Unmanned Aerial Vehicle (UAV) Remote Sensing for Hyperspatial Terrain Mapping of Antarctic Moss Beds based on Structure from Motion (SfM) point clouds A.Lucieer a,* , S. Robinson b , D. Turner a a University of Tasmania, Hobart, Australia (*[email protected]) b University of Wollong, Wollongong, Australia Abstract- This study is the first to use an Unmanned Aerial Vehicle (UAV) for mapping moss beds in Antarctica. Mosses can be used as indicators for the regional effects of climate change. Mapping and monitoring their extent and health is therefore important. UAV aerial photography provides ultra-high resolution spatial data for this purpose. The aim of this study is to use Structure from Motion (SfM) techniques to generate a detailed 3D point cloud of the terrain from overlapping UAV photography. Keywords: Unmanned Aerial Vehicle (UAV), Antarctica, moss beds, Structure from Motion (SfM) point cloud, terrain mapping 1. INTRODUCTION Polar regions are experiencing rapid and severe climatic shifts with major changes in temperature, wind speed and UV-B radiation already observed in Antarctica (Convey et al. 2009; Turner et al. 2005). Since vegetation is isolated to the coastal fringe and climatic records only extend back 50 years, with limited spatial resolution, we urgently need new proxies to determine if coastal climate has changed over the past century. In a manner similar to trees, old growth mosses also preserve a climate record along their shoots. Our ability to accurately date these mosses and map their extent in sufficient spatial detail means that, for the first time, mosses can be used as sentinels to provide crucial information on how the Antarctic coastal climate has changed over past centuries and how biota has responded to these changes (Lovelock & Robinson 2002; Robinson, Wasley, & Tobin 2003; Wasley et al. 2006). The spatial scale of the moss beds (tens of m 2 ) makes satellite imagery (even recent very high resolution imagery of 0.5 m) unsuitable for mapping their extent in sufficient detail. Due to logistical constraints aerial photography is impractical and also does not provide the required spatial resolution. Recent developments in the use of unmanned aerial vehicles (UAVs) for remote sensing applications provide exciting new opportunities for ultra-high resolution mapping and monitoring of the environment. A recent special issue on UAVs highlights that this field has an increasing potential for remote sensing applications (Zhou et al. 2009). Rango et al. (2006) and Hardin & Jackson (2005) developed and used a UAV based on a remote controlled helicopter and a plane capturing <1 cm resolution colour photography for rangeland mapping and monitoring. Several recent studies have highlighted the benefit of UAVs for crop mapping and monitoring (Berni et al. 2009; Hunt Jr et al. 2010; Lelong et al. 2008; Zarco-Tejada 2008). Laliberte & Rango (2009) and Dunford et al. (2009) demonstrated how UAV imagery can be used for mapping natural vegetation using geographic object-based image analysis (GEOBIA) techniques. Finally, Nagai et al. (2009) showed how multiple sensors (visible, near-infrared, and LiDAR) can collect very high resolution data simultaneously from a large UAV. The key advantages of UAVs platform are their ability to fill a niche with respect to spatial and temporal resolution. The imagery acquired from a UAV is at sub-decimetre or even centimetre resolution (i.e. hyperspatial) and UAV imagery can be flown on- demand making it possible to capture imagery frequently allowing for efficient monitoring (i.e. hypertemporal) . In this study, we developed a small UAV based on a remote controlled helicopter carrying three different cameras: visible colour, near-infrared, and thermal infrared for cost-effective, efficient, and ultra-high resolution mapping of moss beds within an Antarctic Special Protected Area (ASPA) near Casey, Windmill Islands, Antarctica. This paper focuses on a new technique, Structure from Motion (SfM), for deriving very dense 3D point clouds from overlapping UAV photography. 2. STUDY AREA The Windmill Islands region near Casey has the most extensive and well-developed vegetation in Eastern Antarctica (Figure 1). The vegetation communities in Antarctica and the sub-Antarctic are undergoing rapid change. Climate change is now recognised as occurring in the high latitudes rendering Antarctica one of the most significant baseline environments for the study of global climate change. Temperature, UVB and changes in water availability have been identified as the three key factors that will change in the Antarctic regions with climate change. Despite this, there have been few long-term studies of the response of Antarctic vegetation to climate (Convey et al. 2009; Robinson, Wasley, & Tobin 2003). Figure 1. Study area: the continent of Antarctica with an arrow in Eastern Antarctica indicating the location of the Windmill Islands (source: Australian Antarctic Data Centre). Most focus of change in the Antarctic region has been on the Antarctic Peninsula where dramatic shifts in temperature of up to 5 degrees Celsius have been recorded (Turner et al. 2005) with subsequent expansion of local plant communities. However, the first documented major change in a terrestrial community in Continental Antarctica has now been reported (King 2009). Preliminary analysis of January 2008 data
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Unmanned Aerial Vehicle (UAV) Remote Sensing for Hyperspatial Terrain Mapping of
Antarctic Moss Beds based on Structure from Motion (SfM) point clouds
A.Lucieer a,*, S. Robinson
b, D. Turner
a
aUniversity of Tasmania, Hobart, Australia (*[email protected]) b University of Wollong, Wollongong, Australia
Abstract- This study is the first to use an Unmanned
Aerial Vehicle (UAV) for mapping moss beds in
Antarctica. Mosses can be used as indicators for the
regional effects of climate change. Mapping and
monitoring their extent and health is therefore important.