The possibility of correctly detecting immersed targets with a lidar through the air-water interface is discussed in this paper. The water surface roughness, in relation with wind direction, greatly disturbs light dispersion. Nevertheless, a detection of immersed targets is always possible. This paper reports on an attempt to improve the quality of detection. It was carried out by a polarimetric coding of optical signals based upon the Stokes-Mueller polarimetric formalism, and by choosing a special orientation for the transceiver.

This paper presents an adaptive polarimetric filtering method to optimize target scattering behaviour in laser imagery. Knowledge of a target's Mueller matrix permits one to calculate its polarization signature. Analysing this signature outlines some particular states of polarization. These states are directly related to the scattering properties of the given target. Using these optimum polarizations for transmission and reception either enhances or removes the associated scattering behaviour.

The reflection polarization properties of a given target evolve according to its surface state and to the illumination angle. The depolarization after reflection produced by an iron target whose surface was progressively debased was studied: its initial surface was polished up to one micron. These results were compared to the depolarization obtained from one Tenon sample and one dark dielectric. In the Teflon sample depolarization is due to volume diffusion whereas in dielectric surface and volume are involved in this process.Polarization is described in the Stokes-Mueller formalism; the matrix obtained was computed to give the degree of polarization for all incident pure-polarization states. Each sample was measured under different angles of incidence. Noise was reduced by a statistical method to optimize the matrix elements.The results are first presented in a global matrix form then, the depolarization phenomenon is analyzed and one classification technique is applied.

The possibility of detecting and identifying targets immersed in the draught zone of a ship with a lidar is discussed in this paper. It is carried out by a polarimetric codification of optical signals. The sea surface roughness, in conjunction with wind direction, greatly disturbs light dispersion. Nevertheless, by using the Stokes-Mueller polarimetric formalism, a classification of immersed targets with various surfaces and covering properties can be laid down.

Detecting and identifying targets immersed in draught zone are necessary for a safe navigation. But with to-day technologies it is very difficult to do it from a ship. Nowadays, this detection still stays a challenge, because sonars are inefficient in the zone just under the waterline.In our laboratory, we succeeded in using lidar as a complementary tool of the sonar. With optical detection, active imagery, various immersed targets were detected, identified and classified according to a Mueller matrix and whatever the perturbations on the sea surface and the wind conditions. The possibility of using a particular polarimetric codage with optical signal is discussed in this paper. The aim was to demonstrate that our lidar tool can be improved by choosing the best polarimetric couple in emission and detection.