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Four of the most significant RHI (Range Height Indicator) radar images showing the recorded Keflavík C-band radar reflectivity on May 22, 2011 from 03:00 UTC till 21:00 UTC. See text for details.
Contexts in source publication
Context 1
... significant RHI (Range Height Indicator) images of the measured radar reflectivity Z Hm (expressed in dBZ, as usual), recorded on May 22, 2011 from 03:00 UTC till 21:00 UTC, are shown in Figure 1. The instantaneous volcanic ash cloud volume V a (t) [m 3 ], which represents the volume of the ash cloud at a given nominal time step t, may be estimated by using a threshold C ath on the estimated concentration C a (r,,) through a regression model as a function of the radar reflectivity at a given position (r,,) with respect to the radar antenna. ...
Context 2
... instantaneous volcanic ash cloud volume V a (t) [m 3 ], which represents the volume of the ash cloud at a given nominal time step t, may be estimated by using a threshold C ath on the estimated concentration C a (r,,) through a regression model as a function of the radar reflectivity at a given position (r,,) with respect to the radar antenna. However, as already noted in Figure 1, the total portion of the ash cloud V a (t) is not detectable by the scanning radar, thus inducing an underestimation of the total ash volume and mass due to the radar observation geometry and the presence of occlusions along the ray paths. In order to partially overcome this problem, we have applied a simple reconstruction of the vertical profile of reflectivity (VPR), based on the assumption of a reflectivity constant value, down to the surface, equal to the lowest measured reflectivity Z Hm (r,,,t). ...
Context 3
... plume maximum height H aM (t) with respect to any (,) can be also extracted once H a (,,t) is estimated. The analysis of the plume maximum height It is worth reminding that the radar-based estimate of H aM (t) suffers of lack of microwave visibility over the vent considering the available observation geometry (see Figure 1) and spurious ground clutter can affect the plume height estimate in a given domain. Figure 3 shows a trend of H aM (t) quite similar when the threshold method is changed and consistent with the results shown in Figure 2. From the near-surface retrieved ash fall rate R a (,,t) gathered by performing a VPR reconstruction, it is possible to obtain the spatial distribution of the radar-derived deposited tephra density or loading D a (,) by means of a temporal integration of R a (,,t) over the available time step by assuming an average constant eruption activity in that interval (of 5 minutes). ...
Context 4
... 3 shows a trend of H aM (t) quite similar when the threshold method is changed and consistent with the results shown in Figure 2. From the near-surface retrieved ash fall rate R a (,,t) gathered by performing a VPR reconstruction, it is possible to obtain the spatial distribution of the radar-derived deposited tephra density or loading D a (,) by means of a temporal integration of R a (,,t) over the available time step by assuming an average constant eruption activity in that interval (of 5 minutes). The retrieved ash mass loading D a (,), shown in Figure 4 in correspondence of the time steps of Figure 1, confirms that coarse ash and lapilli are confined within a relatively small area around the volcano vent with values larger than 200 kg/m 2 . ...
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