TOOLS FOR ESTIMATING ASH FALL THICKNESS: USING REFERENCE PHOTOGRAPHS TO IMPROVE ACCURACY
Volcanic ash fall conditions were simulated using an ash dispersal rig. A set of reference photographs was prepared for ash thicknesses of 1 mm, 5 mm, and 10 mm on common surfaces (i.e. asphalt, grass, flax). Effective photographs show visual differences between various ash thicknesses, with a known scale. A survey (n=77) tested changes in people’s ability to accurately estimate ash thickness with the use of reference photographs of various ash thicknesses. Results confirmed that people tend to overestimate ash thicknesses. Moreover, people are more accurate at estimating ash thickness in close- to medium-shot photographs than long-shot photographs.
Images which depict ash fall deposits at close- and medium-range fields of view with a relevant scale can be readily utilized to collect data for ash fall impact assessments and isopach maps. Effective photographs informing people of volcanic ash fall risk should include universal objects for scales (i.e. a pencil or soda can) and use common perspectives (i.e. low angle shots). Such photographs of various thicknesses of ash on everyday surfaces can be used for public education internationally and can be critical for allowing remote data collection.