FAQs

What automated laser scanning sensors can be used in StrucNet?

StrucNet is not limited to a specific sensor, but we strive for the following minimum criteria:

  • Beam divergence: maximum 0.3 degrees
  • Minimum 100 m range in sunlit conditions with 1 cm resolution or better
  • Full azimuth range with 0.2 deg angular resolution or denser
  • Minimum 0-130 deg zenith range with 0.2 deg angular resolution or denser
  • Laser wavelengths - NIR and SWIR?
  • Tilt sensor? (for reporting on possible change in sensor attitude over time)?

Currently, only 1 sensor is commercially available that fulfils the above criteria: the LEAF sensor from https://www.sensingsystems.com.au/. Any new sensor will need to be properly benchmarked (we currently use the RIEGL VZ-400i for benchmarking)

What is the LEAF sensor?

The LEAF sensor is a low-cost robust terrestrial laser scanner meant to be setup in the study area. It succeeded the VEGNET In-situ monitoring lidar (IML) system (Culvenor et. al. 2014) that was developed with an aim to set up automated permanent scanning stations for frequent acquisitions of lidar point clouds. In other words, it can generate lidar time-series datasets, a concept relatively unknown.

LEAF uses a 905 nm time-of-flight laser with beam divergence of 5 mrad and has a hemispherical scan range of 0–360° in azimuth and 0–130° in zenith.

As the sensor is meant to be installed permanently in the sites, it will be subject to changing weather conditions and possible movements due to animals and humans in the vicinity. It comes equipped with a moisture sensor to alert water ingress and tilt sensor to detect movements.

What settings are used?

Settings that were used to scan at Wytham woods, UK:

  • Five daily scans at 0.45° interval centred at 57.5° azimuth angle.
  • Azimuth resolution of 0.067°
  • Height above terrain: at least 1.3 m, (higher with taller understorey)

How many sensors are installed in the sites?

It is evident that at least one scanner per site is necessary, and primary considerations vary from cost to project requirements. Multiple sensors are recommended as it will provide sensor redundancy in case of failure and characterise the site’s heterogeneity.

How is the sensor setup in the site?

If you are familiar with TLS data acquisitions, you will appreciate that certain preconditions are met in order to carry out successful data acquisitions. One such precondition is the stability of the scanner, which is ensured by using a sturdy tripod or stabilised monopod setup placed on stable ground. Furthermore, the stability may be monitored by the presence of the operators nearby. It is practically impossible to ensure supervision of the LEAF sensor at all times. Therefore, it is essential to establish a stable setup. The figures below depict the setup based on our initial experiences in the field.