CHARACTERIZATION AND DECOMPOSITION OF WAVE-FORMS FOR LARSEN-500 AIRBORNE SYSTEM

The LARSEN 500 airborne laser ranging system developed in Canada is an active remote sensor for the measurement of sea depths in shallow coastal waters. This system transmits a series of laser pulses from an aircraft into the ocean and receives the reflections from the ocean for postmission processing. The nature of the LARSEN waveforms received varies dramatically depending on the turbidity, depth, and the surface roughness of the sea, and the shape and texture of the sea bottom. In many cases, the separation between the surface and bottom reflections, which is essential in estimating the sea depths, is lost and, as a result, unreliable depth estimates are obtained. The contribution is concerned with a method that can accurately decompose a LARSEN waveform into two signal components, namely the surface and bottom reflections, independently of the degree of their overlap. First, a mathematical model that can be used to characterize the LARSEN waveforms received under diverse circumstances is established. This model is then used in conjunction with an optimization technique to facilitate the decomposition of each LARSEN waveform into surface and bottom reflections. The optimized parameters of the mathematical model are then used to give sea depth estimates. The resolution of LARSEN waveforms into two separate components by means of these techniques offers two important advantages. First, sea depths can be readily determined from the time displacement between the two components without human intervention, that is, the processing can be automated. Second, fairly accurate sea depths can be deduced even in cases where the two reflections strongly overlap.