New method for 3-D size measurements of particles using image analysis
|Location||International Geological Congress,oslo 2008|
|Author||Tafesse, Solomon; Fernlund, Joanne; Bergholm, Fredrik; Arvidsson, Mimmi|
|Holding Date||03 September 2008|
A new image analysis method has been developed to determine a 3-D size distribution of coarse clastic sediments. The length, width and thickness of till particles between 2 and 20 cm, are measured in a much more quantitative and accurate way than traditional sieving method can achieve. Digital pictures of the particles were taken in two positions, lying (facing the largest projected area) and standing (facing the smallest projected area).
The images were taken in a portable darkroom of size about 2 m high and 1x1 m square on a bed of glow-in-the-dark beads, so that the background glows and the resulting images consist of silhouettes of the particles. The particles were placed in a non-touching situation at the same location in both lying and standing position, which enables to exactly couple every particle during the image analysis. The image analysis gives the exact measure of the three axes for all clasts which helps to calculate aspect ratios (Length/Width, Width/Thickness, and Length/Thickness ratios) and the volume of every particle, by multiplying the area of the largest projected area with its thickness, and plot a typical cumulative volume curves for the samples instead of cumulative mass curves. Moreover the minimum bounding square of the smallest projected area are almost identical to sieve analysis results, thus we can compare the results of size distribution from this method to the sieve analysis results.
There are more advantages to the new method; the particles are imaged in the field, since one sample consists of one ton of till with as many as two thousand particles, it would be impossible to transport the particles to the laboratory for analysis. Also the equipment is inexpensive and easily constructed. The image analysis program is based on Matlab, which has become a standard language for mathematical operations and graphical presentations.