International Journal of Applied Earth Observation and Geoinformation 33 (2014) 270–279 Contents lists available at ScienceDirect International Journal of Applied Earth Observation and Geoinformation jo ur nal home p age: www.elsevier.com/locate/ jag Validation of measurements of land plot area using UAV imagery Francisco Javier Mesas-Carrascosa ∗ , María Dolores Notario-García, José Emilio Mero ˜ no de Larriva, Manuel Sánchez de la Orden, Alfonso García-Ferrer Porras Department of Graphic Engineering and Geomatics, University of Cordoba, Campus de Rabanales, 14071 Cordoba, Spain a r t i c l e i n f o Article history: Received 12 March 2014 Accepted 12 June 2014 Keywords: UAV ISO 5725 Land policies a b s t r a c t This paper analyzes the potential use of very high resolution UAV imagery to measure the area of land plots to monitor land policies. The method used to monitor land is to measure the area of a set of land plots. Compared to traditional methods based on Global Navigation Satellite System (GNSS) measurements or imagery obtained from aerial or satellite platforms, UAV systems lead to improved cost savings in this task without losing accuracy. The tests were conducted on 25 plots representing all the characteristics of a region (e.g. size, shape, border conditions and land use). We determined technical tolerance as a buffer using ISO 5725. We also assessed the relationship between the buffers obtained for the land plots and the characteristics of the plots. Technical tolerance in the digitized plots was within the range established by the European Union. This result shows the validity of UAV systems for land policy monitoring. © 2014 Elsevier B.V. All rights reserved. Introduction A number of governments and the European Union (2004) have underlined the need to use measuring instruments that are con- trolled by law. In this regard, the methods used to measure areas of land plots using Global Navigation Satellite Systems (GNSS) or aerial and spatial images must be evaluated to determine their tech- nical tolerance as a buffer. In fact, Article 30.1 of EU Commission Regulation No. 796/2004 establishes that the measurement area shall not exceed either 5% of the land plot or a buffer of 1.5 m applied to its perimeter. Also, the maximum tolerance with regard to each land plot shall not, in absolute terms, exceed 1 ha. The European Union has developed technical notes to define an approach for the validation of area measurement methods to provide a standard- ized way to estimate the tools use for area measurements based in ISO 5725 (Kay and Sima, 2009). In this context UAV orthophotos have not been evaluated yet to know if they are valid as a method to measure areas of land plots for monitoring land policies. These land policies define a set of rules on good agricultural and environmental condition designed to prevent soil erosion or to ensure a minimum level of maintenance. These conditions set a percentage of the plot area that has to comply with different characteristics, therefore is important to measure plot area properly. These measurement ∗ Corresponding author at: Departamento de Ingeniería Gráfica y Geomática, Uni- versidad de Córdoba, Campus de Rabanales, edificio Gregor Mendel, 2 a planta, 14071 Cordoba, Spain. Tel.: +34 957 218 537; fax: +34 957 218 537. E-mail address: ig2mecaf@uco.es (F.J. Mesas-Carrascosa). instruments have some problems related with the monitoring pro- cess. GNNS requires a large effort to evaluate all the controlled land. On the other hand, aerial or satellite images sometimes are not taken in the necessary moment. UAV can be an alternative where we can fly controlled land when it is necessary. Satellite and aircraft-based systems are the two platforms most commonly used to collect image data. The imagery is used to derive information to create maps, digital terrain models and orthopho- tos (Beekhuizen and Clarke, 2010; Jianwei et al., 2011; Pieczonka et al., 2011; Reinartz et al., 2011; Saadat et al., 2011). These plat- forms ensure the spatial and spectral quality of the data be used in projects where its geographical extent makes impossible to derive them by traditional on-ground survey. Users can measure coordi- nates, distances, areas and radiances and can also use the data as support for decision-making (Meddens et al., 2011). Depending on the use we make of the data provided by onboard sensors, these platforms may or may not be adequate because of their spatial, spectral, radiometric or temporal resolution. When very high spa- tial resolution is required, depending on the application current satellite-based products have a limited application because they have insufficient spatial resolution (Seelan et al., 2003; Woodcock and Strahler, 1987). High-resolution satellites are not adequate if we need to detect small objects with a size of 0.20 m or less, for example. Conversely, very high spatial resolution imagery such as that obtained using metric aerial cameras tends to have low spec- tral resolution. Therefore, it is difficult to develop applications to assess crops status or conditions. Traditionally, cameras onboard aircraft systems have been developed to obtain metric image data and spectral data has been http://dx.doi.org/10.1016/j.jag.2014.06.009 0303-2434/© 2014 Elsevier B.V. All rights reserved.