Abstract
Abstract. With the appearance of cost effective, easy to fly Unmanned Aerial Vehicles (UAV), a new type of data collection has been enabled: super high resolution multi-spectral, precisely georeferenced imagery and point clouds, collected over high value targets. The high spatial resolution and precise georeferencing accuracy makes information extraction and advanced analytics possible both in the spatial and temporal domain at scales simply not possible to collect from manned aircraft, and at much greater efficiency than can be collected from the ground. One example of this is plant phenotyping for experimental research where a high-accuracy spatial reference needs to be assigned to each plot entry to enable accurate and efficient plot level statistics of plant phenotypic attributes. This paper presents results from an integration of the Trimble APX-15-EI UAV Direct Georeferencing system with the Micasense Altum multi-spectral camera to produce a highly accurate and efficient UAV based mapping solution for advanced spatial and temporal analytics without the use of Ground Control Points (GCP’s). Results from a series of flights over a test range outfitted with GNSS surveyed check points show an orthomap accuracy at the level of 3 cm RMSx,y horizontal can be achieved. The same system flown over a test field operated by researchers at the University of Guelph containing plots of soybean demonstrated pixel-level alignment of the directly georeferenced orthomosaic to the cm-level plot boundaries previously surveyed by the researchers, thus meeting the requirements for automated phenotyping.
Highlights
Direct Georeferencing (DG) of airborne imagers using GNSSAided Inertial systems as an alternative or complement to Aerial Triangulation (AT) has been a standard for manned applications since the early 2000’s (Cramer et al 2000, Hutton et al, 2005)
Instead of being limited to the ground and measuring discrete points with a GNSS receiver operated by a human, a Unmanned Aerial Vehicle (UAV) with a Direct Georeferencing system moves the GNSS receiver into the sky to a vantage point where it can measure multiple points at once using an imager such as a LiDAR or a camera
This paper investigates the use of Direct Georoeferencing on a UAV based multi-spectral imager to efficiently achieve the cm level positioning accuracy required to align the imagery with presurveyed plot boundaries, all without the use of Ground Control Points (GCP’s)
Summary
Direct Georeferencing (DG) of airborne imagers using GNSSAided Inertial systems as an alternative or complement to Aerial Triangulation (AT) has been a standard for manned applications since the early 2000’s (Cramer et al 2000, Hutton et al, 2005). DG brings several advantages to airborne mapping that include eliminating the need to use Ground Control Points (GCP’s) to do georeferencing, reducing sidelap and endlap (or even no sidelap or endlap) requirements, and sensor fusion of multiple imaging payloads in a single platform (such as a LiDAR with a camera). Each of these greatly reduces the cost and increases the overall efficiency of airborne mapping (Mostafa et al, 2001). With a UAV, GNSS becomes a much more viable and cost effective method to accurately georeference data, enabling activities such as temporal analysis to be conducted for applications where GNSS collected from the ground might not be practical or too costly
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