For finer portion (2mm upto big boulders (>256 mm) in debris flow deposits which is hard to analyse taking sample to the lab. I found researchers mentioning about optical granulometry which is not clear to me. It seems photo interpretation in terms of percent by surface area. Does anybody has practical experience on it?
Dear colleague,
here is some literature on a method that is frequently called "photo sieving":
Graham DJ, Reid I, Rice SP. 2005. Automated Sizing of Coarse-Grained Sediments: Image-Processing Procedures. Mathematical Geology 37(1): 1–28.
Carbonneau PE, Lane SN, Bergeron NE. 2004. Catchment-scale mapping of surface grain size in gravel bed rivers using airborne digital imagery. Water Resources Research 40(7): n/a-n/a.
Graham DJ, Rice SP, Reid I. 2005. A transferable method for the automated grain sizing of river gravels. Water Resources Research 41(7): n/a.
Dugdale SJ, Carbonneau PE, Campbell D. 2010. Aerial photosieving of exposed gravel bars for the rapid calibration of airborne grain size maps. Earth Surface Processes and Landforms: n/a-n/a.
Hope this helps
Tobias
Hi Susmita... I read about a method which involves the design of a grid with a given area, to which you can attach a tape measure or other object that works for you as scale. That grid place it directly in the field on the deposit you want to evaluate, and then take a photograph that covers the edges of the grid. Office then you can count and measurements of the clasts. Of course, this method works for clasts to the size of boulders. Another method for rock blocks, is doing field measurements directly on three fundamental axes. Another method that applies to the gravel and boulders, is to measure its dimensions (axes) with a vernier. The latter method can laboratory. To boulders of very large, you can use panchromatic aerial photographs on large scales.
Dear Colleague(s),
according to my experience, another very simple procedure for coarse grain size is the so-called Tricart's method, which in my opinon is much more reliable than photographs.
You have to exclude the largest boulder, when isolated, then assume a grid cell as large as the biggest ones and count up to 100 at any grid cell intersection. By convention, you assume 2 mm for sand grain(s) and 0,001 for clay-loam. A useful 3-D measurement can simply be based by counting, separately, a,b,c-axes.
I have compared both onsite measurements and laboratory analyses on samples of gravel and I saw that plotted results (grain-size curves) are almost identical (!). Try to believe...
Have a good work!
Domenico
Dear Susmita, I have the same question, and I recommend you the ImageJ software which is free and easy to get the particle size of solid grains automatically by recognizing the edge of the solid grains. Here are some publications about this software hoping this helps for you:
Igathinathane C, Pordesimo L O, Columbus E P, et al. Shape identification and particles size distribution from basic shape parameters using ImageJ[J]. Computers & Electronics in Agriculture, 2008, 63(2):168–182.
SCHNEIDER C A, RASBAND W S, ELICEIRI K W. NIH Image to ImageJ: 25 years of image analysis[J]. Nature Methods, 2012, 9(7): 671-675.
Wang A J. Determination of Number and Percentage of Good Eggs from Bom-byx mori F_1 Hybrid Based on ImageJ Processing Technology[J]. Science of Sericulture, 2010, 36(4):702-706.
You can try the free BaseGrain Tool of ETH Zürich.
https://basement.ethz.ch/download/tools/basegrain.html
Best,
Ivo
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