Comparison of four UAV georeferencing methods for environmental monitoring purposes focusing on the combined use with airborne and satellite remote sensing platforms
Padró Garcia, Joan-Cristian (Universitat Autònoma de Barcelona. Departament de Geografia)
Muñoz, Francisco-Javier (HEMAV S.L.)
Planas, Jordi 1950- (Universitat Autònoma de Barcelona. Departament de Geografia)
Pons, Xavier (Universitat Autònoma de Barcelona. Departament de Geografia)

Date:	2019
Abstract:	This work is aimed at the environmental remote sensing community that uses UAV optical frame imagery in combination with airborne and satellite data. Taking into account the economic costs involved and the time investment, we evaluated the fit-for-purpose accuracy of four positioning methods of UAV-acquired imagery: 1) direct georeferencing using the onboard raw GNSS (GNSSNAV) data, 2) direct georeferencing using Post-Processed Kinematic single-frequency carrier-phase without in situ ground support (PPK1), 3) direct georeferencing using Post-Processed Kinematic double-frequency carrier-phase GNSS data with in situ ground support (PPK2), and 4) indirect georeferencing using Ground Control Points (GCP). We tested a multispectral sensor and an RGB sensor, onboard multicopter platforms. Orthophotomosaics at <0. 05 m spatial resolution were generated with photogrammetric software. The UAV image absolute accuracy was evaluated according to the ASPRS standards, wherein we used a set of GCPs as reference coordinates, which we surveyed with a differential GNSS static receiver. The raw onboard GNSSNAV solution yielded horizontal (radial) accuracies of RMSEr≤1. 062 m and vertical accuracies of RMSEz≤4. 209 m; PPK1 solution gave decimetric accuracies of RMSEr≤0. 256 m and RMSEz≤0. 238 m; PPK2 solution, gave centimetric accuracies of RMSEr≤0. 036 m and RMSEz≤0. 036 m. These results were further improved by using the GCP solution, which yielded accuracies of RMSEr≤0. 023 m and RMSEz≤0. 030 m. GNSSNAV solution is a fast and low-cost option that is useful for UAV imagery in combination with remote sensing products, such as Sentinel-2 satellite data. PPK1, which can register UAV imagery with remote sensing products up to 0. 25 m pixel size, as WorldView-like satellite imagery, airborne lidar or orthoimagery, has a higher economic cost than the GNSSNAV solution. PPK2 is an acceptable option for registering remote sensing products of up to 0. 05 m pixel size, as with other UAV images. Moreover, PPK2 can obtain accuracies that are approximate to the usual UAV pixel size (e. g. co-register in multitemporal studies), but it is more expensive than PPK1. Although indirect georeferencing can obtain the highest accuracy, it is nevertheless a time-consuming task, particularly if many GCPs have to be placed. The paper also provides the approximate cost of each solution.
Grants:	European Commission 641762 Ministerio de Ciencia e Innovación CGL2015-69888-P Agència de Gestió d'Ajuts Universitaris i de Recerca 2017/SGR-1690
Note:	Altres ajuts: C.P. is a recipient of a FI-DGR scholarship grant (2016B_00410). X.P. is a recipient of an ICREA Academia Excellence in Research Grant ().
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, i la comunicació pública de l'obra, sempre que no sigui amb finalitats comercials, i sempre que es reconegui l'autoria de l'obra original. No es permet la creació d'obres derivades.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	UAV ; Drone ; Direct georeferencing ; Indirect georeferencing ; ASPRS standards ; Post-Processed Kinematic
Published in:	International journal of applied earth observation and geoinformation, Vol. 75 (March 2019) , p. 130-140, ISSN 1872-826X

DOI: 10.1016/j.jag.2018.10.018

11 p, 3.0 MB

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Research literature > UAB research groups literature > Research Centres and Groups (research output) > Experimental sciences > Grupo de Investigación Métodos y Aplicaciones en Teledetección y Sistemas de Información Geográfica (GRUMETS)
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