Combining mobile and static terrestrial laser scanners to investigate individual crown attributes during foliation

Abstract

Investigating individual crown attributes yields insight into forest canopy properties over large areas; however, effectively mapping single crowns is still an insufficiently exploited topic. Static terrestrial laser scanning (TLS) can render detailed descriptions of crowns and may serve as a substitute for in-field manual measurements. Preliminary work has also accumulated many TLS–crown reference relationships between TLS samplings and specific crown attributes. However, usage of this inventory technique suffers from the need to place TLS systems in multiple locations, which is a laborious process. Mobile terrestrial laser scanning (MLS) is a state-of-the-art survey technology that shows potential for overcoming this limitation because of its strength in efficiently mapping objects. This study attempts to put forward a new methodology with the potential to investigate crown-level properties, particularly during foliation. The rationale is to first explore correlations between MLS- and TLS-derived predictor variables. Given that the resultant MLS–TLS predictor relationships are strong and positive, the specific crown response variables, e.g., biomass and leaf area index, can then be retrieved with the corresponding TLS–crown reference relationships as a priori linkages. This new approach was evaluated based on MLS and TLS data collected during foliation. For instance, the predictor variable of biomass extracted from the MLS data is strongly (r 2 = 0.85) and linearly (intercept and slope of 0.03 and 0.94, respectively) associated with the corresponding TLS data. The test results indicate that MLS is applicable for characterizing the processes of foliation at the crown level, and the proposed methodology has been primarily validated for investigation of individual crown attributes.