What we need in thermal infrared (TIR) data to forecast volcanic activity: From new ground-based sensors to a rapid-revisit orbital concept

Thermal monitoring of volcanic activity has become common over the past 25 years and is well integrated into the set of tools at several volcano observatories. These data are acquired from a range of sensors including permanent ground-stations, less frequent campaign mode deployments from the ground and air, as well as orbital remote sensing. The fundamental ability to forecast a new eruption using orbital TIR data remains aspirational despite decades of data acquisition, modeling, and analysis. In contrast, large-scale thermal change detection is routine and used to rapidly identify a new eruption and monitor its evolution. Sensors with lower spatial (≥ 1 km) and higher temporal (≤ 24 h) resolutions are best suited for acquiring these data and provide near-real time information. Our recent work examines higher spatial, lower temporal resolution low-Earth orbit data to identify precursory thermal eruption signals. Foundational to this is the ability to retrieve accurate subtle (1-2 K) temperature changes, which are easily overlooked using current change detection approaches. Long time series orbital TIR data enable a unique opportunity to quantify these low-level anomalies and small eruption plumes over long periods. Most significant is the finding that the smaller, subtle detections served as precursory signals in ~81% of eruptions. Over the next decade, several high spatial (~ 60 m) resolution orbital sensors are planned that provide near-daily TIR data at every volcano, vastly improving thermal baselines and detection of new activity. One of these, the Surface Biology and Geology (SBG) mission, contains an infrared instrument, which also plans volcano-specific data products that are crucial for accurate daily monitoring of volcanic temperatures and degassing rates. In preparation for the SBG mission’s Volcanic Activity (VA) data product, we have developed a low-cost, ground-based, multi-wavelength TIR sensor known as the MMT-gasCam. NASA has funded a plan to use this instrument to measure small, passive plumes in emission to determine the detection threshold of sulfur dioxide in the TIR, its conversion to sulfate aerosol, and the temperature of the emitted gas/vent in volcanic plumes. Results will help to validate the future VA data product. However, despite the promise of SBG data, the fundamental step-change in orbital volcanology will not come until high-speed orbital data are possible. A proposed hypertemporal TIR mission would acquire these data at sub-minute scales to determine mass and thermal flux rates of gas emissions, eruptive ash plumes, and lava flows. With such a mission, data now acquired by current ground-based cameras will become possible from orbit for the first time.