**3.5. Complementary techniques and their interrelation**

Aerial imagery has the ability to display portions of the object from a different perspective. Oblique images, those that are not restricted by the verticality of the shot, open a wide range of applications in forensics, either as a supplement to the understanding of the scene, or for extracting added information to the terrestrial one. Aerial images can be integrated into more complex systems, such as GIS, by georeferencing. Surveying tools such as GNSS provide 3D information of significant points in the aerial images in order to link them to global coordinate

There are basically two built‐on types of UAV: rotary wing and fixed wing (**Figure 7b**). The most extended are the electrical multirotors, being the most common configurations those which have 4, 6 or 8 propellers (**Figure 7a**). Multirotors improve the performance of radio control helicopters increasing manoeuvrability and stability in the air. Electrical engines also are able to reduce vibrations, an extremely important matter to achieve high‐quality images. On the other hand, the presence of multiple engines increases the security by diminishing the

**Figure 7.** Unmanned vehicles employed in forensic science. Multirotor (a); fixed‐wing (b) and ground vehicles (c).

Mission planning optimizes the process of data collection. Flying over complex scenarios, the operator can take advantage of the high manoeuvrability of multirotors turning off automated control of the route and turning on manual control. For this purpose, real‐time display devices are available putting virtually the operator in the point of view of the camera in the air.

UAV platforms are composed of independent devices, being possible to customize the configuration of the payload. This makes possible to have on‐board different types of cameras: SLR cameras, video, thermal, multispectral. The possibility of integrating the data coming from different sensors provides a new level of interpretation to complex and large scenarios in

Regarding the terrestrial unmanned systems (**Figure 7c**), also known as unmanned ground vehicles (UGV), they can be used for inspection or target location in indoor areas or GNSS‐ denied environments. Their size can be easily scaled accordingl to the mission objectives and payload. They share the advances in the UAV field, such as the mission planner for outdoor environments. However, they take advantage of robotics, being possible add as payload a remote controlled manipulator arm, for inspection tasks. In all cases, the autonomous explo‐

reference systems.

14 Forensic Analysis - From Death to Justice

forensic analysis.

possibility of failure of any component.

Due to its transversal and multidisciplinary character, geomatic techniques are suitable and provide added value in forensic science, from crime scene reconstruction to post‐mortem analysis. The main common feature of the individual techniques that could be grouped into the geomatic science, it is their non‐invasive and non‐destructive character. The taxonomy of the 3D measuring methods is structured according to the electromagnetic energy interaction, been mainly the analysis and processing of reflected or transmitted energy. However, each one has its own advantages in terms of achievable precision, data resolution, flexibility, portability or radiometric resolution. In order to summing up all and with the aim of providing a comprehensive classification, in **Figure 8**, a selection of the sensors and techniques currently

**Figure 8.** Relationship between different geomatics methods employed in forensic science.

used in forensic science are ranked according to their precision and the size of the studied object and/or scene. A more detailed description of the individual techniques and their variants can be found in [12].

The portability is a common relevant factor, due to the need of moving sensors around the object or scene to carry out a proper data acquisition. Although in some cases, the evidence could be moved to the forensic lab, geomatic sensors should provide a medium degree of mobility and portability.

Although some geomatic techniques have showed to complement a full spectrum of possibil‐ ities, some of them could provide added value in forensic analysis.

In order to surpass the limitations of precision and resolution of TLS, focused on the recording of medium or large scenes, sometimes more precision and resolution are required for the 3D modelling of small objects or evidences. In these cases, the coordinate measuring machine (CMM) or handheld scanner could offer an alternative. These systems allow tactile and discrete point measurement and massive point acquisition using a linear scanner. However, the main problem of CMM is its portability and its lack of radiometry.

CMM and handheld techniques are highly useful in soft and nonparametric surfaces where any contact will disturbance the previous measurements, or worse, affect the preservation of the evidence. The unique geometric counterpart is the limitation in depth acquisition, being unable to acquire data in holes of small diameter or deep holes.

On the other hand, sometimes the precision is not always a critical factor, being crucial the ability to discover hidden information in the scene. At this point, the ground penetrating radar (GPR) has been proved as useful technique for detection of underground structures, mainly clandestine graves [13] but not limited, being other alternatives the search for buried weapons, drugs, hazardous waste, etc.

The main advantages are the non‐invasiveness property and the capability to cover wide areas (outdoors and/or indoors). However, its applicability is limited to the specialized training in data acquisition, processing and data interpretation [14], being also critical the data acquisition planning, since the bigger the suspicious area the lower efficiency in its detection. Moreover, this sensor should be combined with an alternative system to georeference it according to an external reference frame. Due to its simplicity, portability, and appropriate precision, the GNSS systems are chosen to connect the GPR data with a global frame.

For a more extensive review of geomatic/geoscience methods applied to forensic search, please refer to [15].
