Impact of atmospheric water vapor on the thermal infrared remote sensing of volcanic sulfur dioxide emissions: A case study from the Pu'u 'O'o vent of Kilauea Volcano, Hawaii

The December 18, 1999, launch of NASA's Terra satellite put two multispectral thermal infrared imaging instruments into Earth orbit. Experiments with airborne instruments have demonstrated that the data from such instruments can be used to detect volcanic SO2 plumes and clouds. However, one of the greatest challenges that will confront efforts to monitor volcanic SO2 emissions from space is the need to characterize the local atmosphere. In this paper we evaluate the sensitivity of the SO2 retrieval procedure to our knowledge of the local atmospheric conditions. We compare SO2 retrievals obtained with distant (radiosonde) and local (Fourier transform infrared (FTIR) soundings) atmospheric measurements and find that the relative difference is typically +/-25%. For ground temperature retrievals the relative difference is +/-1.5%. These results lead us to conclude that while local measurements of atmospheric conditions are preferable, useful retrievals can be obtained using atmospheric measurements from distant sites. In addition, we find very good agreement between SO2 and ground temperature retrievals obtained from thermal infrared imagery and FTIR soundings.