volcano, Japan (Shinohara, 2013). The weights of such
systems vary from 1.5 to 3 kg. The
UAV
used in Shinohara
(2013) was a helicopter with a fuel engine and 710 mm stan-
dard carbon fiber blades; its weight is 5.2 kg. The helicopter
dimensions were 1410 × 465 × 190 mm.
Krüll
et al.
(2012) used sensors for gas and smoke detec-
tion based on semiconductor technology. Hydrogen produced
in open fires and also hydrocarbons C
x
H
x
, generated during
the fire evolution are detected. They are also able for dis-
criminating among dust, mist, or other aerosols. The
UAV
is a
quad-copter with a diameter of about 1vm, a weight of about
1 kg. Data are transmitted to a ground control station though
wireless local area network (
WLAN
).
Sonars
Misnan
et al.
(2012a and 2012b) experimented with 2D sonar
and the associated analytical process for ranging and mapping
surfaces with an
UAV
flying at low altitudes. The transmitter
and receiver are placed close among them to achieve maxi-
mum accuracies. This technology, based on sound waves, is
rarely used in
UAVs
for remote sensing, but is used widely in
navigation where ultrasonic sensors are useful in
UAVs
for col-
lision avoidance during navigation.
Communications/Data Transmission
In remote sensing applications, communications become
of special interest either for coordination and collaboration
between
UAVs
or for data transmission. With such motivation,
GPS
and
VHF
/
UHF
antennas were integrated into
UAVs
(Strojny
and Rojas, 2009).
The data acquired in
UAVs
must be transferred for process-
ing or for integration with other systems or data. High-speed
modems were designed for high-speed wireless data transmis-
sion, suitable for surveillance or reconnaissance tasks (Rupar
et al.
, 2009).
Bhaskaranand and Gibson (2011) developed a low-com-
plexity encoding approach for high speed data transmission.
Data transmission represents a challenge particularly with the
growing interest for its use in real-time applications, includ-
ing those that send real-time video for monitoring events.
Municipalities and other institutions are demanding high
performance surveillance services, where video strips must be
transmitted to a
GCS
for monitoring purposes (Israel, 2011).
Embedded or blade antennas are elements onboard
UAVs
for transmission or reception. The embedded operational
systems preserve the aerodynamic characteristics of the air-
craft (Patrovsky and Sekora, 2010). Abdelkader
et al.
(2013)
used antennas to identify lagrangian micro-sensors drifting in
flooded areas to monitor the evolution of the flooding.
The Smartphone proposed in Yun
et al.
(2012) and Kim
et
al.
(2013) uses 3G internet accesses for communication with the
ability to become a remote server for storing images and data.
Radio communications, including
UHF
, are feasible for im-
age transmission, after compression, achieving ranges of 2 to 5
km with low and high directivity antennas (Wada
et al.
, 2015).
As an intrinsic element in communications,
UAVs
can be
used as nodes in
WSN
, establishing links to other nodes which
can be fixed or moving, including other
UAVs
(Antonio
et al.
,
2012). Additionally, the
UAV
can serve as a sink of data col-
lection to be sent to other nodes. Also in the context of
WSN
,
Tuna
et al.
(2012 and 2014) proposed a team of
UAVs
, tested
with helicopters, for establishing an effective communica-
tion system considered as essential after natural disasters for
rescue operations. The proposed system is a post-disaster so-
lution where each
UAV
in the team has an onboard computer
which runs three main subsystems responsible for end-to-end
communication, formation control and autonomous naviga-
tion in communication with a
GCS
. Different works addressed
the wireless communication problem where the experiments
were conducted for testing some problems related to this
issue, involving positioning, coverage, throughput, or channel
modeling among others (Zhan
et al.
, 2006 and 2011, Burda-
kov, 2010; Li and Zhang, 2010; Xin
et al.
, 2010; Olsson
et al.
,
2010; Yanmaz
et al.
