Data
gathered by the variety of sensors installed on the unmanned aerial vehicle
(UAV) is an essential component of the vehicle’s mission. The methods of data
storage, processing, and dissemination can differ from one system to another.
This paper focuses on the Draganflyer X8 helicopter UAV used for aerial video
and photography. This UAV performs a variety of missions including wildfire
control, law enforcement operations, crime scene investigations, industrial
inspections, and commercial photography and videography. The Draganflyer features
a quadcopter design which allows the vehicle to ”hover and stare.” The UAV has eight
blushless electric motors which allow for heavier sensor payload capability and
more flight stability even in the windy conditions. The Draganflyer X8 can
carry up to 1.7 pound in camera equipment for photo/video and surveillance
missions and can fly for up to 20 minutes on one battery charge (Draganfly, n.d.).
The
UAV’s sensors suit includes camera equipment and a total of eleven sensors
which are responsible for vehicle position and control. The standard camera
sensor is a Sony NEX5R with an optional thermal FLIR (Forward Looking
Infra-Red) attachment. The camera features a remote tilt, shutter, and a wireless
video feed (FLIR Tau 320 9Hz). The video recorder also has onboard data storage.
As an option, the Draganflyer can be equipped with a remotely operated 10MP
still camera and a 1080p video camera ("Draganflyer X8," n.d.).
Figure 1 depicts the Draganflyer X8 and points out some of its key features.
Figure
1.
Draganflyer X8 and its sensors and features. Adapted from “Draganflyer X8 tech
specs,” by Draganfly, n.d. Retrieved from
http://www.draganfly.com/uav-helicopter/draganflyer-x8/specifications/
Copyright by Draganflyer.
An
additional upgraded camera sensor for the Draganflyer X8 is the new IP video
camera. The IP video cameras distribute digital video via an 802.11n 5.8GHz Wi-Fi
connection. The advantage of digital video is that it is less susceptible to random
noise than standard analog video. The captured picture is changed to zeros and
ones which in turn are transferred as high and low power radio signals. The
receiver changes these low and high power signals back to zeros and ones where
a computer reconstructs it back into a video. This digital data transmission
method eliminates the negative effects of signal noise. The video is
transmitted over a dedicated wireless network and is encrypted for additional
security. This also safeguards the data from unauthorized viewing ("Digital and raw data,"
n.d.). The digital video can be stored in the internal memory before transmitting
it to the ground station. Also a real-time video stream can be transmitted over
the internet to the end user.
The data format produced by the Draganfly varies
depending on its mission. For commercial photo missions the digital camera
records images in the most common formats such as JPG, BMP, and TIFF. Basically,
when a picture is transferred from a camera, it’s coded as different lighting
and color shades for each pixel on the camera’s charge coupled device (CCD)
device.
The CCD chip consists of an array of light sensitive pixels. Each pixel
generates an electric current when a photon strikes it, this is known as the
photoelectric effect. This current is read from each pixel and then recorded in
memory as a series of light levels and colors as a raw image. After that raw
format is converted into JPG, TIFF, or BMP format.
However, for law enforcement
applications the raw file format is the best form of data used as evidence. By
using the raw file format in the investigation law enforcement personnel are
less likely to miss any detail, which may be lost during image processing.
The
ground control station (GCS) connects to the UAV via a 2.4GHz control, sensor,
and adjustment link with the Dragan Eye Pro 5.8GHz wireless video receiver. The
video feed from the vehicle can be viewed in real time either on the monitor or
using video glasses. The handheld GCS is optional, but it features an innovative
design by combining the handheld controller and the video terminal in one compact
station. It runs on a Linux operating system on an Intel Atom processor. The operator
can fly the vehicle, view the video feed form the camera, and monitor UAV
status on the same display. Figure 2
represents split view screen for video monitoring and the flight parameters
display.
Figure
2.
Flight parameters and video screen. Adapted from “Draganflyer X8 tech specs,”
by Draganfly, n.d. Retrieved from
http://www.draganfly.com/uav-helicopter/draganflyer-x8/specifications/
Copyright by Draganflyer.
Several
sensors are installed on the X8, which support the vehicle’s navigation,
control, and autonomy levels. These sensors include: 3 gyros, 3 magnetometers,
3 accelerometers, an inertial measurement unit (IMU), a barometric pressure
sensor, and a GPS receiver. The pilot can choose the vehicle’s degree of
autonomy, which include altitude hold, position hold or manual throttle. The operator
can select manual throttle mode during which he can control vehicle’s altitude
by use of thrust and the UAV will automatically holds the selected heading and
maintain level flight using the IMU and magnetometer. A preset altitude can be
also automatically controlled using the pressure sensor. Automatic position
hold is accomplished by using a combination of the pressure sensor and the GPS (Nahon, Sharf, Harmat, & Khan,
n.d.).
The
GPS sensor is a nice addition to the sensor suit of the UAV. The GPS is used
for vehicle tracking, navigation, and position hold. The GPS has a backup power
supply Lithium polymer battery, providing redundancy in case the main power
source is depleted. It also ensures that vehicle location and speed data will
be accessible to the operator even in case of main power failure. The GPS
position update rate is 4Hz. All the GPS data is being uploaded to the “black
box” recorder on the Draganflyer.
The
“black box” flight recorder feature becomes handy for post flight study, crash
log reviews, or malfunctions troubleshooting. The “black box” consists of
removable 2GB MicroSD memory card installed onboard of the UAV. It loges data
from onboard sensors and records such parameters as datalink quality, speed,
orientation, altitude, and heading.
Power to the vehicle’s motors and sensors is supplied by the rechargeable
14.8V Lithium Polymer battery with 5400mAh capacity ("The Draganfly technical
reference manual," n.d.). Voltage requirements for the camera sensor
is 8 Volts to 32 Volts and power consumption is less than 2 Watts. The
Dragan Eye 5.8GHz Wireless Video
Transmitter is regulated at 5V DC and capable of sourcing 0.8A (RCtoys, n.d.). Barometric
pressure sensor and airspeed sensor’s power requirements are between 3V and
16V. For the accelerometers, power requirements range between 4V to 16V for low
G sensor, and between 4 to 6 V for high G sensor ("Draganfly technical
reference manual," n.d.).
The Draganflyer X8 features a low battery power warning system, which
monitors the battery voltage and transmits voltage information to the operator
control station. Both audible and visual warnings will alert pilot of a low
power situation. This alert allow enough time for the operator to land the
vehicle safely. The GPS position will be recorded for vehicle retrieval.
The
UAV uses two different frequency bands. One for its video sensor data downlink and
separate one for the control signals. This technique reduces interference
between the two frequency bands. The control signal is broadcasted at 2.4GHz
and the video signal is transmitted at 5.8GHz.
The
author recommends a possible improvement for the UAV’s data handling and
treatment. It is possible to use the cloud architecture for data processing and
distribution. By downloading real-time video and photo data to cloud, multiple
users can have access to it simultaneously. It would be especially beneficial
for law enforcement, crowd control, reconnaissance, search and rescue, and
wildfire control. The Cloud architecture would provide secure data storage, and
easy fast access to the necessary data for the end user. The Cloud architecture
would also be useful if several UAVs were used to perform a certain mission at
the same time. For example, if a formation of the UAVs were used to survey the
large area, uploading the video data to the cloud would allow the user to view
the “bigger picture” in real time with fast access.
References
No comments:
Post a Comment