The utility of Sentinel-2 Vegetation Indices (VIs) and Sentinel-1 Synthetic Aperture Radar (SAR) for invasive alien species detection and mapping

Onisimo Mutanga,Perushan Rajah,John Odindi,Zolo Kiala

doi:10.3897/natureconservation.35.29588

Abstract

The threat of invasive alien plant species is progressively becoming a serious global concern. Alien plant invasions adversely affect both ecological services and socio-economic systems. Hence, accurate detection and mapping of invasive alien species is valuable in mitigating adverse ecological and socio-economic effects. Recent advances in active and passive remote sensing technology have created new and cost-effective opportunities for the application of remote sensing to invasive species mapping. In this study, new generation Sentinel-2 (S2) optical imagery was compared to S2 derived Vegetation Indices (VIs) and S2 VIs fused with Sentinel-1 (S1) Synthetic Aperture Radar (SAR) imagery for detecting and mapping the American Bramble (Rubuscuneifolius). Fusion of S2 VIs and S1SAR imagery was conducted at pixel level and multi-class Support Vector Machine (SVM) image classification was used to determine the dominant land use land cover classes. Results indicated that S2 derived VIs were the most accurate (80%) in detecting and mapping Bramble, while fused S2 VIs and S1SAR were the least accurate (54%). Findings from this study suggest that the application of S2 VIs is more suitable for Bramble detection and mapping than the fused S2 VIs and S1SAR. The superior performance of S2 VIs highlights the value of the new generation S2 VIs for invasive alien species detection and mapping. Furthermore, this study recommends the use of freely available new generation satellite imagery for cost effective and timeous mapping of Bramble from surrounding native vegetation and other land use land cover types.

Highlights

Global biodiversity is increasingly becoming susceptible to pressure from invasive species (Butchart et al 2010)
This study contributes to the evaluation of economically viable, efficient and large scale invasive alien species detection and mapping
Conventional S2 optical imagery was used as a benchmark for comparison with results achieved using S2 Vegetation Indices (VIs) and fused VIs and S1 Synthetic Aperture Radar (SAR) imagery

Summary

Introduction

Global biodiversity is increasingly becoming susceptible to pressure from invasive species (Butchart et al 2010). The rapid spread of invasive alien plants in several regions of the world has adversely impacted ecosystem health, native species diversity and local and national economies (Pysek et al 2012; Schirmel et al 2016; Convention on Biological Diversity 2009). Increased costs associated with invasive alien species eradication and management programmes puts further pressure on biodiversity (Marbuah et al 2014). The severity of the problem has increased the impetus on development of efficient and cost-effective approaches for the control and management of invasive alien plant species. Originating from North America, Bramble belongs to the Rosaceae family and has adverse direct and indirect impacts on biodiversity that include changes in nutrient cycling, increase in soil erosion, reduction in rangeland carrying capacity and viability, as well as effects on natural plant succession, fire patterns and behaviour and hydrological processes (Henderson 2001)

Methods

Results

Discussion

Conclusion