"GPS-denied environments are areas in which GPS signals sent from satellites can not reach an earth-bound GPS receiver, ultimately leaving GPS-reliant technologies without function."
GPS-based technologies are an integral part of our daily lives, and their applications are practically endless. While civilians primarily rely on GPS when using Google Maps or other navigational tools, there are more significant uses for GPS technologies, many of which involve policing, military operations, and emergency search and rescue.
But what happens when GPS fails to function in a specific location or a wider geographic area?
These areas are called GPS-denied environments, and they can have severe implications on public safety, government and military operations, and the planet.
Below, we explore the reasons why GPS is denied in certain places, the potential impacts of these situations, and the solutions available to navigate GPS-degraded and GPS-denied environments.
What are GPS Denied Environments?
GPS-denied environments are areas in which GPS signals sent from satellites can not reach an earth-bound GPS receiver, ultimately leaving GPS-reliant technologies without function.
There are several reasons for GPS signals not reaching a receiver in a location, and it can be challenging to identify the cause.
A few of the most common reasons for failed GPS signals in a specific environment are:
No direct line of sight between the satellites and the GPS receiver.
Line of sight issues could arise due to buildings in urban environments, tunnels & underground infrastructure, or various other kinds of physical obstructions.
These types of obstructions can even occur when a GPS receiver is indoors.
Geological structures or land topography.
Mountain ranges, canyons, forests, or other areas with thick vegetation could have geological implications for GPS availability.
If a GPS signal is trying to reach a receiver located underwater, GPS denial is also likely.
Intentional or unintentional GPS jamming.
GPS jamming can happen intentionally or unintentionally and can render GPS devices useless if the signal jamming is within range and strong enough to overpower the legitimate signal.
GPS jamming is becoming more common, and since GPS jammers are easy to purchase online, more people are using them.
GPS-Denied Environments vs. GPS-Degraded Environments
While a GPS-denied environment is a location where GPS signals cannot reach the respective receiver, a GPS-degraded environment describes a situation where GPS signals are so weak that the service or function of the GPS device is unreliable or inaccurate.
Many times, the reasons that GPS signals might be degraded (too weak to function correctly) are the same reasons that GPS signals might be denied altogether.
GPS degradation can occur when GPS signals do not have a direct line-of-sight to the receiver, when a signal is reflected off of buildings or other physical structures, or when GPS jamming or interference is present.
Challenges of GPS-Denied Environments
From navigation challenges to data collection difficulties, GPS failure creates hard-to-navigate scenarios for a wide range of activities.
Whether trying to operate a drone in a conflict zone or trying to find your way to the nearest hospital in an emergency, GPS degradation creates risks that must be considered carefully.
Navigation and Orientation
Navigation in GPS-denied environments is difficult because, without GPS, it becomes nearly impossible to determine an accurate and timely location or orient a craft like a UAV without error.
GPS provides precision location information by triangulating GPS signals from satellites, so when these data are unavailable, there is no immediate method for determining precise and accurate receiver locations.
Further, GPS provides a clear navigational picture with reference points that are used for tracking and navigation when a GPS interruption occurs. While short GPS interruptions can be overcome with GPS reference data, the complete absence of GPS gives no data or reference points that can be used to continue accurate navigation.
Orientation is difficult in GPS-denied environments for most of the same reasons navigation is difficult.
Reference data is used when GPS is available to orient UAVs and other devices in space. So, without any reference data in a prolonged GPS outage, it becomes extremely difficult to position a device without error.
While historical reference data can be used during a short GPS outage to keep a device oriented, the sensors and technologies experience drift issues when under a prolonged data outage.
As you can imagine, inaccurate positioning for something like a drone while operating in a conflict area could pose serious risks to humans or military operations.
Communication
While not always the case, GPS-denied environments are often the result of signal interference, be it from GPS jamming or physical obstructions. As you might assume, if GPS signals have trouble or cannot make it to their receiver due to interference, the same might be true for communications signals.
If GPS is unavailable because the area is so remote, the environment may also lack the infrastructure needed to communicate properly.
For example, there are no cell towers in the middle of oceans or in extremely rural areas on land, so basic forms of communication may be unavailable if the GPS is also unavailable.
Another potential scenario is signal congestion.
If GPS is denied due to signal interference, the same might be true for standard communications technologies. Signal congestion can even happen when there are too many communications systems in operation in a specific area, which could result in complete denial of communications or the degradation of communication quality and fluidity.
Data Collection
Data collection is most often difficult in GPS-degraded environments because precision location and navigation are needed to collect accurate and useful data. This is particularly true for scientific applications, military operations, and other similar scenarios.
As you can imagine, data is only actionable if it’s accurate, and almost all modern uses for data rely on the accuracy and dependability of modern data collection methods.
