Steps to build a DIY low-cost fixed-wing drone for biodiversity conservation

constant altitude of 100 m AGL and a maximum telemetry range of around 20 km, covering an area of 1.7 km2 with 2.8 cm px-1 GSD. As a reference, the model in circular survey pre-pro- grammed flights was able to survey 10 ha in four minutes flying at 100 m AGL (2.8 cm px-1 images); six minutes flying at 75 m AGL (2.1 cm px-1 images); seven minutes flying at 50 m AGL (1.4 cm px-1 images); and 13 minutes, flying at 25 m AGL (0.7 cm px-1 images) always including take-off and landing (Table 1). For both specific and circular grid for the lawnmower flight at 100 and 120 m AGL it was possible to identify deforestation spots smaller than 5 m2, opening of small trails and vegeta- tion clearings that are difficult to detect by satellite images (Fig 5). We could also easily detect and identify medium size animals (such as a domestic dog, 1 m size) on the images obtained in flights with the embarked camera at 25 m AGL, which were less easily detectable although still noticeable at around 50 m. For the last two flights with a specific grid pattern and at 120 m AGL it was possible to obtain images with a resolution of 3.3 cm px-1 in which we could identify trails in the vegeta- tion and degraded areas inside an area of 1 km2. The drone images were processed in this case to create an orthomosaic map using the Agisoft Metashape (version 1.5.5; www.agisoft.com). Fig 5. Comparison between Above Ground Level (AGL), Ground Sample Distance (GSD) and flight duration. Images with a 10x zoom of a dog and a deforestation spot at (a) 100 m; (b) 75 m; (c) 50 m; and (d) 25 m AGL.

https://doi.org/10.1371/journal.pone.0255559.g005 PLOS ONE Building a DIY low-cost fixed-wing drone for biodiversity conservation PLOS ONE | https://doi.org/10.1371/journal.pone.0255559 August 13, 2021 11 / 17