K K Singh
Articles written in Journal of Earth System Science
Volume 117 Issue 3 June 2008 pp 219-225
In this paper,we report observations of unusual whistlers recorded at Jammu (geomag.lat.= 22° 26′N; 𝐿 =1.17), India on March 8, 1999 during the daytime. They are interpreted as one-hop ducted whistlers having propagated along higher 𝐿 -values in closely spaced narrow ducts from the opposite hemispheres. After leakage from the duct, the waves might have propagated in the earthionosphere waveguide towards the equator in surface mode.Tentative explanation of the dynamic spectra of these events is brieﬂy presented.
Volume 118 Issue 1 February 2009 pp 11-26
The inﬂuence of topographic effects in optical satellite imagery is not investigated very extensively in the Himalayan terrain.The topographic variability causes a problem of differential illumination due to steep and varying slopes in rugged Himalayan terrain. Therefore,topographic corrections are essential for qualitative and quantitative analysis of snow cover applications.The present paper discusses the implementation of different topographic correction models on AWiFS sensor onboard IRS P6 satellite images and the qualitative and quantitative comparative analysis in detail.Both the Lambertian and non-Lambertian assumptions have been considered in the present analysis with the aim to explore best suitable empirical model for rugged terrain.The main topographic methods implemented are:
Civco ’s modi ﬁed version of cosine correction
two-stage normalization and
slope matching technique.
Lambertian assumptions are found to be very unrealistic over Himalayan terrain as these lead to either underestimation or overestimation of physical parameters signiﬁcantly both on sunlit slopes as well as the slopes away from the Sun.This problem is overcome by considering non-Lambertian assumption.Minneart constant and C-correction coefficients for all AWiFS satellite bands are estimated using regression analysis.All the results due to topographic effects are investigated qualitatively and quantitatively using four criteria namely visual analysis,validation with ﬁeld measurements (
Volume 118 Issue 3 June 2009 pp 209-216
This paper reports quasi-periodic pulsing hiss emissions recorded during daytime in the frequency range of 50 Hz –15 kHz at low latitude station Jammu (geomag.lat.=22° 26′N; 𝐿 =1.17). It is noted that pulsing VLF emissions are a rare phenomena at low latitudes.The various spectrograms of pulsing VLF hiss emissions presented in this paper clearly show band limited spectrums regularly pulsing with almost equal period of the order of few seconds in the frequency range of ∼3-8 kHz. Generation and propagation mechanism of these emissions are brieﬂy discussed.