# Quality Assessment of Photogrammetric Methods--A Workflow for Reproducible UAS Orthomosaics  
[PERSON]  
1 Department of Geography, Philipps-University Marburg, Deutschhausstr. 10, 35037 Marburg, Germany; [EMAIL_ADDRESS] (N.F. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.S.); [EMAIL_ADDRESS] (L.W. ); [PERSON]RESS] (C.R. ); [EMAIL_ADDRESS] (T.N.) [PERSON]  
1 Department of Geography, Philipps-University Marburg, Deutschhausstr. 10, 35037 Marburg, Germany; [EMAIL_ADDRESS] (N.F. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.S.); [EMAIL_ADDRESS] (L.W. ); [PERSON]RESS] (C.R. ); [EMAIL_ADDRESS] (T.N.) [PERSON]  
1 Department of Geography, Philipps-University Marburg, Deutschhausstr. 10, 35037 Marburg, Germany; [EMAIL_ADDRESS] (N.F. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.S.); [EMAIL_ADDRESS] (L.W. ); [PERSON]RESS] (C.R. ); [EMAIL_ADDRESS] (T.N.) [PERSON]  
1 Department of Geography, Philipps-University Marburg, Deutschhausstr. 10, 35037 Marburg, Germany; [EMAIL_ADDRESS] (N.F. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.S.); [EMAIL_ADDRESS] (L.W. ); [PERSON]RESS] (C.R. ); [EMAIL_ADDRESS] (T.N.) [PERSON]  
2 GAMES Group, Department of Horticulture, Fruit, Growing Botany and Garding, University of Lleida, 25198 Lleida, Spain; [EMAIL_ADDRESS] (C.M.R. ); [EMAIL_ADDRESS] (M.-T.S.) Seviss Federal Institute for Forest, Snow and Landscape Research WSL, Zurcherstr. 111, 8903 Birremdsdorf, Switzerland; [EMAIL_ADDRESS]  
Geoscience Barcelona (GEO3 BCN--CSIC), 08028 Barcelona, Spain; [PERSON]@geo3 bcn.csic.es  
Laboratory ECOFUN, Forest Science and Technology Centre of Catalonia (CTFC), 25280 Solsona, Catalonia, Spain  
Correspondence: [EMAIL_ADDRESS]  
November 5, 2021 November 5, 2021 November 5, 2020 November 5, 2021 November 5, 2021 November 5, 2021 November 5, 2020 November 5, 2021 November 5, 2021 November 5, 2  
Applications of UAS can be structured into two main components: the acquisition of individual images--including the flight planning--with an unmanned aerial vehicle (UAV) for a particular region of interest and the processing of these images with photogrammetric methods to obtain georeferenced orthophoto mosaics [8; 14; 15; 16] or digital surface models [8; 17; 18]. Studies on the development of workflows for UAS are sparse, often exclude the flight planning and are mostly tied to a very specific application [4; 19]. A generalized, flexible and commonly accepted workflow is still missing [13]. Standardized protocols and quality assessments are needed for a better understanding and appropriate use of UAS imagery. Since the final product quality depends on the initial image capturing, flight planning is one important aspect in a common workflow scheme. For example, the flight height in conjunction with the used sensor (RGB, multispectral or hyperspectral) affect the ground sampling distance (GSD, i.e., pixel size or spatial resolution) of the images and in conjunction with the flight path affect the overlap of the individual images which is a key factor for the successful image processing [20]. A fully reproducible study therefore must include the flight path and parameters as well as the camera configuration metadata. For ready-to-fly consumer UAV, flight planning is usually done in software which is tied to the specific hardware (e.g., the DJIFlightPlanner for DJI drones). These commercial solutions often do not provide the full control of autonomous flights and access to metadata which makes it difficult to integrate flight planning in a generalized workflow. In this respect, open hardware/software solutions like Pixhawk based systems and the MAVlink protocol (mavlink.io) are advantageous. To complete the metadata, environmental conditions during the flight like sun angle and cloudiness that also have impacts on the image quality [21] should be recorded. Equally or even more important for valid results and their use in subsequent data analysis or synthesis is a quality assessment of the resulting image products in terms of their spatial accuracy and reproducibility.