A combined colour-infrared imaging technique for measuring water surface over non-horizontal bottom

This paper presents a combined colour-infrared imaging technique based on light refraction and absorption for measuring water surface over a non-horizontal fixed bottom known a priori. The procedure requires processing simultaneous visible and near-infrared digital images: on the one hand, the apparent displacement of a suitable pattern between reference and modulated visible images allows to evaluate the refraction effect induced by the water surface; on the other hand, near-infrared images allow to perform an accurate estimate of the penetration depth, due to the high absorption capacity of water in the near-infrared spectral range. The imaging technique is applied to a series of laboratory tests in order to estimate overall measurement accuracy. The results prove that the proposed method is robust and accurate and can be considered an effective non-intrusive tool for collecting spatially distributed experimental data.