Limited coverage, signal obstruction, inaccurate sensor data, and the inability to meet high computational demands make data collection in GPS-denied environments out of reach in many scenarios.
Impacts of GPS-Denied Environments
The impacts of GPS-denied and degraded environments can vary drastically. Often, the impact on everyday civilians is limited, but when it comes to military operations, GPS degradation can hold serious consequences.
Civilian Impacts
As civilians, almost all of us have had the chance to experience GPS degradation first-hand. You’ve probably lost signal on your Google Maps while driving through a mountainous area, lost connection to your device while driving through a tunnel, or experienced painfully slow loading speeds when you need quick navigation.
It happens, and most of it happens when GPS signals cannot reach their target receiver uninterrupted.
Still, the fallout from GPS-denied or GPS-degraded environments doesn’t often hold life-threatening consequences for civilians, as most cases simply result in inconvenience.
Real-World Civilian Impacts:
An example of GPS denial due to interference occurred in January of 2022 when GPS signals failed to reach the Denver International Airport.
This instance, which was considered a GPS-denied environment during the outage, caused severe disruptions at distances of up to 50 miles around the airport. Civilian flights were disrupted and delayed for over 30 hours, and officials stated that the reason was due to unintentional GPS interference.
Military Impacts
GPS technologies are an integral and essential part of military operations. On the battlefield or anywhere else where GPS technologies are used to execute missions and keep soldiers safe, the denial of GPS signals can create severe risk.
In conflict zones, the most common reason for a GPS-degraded or GPS-denied environment is due to GPS jamming.
GPS jamming and other types of electronic warfare are incredibly common in today's military conflict landscape, and as GPS jamming and interference technologies evolve, so does the need for defensive action.
Since navigation and communication are imperative to military operations, GPS-denied environments make it dangerous and difficult to operate without error.
Real-World Military Impacts:
One example of the impacts GPS-denied environments can have on militaries takes us to the nation of Myanmar. Myanmar is in the midst of a civil conflict between the military government and the democratic-hopeful civilian groups across the country.
One way that the military has been battling the civilian groups is by using electronic warfare and RF signal jamming, resulting in loss of communication and the inability to do things like detonate explosives remotely or fly drones in conflict areas.
However, civilian militias are finding new ways to overcome GPS jamming and navigate in GPS-denied environments.
GPS-Denied Solutions
While modern technology offers dozens of possible solutions to navigate GPS-denied and GPS-degraded environments effectively, there are some that are more common than others.
The following solutions are widely used due to their effective integration into modern technologies and past success in navigating environments without available GPS signals.
Intertial Navigation Systems (INS)
Inertial Navigation systems (INS) are among the most commonly considered solutions for navigating GPS-denied environments due to their ability to function (provide accurate position and orientation data) without the use of external signals like those from GPS.
Inertial Navigation Systems are composed of accelerometers, gyroscopes, and computational units that work in unison to measure changes in orientation and velocity to compute position over time and space.
An accelerometer measures an object's movement, providing data on speed changes, while a gyroscope measures a device's rotation. Gyroscopes can assess changes in an object’s orientation, ultimately helping update and maintain a reference frame for movement.
While the above features help track an object or device's movements and orientation, data integration is another vital component of INS success.
Dead reckoning, which is the process of calculating the position of an object using previous location data, is used in combination with other components of INS to improve accuracy and navigation in GPS-denied environments.
Sensors are also an integral part of data integration, where things like barometers, magnetometers, and more are used to optimize and correct sensor drift issues.
Optical and Sensor Fusion
Part of successfully navigating GPS-denied environments involves cameras and multiple types of sensors that, when used in unison, provide a better understanding of position, orientation, and movement.
Different sensors are able to measure and calculate different aspects of timing, navigation, and orientation. As mentioned above, accelerometers and gyroscopes can help determine the acceleration of an object along different axis’ and measure rotational changes.
Alone, the data from each device is limited. When used together, however, these systems provide a far better understanding of how an object is moving or should move in time and space.
Other types of sensors used to navigate GPS-denied environments include ultrasonic sensors, LIDAR, stereo vision, barometers, and more.
RF Navigation
Radio Frequency (RF) navigation is another method used in certain scenarios where GPS data is unavailable.
An example of this would be when GPS jamming or other RF interference is occurring in the open ocean. This could be due to military operations, conflict zones, or unintentional jamming.
Regardless of the reason, RF data could be available to track a ship's or other objects' movements.
If a ship’s AIS navigational system is turned off, for example, RF emissions data can be used to track the ship as long as satellites equipped with the right RF sensors are available.
While RF signals may not always be available in a GPS-denied environment, there are scenarios in which the data can be used to help navigate, predict, or correct an object's position and more.
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