Geostatistical characterisation of centimetre-scale spatial structure of in vivo fluorescence

We present the first quantitative evidence of 2-dimensional non-random spatial structure for in vivo fluorescence distributions measured at scales of centimetres. To determine the presence of non-random structure and to quantify levels of spatial complexity, 2 common geostatistical analysis techniques, namely Moran's I spatial autocorrelation statistic and single-dimension fractal analysis, were employed. Samples were collected at 4 and 2 cm resolution from 2 coastal environments in South Australia; 50% of the distributions were spatially autocorrelated and 60% exhibited fractal scale dependence (with a fractal dimension, D-F, ranging from 1.54 to 1.89). Comparison of distributions sampled in the horizontal and vertical indicate that structural complexity is equally important in both planes. Structural complexity was greater at 2 cm than at 4 cm, suggesting that structure may arise at or below the 2 cm scale. This observation is in direct conflict with the general assumption that turbulence homogenises distributions at these scales.