Airborne lidar system with variable field-of-view receiver for water optical properties measurement

The shape of signal from sea water column obtained with an oceanographic lidar is not sufficient to pick out a contribution from a separate physical characteristic of the water. A possible approach consists in compensating the deficiency in information obtained from return signal of traditional depth-sounding lidar by using a variable field-of-view (FOV) receiver which register simultaneously (or subsequently) return signals obtained with several different FOV's. The proposed method calls for at least three FOV angles to be involved - a narrow one (approximately equal to lidar transmitter (laser beam) divergence), a wide (FOV plane angle of 50-70 mrad), and an intermediate (the angle of the order of 15-25 mrad). The approach is based on the fact that the waveforms, or the lidar backscatter return variations with depth for the narrow-, the wide-, and the intermediate-FOV receiver correspondingly, are different functions of seawater IOPs. The functions are established theoretically using a sophisticated model of lidar return that allows for a wide variety of shapes of the volume scattering function; a characteristic of the actual VSF shape (for forward scattering) is to be determined, in parallel with IOP estimates, from the recorded lidar waveforms. It seems to be of significance that a system to realize the proposed method may be created on the base of an existing hydrographic (bathymetric) lidar with only a simple enough modification of basic optical scheme.