The focus of this study is the leaf litter in forest, where crickets and their predators live in, and the effects of this micro-habitat on the background air flows. Crickets use air flow produced by running predators, in particular spiders, to escape. However, the noise in the environment (signal-to-noise ratio) due to air turbulence is totally unknown. To characterise this noise using experimental fluid dynamics over real and artificial leaf litter, we first need to determine the geometrical structure of the litter.
In order to study this complex structure, we realised a 3D scanning of the litter. The sample size is 0.5m x 1m. We realised samples in litter of oaks and beeches, and litter of beeches and pines. These samples are scanned with a laser. The use of this laser allows us to determine the micro topography of the litter surface with a spatial resolution of 0.5 mm. For each sample, we have a Digital Model Elevation (DEM) of the litter surface. In each DEM, we extracted 9 windows of 200pixels x 500pixels in order to apply spatial statistics. An experimental variogram is then calculated, allowing us to identify interesting properties the spatial structure of the topography. In particular, we identified a spatial scale, of several centimetres, which is homogenous and corresponds both to the scale of a portion of a leaf and to the scale at which a chase between predator and prey can occur.
3D mapping of litter surface elevation. Close investigation of litter surface geometry shows that litter surface is spatially structured, with a tight link between geometrical properties and biological (eg. size of leaves) and chemical (decomposition time)