Rodgers, Mel

Unoccupied aircraft systems (UAS) are developing into fundamental tools for tackling the grand challenges in volcanology; here, we review the systems used and their diverse applications. UAS can typically provide image and topographic data at two orders of magnitude better spatial resolution than space-based remote sensing, and close-range observations at temporal resolutions down to those of video frame rates. Responsive deployments facilitate dense time-series measurements, unique opportunities for geophysical surveys, sample collection from hostile environments such as volcanic plumes and crater lakes, and emergency deployment of ground-based sensors (and robots) into hazardous regions. UAS have already been used to support hazard management and decision-makers during eruptive crises. As technologies advance, increasing system capabilities, autonomy and availability, supported by more diverse and lighter-weight sensors, will offer unparalleled potential for hazard monitoring. UAS will provide opportunities for pivotal advances in our understanding of complex physical and chemical volcanic processes.

Measuring seafloor motion in shallow coastal water is challenging due to strong and highly variable oceanographic effects. Such measurements are potentially useful for monitoring near‐shore coastal subsidence, subsidence due to petroleum withdrawal, strain accumulation/release processes in subduction zones and submerged volcanoes, and certain freshwater applications, such as volcano deformation in caldera‐hosted lakes. We have developed a seafloor geodesy system for this environment based on an anchored spar buoy topped by high‐precision GPS. Orientation of the buoy is measured using a digital compass that provides heading, pitch, and roll information. The combined orientation and GPS tracking data are used to recover the three‐dimensional position of the seafloor marker (anchor). A test system has been deployed in Tampa Bay, Florida, for over 1 year and has weathered several major storms without incident. Even in the presence of strong tidal currents which can deflect the top of the buoy several meters from vertical, daily repeatability in the corrected three‐component position estimates for the anchor is 1–2 cm or better.

We present a new methodology using bottom pressure recorder (BPR) measurements in conjunction with sea level, water column, and barometric data to assess the long-term vertical seafloor deformation to a few centimeters accuracy in shallow water environments. The method helps to remove the apparent vertical displacement on the order of tens of centimeters caused by the BPR instrumental drift and by seawater density variations. We have applied the method to the data acquired in 2011 by a BPR deployed at 96m depth in the marine sector of the Campi Flegrei Caldera, during a seafloor uplift episode of a few centimeters amplitude, lasted for several months. The method detected a vertical uplift of the caldera of 2.5 +/-1.3 cm achieving an unprecedented level of precision in the measurement of the submarine vertical deformation in shallow water. The estimated vertical deformation at the BPR also compares favorably with data acquired by a land-based GPS station located at the same distance from the maximum of the modeled deformation field. While BPR measurements are commonly performed in deep waters, where the oceanic noise is relatively low, and in areas with rapid, large-amplitude vertical ground displacement, the proposed method extends the capability of estimating vertical uplifts from BPR time series to shallow waters and to slow deformation processes.