Overlap Correction Function Based on Multi-Angle Measurements for an Airborne Direct-Detection Lidar for Atmospheric Sensing.

We estimate the overlap function (accounting for near-field effects) for an airborne nadir-mounted lidar, based on multi-angle measurements of an atmospheric scene obtained during two flights. For each atmospheric layer, a regression on the logarithm of the range-corrected signal versus the secant of the off-nadir angle allowed evaluation of the optical depth and the backscattering coefficient multiplied by the lidar constant. These quantities allow for computation of the lidar signal unaffected by the overlap effect, and then for determination of the overlap correction function. Its evolution over time can also help to detect changes in the alignment. The method is easy to implement as long as a scanning capability is available, and it can be applied in aerosol-free or aerosol-laden conditions, the requirement being a constant and horizontally homogeneous atmosphere during the measurements. For multichannel lidars, the method can be applied separately for each channel.