Integrated Ash Product

The following table summarizes all the products that constitute the MACE integrated products. All the products will be delivered in clear sky condition, with the exception of the ash detection map that will be delivered also in cloudy sky conditions.

MACE ash products

 Measurement Units

Note

Ash mass map

t/km2

Products delivered in clear sky conditions

Ash effective radius

μm

 

Ash AOD at 0.55 μm

-

 

  Ash concentration map  

mg/m3

 

Ash height map

km

 

Ash detection map

-

   Product delivered in clear and cloudy sky conditions   

MACE has been applied to different clear sky events as Etna (Italy) 23 November 2013 and 4 December 2015 and Calbuco (Chile) 24 April 2015. Moreover the procedures developed for the ash detection in cloudy sky conditions have been tested on the Etna 27 July 2001 and 12 May 2011 and the Eyjafjallajokull April-May 2010 eruptions.

Analysis of the 23 November 2013 Etna test case

The analysis of the 23 November 2013 Etna test case has been completed considering all the available satellite and ground measurements. The tables below summarize the acquisition time of each dataset and the ash parameters retrieved by using the different sensors.

    Acquisition time of satellite and ground based datasets             Ash parameters retrieved from each sensor

 

In the MACE scheme the volcanic plume altitude is also retrieved from the geometric parallax between the GEO-SEVIRI measurements and the ground Radar data. The parallax is the displacement in the apparent position of a target viewed along two different lines of sight. In the case of an atmospheric cloud, knowing the geometry by which two sensors look at the same cloud along two different views, it is possible to retrieve the displacement of the cloud from its actual position and, from it, the target’s altitude by trigonometric considerations. MACE made use of the image cross correlation analysis between the ash plume horizontal patterns derived by the two pairs of nearly simultaneous sensor acquisitions.

The following figure shows an example of the parallax displacement as seen when from SEVIRI and Radar images collected simultaneously at 10:30 UTC.

 Example of parallax displacement between the volcanic cloud seen from satellite SEVIRI and ground Radar data using nearly simultaneous acquisition time (10:30 UTC).

The volcanic plume altitudes retrieved from the SEVIRI-Radar parallax, have been compared with the plume altitudes computed from the ground visible (VIS) camera installed in Catania at about 27 km from the Etna summit craters. Taking into account the VIS camera instrumental limitations (the maximum measurable altitude is 10 km), the results are in good agreement.

The volcanic cloud thickness is computed directly from the Radar images. Figure below shows an example of the estimation procedure. The area contoured in the left panel marks the region of higher values of the Radar Doppler spectrum width which can be consistent with the plume transportation fostered by the horizontal advection (black dashed line) and the ash particles fallout (red solid line). The advection signal can be used to retrieve the volcanic cloud thickness that in this case is estimated to be about 2 km.

Radar Doppler spectrum (left) showing the difference between the volcanic ash advection and the fallout. Volcanic ash advection and fallout retrieved from VIS camera (right).

The Radar volcanic cloud thickness is compared with the values obtained by analyzing the VIS camera images. Right panel of the above figure shows a VIS camera image in which the two areas confined by the black and red lines indicate the advection and fallout respectively. The thickness of the VIS advection area (about 2 km) is in good agreement with the thickness of the advection area retrieved in the Radar images.

The MACE integration between satellite and ground measurements, lead to the identification of two volcanic cloud layers. The upper (at about 11 km) mainly composed by volcanic ice particles, while the lower (at about 6 km) mainly composed by volcanic ash particles.

SEVIRI BTD image collected at 12:30 UTC. The red and cyan contours represents the volcanic ash and ice clouds respectively. The red and cyan dotted lines are the HYSPLIT forward trajectories at 6 and 11 km respectively.

To validate the presence of the two volcanic clouds layers, the HYSPLIT forward trajectories have been used. Figure above shows the SEVIRI BTD (Brightness Temperature Difference) image collected at 12:30 UTC, in which the HYSPLIT forward trajectories from 09:00 UTC by considering an emission height of 11 (cyan dashed line) and 6 km (red dashed line) have been superimposed. The two trajectories fit well the movement of the ash (red contours) and ice (cyan contours) volcanic clouds identified by the SEVIRI BTD images.

Finally, the total ash mass emitted can be obtained by adding the ash masses retrieved from both the Radar and SEVIRI systems. The ash total mass retrieved from these two systems is approximately the total mass retrieved by the Radar system that has been estimated to be about 3 x109 ± 1x109 kg. This value is in good agreement with the value obtained by analysing the tephra deposit, of about 1.3 x109 ± 1.1x109 kg.