  X-rays and gamma-rays from astronomical sources such as solar flares are
mostly absorbed by the Earth's atmosphere. Resulting electron-ion production
rate as a function of height depends on the intensity and wavelength of the
injected spectrum and therefore the effects vary from one source to another. In
other words, the ion density vs. altitude profile has the imprint of the
incident photon spectrum. In this paper, we investigate whether we can invert
the problem uniquely by deconvolution of the VLF amplitude signal to obtain the
details of the injected spectrum. We find that it is possible to do this up to
a certain accuracy. Our method is useful to carry out a similar exercise to
infer the spectra of more energetic events such as the Gamma Ray Bursts (GRBs),
Soft Gamma Ray Repeaters (SGRs) etc. by probing even the lower part of the
atmosphere. We thus show that to certain extent, the Earth's atmosphere could
be used as a gigantic detector of relatively strong events.
