NOPR Collection:

Study on the update rate of correction message to reduce SA effect in DGPS mode

Thu, 01 Apr 1999 00:00:00 GMT

Title: Study on the update rate of correction message to reduce SA effect in DGPS mode Authors: Banerjee, P; Bose, Anindya; Mukherjee, Somik; (Bose), A Guha; Mathur, B S Abstract: The differential global positioning system (DGPS) is a typical use of the GPS, where the errors in measurement using GPS are calculated at a surveyed location and transmitted to the remote users within some specific geographic distance. The error due to the selective availability (SA), which otherwise cannot be removed also gets cancelled with the use of DGPS. The update rate of this correction message to the users is one of the factors governing the achievable accuracy of DGPS. This paper shows that the correction message remains valid only up to 5s to achieve high accuracy level in DGPS mode. Page(s): 84-86

Role of field aligned currents and parallel electric field on the generation of whistler mode instability in the earth's magnetosphere

Thu, 01 Apr 1999 00:00:00 GMT

Title: Role of field aligned currents and parallel electric field on the generation of whistler mode instability in the earth's magnetosphere Authors: Maru, Harsha; Kumar, Sushil; Gwal, A K Abstract: Dispersion relation for the whistler mode waves in an anisotropic bi-Maxwellian magnetoplasma in presence of field aligned currents and parallel electric field has been reformulated to study their effects on whistler mode waves. The results show that waves grow in amplitude for both parallel electric field and field aligned currents. The effect of electric field is pronounced towards lower frequency spectrum, whereas the effect of field aligned currents is more towards higher frequency spectrum. This study is significant to express their effects on different types of wave phenomena and their amplification. Page(s): 95-102

Propagation of VLF electromagnetic waves penetrating the lower ionosphere

Thu, 01 Apr 1999 00:00:00 GMT

Title: Propagation of VLF electromagnetic waves penetrating the lower ionosphere Authors: Kai, Li; Weiyan, Pan Abstract: Propagation of VLF electromagnetic waves penetrating the lower ionosphere from above to below is analyzed. A two-dimensional Fourier transformation is employed to compute the effect on propagation of VLF electromagnetic waves by the lower ionosphere. The formula of the magnetic field on the sea surface generated by the space borne transmitter and antenna has been obtained. Page(s): 87-94

Derivation of vertical aerosol profiles in lower stratosphere and upper troposphere using twilight photometry

Thu, 01 Apr 1999 00:00:00 GMT

Title: Derivation of vertical aerosol profiles in lower stratosphere and upper troposphere using twilight photometry Authors: Nighut, D N; Londhe, A L; Jadhav, D B Abstract: A photometer has been designed and developed for observation of the zenith sky illumination during the twilight period to monitor the vertical profile of aerosols. A red gelatin filter centered at 700 mm (50 nm half bandwidth) and RCA 6199 photomultiplier tube were selected for the photometer. The experimental set-up and method of data analysis to derive vertical profile of atmospheric aerosols have been presented. The observations were carried out at tropical location Pathardi(19^o 9'N, 75^o 10' E) during the period 1 Jan. 1993 - 31 Dec. 1994. The intensity parameter, -(Idh)^-1dI, was determined and its changes attributed to the variation in the structure of the atmosphere resulted due to changes in aerosol density. An algorithm is developed for the estimation of vertical profile of aerosols in terms of number density. The estimated vertical profile of aerosols compares well with other methods of observations. Page(s): 75-83