Abstract
This study presents a new methodological approach for assessment of spatial and qualitative aspects of forest disturbance based on the use of multispectral imaging camera with the UAV photogrammetry. We have used the miniaturized multispectral sensor Tetracam Micro Multiple Camera Array (μ-MCA) Snap 6 with the multirotor imaging platform to get multispectral imagery with high spatial resolution. The study area is located in the Sumava Mountains, Central Europe, heavily affected by windstorms, followed by extensive and repeated bark beetle (Ips typographus [L.]) outbreaks in the past 20 years. After two decades, there is apparent continuous spread of forest disturbance as well as rapid regeneration of forest vegetation, related with changes in species and their diversity. For testing of suggested methodology, we have launched imaging campaign in experimental site under various stages of forest disturbance and regeneration. The imagery of high spatial and spectral resolution enabled to analyse the inner structure and dynamics of the processes. The most informative bands for tree stress detection caused by bark beetle infestation are band 2 (650nm) and band 3 (700nm), followed by band 4 (800 nm) from the, red-edge and NIR part of the spectrum. We have identified only three indices, which seems to be able to correctly detect different forest disturbance categories in the complex conditions of mixture of categories. These are Normalized Difference Vegetation Index (NDVI), Simple 800/650 Ratio Pigment specific simple ratio B1 and Red-edge Index.
Highlights
Disturbance is the key control of the dynamics of forest ecosystems across various environments (Frelich, 2002)
Multi-temporal medium or low resolution satellite datasets like Landsat (TM/ETM+) and SPOT (Hais et al, 2009; Latifi et al, 2014), Colour-Infrared (CIR) images captured by manned aircraft (Heurich et al, 2010), TerraSAR-X and RapidEye data (Ortiz et al, 2013; Adamczyk and Osberger, 2015), or airborne pushbroom imagining radiometer (Campbell et al, 2004) have been used for monitoring of disturbances by bark beetle infestation
The multirotor Unmanned Aerial Vehicle (UAV) equipped with the multispectral camera μMCA Snap 6 was first applied to test the applicability of the sensor for such analysis on the example of mid-latitude forest, attacked by the extensive bark beetle infestation
Summary
Disturbance is the key control of the dynamics of forest ecosystems across various environments (Frelich, 2002). Conventional remote sensing (RS) methods are not always appropriate for monitoring forest disturbance dynamics in the case of rapid calamity mapping of small privately owned forest stands due to a high operating cost or limited spatial and temporal image data (Chambers et al, 2007). These applications require low-cost but high-resolution RS data and acquisition on demand. By addressing the limitations of conventional remote sensing approaches in forestry, Unmanned Aerial Vehicle (UAV) equipped with a multi or hyperspectral camera may provide accurate means of monitoring pest infestation at the stand and even species level (Lehmann et al, 2015)
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