New Advances in Dial-Lidar-Based Remote Sensing of the Volcanic CO2 Flux

Abstract

We report here on the results of a proof-of-concept study aimed at remotely sensing the volcanic CO 2 flux using a Differential Adsorption lidar (DIAL-lidar). The observations we report on were conducted in June 2014 on Stromboli volcano, where our lidar (LIght Detection And Ranging) was used to scan the volcanic plume at ∼3 km distance from the summit vents. The obtained results prove that a remotely operating lidar can resolve a volcanic CO 2 signal of a few tens of ppm (in excess to background air) over km-long optical paths. We combine these results with independent estimates of plume transport speed (from processing of UV Camera images) to derive volcanic CO 2 flux time-series of ≈16-33 min temporal resolution. Our lidar-based CO 2 fluxes range from 1.8 ± 0.5 to 32.1 ± 8.0 kg/s, and constrain the daily averaged CO 2 emissions from Stromboli at 8.3 ± 2.1 to 18.1 ± 4.5 kg/s (or 718-1565 tons/day). These inferred fluxes fall within the range of earlier observations at Stromboli. They also agree well with contemporaneous CO 2 flux determinations (8.4-20.1 kg/s) obtained using a standard approach that combines Multi-GAS-based in-plume readings of the CO 2 /SO 2 ratio (≈8) with UV-camera sensed SO 2 fluxes (1.5-3.4 kg/s). We conclude that DIAL-lidars offer new prospects for safer (remote) instrumental observations of the volcanic CO 2 flux.Keywords: volcanic CO 2 , DIAL-lidar, Stromboli, remote sensing, CO 2 flux INTRODUCTION A major step forward in ground-based volcano monitoring has recently arisen from the advent of modern instrumental techniques and networks for volcanic gas observations (Galle et al., 2010;Oppenheimer et al., 2014;Saccorotti et al., 2014;Fischer and Chiodini, 2015). Such technical advances provide improved temporal resolution relative to traditional direct sampling techniques (Symonds et al., 1994;Giggenbach, 1996). As longer-term volcanic gas records increase in number and quality, full empirical evidence is finally emerging for increased CO 2 flux emissions prior to eruption of mafic to intermediate volcanoes (Aiuppa, 2015). Precursory plume CO 2 flux increases have been now detected at several volcanoes, including Etna (Aiuppa et al., 2008;Patanè et al., 2013), Kilauea (Poland et al., 2012), Redoubt (Werner et al., 2013), Turrialba (de Moor et al., 2016a), and Poas (de Moor et al., 2016b).At Stromboli (in Italy), however, CO 2 flux observations have been particularly valuable for interpreting, and eventually predicting, the volcano's behavior (Aiuppa et al., 2010a Stromboli, the "regular" mild strombolian activity is occasionally interrupted by larger-scale vulcanian-style explosions, locally referred as "major explosions" or (in the most extreme events) "paroxysms" (Rosi et al., 2006(Rosi et al., , 2013Andronico and Pistolesi, 2010;Pistolesi et al., 2011;Pioli et al., 2014). These explosions, although short-lived (tens of seconds to a few minutes), represent a real hazard for local populations, tourists and volcanologists, since they produce fallout of coarse pyroclastic materials over w...

Volcanic Plume CO2 Flux Measurements at Mount Etna by Mobile Differential Absorption Lidar

“…The reader is referred to previous work [9,[22][23][24] for details on instrumental setup and data processing. The systematic error associated with the derived CO 2 concentrations is dominated by imprecision in wavelength setting [22].…”

“…Thanks to a photo-acoustic cell filled with pure CO 2 at atmospheric pressure and temperature, the ON and OFF wavelengths were set before each atmospheric scan. The residual imprecision [23] of ±0.02 cm −1 (half laser linewidth: half width at half maximum of the energy transmitted by the laser system (J) vs the wavenumber (cm −1 )) implies a systematic error on CO 2 concentrations of 5.5% [24]. The statistical error of CO 2 measurement has been calculated by usual error propagation techniques from the standard deviation of the lidar signal.…”

“…Table 1 compares the instrumental set-up during the Mt. Etna field campaign, with those used at Solfatara [9,22], and Stromboli [23,24]. Figure 2 shows examples of lidar returns obtained during our Etna campaign.…”

“…Etna in 2008 [20] and at Stromboli Volcano in 2009 [21] to measure the volcanic plume water vapor flux. More recently, lidars were first been used to target volcanic CO 2 [9,10,[22][23][24]. Our lidar BILLI (BrIdge voLcanic LIdar) [22], for example, has recently been used to successfully retrieve three-dimensional tomographies of volcanic CO 2 in the plumes of Pozzuoli, Solfatara in 2014 [9] and Stromboli volcano in 2015 [23,24].…”

“…More recently, lidars were first been used to target volcanic CO 2 [9,10,[22][23][24]. Our lidar BILLI (BrIdge voLcanic LIdar) [22], for example, has recently been used to successfully retrieve three-dimensional tomographies of volcanic CO 2 in the plumes of Pozzuoli, Solfatara in 2014 [9] and Stromboli volcano in 2015 [23,24]. As such, although gas-sensing lidars remain far less exploited in volcanology than those targeting volcanic ash/particles [25,26], this novel application field may expand rapidly in the near future.…”