A GPS-denied environment is a location or situation where the Global Positioning System (GPS) signals are not available at all. This can occur for a number of reasons:
- Indoor Locations: Buildings often block GPS signals, making them unavailable inside.
- Underground or Underwater: Similarly, GPS signals can't penetrate underground or underwater.
- Jamming or Spoofing: GPS signals can be intentionally disrupted or blocked using devices known as GPS jammers. Additionally, they can be spoofed, or faked, to provide incorrect information.
- Space: Beyond a certain altitude, GPS signals become unreliable or unavailable. This is significant for certain types of drones or other high-altitude vehicles.
In these GPS-denied environments, autonomous systems like drones or rescue robots need to use other methods to determine their position and navigate. These can include methods like dead reckoning, where the system estimates its position based on a previously known position and its estimated speed and direction of movement, or it can include using other types of sensors like lidar or radar, or methods like visual odometry or simultaneous localization and mapping (SLAM), which use cameras or other sensors to estimate position based on the surrounding environment.
These systems often use a combination of these methods, in a technique known as sensor fusion, to provide more reliable navigation when GPS isn't available. In fact, designing systems that can operate effectively in GPS-denied environments is a major area of research in robotics and autonomous systems.