Earth Observation Data Group: publications

Identifying volcanic endmembers in hyperspectral images using spectral unmixing

Proceedings of SPIE--the International Society for Optical Engineering SPIE, the international society for optics and photonics 9242 (2014) 924215-924215-6

Authors:

Alessandro Piscini, Elisa Carboni, Fabio Del Frate, Roy Gordon Grainger

Systematic satellite observations of the impact of aerosols from passive volcanic degassing on local cloud properties

Atmospheric Chemistry and Physics European Geosciences Union (2014)

Authors:

SK Ebmeier, AM Sayer, RG Grainger, TA Mather, E Carboni

Abstract:

Abstract. The impact of volcanic emissions is a significant source of uncertainty in estimations of aerosol indirect radiative forcing, especially with respect to emissions from passive degassing and minor explosions. Understanding the impact of volcanic emissions on indirect radiative forcing is important for assessing present day atmospheric properties and also to define the pre-industrial baseline to assess anthropogenic perturbations. We present observations of the time-averaged indirect aerosol effect within 200 km downwind of isolated island volcanoes in regions of low present-day aerosol burden using MODIS and AATSR data. Retrievals of aerosol and cloud properties at Kīlauea (Hawai'i), Yasur (Vanuatu) and Piton de la Fournaise (Réunion) are rotated about the volcanic vent according to wind direction, so that retrievals downwind of the volcano can be averaged to improve signal to noise ratio. The emissions from all three volcanoes, including those from passive degassing, strombolian activity and minor explosions lead to measurably increased aerosol optical depth downwind of the active vent. Average cloud droplet effective radius is lower downwind of the volcano in all cases, with the peak difference in effective radius of 4–8 μm at the different volcanoes. A comparison of these observations with cloud properties at isolated islands with no significant source of aerosol suggests that these patterns are not purely orographic in origin. This approach sets out a first step for the systematic measurement of the effects of present day low altitude volcanic emissions on cloud properties. Our observations of unpolluted, isolated marine settings may also capture processes similar to those in the pre-industrial marine atmosphere.

Systematic satellite observations of the impact of aerosols from passive volcanic degassing on local cloud properties

Atmospheric Chemistry and Physics Copernicus Publications 14:19 (2014) 10601-10618

Authors:

SK Ebmeier, AM Sayer, RG Grainger, TA Mather, E Carboni

Correcting the record of volcanic stratospheric aerosol impact: Nabro and Sarychev Peak

Journal of Geophysical Research: Atmospheres American Geophysical Union (AGU) 119:17 (2014) 10-364

Authors:

M Fromm, G Kablick, G Nedoluha, E Carboni, R Grainger, J Campbell, J Lewis

Simplifying the calculation of light scattering properties for black carbon fractal aggregates

Atmospheric Chemistry and Physics European Geosciences Union (2014)

Authors:

AJA Smith, RG Grainger

Abstract:

Abstract. Black carbon fractal aggregates have complicated shapes that make the calculation of their optical properties particularly computationally expensive. Here, a method is presented to estimate fractal aggregate light scattering properties by optimising simplified models to full light scattering calculations. It is found that there are no possible spherical models (at any size or refractive index) that well represent the light scattering in the visible, or near-thermal infrared. As such, parameterisations of the light scattering as a function of the number of aggregate particles is presented as the most pragmatic choice for modelling distributions of black carbon when the large computational overheads of rigorous scattering calculations cannot be justified. This parameterisation can be analytically integrated to provide light scattering properties for log-normal distributions of black carbon fractal aggregates and return extinction cross-sections with 0.1% accuracy for typical black carbon size distributions. Scattering cross-sections and the asymmetry parameter can be obtained to within 3%.

51��