CUSTOM INSTRUMENTATION FOR DRONE MEASUREMENTS OF VOLCANIC GASES
We are designing and building custom instrumentation to quantify the SO2 content of the plume, and focus on the conversion of SO2 gas to acidic aerosols. Column SO2 gas concentrations will be measured in the volcano plume by using upward looking Thermal Infrared (TIR) sensors mounted on low flying (below 100 m) drones. The small TIR sensors will employ band pass filters to measure radiance at several wavelengths. Inversion algorithms will be used to derive SO2 column path concentrations from the radiance measurements. Such column measurements are needed at multiple locations downwind to investigate the rate of conversion.
Column aerosol concentration will be derived from UV-VIS-NIR down-welling spectral radiances, which can be converted to aerosol column mass concentrations using models developed for aerosol size distributions and radiative transfer inversion calculations. In addition to the hardware, new retrieval algorithms are being developed to derive SO2 path concentrations from TIR spectral measurements. Many (~25) different SO2 path concentrations (0 - 40 ppm-m) have been modeled using MODTRAN5. The relationship between the SO2 path concentration and the TIR radiance ratio will be used to derive SO2 path concentrations, assuming that the volcano plume and the ambient air are at the same temperature. This is a valid assumption far downwind from the volcanic vent, where the height of the plume levels off.
We hope to test our instrument before this meeting, which will ultimately fly on a Matrice 100 drone providing ~30 minutes of flight time. Once a single instrument is developed, we will also explore the advantages of multiple drones working collaboratively to simultaneously measure the plume from different places and/or under different viewing geometries.