Moiré as a low-cost, robust, optical-technique to quantify soil surface condition

The microtopography of the soil surface is important for water entry, run-off and aeration. Despite the need there remain limited options for accurate, robust, low-cost, field based methods to measure soil surface microtopography such as created by the passage of agricultural machines including tyres and tracks. The Moiré technique (MT) has been used for shape analysis of biological samples. The technique uses an interference phenomenon created by light gratings projected onto the surface of interest. First, using commonly available equipment, we calibrated the technique against objects of known shapes and dimensions and achieved a sensitivity of about 1 mm. We then used the technique in the field, with the same equipment, to assess the imprint created by the tread pattern of a tyre during a single passage of a tractor and to determine the depth of imprint created after multiple passes of the same tractor. The area of the soil surface studied was 450. ×. 600 mm. All image processing and analysis of the data were done using a standard lap-top computer with free platform software. To within the sensitivity of the deployed MT we were able to determine features such as surface roughness and depth of rutting and by subtraction to determine the consequences of multiple passes. We conclude that the MT has wide utility for studying soil surface conditions. Further as all the equipment is commonly available and the software is free platform the use of the MT in this form can be very widely adopted.