Remote Aerial Survey
Enter the Drone
Robert Demaus
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A drone’s eye view of the roof of Boscobel House, Shropshire |
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Until recently, the detailed visual
inspection of tall or potentially
dangerous structures and inaccessible
roofs was a difficult and usually expensive
operation, often requiring specialised
access platforms or scaffolding, or the use
of specially trained rope-access technicians.
Even relatively simple tasks such as checking
parapet gutters for blockages, that might
traditionally have been done from a ladder,
have more recently required relatively
expensive access provision to minimise risk.
Now an exciting new technology is
emerging that allows highly detailed surveys
of buildings or parts of buildings that were
previously difficult to access, without the
operator or surveyor leaving the ground.
Unmanned aerial systems (UASs) [1], or drones
as they are more popularly known, seem to
have flown into the public consciousness
only relatively recently, but now hardly a day
goes by without some mainstream news item
involving their use, or indeed, abuse, with
numerous and sometimes wild claims being
made about how they might impinge on our
lives in the future.
Of course, the terms UAS and drone
cover a very wide assortment of devices and
an ever-expanding range of real, imagined or
potential applications. For most people, the
terms remain associated with their military
applications and at this level they represent
a sinister and questionable form of lethal
weapon, or at best, an effective way of keeping
a watchful eye on both friend and foe.
However, the type of UAS that is starting
to have practical applications in the field
of building surveys actually has far more
in common with the model aeroplanes and
radio-controlled helicopters that enthusiasts
have been flying for many years. What has
allowed them to develop into a very useful
tool is the adoption and integration of the
rapidly developing technologies of the
mobile phone industry: many of the most
important components, such as gyroscopes,
GPS units, accelerometers, batteries, and
wi-fi transmitters, have all become much
smaller, much more sophisticated and very
much cheaper due to the intense pressure for
innovation. As well as incorporating much
of the technology, many systems are now
designed to use a smart phone or tablet as part
of the control and viewing systems.
Technological advances are so rapid that
what might have required a UAS costing
several thousands of pounds, can now be
achieved using machines that cost only a few
hundred pounds. As a result, UAS aircraft
now provide a practicable stable platform,
ideally suited for controlled visual survey of all
types of buildings and other structures.
SPECIFICATIONS
Most types of UAS used for building survey
consist of four basic elements:
- The aircraft is usually a battery-powered
multi-rotor ‘helicopter’. Typically it will
be fitted with an array of technology
to allow it to perform as a safe and
stable platform. This will include an
integrated GPS auto-pilot system which
provides altitude lock and position
holding, and a stable hovering capability,
which allows steady and predictable
flight paths even in windy conditions.
Flight time depends on many factors
including battery capacity, payload and
weather conditions, but will be typically
10-30 minutes. This may not seem long,
but a lot of building can be surveyed in
detail in that time, and if necessary it is
simple to land and ‘refuel’ with a fresh
battery. Many of the more sophisticated
types of UAS will automatically fly
back to the point of launch.
- The camera, which can vary from the
very small and ubiquitous GoPro to high
resolution DSLRs or video cameras.
The cameras used are often also fitted
with wi-fi, transmitting live video to a
screen (often a smart phone or tablet)
attached to the remote control unit.
Known as ‘first person view’ or FPV,
the technology gives the pilot on the
ground the view from the plane.
- The base station or remote control
unit is essentially the equivalent of the
cockpit in a conventional aircraft, with
controls for the aircraft’s speed height,
direction and orientation. Flight data
such as altitude, distance and speed
is fed back to the base station along
with important safety parameters such
as battery condition. It is also often
possible to take full control of the camera
settings and operation whilst in flight.
- The pilot (on the ground) is kept very
busy during the flight. There is a mass of
information constantly streamed from
the aircraft and the camera to the base
station, and the pilot must maintain direct
line-of-vision contact with the aircraft
at all times. UAS has become very much
easier to operate, and with GPS fitted,
many aircraft will hover in a geo-stationary
position if the operator loses the plot
and lets go of the controls: this is not
necessarily recommended, but can allow
a breathing space to make adjustments
to cameras and regain orientation and
bearings. Quite apart from regulatory
compliance (see below), a pilot needs
considerable experience and competence
to avoid damage to the aircraft, which are
built to minimise weight and are therefore
not particularly robust. Furthermore, although lightweight – typically 1-3kg
– they could do a great deal of damage
to a stained glass window. What might
seem to be easy to control and relatively
slow moving when flying in open air,
suddenly seems very much faster and
friskier when close to solid objects.
REGULATIONS
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A typical compact (approximately 500mm wide)
four-rotor UAS carrying a GoPro video camera, as
used for the aerial survey of Boscobel House. |
In the United Kingdom, the Civil Aviation
Authority is the regulatory authority for
all matters associated with non-military
aviation, including the operation of UAS.
Practice and regulation of small unmanned
aircraft has evolved out of the hobbyists’
use of radio-controlled model aircraft,
and remains reasonably simple and
straightforward, but as commercial use of
UAS increases, regulations and restrictions
are likely to become more stringent.
