We have studied the electric E⃗ and magnetic B⃗ fields by displaying the arrival directions through a 2D image named spectral- directionalogram (SD-gram). This technique maps electromagnetic field directions in time and frequency space. We tested the method through modeling experiments. An exclusive case is explained theoretically. In addition, method is applied on the two field data sets. One was acquired on the land and other in the ocean. The land data, is studied for the 50 Hz and har- monics. The frequencies are continuous in the direction during a time range, while splittings are observed during the other. In the second example, we have used marine electromagnetic data. The spectrogram suggests two anomalies, one close to 1 Hz and the other having a broad spectral range between 1 to 0.08 Hz. We hypothesize two possible causative sources, microseisms and degassing of a mud volcano. Out of these two choices, one can be easily falsified using the SD-gram. These examples highlight the usefulness of the technique in the data analysis. Moreover, the electromagnetic noise caused by the ocean waves have different spectral damping characteristics compared to those of plane waves. Therefore, we are proposing a new damping relation for the ocean, where dispersion is a dominant case.
Citation: Kaushalendra Mangal Bhatt and Ajay Manglik, 2021. Marine Geophysical Research, 42:32 https://doi.org/10.1007/s11001-021-09454-w