Mobile sensors and monitoring robots
Advances in mobile sensors and monitoring robots have increased the spatial resolution of environmental sensing, enabling capabilities such as detecting the location of pollution hotspots within water bodies (Powers et al., 2018). Mobile sensors can be divided into those designed to travel passively within water currents (Marchant et al., 2015, Gardner et al., 2020), and those that are actively mobilised using robotic technology. Unmanned robots are a promising solution for sensing in hard-to-reach locations, enabling spatially continuous data collection and monitoring over longer distances and time periods.
Unmanned/unpiloted aerial vehicles (UAV), also known as aerial drones, can monitor large areas and use multi-spectral imaging and on-board probes and samplers to measure parameters such as algal blooms, temperature and light. Small-scale, uncrewed surface vehicles/vessels (USV), also known as unmanned surface vehicles/vessels can be equipped with on-board bathymetric, light detection and ranging (LiDAR), GPS, and flow sensors, which enable correlation of geographical and hydrological parameters with water quality sensing (e.g. temperature, suspended solids concentration and hydrocarbon concentration (Martinez Vargas et al., 2023)). In addition to carrying water quality sensors, samplers are also beginning to emerge with the ability to automate water sample collection and analysis on-board USVs, providing further potential for monitoring in-situ ecosystem processes (e.g. biochemical oxygen demand for respiration) (Fornai et al., 2012, Shabani et al., 2021). The availability of relatively low-cost autonomous underwater vehicles (AUV), USVs and miniaturised environmental sensors has already led to the emergence of commercially available sensor deployment robots (Lee et al., 2023). These devices are typically remotely controlled, with the state-of-the-art ability to navigate autonomously due to advances in artificial intelligence and ML and particularly deep learning (DL) methods (Qiao et al., 2023).
Remaining obstacles to the use of robotic mobile sensing include legal constraints and physical limitations, such as achievable battery life. Autonomous navigation remains a challenge due to the high non-linearity and uncertainty of natural, and particularly, aquatic environments. As a result, AUVs are not yet well-developed for use in rivers, as the complex, low visibility environment is difficult to navigate, and many communication and localisation technologies (e.g. GPS) cannot be used underwater. However, USVs and AUVs are well established in marine monitoring, showing the potential of this technology to be applied within rivers with further development.