Analysis of soliton gas with large-scale video-based wave measurements

An experimental procedure for studying soliton gases in shallow water is devised. Nonlinear waves propagate at constant depth in a 34-m-long wave flume. At one end of the flume, the waves are generated by a piston-type wave-maker. The opposite end is a vertical wall. Wave interactions are recorded with a video system using seven side-looking cameras with a pixel resolution of 1 mm, covering 14 m of the flume. The accuracy in the detection of the water surface elevation is shown to be better than 0.1 mm. A continuous monochromatic forcing can lead to a random state such as a soliton gas. The measured wave field is separated into right- and left-propagating waves in the Radon space and solitary pulses are identified as solitons of KdV or Rayleigh types. Both weak and strong interactions of solitons are detected. These interactions induce phase shifts that constitute the seminal mechanism for disorganization and soliton gas formation. Graphic abstract