Radiometric calibration framework for ultra-high-resolution UAV-derived orthomosaics for large-scale mapping of invasive alien plants in semi-arid woodlands : Harrisia pomanensis as a case study

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dc.contributor.author Mafanya, Madodomzi
dc.contributor.author Tsele, Philemon
dc.contributor.author Botai, J.O. (Joel Ongego)
dc.contributor.author Manyama, Phetole
dc.contributor.author Chirima, George J.
dc.contributor.author Monate, Thabang
dc.date.accessioned 2018-08-21T10:27:07Z
dc.date.issued 2018
dc.description.abstract Orthomosaics derived from consumer grade digital cameras on board unmanned aerial vehicles (UAVs) are increasingly being used for biodiversity monitoring and remote sensing of the environment. To have lasting quantitative value, remotely sensed imagery should be calibrated to physical units of reflectance. Radiometric calibration improves the quality of raw imagery for consistent quantitative analysis and comparison across different calibrated imagery. Moreover, calibrating remotely sensed imagery to units of reflectance improves its usefulness for deriving quantitative biochemical and biophysical metrics. Notwithstanding the existing radiometric calibration procedures for correcting single images, studies on radiometric calibration of UAV-derived orthomosaics remain scarce. In particular, this study presents a cost- and time-efficient radiometric calibration framework for designing calibration targets, checking scene illumination uniformity, converting orthomosaic digital numbers to units of reflectance, and accuracy assessment using in situ mean reflectance measurements (i.e. the average reflectance in a particular waveband). The empirical line method was adopted for the development of radiometric calibration prediction equations using mean reflectance values measured in only one spot within a 97 ha orthomosaic for three wavebands, i.e. red, green and blue of the Sony NEX-7 camera. A scene illumination uniformity check experiment was conducted to establish whether 10 randomly distributed regions within the orthomosaic experienced similar atmospheric and illumination conditions. This methodological framework was tested in a relatively flat terrain semi-arid woodland that is invaded by Harrisia pomanensis (the Midnight Lady). The scene illumination uniformity check results showed that at a 95% confidence interval, the prediction equations developed using mean reflectance values measured from only one spot within the scene can be used to calibrate the entire 97 ha RGB orthomosaic. Furthermore, the radiometric calibration accuracy assessment results showed a correlation coefficient r value of 0.977 (p < 0.01) between measured and estimated reflectance values with an overall root mean square error of 0.063. These findings suggest that given the entire scene being mapped is experiencing similar atmospheric and illumination conditions, then prediction equations developed using mean reflectance values measured in only one spot within the scene can be used to calibrate the entire orthomosaic in semi-arid woodlands. The proposed methodological framework can potentially be tested and adapted for use in large-scale crop mapping and monitoring in precision agriculture, land-use/land-cover classification as well as plant species delimitation, particularly for mapping widespread invasive alien plants such as H. pomanensis. en_ZA
dc.description.department Geography, Geoinformatics and Meteorology en_ZA
dc.description.embargo 2019-07-03
dc.description.librarian hj2018 en_ZA
dc.description.sponsorship The South African National Department of Environmental Affairs through its funding of the South African National Biodiversity Institute Directorate: Biological Invasions, project number [P038]. en_ZA
dc.description.uri http://www.tandfonline.com/loi/tres20 en_ZA
dc.identifier.citation Madodomzi Mafanya, Philemon Tsele, Joel O. Botai, Phetole Manyama, George J. Chirima & Thabang Monate (2018) Radiometric calibration framework for ultra-high-resolution UAV-derived orthomosaics for large-scale mapping of invasive alien plants in semi-arid woodlands : Harrisia pomanensis as a case study, International Journal of Remote Sensing, 39:15-16, 5119-5140, DOI: 10.1080/01431161.2018.1490503. en_ZA
dc.identifier.issn 0143-1161 (print)
dc.identifier.issn 1366-5901 (online)
dc.identifier.other 10.1080/01431161.2018.1490503
dc.identifier.uri http://hdl.handle.net/2263/66300
dc.language.iso en en_ZA
dc.publisher Taylor and Francis en_ZA
dc.rights © 2018 Informa UK Limited, trading as Taylor & Francis Group. This is an electronic version of an article published in International Journal of Remote Sensing , vol. 39, no. 15-16, pp. 5119-5140, 2018. doi : 10.1080/01431161.2018.1490503. International Journal of Remote Sensing is available online at : http://www.tandfonline.com/loi/tres20. en_ZA
dc.subject Unmanned aerial vehicle (UAV) en_ZA
dc.subject Reflection en_ZA
dc.subject Root mean square errors en_ZA
dc.subject Remotely sensed imagery en_ZA
dc.subject Radiometric calibrations en_ZA
dc.subject Illumination uniformity en_ZA
dc.subject Illumination conditions en_ZA
dc.subject Correlation coefficient en_ZA
dc.subject Biodiversity monitoring en_ZA
dc.subject Remote sensing en_ZA
dc.subject Radiometry en_ZA
dc.subject Mean square error en_ZA
dc.subject Mapping en_ZA
dc.subject Land use en_ZA
dc.subject Image enhancement en_ZA
dc.subject Forecasting en_ZA
dc.subject Calibration en_ZA
dc.subject Biodiversity en_ZA
dc.subject Antennas en_ZA
dc.title Radiometric calibration framework for ultra-high-resolution UAV-derived orthomosaics for large-scale mapping of invasive alien plants in semi-arid woodlands : Harrisia pomanensis as a case study en_ZA
dc.type Postprint Article en_ZA


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