Modelling forest road trafficability with satellite-based soil moisture variables

ABSTRACT

Recent decades have seen increased temperatures and precipitation in the Nordic countries with long-term projections for reduced frost duration and depth. The consequence of these trends has been a gradual shift of delivery volumes to the frost-free season, requiring more agile management to exploit suitable weather conditions. Bearing capacity and trafficability are dependent on soil moisture state and in this context two satellite missions offer potenially useful information on soil moisture levels; NASA’s SMAP (Soil Moisture Active Passive) and ESA’s Sentinel-1. The goal of this pilot study was to quantify the performance of such satellite-based soil moisture variables for modeling forest road bearing capacity (e-module) during the frost-free season. The study was based on post-transport registrations of 103 forest road segments on the coastal and interior side of the Scandinavian mountain range. The analysis focused on roads of three types of surface deposits. Weekly SMAP soil moisture values better explained the variation in road e-module than soil water index (SWI) derived from Sentinel-1. Soil Water Index (SWI), however, reflected the weather conditions typical for operations on the respective surface deposit types. Regression analysis using (i) SMAP-based soil dryness index and (ii) its interaction with surface deposit types, together with (iii) the ratio between a combined SMAP_SWI dryness index and segment-specific depth to water (DTW) explained over 70% of the variation in road e-module. The results indicate a future potential to monitor road trafficability over large supply areas on a weekly level, given further refinement of study methods and variables for improved prediction.

KEYWORDS:

• Bearing capacity
• LFWD
• satellite radar
• climate change

Acknowledgements

The authors thank Dag Skjølaas of the Federation of Norwegian Forest Owners, the participating forest owners associations (Allskog, Glommen-Mjøsen Skog, Viken Skog, AT-Skog, Vestskog) as well as the respective financiers (Skogtiltaksfondet and Utviklingsfondet for Skogbruket) for making this study possible. We also thank Paul Geladi and Anders Brundin for their help with multivariate analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.