Robust watermarking of airborne LiDAR data

Abstract

This paper presents a novel robust approach developed specially for watermarking airborne LiDAR data, which consist of a large cloud of geo-referenced points and has some unique characteristics. The approach consists of the following steps: (1) Defining the marker circular areas, in which the watermark bit will be embedded; (2) Dividing the marker circular areas uniformly into smaller circular areas by applying the sunflower seed distribution algorithm; (3) Using the points in these smaller circular areas to construct the input values for the Discrete Cosine Transformation (DCT); (4) Changing the last DCT coefficient; (5) Perform Inverse Discrete Cosine Transformation (IDCT), and perturbing the points within smaller circular areas according to the output values from this inverse transformation. Applying our approach, the watermark was dispersed into a set of points within the marker circular areas. The watermark bits are embedded multiple times in different marker circular areas. Thus, the robustness of the watermark was increased against various attacks. The watermark extraction process is practically the same, except in the final step, in which only the sign of each last DCT coefficient is checked, and decisions are made about the value of the watermark bits. Several experiments were performed to analyse the robustness of our watermarking schema against the most probable attacks.