DJI Zenmuse L3

The DJI Zenmuse L3 is a long-range LiDAR payload for the Matrice 400. It is a complete system with laser scanner, positioning system and two RGB mapping cameras of 100 MP each in 4/3 format, and serves the surveying of large areas and hard-to-reach terrain.

The laser works at 1,535 nm, a wavelength range the eye tolerates better than 905 nm because the light is absorbed before it reaches the retina; this allows higher pulse energy and so greater range. The range is 2,000 m at 80 % reflectivity and 100 kHz, but only 700 m at 10 % reflectivity and 350 kHz: range depends on reflectivity and pulse frequency. Instead of a point rate, DJI quotes the pulse frequency of 100 to 2,000 kHz; pulses and points are not the same, since several echoes per pulse yield several points. Up to 16 echoes per pulse, an 80 × 3° line scan, 4 cm horizontal and 3 cm vertical accuracy (RMSE) at 120 m and a position rate of 200 Hz characterise the scanner. The payload weighs 1.60 kg without the Single-Gimbal-Connector and has IP54.

The laser class given by the manufacturer (IEC 60825-1) must be observed. The weight counts towards the take-off mass of the Matrice 400; the EU class limits are 4 kg (C2) and 25 kg (C3 and C4). Surveys of large areas are often flown in the specific category, above all for flights beyond visual line of sight. Point clouds and images of built-up areas touch data-protection law.

A high pulse frequency means denser points but shorter range; anyone flying at great heights chooses lower frequencies. The 16 echoes pay off in dense forest and terrain under vegetation. Wear points are the scanner window, the connectors and the damping; the alignment of scanner and positioning system must stay stable.