LiDAR Laser Returns
Laser pulses emitted from a lidar system reflect from objects both on
and above the ground surface: vegetation, buildings, bridges, and so
on. One emitted laser pulse can return to the lidar sensor as one or
many returns. Any emitted laser pulse that encounters multiple
reflection surfaces as it travels toward the ground is split into as
many returns as there are reflective surfaces.
The first returned laser pulse is the most significant return and will
be associated with the highest feature in the landscape like a treetop
or the top of a building. The first return can also represent the
ground, in which case only one return will be detected by the lidar
system.
Multiple returns are capable of detecting the elevations of several
objects within the laser footprint of an outgoing laser pulse. The
intermediate returns, in general, are used for vegetation structure,
and the last return for bare-earth terrain models.
The last return will not always be from a ground return. For example,
consider a case where a pulse hits a thick branch on its way to the
ground and the pulse does not actually reach the ground. In this case,
the last return is not from the ground but from the branch that
reflected the entire laser pulse.
Best Answer
The simple answer is that lidar sensors coupled with NIR cameras can collect point cloud data that can then have the NIR values "embedded" with them, the same way RGB values can be assigned to point cloud data collected with high res photos.