"Volcanoes are not laid out for convenience," said Peter Francis, professor of volcanology in The Open University's department of earth sciences. To provide greater safety in ground-based measurements, Francis' team has used solar occultation spectroscopy to remotely analyze plume gases with a Fourier transform infrared (FTIR) spectrometer.
By using the sun as the IR source, it also obtains higher signal-to-noise ratios for certain constituents, he said. The only geometric constraint is that researchers must view the sun through the plume, which enables them to employ a variety of measurement configurations.
The team applied the technique in measurements at low sun angles on the Caribbean island of Montserrat and in cases where thin clouds partially obscure the sun. High elevations without interference from water vapor or falling ash are prime locations for the solar method, Francis said.
The researchers hope that several planned improvements to the FTIR system will allow greater use of the solar occultation method in volcanic plume analysis.