Plume Height Time-Series Retrieval Using Shadow in Single Spatial Resolution Satellite Images

Abstract

Volcanic plume height is a key parameter in retrieving plume ascent and dispersal dynamics, as well as eruption intensity; all of which are crucial for assessing hazards to aircraft operations. One way to retrieve cloud height is the shadow technique. This uses shadows cast on the ground and the sun geometry to calculate cloud height. This technique has, however, not been frequently used, especially not with high-spatial resolution (30 m pixel) satellite data. On 26 October 2013, Mt Etna (Sicily, Italy) produced a lava fountain feeding an ash plume that drifted SW and through the approach routes to Catania international airport. We compared the proximal plume height time-series obtained from fixed monitoring cameras with data retrieved from a Landsat-8 Operational Land Imager image, with results being in good agreement. The application of the shadow technique to a single high-spatial resolution image allowed us to fully document the ascent and dispersion history of the plume–cloud system. We managed to do this over a distance of 60 km and a time period of 50 min, with a precision of a few seconds and vertical error on plume altitude of ±200 m. We converted height with distance to height with time using the plume dispersion velocity, defining a bent-over plume that settled to a neutral buoyancy level with distance. Potentially, the shadow technique defined here allows downwind plume height profiles and mass discharge rate time series to be built over distances of up to 260 km and periods of 24 h, depending on vent location in the image, wind speed, and direction.

Anatomy of a Paroxysmal Lava Fountain at Etna Volcano: The Case of the 12 March 2021, Episode

“…Thus, it is noteworthy that this amount was sufficient to feed an ash plume 11-13 km high (Table 2, Figures 4 and 5) expanding for hundreds of kilometers from the vent (Figures 8 and 9), and covering a sky surface of up to 1900 km 2 and a distance of~140 km from the vent in two and half hours. This matches a plumecloud expanding for 60 km from the vent in just 50 min during a previous paroxysmal episode [89], and fully displays the hazard posed by the ash cloud to aviation safety and circulation also because of growing airline traffic [91][92][93]. It is, thus, of paramount importance to use monitoring data to develop simple equations, such as those used during recent effusive eruptions at Etna [94,95], which might allow for fast and reliable estimates useful for hazard assessment during the earlier phases of an explosive paroxysm.…”

“…It corresponds to an acceleration of the jet that is responsible for the peak IER (Table 2) and the greater cooling and fragmentation of pyroclasts [25,33,44]. The heat released during the lava fountain phase is sufficient to rise a large volume of fine-grained pyroclasts (ash) up into the atmosphere, causing it to spread for several hours around the volcano, and to travel distances of several tens of kilometers [89].…”

VIGIA: A Thermal and Visible Imagery System to Track Volcanic Explosions

“…Another example of permanent deployment based on thermal cameras for volcanic surveillance was described by Patrick et al (2014) [34], who installed thermal cameras between 2010 and 2012 at Kilauea and Mauna Loa in order to monitor lava lakes, intracrater vents, fissure eruptions, lava flows and fumarolic activity. During the subsequent years, image processing algorithms using visible images were implemented to calculate plume heights [50,53] and to estimate mass eruption rates [54]. In 2014, a team from Laboratoire Magmas et Volcans (LMV) and the Observatoire de Physique du Globe de Clermont Ferrand (OPGC) implemented an integral system based on thermal and visible imagery to monitor the lava dome dynamics at the Merapi volcano [25].…”

Measuring Glacier Elevation Change by Tracking Shadows on Satellite Monoscopic Optical Images

“…This method was originally proposed by [16] to solve the inverse problem, i.e., determining the height of the objecta building in that casethat casts the shadow, and successively adopted in other similar studies [17], [18]. Applications of clinometry in earth science are less common [15], [19], [20], but recently, [21] and [22] proposed to use such a method to assess glacier elevation change using manual shadow delineation in specific points.…”