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.