CUSTOM INSTRUMENTATION FOR DRONE MEASUREMENTS OF VOLCANIC GASES

Drones offer exciting possibilities for collecting new types of data for many Earth science applications. Here we focus on the measurements to be made to further the understanding of volcanic eruption plumes in Hawaii. Constraints for such measurements include the required small size (<100 cm³), low mass (<1 kg), and low power (<10 W) requirements for next generation instrumentation to be flown on drones. Measurements are also constrained by the short-duration (<30 min.) of flights to collect science-quality data over a few km².

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.