexity of the array antenna. The 4×15 array was constructed using four-element Yagi-Uda antennas and was fed using a combination of co-axial and open-wire transmission lines. The performance of the antenna was qualitatively checked using the electrojet as a target. Moreover, the beam orientations and beamwidths of the antenna were verified using the sun as a radio source when it transitted over the beams. The performance parameters of the antenna were found to be very close to those computed theoretically. Page(s): 98-105

Vertical velocity, horizontal divergence and turbulence associated with tropical mesoscale convective system

2016-07-20T04:36:32Z

Title: Vertical velocity, horizontal divergence and turbulence associated with tropical mesoscale convective system Authors: Rao, D Narayana; Singh, H Randhir; Rao, S Vijaya Bhaskara Abstract: The MST radars have been used to measure directly the vertical motions above the radar site. Vertical velocity profiles and horizontal divergence/convergence derived from the vertical velocity using the mass continuity equation as well as eddy dissipation rate estimated under strong-to-moderate convection period are presented in the paper. Data obtained from the Indian MST radar located at Gadanki(13.5^oN, 79.8°E) have been used. The height range of the study is from 4 km to 20 km. The aim of the present study is to calculate the horizontal divergence from the vertical velocity and then to find the extent of the enhancement in the vertical velocity and horizontal divergence as well as turbulence distribution during the well developed tropical mesoscale disturbances. Strong enhancement is observed in the vertical velocity and the horizontal divergence/convergence. Maximum turbulence has been observed near the top of the cloud and above. Eddy dissipation rate of the order of 0.007m²s^-3 has also been observed. Page(s): 91-97

HF backscatter radar at the magnetic equator : System details and preliminary results

2016-07-20T04:35:54Z

Title: HF backscatter radar at the magnetic equator : System details and preliminary results Authors: Janardhanan, K V; Rao, D Ramakrishna; Viswanathan, K S; Murthy, B V Krishna; Shenoy, K S V; Mohankumar, S V; Kamath, K P; Mukundan, K K; Sajitha, G; Shajahan, M; Ayyappan, C Abstract: A phase coherent, pulsed, monostatic and moderately high power HF Doppler radar, operating at 18 and 9 MHz has been installed at the magnetic equatorial station, Trivandrum (8.5°N, 77°E; dip 0.5°N), India. It is a powerful tool to study the plasma instability processes responsible for the generation of equatorial electrojet (EEJ) and equatorial spread-F (ESF) irregularities. A novelty in the radar system is the usage of the same phased array antenna at the two harmonically related frequencies of 18 and 9 MHz. The radar employs Doppler beam swinging (DBS) technique with beam orientations of vertical and ±30° off zenith in the E-W plane, providing the unique capability of obtaining both zonal and vertical drifts of the ionospheric irregularities. The radar is also capable of providing zonal wind information in the region of 80-95 km. The new radar has opened up the possibilities of investigating different aspects of EEJ, like the E-W spectral asymmetry, diurnal pattern of the electric field and the effect of small scale plasma turbulence on the large scale EEJ altitude structure. In this paper the detailed system description, data processing scheme and some preliminary results obtained using the radar at 18 MHz are presented. Page(s): 77-90