A numerical model has been described to estimate the effective thermal conductivity of moist soils, considering the effective continuous medium approximation and taking all possible interactions. Numerical solutions of the exact formulations are presented. Experimental measurements have been carried out for the thermal conductivity of dune sand at different moisture contents employing the method of unsteady state line source. The predicted and measured values show reasonable agreement.

An experimental study has been done to investigate the heat conduction and moisture distribution through the different layers of unsaturated soil. The soil is taken in the form of cylindrical columns in vertical and horizontal positions. The two ends of the cylindrical column were maintained at different constant temperature. The effective thermal conductivity was measured by dynamical method after achieving steady state. The distribution of moisture in the soil column was determined by gravimetric technique. The effective thermal conductivity (ETC) has also been predicted by temperature dependent model developed by Singhet al (1988). A close agreement has been found in experimental and predicted values of ETC.

The matched filtering technique is based on the digital-construction of theoretical whistlers and their comparison with observed whistlers. The parameters estimated from the theoretical and experimental whistler curves are matched to have higher accuracy using digital filters. This yields a resolution ten times better in the time domain. We have tested the applicability of this technique for the analysis of whistlers recorded at Varanasi. It is found that the whistlers have propagated along L>2 and have wave normal angles after exiting from the ionosphere such that they propagate towards equator in the earth-ionosphere wave-guide. High-resolution analysis shows the presence of fine structures present in the dynamic spectrum. An effort is made to interpret the results.

Recently, we have succeeded in recording VLF emissions at the Indian Antarctic station, Maitri (geom. lat. 62°S, geom. long. 57.23°E,L = 45) using a T-type antenna, pre/main amplifiers and digital audio tape recorder. VLF hiss in the frequency ranges 11–13 kHz and 13–14.5 kHz and some riser-type emissions in the frequency range 3–5 kHz and magnetospheric lines at about 6.2, 8.0 and 9.2 kHz are reported for the first time. The generation and propagation mechanism of these emissions are discussed briefly.