NOPR Collection:

Moment method analysis of metallic cylinder and truncated cone used in orbital satellites

Thu, 01 Jun 1995 00:00:00 GMT

Title: Moment method analysis of metallic cylinder and truncated cone used in orbital satellites Authors: Das, B N; Chakrabarty, S B; Mallick, A K Abstract: The paper presents an analysis for the evaluation of capacitance and charge distribution of metallic cylinder and truncated cone of finite length and isolated in free space using moment method formulation employing pulse and delta functions as basic function and testing function, respectively. The elements of the matrix to be inverted in the process of application of the moment method are found by diving the structure into sections of equal axial length which are further subdivided into curvilinear rectangles along the circumferential direction of each cylindrical section. The curvilinear rectangles are finally approximated by planer rectangles. Expression for the capacitance and charge distribution is derived in terms of the elements of the inverted matrix. Modifications of capacitance due to top and bottom flat surfaces is evaluated. Numerical data on these parameters are presented. Page(s): 151-157

Study of ionospheric scintillations near the crest of equatorial anomaly in India using digital data base

Thu, 01 Jun 1995 00:00:00 GMT

Title: Study of ionospheric scintillations near the crest of equatorial anomaly in India using digital data base Authors: Pathak, K N; Jivrajani, R D; Mathew, Boby; Joshi, H P; Iyer, K N Abstract: The ionospheric amplitude scintillations imposed on VHF signals transmitted from geostationary satellite FLEETSAT (73°E) were recorded at Rajkot sub-ionospheric dip lat. 15.3°N) near the crest of the equatorial anomaly in India using conventional analog recording during 1987-93. Also data were recorded using digital data acquisition system during the period August 1991 to March 1993. The latter data have been subjected to autocorrelation and power spectrum analysis. Parameters such as scintillation index S₄, fading rate, autocorrelation interval and spectral index have been derived from each 5-min data length satisfying certain selection criteria. Scintillation index S₄ is maximum (>1) around the generation phase at pre-midnight hours and decrease to ~0.6 as the night progresses. The fading rate also decreases from ~120 fades/min in the pre-midnight hours to ~20 fades/min in post-midnight hours. Spectra are relatively flat (spectral index ~1) during the generation phase of irregularities and steepen (spectral index ~3 to 5) towards the decay phase. Observations using the spaced receiver technique have enabled the determination of E-W velocity of the irregularities which together with the autocorrelograms yield the spatial correlation length. The spatial correlation length at this anomaly crest location is substantially smaller than that reported for magnetic equatorial location and comparable to that at another crest location, Ascension Island. Page(s): 138-150

A morphological study of VHF scintillations at Agra

Thu, 01 Jun 1995 00:00:00 GMT

Title: A morphological study of VHF scintillations at Agra Authors: Singh, Birbal Abstract: A morphological study of scintillations in the VHF signals at 244.16 MHz from satellite, FLEETSAT, has been made at Agra (geogr. Lat., 27.2°N; geogr. Long., 78°E) and reported in this paper. It is shown that the scintillations occurred at Agra mostly during nighttime, predominantly in pre-midnight hours, with peak-to-peak amplitude variation of less than 15 dB. The occurrence is highly increased during equinoxes and considerably reduced during summer. The activity is found to vary substantially during magnetically disturbed periods in the post- and pre-midnight hours of winter and summer. The daytime scintillations are slow and weak and occur rarely. The scintillation index for nighttime scintillation fluctuates between 20 and 45% from pre- to post-midnight hours in winter and equinoxes and falls smoothly below 10% in summer. Most of the present results are found to be similar to those at Varanasi (another station outside the anomaly zone), but differ markedly with those at other stations near and inside the zone. Page(s): 131-137

Some studies on post-sunset maximum of a long distance LF signal

Thu, 01 Jun 1995 00:00:00 GMT

Title: Some studies on post-sunset maximum of a long distance LF signal Authors: De, B K; Sarkar, S K Abstract: Disappearance of electrons in the D region of the ionosphere gives rise to post-sunset maximum (PSM) in the signal amplitude of 40 kHz radio wave propagated over a long distance from Sanwa (Japan) to Calcutta. It has been noticed that there is a time lag between PSM and ionospheric sunset. This time lag has been studied in relation to the position of the overhead sun. It has been found that in most of the geomagnetically active days PSMs are missing due to extra-ionization in the ionospheric D region. Page(s): 126-130