Snow replica method for three-dimensional X-ray microtomographic imaging

Visualisation and quantification of snow structures at a scale of a few millimetres is important to understand the mechanical, thermal and electromagnetic properties of snow. Often snow samples have to be transported from remote locations or they need to be stored before there structure can be measured. To prevent snow metamorphism in such samples they can be conserved by filling the pore space with a solidifying liquid (e.g. diethyl phthalate). Surface sections, and to an even greater degree three-dimensional (3D) reconstructions of cast snow samples, are difficult to prepare, and automatic image processing is notoriously difficult and often requires manual evaluation.

We have developed a new method to measure the 3D structure of cast snow samples. Snow samples, cast with diethyl phthalate (DEP) and frozen, are cut to a sample size of a few centimetres diameter and up to 10 cm height. The ice of these samples is then sublimated in high vacuum, and the remaining negative structure (replica) is imaged using X-ray micro-tomography (micro-CT). The accuracy of the method is demonstrated by comparing micro-CT scans of the original snow structure and the replica.

The method allows easy transportation of samples, requires little manual interaction, has a very high spatial resolution of up to 10 micrometres, and is environmentally friendly.

Fig. 1. A comparison between the original snow structure (1st column) and the replica (2nd column) shows that the replica is the negative of the original structure. Digital inversion of the negative gives an image that corresponds to that of the original snow (3rd column). The small differences (red=positive, blue=negative) between the images is caused by small shifts in the positioning of the sample during the micro-CT measurement (4th column).

Fig. 2. Following the changes in one cross-section during the storage under vacuum, shows that the sublimation front progresses towards the centre of the sample (length of the scale bar: 5 mm).

Download:

CastingSnowPhthalate.pdf

Poster_Replica.pdf