Abstract
During explosive eruptions, the real-time estimation of the mass eruption rate (MER) is challenging although crucial to mitigate the impact of erupted tephra. Microwave radar techniques at L- and/or X-bands, as well as thermal infrared imagery, can provide a reliable MER estimation in real time. Using lava fountains of 3–5 December 2015 at Mt. Etna (Italy) as test cases, we investigate the differences amongall these remote sensing methods and introduce a new approach, called the near source approach (NSA) using only X-band radar data. We also extend the volcanic advanced radar retrieval methodology to estimate the gas-tephra mixture density near the volcanic crater. The analysis of uncertainty is carried out comparing the NSA with the mass continuity approach (MCA), top plume approach (TPA) and surface flux approach (SFA), already used to estimate the MER of other Etna explosive events. The analysis allows us to identify the optimal real-time MER retrieval strategy, showing the potential and limitations of each method. We show that the MCA method, entirely based on the X-band radar data processing, is the best strategy with a percentage uncertainty in the MER estimation of 22.3%, whereas other approaches exhibit a higher uncertainty (26.4% for NSA, 30% for TPA, and 31.6% for SFA).
Highlights
During explosive volcanic eruptions, volcanic particles of various dimensions, ranging from a few microns up to tens of centimeters, are injected into the atmosphere [1], [46]
In panels a1-a4 we show the QM and QV estimates as a function of time t, derived from: (i) Top Plume Approach (TPA) methods, i.e., using the top-plume altitude HTP, retrieved from the XWR within the DB12 model; ii) Mass Continuity Approach (MCA) method and iii) Near Source Approach (NSA) method, both derived from the XWR measurements
Starting from the 3 methodologies already known in the literature (MCA, TPA and Surface Flux approach (SFA)), a new NSA approach has been introduced and tested
Summary
Volcanic particles of various dimensions (tephra), ranging from a few microns up to tens of centimeters, are injected into the atmosphere [1], [46]. The area affected by tephra fallout can extend thousands of square kilometers around the eruptive vent Recent volcanic crises, such as those associated with Eyjafjallajökull (Iceland) in 2010 and Cordón-Caulle (Chile) in 2011, have demonstrated the need for a better real-time assessment of the eruption source parameters (ESPs), namely column height, MER, total erupted mass (TEM), and total grain-size distribution (TGSD). The XWR performs a 3-D scan of the surrounding scene as a function of range, azimuth, and elevation with five azimuthal scans per minute; (ii) the fixed-pointing L-band Doppler radar VOLDORAD-2B (VDR, wavelength of 23.5 cm) for the nearcrater detection of erupted material during Etna’s explosive events This Doppler radar measures both the radial velocity vr and the received backscattered power that characterizes the amount of detected tephra at high time resolution (i.e., 0.2 s; cf open-access data base used in this study [44]).
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