Monitoring:  | Gas | Ground Deformation | Hydrologic | Remote Sensing | Seismicity |

Airborne detection of SO₂ gas using a
FTIR spectrometer

The volcanic gas plume from the Pu`u `O`o cinder-and-spatter cone (right) provided the ideal testing ground for measuring SO2 with a prototype Fourier transform infrared spectrometer (FTIR) made to USGS specifications. The FTIR was mounted in an airplane configured for sampling outside air and then flown through the plume about 1 km downwind from the Pu`u `O`o vent. Eight traverses were made through the plume at different elevations (see sketch of ladder traverses). A COSPEC was used simultaneously to check the FTIR results.

View of Pu`u `O`o is toward the southwest Photograph by K.A. McGee on September 19, 1995

Sketch of the plume downwind from Pu`u `O`o on 19 September 1995 showing the concentration (ppm) of sulfur dioxide gas measured by the prototype FTIR. The view is upwind toward Pu`u `O`o into the page. Winds were from the northeast at about 20 km/hr. An emission rate of 2,160 tonnes/day of SO2 was calculated from these measurements. This rate agrees closely with measurements made by a COSPEC, the traditional method for measuring volcanic SO2 emission rates.

Reference

McGee, K.A., and Gerlach, T.M., 1998, Airborne volcanic plume measurements using a FTIR spectrometer, Kilauea volcano, Hawaii: Geophysical Research Letters, vol. 25, n. 5, p. 615-618.

Methods of monitoring volcanic gases

• Measuring gas-emission rates in volcanic plumes
• Direct gas sampling and laboratory analysis
• Continuous on-site gas monitoring
• Soil-efflux measurements