## 2 Materials and Methods
### Remote Sensing: Thermal, RGB, and DTM Acquisitions  
The graphic documentation of archeological heritage in Spain [29; 30] and Europe [31; 32] has advanced rapidly in recent years, owing to the development of consumer UAVs and user-friendly, high-performance photogrammetric software. This technology was used to conduct three photogrammetric acquisition campaigns in the surroundings of the CCB and at the top of the castle (Figure 3).  
The first airborne survey (30 June 2014 at 12 p.m. UTC + 01:00) covered an area measuring 1040 hectares. The survey was carried out using two sensors mounted simultaneously on board in a Cessna aircraft flying at 250 m above ground level. The first sensor was a FLIR SC655 thermal camera (FLIR Systems, Inc., Wilsonville, OR, USA) with a resolution of \(640\times 480\) pixels, which was equipped with a 13.1 mm F1.3 lens connected to a computer via USB2.0 protocol. The spectral response was in the range 8-12 \(\upmu\)m. The camera was calibrated in the laboratory (Quantalab; IAS-CSIC, Cordoba, Spain) to obtain radiance values. A total of 5133 images were acquired during this survey. Orthorectification and imagery mosaicking were conducted using the structure from motion method (SfM) to obtain two thermal mosaics in Kelvin degrees with a spatial resolution of 0.37 m/px. The second sensor for this first campaign was an RGB sensor (NIKON D800E). A total of 3473 images were acquired. Orthorectification and imagery mosaicking were conducted as described above for thermal mosaic images, allowing us to obtain a very high-resolution orthophoto and a digital surface model (DSM) with a spatial resolution of 0.036 m/px.  
For the second campaign, a UAV survey was performed (1 March 2016 at 12 p.m. UTC + 01:00). The UAV-based photogrammetric data acquisition campaign was conducted with a Sony Alpha 5000 20.1 MP RGB sensor mounted onboard a UAV flying at 80 m above ground level. The UAV platform was a multicopter (rotary-wing UAV). Two flights were made due to differences in the terrain elevation. The flight plans were designed in grid mode to ensure the best overlap. A total of 809 images covering an area of 22.49 hectares were acquired. Seven ground control points were measured with GPS to  
Figure 3: Orthophotogrammetric acquisition survey of the area surrounding the CCB and the medieval Castle of Belmez, performed by aircraft and drone with RGB and thermal sensors. Images from Quantalab-IAS/CSIC and ZNIR for “Ager Mellariensis”/AEI FEDER HAR 77136-R.  
ensure the accuracy and spatial location of the model. Orthorectification and imagery mosaicking were conducted using SfM, allowing us to obtain a very high-resolution orthophoto and a DSM with a spatial resolution of 0.025 m/px.  
The goal of the third campaign was to document the castle walls. A UAV-based photogrammetric data acquisition campaign (2 March 2016 at 12 p.m. UTC + 01:00) was conducted with the same Sony Alpha 5000 20.1 MP RGB sensor and the same rotary-wing UAV. The flight was performed in manual mode due to the complexity of the castle structures. A total of 441 images of the castle walls and tower were acquired. Seventy-five ground control points were measured using a total station to ensure the accuracy and spatial location of the model. Orthorectification and imagery mosaicking were conducted using SfM to obtain a very high-resolution orthophoto of all of the structures (<0.001 m/px).