http://nopr.niscpr.res.in/handle/123456789/25573 2026-10-10T12:25:35Z http://nopr.niscpr.res.in/handle/123456789/25888 Title: Characteristics of the observed low latitude very low frequency emission periods and whistler-mode group delays at Jammu Authors: Lalmani; Kumar, Rajou; Singh, Rajesh; Singh, Birbal Abstract: First observations on the relationship between whistlers and periodic very low frequency (VLF) emissions observed at low latitude ground station Jammu (geomagn. lat., 22° 26<i>'</i> N; <i>L </i>= 1.17) are presented. The results have been discussed in the present paper. To explain the results it is proposed that the periodic VLF emissions are generated near the equatorial region at <i>L ~ </i>1.2 as a result of interaction between trapped energetic particles and one-hop whistlers under cyclotron resonance mechanism and propagated to the ground station Jammu in nonducted mode of whistler propagation. Page(s): 214-216 2001-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/25887 Title: Ionospheric electron content near anomaly crest as precursor of earthquake Authors: Devi, M; Barman, M K; Barbara, A K; Depueva, A Abstract: Ionospheric electron content (IEC) values, derived from Faraday rotations of VHF radio beacons from satellites and recorded at an equatorial anomaly crest station, Guwahati (lat.26.2° N, long.91.75°E; and situated at a seismically active zone of east Himalayas), have been examined to see if these data could be used as precursor of earthquake. The earthquake events are so selected that the epicentres lie within 12°-30° N and 81°- 120^oE. The paper analyses IEC variations during and prior to an earthquake event, in relation to epicentric position. Page(s): 209-213 2001-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/25886 Title: Triangular microstrip stacked antenna for dual band operation Authors: Vasistha, Prashant; Vishvakarma, Babau R Abstract: Experimental investigations conducted on triangular microstrip stacked antenna (TMSSA) to achieve dual band operation by optimizing the number of elements reveal that TMSSA attains the maximum -10 dB return-loss band of 688.6 MHz for (1+3) structure for second resonance. The air gap spacing of 2.5 mm in (1+1) structure improved -10 dB return-loss (RL) band by 612.14 MHz as compared to 242.3 MHz for zero spacing in first resonance (<i>f</i>_rl)<i>. </i>It is also observed that -10 dB return-loss band depends heavily on the angular rotation (non-alignment) in the (1+1) structure. Page(s): 205-208 2001-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/25885 Title: Response of microwave scattering from crop (wheat) and crop covered soil moisture for remote sensing Authors: Singh, D; Sharan, S K; Singh, K P Abstract: The present study investigates the potential use of active microwave observations at 9.5 GHz frequency of X-band to monitor soil moisture and vegetation leaf area index (LAI) over a wheat cover for remote sensing. Using an X-band (9.5 GHz) scatterometer, measurements have been made out for different growth stage of crop (wheat). The leaf area index (LAI) is an important parameter for understanding the crop characteristics. Here an attempt has been made to highlight the effect of crop (wheat) LAI and crop covered soil moisture (<i>m</i>_g) on microwave scattering. Using simple scattering model, an empirical relation has been developed for observing the LAI and <i>m</i>_g<i> </i>effect on scattering coefficient. The angular and polarization dependence of scattering coefficient on crop LAI and crop covered soil moisture has been investigated, which indicates that, when incidence angle is less than 30°, the crop (wheat) covered soil moisture is well observed, whereas when the incidence angle is greater than 30°, crop effect is more dominant at 9.5 GHz<i>. </i>The VV-polarization is more sensitive to sense the crop effect than HH-polarization. This type of study is helpful to make the algorithm for air- or space-borne data to access the crop parameters and crop covered soil moisture. All the data can also be used as reference data for space-borne sensors. Page(s): 198-204 2001-08-01T00:00:00Z