Dual-stage MTA resolution for airborne laser scanning

Airborne laser scanning with time-of-flight LIDAR has evolved into a key technology for a variety of mapping applications. Determining measurement range requires associating each received echo pulse with its respective emitted laser pulse, but this association is ambiguous if the round-trip time of the pulse exceeds the pulse repetition interval. We introduce a dual-stage approach to this multiple time-around (MTA) ambiguity resolution problem which performs MTA zone assignment not only based on the raw, temporally successive LIDAR measurements, but also in an additional second step after geo-referencing, based on 3D point coordinates. This second stage processes all echoes which are not assigned to a definitive MTA zone by the first stage (standard code-based MTA resolution), and determines the most likely MTA assignment as the one resulting in the highest local point density. This allows introducing information not just from consecutive laser pulses or scan lines, but also from multiple overlapping scan strips. We discuss dual-stage MTA resolution and analyze its advantages over traditional MTA resolution, especially for difficult target situations.