  The paper describes how to recover the sensor trajectory for an aerial lidar
collect using the data for multiple-return lidar pulses. This work extends the
work of Gatziolis and McGaughey (2019) by performing a least-squares fit for
multiple pulses simultaneously with a spline fit for the sensor trajectory. The
method can be naturally extended to incorporate the scan angle of the lidar
returns following Hartzell (2020). This allows the pitch and the yaw of the
sensor to be estimated in addition to its position.