Essentially, the operator is fully
responsible for the safe operation of any
flight. In many circumstances a permission
(not a licence) from the CAA is required, for
example, if you intend to fly the UAS on a
commercial basis, or fly a camera/surveillance
fitted aircraft within congested areas, or close
to people or properties (vehicles, vessels or
structures) that are not under your control.
The CAA permission must be renewed
every 12 months and requires payment of a
modest fee depending on the weight of the
UAS. However, the ‘pilot’ does not need any
formal qualification (the Basic National UAS
Certificate for example) if the UAS is under
20kg and is flown in direct line of sight, within
500 metres horizontally and at a height not
exceeding 400 feet. CAA permission is not required for
‘practice’ or demonstration flights, or if the
aircraft will not be flown close to people
or properties, and there is no ‘valuable
consideration’ (i.e. payment) for the flight.
Whatever the circumstance, anyone
contemplating any form of UAS flying
should familiarise themselves with the CAA
requirements (which are clearly defined
on their website), demonstrate adequate
competence as required and ensure that
they have adequate public and professional
liability insurance in place, and that they and
their insurers do actually understand the
competencies required and risks involved.
APPLICATIONS
At present, for the price of a good pair of
binoculars, a very capable ready-to-fly UAS
can reliably carry out detailed visual surveys
of inaccessible areas of buildings and other
structures. In a matter of minutes, detailed
images of high level stonework, inaccessible
metalwork such as weather vanes, chimney
stacks and concealed roofs and valley gutters
can be obtained. As always, it is far better if
the operator of the technology also has great
experience of surveying historic buildings,
so knows what to look for and where, and is
capable of identifying and analysing current
and potential faults. With instant FPV images
beamed back to the ground, this allows the
pilot/surveyor to concentrate in particular
detail on specific problem areas.
UAS aircraft can also be flown inside
large buildings, but this requires much
greater skill than flying outdoors. Proximity
sensors are now being developed that will
greatly reduce the risk of collision or damage.
Payload is always limited, but the aircraft
can carry very bright LED lights in addition
to cameras, which allows the detailed
visual survey of high vaulted roofs in large
churches and cathedrals, for example.
Aerial digital images from a UAS can be
integrated with terrestrial images of widely
different resolutions using currently available
software which can then process them to
produce 3D models of complex buildings such
as castles and cathedrals. Currently accuracy
is limited (typically 5mm to 20cm, across a
large and complex building, depending on the
system used) but should improve over time.
With any new technology, there is
often a rush of enthusiasm for its adoption.
It is quite possible for anyone to go out
and buy a £500 UAS and claim to be able
to survey your building. However, it is
most important that the operator is just
as fully experienced in interpreting and
diagnosing faults in historic buildings,
as they need to be in operating a UAS.
PREDICTIONS
As in the early stages of any new technology,
be it computers, mobile phones or indeed
manned aircraft, capabilities massively
and rapidly improve and real costs drop.
Predictions made in these early stages can
appear very wide of the mark only a short
time later, but UAS will almost certainly
become an accepted and common tool in
a specialist surveyor’s toolbox.
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One of the chimneys at Boscobel: photos taken by UAS can quickly provide important information for a
quinquennial inspection and for programming maintenance |
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Already, a
simple and palm-sized UAS aircraft, but still
with on-board camera, video recording and
a 100m range, can be bought for under £100
(thumb-sized and smaller are also available).
At the moment, a UAS can only inspect and
record, and further miniaturisation may not
offer much advantage, but greater control
and payload capacity might, for example,
allow accurate application of weed-killers to
inaccessible places.
What makes UAS technology particularly
interesting and difficult to predict is that
its emergence coincides with the arrival of
practical and relatively cheap 3D printers.
These two emergent technologies neatly fit
in with and greatly strengthen the worldwide
growth of the ‘Maker Movement’, with many
thousands of individuals around the world
openly sharing knowledge and skills. The
further development of UAS for civilian and
specific uses does not depend on military
funding or even big business.
At the current state of development,
compact and modestly priced UAS can reliably
provide detailed information that would
otherwise require the use of expensive and
time-consuming scaffolding, hydraulic access
platforms or specialist rope-access. A tall,
dangerous or inaccessible structure can be
surveyed very economically in a few minutes,
that might otherwise have taken many days
and cost thousands of pounds. It therefore
becomes economically viable to check
potential trouble spots such as inaccessible
valley and parapet gutters on a regular basis.
At the very least, a UAS survey should be
considered an essential element of every
quinquennial survey.
Notes
[1] The Civil Aviation Authority prefers the term Unmanned Aerial Systems (UAS), as this is deemed to include the
operator on the ground as part of the system, but Unmanned Aerial Vehicle (UAV) and drone remain in popular use.
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The Building Conservation Directory, 2015
Author
ROBERT DEMAUS specialises in the non-destructive
assessment of buildings and
the detection and assessment of decay,
weakness and fire damage in structural
timber. He is a director of Demaus Building
Diagnostics Ltd.
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