Effect of forest structure and health on the relative surface temperature captured by airborne thermal imagery – Case study in Norway Spruce-dominated stands in Southern Finland

ABSTRACT

The effect of forest structure and health on the relative surface temperature captured by airborne thermal imagery was investigated in Norway Spruce-dominated stands in Southern Finland. Airborne thermal imagery, airborne scanning light detection and ranging (LiDAR) data and 92 field-measured sample plots were acquired at the area of interest. The surface temperature correlated most negatively with the logarithm of stem volume, Lorey’s height and the logarithm of basal area at a resolution of 254 m² (9 m radius). LiDAR-derived metrics: the standard deviations of the canopy heights, canopy height (upper percentiles and maximum height) and canopy cover percentage were most strongly negatively correlated with the surface temperature. Although forest structure has an effect on the detected surface temperature, higher temperatures were detected in severely defoliated canopies and the difference was statistically significant. We also found that the surface temperature differences between the segmented canopy and the entire plot were greater in the defoliated plots, indicating that thermal images may also provide some additional information for classifying forests health status. Based on our results, the effects of forest structure on the surface temperature captured by airborne thermal imagery should be taken into account when developing forest health mapping applications using thermal imagery.

KEYWORDS:

• Remote sensing
• defoliation
• airborne thermal imagery
• Ips typographus
• forest mensuration and management
• airborne laser scanning
• forest health

Acknowledgments

We would like to thank Katri Tegel and Tuija Suihkonen from Arbonaut Ltd. for assisting with the field measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The LiDAR, thermal and plot data sets applied in the paper have been made available by Arbonaut Ltd., within the scope of the THERMOLIDAR project. The THERMOLIDAR project is funded under the Framework 7 Theme Research for the benefit of SMEs under the Capacities Program of the European Commission. The Academy of Finland is acknowledged for its financial support, in the form of the Centre of Excellence in Laser Scanning Research (CoE-LaSR). This work was supported by The Finnish Society of Forest Science under [grant number 201510040].