An alternative to LiDAR technology has been tested in New Zealand with promising results. The more cost-effective alternative provides a means for remote sensing, data capture and the development of digital terrain models to support forest inventory management.
Airborne LiDAR technology has long provided a valuable tool for remote sensing, by using scanners that measure various points on the surface of forest objects. This allows for 3D representations of the forest to be created, which can be useful for a number of areas in forest management.
LiDAR does, however, have a number of disadvantages, not least its cost. At $3 to $15 per hectare, its use for monitoring the vast expanses of forest associated with Australia and New Zealand can be an expensive exercise. Other downsides of LiDAR include the length of time taken to acquire the information due to flight delays and long processing times, plus the difficulties associated when using the technology in areas with persistent cloud cover.
Recently, an alternative has been tested in the form of interferometric synthetic aperture radar (InSAR). InSAR operates in what is known as the ‘microwave region’, which means data capture is possible day or night, regardless of cloud cover. It is also relatively inexpensive when compared to its alternatives, at approximately $0.16 per hectare.
InSAR is already being used in some countries for forest data collection, but because measuring New Zealand’s forests has some distinct challenges, including steep terrain and dense canopies, additional research was required to confirm its effectiveness.
Ellen Leonardo, Remote Sensing Scientist at New Zealand-based research company Scion, recently conducted a study that compared InSAR and LiDAR data from Geraldine Forest in New Zealand’s Canterbury.
The results showed that, while LiDAR proved to be more precise than InSAR, the data needed to estimate forest attributes including height and total volume captured by InSAR was still reasonably accurate. There is also the potential for future improvement, if InSAR can be successfully used in combination with data from other sources.
The Scion Geomatics team also studied and evaluated a third technique, known as satellite photogrammetry. While InSAR was found to be the most inexpensive means of data capture, satellite photogrammetry was shown to be more precise.
Ms. Leonardo said InSAR may not be the most precise source of forest inventory information, but it does still have some distinct advantages.
“Forest managers should consider all factors when choosing the most suitable remote sensing system to use,” Ms. Leonardo concluded.
Source: Forest Growers Research
