2-D tomography of volcanic CO2 from scanning hard-target differential absorption lidar: the case of Solfatara, Campi Flegrei (Italy)

摘要

Solfatara is part of the active volcanic zone of Campi Flegrei (Italy), adensely populated urban area where ground uplift and increasing groundtemperature are observed, connected with rising rates of CO emission. Amajor pathway of CO release at Campi Flegrei is diffuse soil degassing,and therefore quantifying diffuse CO emission rates is of vitalinterest. Conventional in situ probing of soil gas emissions withaccumulation chambers is accurate over a small footprint but requiressignificant time and effort to cover large areas. An alternative approach isdifferential absorption lidar, which allows for a fast and spatiallyintegrated measurement. Here, a portable hard-target differential absorptionlidar has been used to acquire horizontal 1-D profiles of column-integratedCO concentration at the Solfatara crater. To capture heterogenicfeatures in the CO distribution, a 2-D tomographic map of the COdistribution has been inverted from the 1-D profiles. The scan was performedone-sided, which is unfavorable for the inverse problem. Nonetheless, theresult is in agreement with independent measurements and furthermore confirmsan area of anomalous CO degassing along the eastern edge as well as thecenter of the Solfatara crater. The method may have important implicationsfor measurements of degassing features that can only be accessed from limitedangles, such as airborne sensing of volcanic plumes. CO fluxesretrieved from the 2-D map are comparable, but modestly higher than emissionrates from previous studies, perhaps reflecting an increase in CO fluxor a more integrated measurement or both.