Instrumentation & Measurement Magazine 24-4 - 92

can be stated that the measurement uncertainty is affected by
several influence quantities that change according to the kind
of sensor embedded on the UAV. The choice of the sensor to be
embedded on board directly affects the design parameters of
the UAV itself, such as the power consumption.
Design of UAV-based Measurement
Instruments
A traditional approach for designing UAV platforms is to select
the sensors to be embedded onboard, according to the
specific application and the datasheet provided by the manufacturer,
and then to size the UAV according to the following
parameters: weight, energy consumption, and data communication
interface.
The weight is the main parameter for sizing the motors,
the propellers, and the frame of the UAV. The main contributors
to the UAV weight are: the payload, which embeds the
sensors chosen according to the application; the frame, where
its contribution on the total weight of the UAV can be reduced
by using carbon fiber frames or frames of other materials; the
brushless motors; and the battery. By knowing the total weight
of the UAV, the number of motors and the type of motor is
chosen.
The battery for supplying the UAV with electrical energy is
sized according to its power consumption for the desired time
of flight for a mission. In that case, usually, the main contributors
to the UAV power consumption are the motors.
The most commonly used communication interface for the
link between the UAV onboard computer and the ground control
station for short-distance is the Wi-Fi. This communication
interface allows the exchange of data related to the remote
control, the telemetry (the navigation measurements) and the
data acquired by the sensor embedded on the payload. On the
other hand, to cover long-range distances (i.e., 10 km in free
space), the main adopted communication interface is based
on the Coded Orthogonal Frequency-Division Multiplexing
(COFDM) standard.
In the traditional design approach, the designer does not
evaluate a mathematical model that allows estimating the
measurement uncertainty by considering the UAV as a whole,
but he/she chooses the sensors by looking into their single
specifications. Usually, several tests are performed after the
deployment of the platform to assess its measurement uncertainty.
Sometimes, the obtained uncertainty values do not
comply with the application requirements or are larger than
the expected ones. In such cases, a new platform must be designed
and deployed. This process is inefficient in terms of
time and costs. On the other hand, by using a mathematical
model to describe the measurement procedure, it is possible
to optimize a priori the flight parameters to obtain the desired
measurement uncertainty.
For all of these reported reasons, it is important to consider
the assessment of the measurement uncertainty within
the design steps of the UAV-based measurement instrument
[12]. Finally, a UAV-based measurement instrument can be designed
according to the following steps (Fig. 3):
Step 1 - definition of the measurand, depending on the
application;
Step 2 - definition of the target uncertainty and the measurement
range for the specified measurand;
Step 3 - uncertainty analysis of the measurand by considering
a mathematical model that describes the measurement procedure
and the identified uncertainty sources;
Step 4 - definition of the requirements related to the sensors for
navigation and the sensors for mission to be embedded on the
UAV payload, according to the uncertainty analysis results;
Step 5 - definition of the data communication interface;
Step 6 - definition of the UAV platform according to the weight
and the energy consumption constraints.
Case Study: 3D Reconstruction of
Archaeological Sites
The proposed design procedure has been applied for the development
of a UAV-based measurement instrument for the
3D reconstruction of archaeological sites. In particular, the aim
of the measurement performed by the UAV during flight is to
provide a 3D map that contains geometrical measurements related
to wide archaeological sites or archaeological sites with
difficult access. The uncertainty of the geometrical measurements
has a direct impact on the minimum size of the surveyed
structures that can be correctly recognized. For example,
for measuring the geometrical dimensions of a sculpture, a
smaller measurement uncertainty is required with respect to
the case of measuring the length of an historic road.
According to the design procedure previously presented,
each step carried out for the UAV platform development is
described:
Step 1 - The definition of the measurand according to the application.
In the considered case study, the measurands are the
geometrical dimensions (height, width, and length) of each
Fig. 3. The proposed design steps for a UAV-based measurement instrument.
92
IEEE Instrumentation & Measurement Magazine
June 2021
Instrumentation & Measurement Magazine 24-4

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