Background and History

March 2008

The Hawaiian Volcano Observatory (HVO) has a long history of sulfur dioxide (SO2) emission rate measurements dating back to 1975, with a regular effort commencing in 1979. These measurements were made primarily with the ultraviolet (UV) Correlation Spectrometer (COSPEC) in vehicle-based traverses, supplemented by tripod-mounted measurements. The data were reduced by hand.

Beginning in 2001, collaboration between researchers at the Hawaii Institute of Geophysics and Planetology (HIGP) and the gas geochemistry researchers of HVO began, initially as part of a NASA Earth Observing System (EOS) Interdisciplinary Science program. During this collaboration, HIGP personnel developed a new miniaturized UV spectrometer system, the FLYSPEC, which is significantly smaller, lighter, and more portable than existing remote sensing instruments, including not only the COSPEC, but FTIR and standard DOAS systems. The FLYSPEC is mechanically simpler than these other instruments, incorporates real-time GPS, automated calibration, is significantly more rugged, and can be produced at ~10% of the cost of the COSPEC. The principle of operation involves measurement of the scattered solar ultraviolet energy of specific wavelengths absorbed in proportion to a gas concentration and plume thickness, yielding a concentration-pathlength (ppm-m). The measured absorption is automatically calibrated against the absorption of internal gas calibration reference cells of known concentration. In a simplified manner, the product of the integrated absorbance profile and gas plume speed yields the emission rate of the source. (Stoiber et al., 1983)

A series of collaborative validation measurements were made during 2002 - 2003, comparing SO2 emission rate results derived from data collected simultaneously with the both the COSPEC and the FLYSPEC (Horton et al., 2006a). With refinement in both hardware and data acquisition and reduction software, the FLYSPEC was tuned to be user-friendly, fast, and convenient. In 2004, HVO continued to cross-compare the two instruments running side-by-side for 8 months with a resulting r2 = 0.994 between the data sets (Elias and Sutton, 2007). These extensive validation tests have shown that the FLYSPEC data are reliable and virtually identical to those obtained from COSPEC. The FLYSPEC has proven capable of measuring SO2 emission rates of from a few tonnes per day to thousands of tonnes per day at detection limits as low as 1.5-4 ppm-m. In September 2004, the FLYSPEC effectively replaced the COSPEC at HVO. In 2006, a U.S. Utility Patent was issued to the University of Hawaii for FLYSPEC (Horton et al., 2006b).


Elias, T. and A.J. Sutton, 2007, Sulfur dioxide emission rates from Kilauea Volcano, Hawaii, an update: 2002-2006: U.S. Geological Survey Open-File Report 2007-1114. - (PDF)

Horton, K. A., G. Williams-Jones, H. Garbeil, T. Elias, A. J. Sutton, P. Mouginnis-Mark, J. N. Porter, S. Clegg. Real-time measurement of volcanic SO2 emissions: Validation of a new UV correlation spectrometer (FLYSPEC), Bull. Volc. 68: 4, 323-327, 2006a, DOI 10.1007/s00445-005-0014-9. - (PDF)

Horton, K.A., J. Porter, P. Mouginis-Mark, C. Oppenheimer, H. Garbeil, 2006b, Apparatus for Measuring Radiation and Method of Use (FLYSPEC), U.S. Utility Patent No. 7,148,488.

Stoiber, R.E., L.L. Malinconico, S.N. Williams, 1983, Use of the correlation spectrometer at volcanoes. In: Tazieff H, Sabroux JC (eds) Forecasting Volcanic Events. Elsevier, New York, p. 424-444.