IEEE Consumer Electronics Magazine - January/February 2023 - 25

Coordination
Rapid changes in air pollutant concentrations
at different locations and altitudes combined
with obstacles in the environment (e.g., buildings
and trees) pose challenges to the UAV coordination
and call for real-time navigation and
path planning capability. Common UAV coordination
mechanisms have been designed for optimizing
the movements of multiple UAVs without
considering the information other sensors in the
city provide.5 Maximizing the usefulness of air
quality data requires hybrid planning solutions
that can take into account information captured
by existing (ground or near ground level sensors)
air quality sensing infrastructure and
adapt to changes in the availability of the information.13
For example, rush hours produce
dense measurements around congested junctions,
but understanding dispersion patterns
requires sampling vertically in the downstream
wind direction of these junctions. The exact
form of the movement depends on the requirements
of models integrating the information, but
generally they are based on spatial sampling
strategies and use static or dynamic transects
that are divided according to a predefined spatial
resolution.14
Situational Awareness
Autonomous UAV operations require a high
degree of situational awareness from the participating
UAVs. First, UAVs need to be able to avoid
collisions with urban infrastructure or other
UAVs. Existing mechanisms for collision avoidance,
e.g., computer vision or sound based, are
mostly designed for horizontal movements without
accounting for potential obstacles in vertical
directions. Another challenge for situational
awareness results from navigating in dense
urban environments as the urban structures
may result in blind spots that prevent UAVs of
having a line of vision with nearby obstacles. Situational
awareness is also challenged by
weather conditions. Even if UAVs are capable of
navigating in challenging conditions, including
in rain and in the presence of strong wind gusts,
the weather has an effect on pollutants and
causes problems in ensuring accurate pollutant
measurements. For example, reactive gaseous
compounds, such as SO2 and H2 react with
January/February 2023
water, making it difficult to collect measurements
in rainy or highly humid conditions. Similarly,
PM2:5 may absorb water that causes the
particles to become heavier and fall to the
ground. This requires UAVs to integrate models
that can account for the current weather conditions
and adapt sampling patterns to maximize
the quality of collected information.
Power and Operational Time
Power is a bottleneck as consumer-grade UAVs
tend to have short operational time, only supporting
flying times between half an hour to one hour.
City-scale operations would require flying times of
several hours-or a mechanism that transports
the UAVs to different locations while also charging
them. For example, we could envision UAVs being
transported by public transport infrastructure or
cars (e.g., taxis or delivery trucks) and only flying
briefly at the destination location while charging
their batteries during the transit periods.Overcoming
the energy bottleneck thus requires both novel
energy management solutions, e.g., energy harvesting
or wireless charging techniques that can support
charging the UAVs during transit, and novel
data collectionmodels that canmaximize the benefits
of UAVs while reducing their use outside of
measurement collection. These measures can also
help compliance with regulations. For example,
many countries restrict operations that go beyond
line-of-sight. Limiting the UAV operations to vertical
column sampling or spot samples from horizontal
locations that have partial coverage helps to
ensure the UAVs remain close to the entity that is
coordinating their operations. Note that operating
air quality sensors and processing the data tends
to have a low power consumption and can be supported
by a separate power source that is integrated
directly with the sensor carried as payload.
For example, the sensor considered in our experimentsispowered
by 1 4 rechargeable batteries
that are integrateddirectly onto the sensor.
Communications
Efficient and robust communications provide
the foundation for city-scale operations. UAVs
sampling air quality data at different locations
within the city need to connect to different networks
that may support different technologies
and have different characteristics, e.g., how far
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IEEE Consumer Electronics Magazine - January/February 2023

Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - January/February 2023
