Spectrally High resolution Infrared measurements for the characterisation of Volcanic Ash: a new way to study volcanic processes
SHIVA is a NERC funded project to study the properties of volcanic ash using ground and space-based high resolution infrared spectrometer measurements.
The composition, grain-size and morphology of volcanic ash particles contains important information about the processes of magma ascent and fragmentation in volcanic eruptions (e.g. Heiken and Wohletz, 1985; Rust and Cashman 2011). The size and shape of ash particles is also critical in influencing the transport of ash through the atmosphere (e.g. Bonadonna et al., 1998; Riley et al., 2003), and its subsequent far-field impacts on people, infrastructure and ecosystems (e.g. Stewart et al., 2006, Bebbington et al., 2008; Durant et al., 2010 ). While recent ash-rich volcanic eruptions in Iceland (e.g. Eyjafjallajökull, 2010) and Chile (e.g. Chaiten, 2008; Puyehue- Cordon Caulle, 2011) have provided considerable new insights into the details of ash formation, transport and deposition, they have also highlighted the need for new work to improve the quantification of the properties of ash in volcanic plumes from remote-sensing observations.
Our approach is to develop a reference database of ash optical properties (spectral values of extinction coefficient, single scatter albedo and phase function) based on literature values of refractive index particle size and morphology, complemented by values measured by our project partners. Importantly, during the project, the sparse literature values of ash refractive index will be extended by laboratory measurements that will become available through a NERC funded laboratory study of volcanic ash.
The database of ash optical properties will form the basis of optimal estimation schemes to estimate ash properties from high resolution infrared spectra, i.e.
i) ash composition, optical depth and effective radius determined from transmission spectra near volcanic vents (FTIR)
ii) ash composition, altitude, optical depth and effective radius determined from emission spectra measurements by the nadir viewing Infrared Atmospheric Sounding Interferometer (IASI)
ii) ash composition, altitude, optical depth and effective radius determined from emission spectra measurements by the limb viewing Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)
An important aspect of this approach is the inherent quality control provided in the OE approach that allows the errors in any retrieval assumptions to be quantified. The retrieval schemes will be validated by comparing the results with geochemical and petrology analysis and laboratory measurements of refractive index from ash samples. In addition we will use correlative satellite data to ascertain the effects of sub-pixel variation and contamination by cloud.
Finally we will work with our project partners to understand the observed variation in ash characteristics in terms of volcanic processes. To expedite this discussion we plan to have two volcanic ash workshops during the project, and regular teleconferences with all project participants.
Aim and Objectives
The overarching aim of this project is to identify ash composition from information contained in infrared spectra and to study the change in composition during an eruption, in order to better understand the volcanic processes that control eruptive activity.
The objectives that support this aim are:
O1. To develop algorithms using new ash optical properties to retrieve ash characteristics from data collected with three different hyperspectral observing systems: ground-based absorption spectra and satellite-based emission spectra (from the limb and from nadir).
O2. To validate the results with geochemical and petrological analysis of ash samples and with reference to laboratory refractive index measurements of ash samples.
Scheduled SHIVA meetings
- Informal pre kick-off dinner at the EGU 2013, Vienna
- Kick-off workshop, Oxford 26th July 2013 (talks: ftp://ftp.atm.ox.ac.uk/pub/user/elisa/shiva/workshop/)
- Closing Meeting, Oxford summer 2016