, 2011; Lin
et al.
, 2011, Yanmaz, 2012;
Zhou
et al.
, 2012b; Rohde
et al.
, 2013).
Atmospheric Instrumentation
Corrigan and Ramanathan (2008a) introduced a set of atmo-
spheric instruments specifically designed for
UAVs
, specifical-
ly: (a) optical and condensation particle counters for detecting
particles in the atmosphere above 10 nm; (b) aethalometer for
measuring the concentration of particles based on the absorp-
tion of a beam of light; (c) sampling of aerosols; (d) probe for
temperature and relative humidity; (e) cloud droplet spec-
trometer between 1 and 50 µm; (f) pyranometer for measuring
solar irradiance; (g) photosynthetically available radiation (400
nm - 700 nm); (h) liquid water content probe for measuring the
water in the clouds; and (i) video camera for cloud detection.
Corrigan
et al.
(2008b) described the use of several devices
for data air analysis, including a meteorological system (pres-
sure, temperature, and relative humidity), an optical particle
counter, and an aerosol absorption photometer. These systems
are installed onboard an
UAV
with a maximum takeoff weight
of 27 kg, a wingspan of 2.6 m and an overall length of 1.9
m. The aircraft can lift a 5 kg payload in a 12 l compartment
while carrying 8 l of fuel.
Bates
et al.
(2013) measured vertical distribution of aerosols
on Svalbard, Norway. The
UAV
was equipped with: (a) one
mixing condensation particle counter;(b) one three-wavelength
absorption photometer, a Multi-Channel Chemical Filter
Sampler (
MCCFS
) consisting of eight, off-the shelf filter hold-
ers with 13 mm of diameter and a magnetically driven, rotary
valve manifold to distribute the vacuum/flow from one central
pump to each of the separate sampling channels; and (c) two
probes of temperature and relative humidity to collect data at
different atmospheric layers. The aircraft weighs 16.3 kg with-
out payload and fuel (27.7 kg maximum takeoff weight). The
wingspan is 2.7 m, height is 0.62 m, and length is 1.92 m.
A spectrometer probe and an electrostatic collector for aero-
sol measurements, size and distribution, were the instruments
adapted for
UAVs
in addition to temperature and humidity
relative probes for measurements (Claussen
et al.
, 2013).
Pressure, temperature, and relative humidity are atmo-
spheric variables that can be measured with specific instru-
ments onboard
UAVs
. In Mayer (2011) and Reuder
et al.
(2009), a
SUMO
(Small Unmanned Meteorological Observer) system with
wingspan 0.80 m, length 0.75 m, height 0.23 m, and
TOW
of 580
g was the system equipped with such sensors with the ability of
capturing data at 2 Hz. Cook
et al.
(2013) used a probe, onboard
a wing-fixed
UAV
, with humidity and temperature sensors for
coastal atmospheric research in New Zealand.
Brown
et al.
(2011) described the upgrading, for the deploy-
ment on the Global Hawk
UAV
platform, of the existing high-
altitude monolithic microwave integrated circuit sounding
radiometer, with a 25-channel cross-track scanning microwave
sounder with channels near the 60 and 118
GHz
oxygen lines
and the 183
GHz
water-vapor line. The upgrading consisted of
the addition of a front-end, low-noise amplifier developed by
JPL, to the 183
GHz
channel. This instrument was used in three
hurricane field campaigns for atmospheric observations, in-
cluding temperature, water-vapor, cloud-liquid water, convec-
tive intensity, precipitation, and 3
D
storm structure.
Radiation Instruments
Some nuclear and radiation accidents and incidents (Wikipe-
dia, 2015) have motivated the design and development of radi-
ation sensors onboard
UAVs
; one of which was the instrument
proposed by Towler
et al.
(2012) onboard a helicopter with
20 kg of weight, together with imagery sensors. The sensor is
a lightweight sodium-iodide scintillating crystal to convert
290
April 2015
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
