Validating Subglacial Volcanic Eruption Using Ground-Based C-Band Radar Imagery

Abstract

The main phase of the moderately sized November 2004 eruption of the Grimsvotn volcano, located in the center of the 8100 km(2) Vatnajokull glacier, was monitored by the Icelandic Meteorological Office C-band weather radar in Keflavik, 260 km west of the volcano. The eruption plume reached a height of 6-10 km relative to the vent. The distribution of the most distal tephra was measured in the autumn of 2004, while the deposition on the glacier was mapped in the summers of 2005 and 2006. The tephra formed a well-defined layer on the glacier in the region north and northeast of the craters. The total mass of the tephra layer is quantitatively compared with the retrieved values, obtained from an improved version of the volcanic ash radar retrieval (VARR) algorithm. VARR was statistically calibrated with ground-based ash size distribution samples, taken at Vatnajokull, and by taking into account both antenna beam occlusion and wind-driven plume advection. The latter was implemented by using a space-time image phase-based cross-correlation technique. Accuracy of the weather radar records was also reviewed, noting that a large variability in the plume height estimation may be obtained using different approaches. The comparisons suggest that, at least for this subglacial eruption, the surface tephra mass, estimated by using the VARR inversion approach, is in a fairly good agreement with in situ measurements in terms of spatial extension, distribution, and amount

Interpretation of observed microwave signatures from ground dual polarization radar and space multi-frequency radiometer for the 2011 Grímsvötn volcanic eruption

“…The MAP estimation of ash class c corresponds to the maximization with respect to c of the posterior pdf p(c|x m ) under the assumption of multivariate Gaussian pdf's. So far, VARR outputs have been tested with ground data in Marzano et al (2012b) and compared with satellite data and plume model simulations in Montopoli et al (2013) providing reasonable results when C-band radar data are used.…”

“…In the case of SPC, the version of VARR for single polarization radar systems, VARR-SP, is used considering only Z HH for both steps of ash classification and estimation of TCC. The quality of the ash retrieval of SPC has been already tested in Marzano et al (2012b) where comparisons with ground measurements and models outputs are performed. To allow a better evaluation of the results, TCCs are averaged on the same reference grid of SSMIS to match its coarser grid resolution.…”

“…In this respect, the exploitation of passive microwave sensors represents a good opportunity to probe ash clouds, despite some inherent limitations (Delene et al, 1996;Grody and Basist, 1996;Marzano et al, 2012b;Montopoli et al, 2013).…”

Microwave Radiometric Remote Sensing of Volcanic Ash Clouds From Space: Model and Data Analysis

“…The Grímsvötn volcano, located in the northwest of the Vatnajökull glacier in southeast Iceland is one of Iceland's most active volcanoes (e.g., [7]). The eruption in 2011 started on the late afternoon of May 21.…”

“…When the observation is close to the volcano vent, remote sensing instruments can be used to estimate the so-called near-source eruption parameters. The most common near-source parameters are the plume height, the tephra eruption rate, and mass [7]. The retrieval of these parameters is crucial as an input for dispersion models that are designed to quantitatively predict geographical areas likely to be affected by specific levels of ash concentrations.…”