Manned Aircraft and UAV's shut off GPS to train for future wars

the Air Force is preparing for conditions it terms anti-access, area-denial: when air assets are needed against an enemy with the ability to deny capabilities such as GPS.
 Pilots shut off GPS, other tools to train for future wars | Air Force Times | airforcetimes.com
Dealing With The Chinese Apocalypse

While the GPS signal at the earth's surface is very weak, it is difficult but possible to jam against more sophisticated SAASM and M-code receivers. and see GPS Jamming

This may degrade manned operations, but will shut down most current UAV operations if GPS is jammed over a significant area. Old standbys such as vision based, SAR aided TERCOM, celestial, and pure inertial will be expensive to add in and each by itself will have problems and limitations. All Source Data fusion navigation as proposed by Williams and Crump may be required,

Abstract. The drive towards utilizing small, cheap, autonomous aerial vehicles for military operations means that navigation systems that are robust to GPS denial must be employed. The simplest option available is to increase the accuracy of the inertial measurement unit (IMU), but this can substantially increase the price per operational unit. This paper presents an overview of the All Source Navigation system developed by BAE Systems Australia based on inexpensive MEMS IMUs and a supporting image processing unit. The navigation system is capable of sustaining the operational flight capability of the vehicle for prolonged periods of time compared to the pure inertial solution. At its core, All - Source Navigation makes use of SLAM techniques . A variety of additional aiding sources are fused into the inertial navigation solution to g ive improved navigational accuracy during flight. The system is capable of performing both conventional static, as well as in flight alignment. All Source Navigation is demonstrated on the Kingfisher 2 UAV platform at the West Sale test facility.

 

Another Kalman filter based approach is proposed by Srikanth Saripalli of the School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA in “State Estimation for UAVs in GPS-denied Environments”. State Estimation for UAVs in GPS-denied ... - ResearchGate

Abstract: UAVs flying at high altitudes can normally rely on GPS for accurate position and velocity estimates. However, navigation through areas such as canyons and under forest canopy, where GPS coverage is transient or unavailable, necessitates an alternative approach. In these situations, a position estimate can be obtained using vision. This paper develops an algorithm that uses cheap accelerometers and gyroscopes and combines them with position estimates from vision in an extended kalman filter framework to provide precise position and orientation information. We show preliminary experimental results that prove that our technique can be used for accurate positioning information for UAVs in GPS-denied environments.

 or "Autonomous Flight in GPS-Denied Environments Using MonocularVision and Inertial Sensors" by Allen D. Wu, Eric N. Johnson, Michael Kaess, Frank Dellaert, and Girish Chowdhary.

Abstract: A vision-aided inertial navigation system that enables autonomous flight of an aerial vehicle in GPS-denied environments is presented. Particularly, feature point information from a monocular vision sensor are used to bound the drift resulting from integrating accelerations and angular rate measurements from an Inertial Measurement Unit (IMU) forward in time. An Extended Kalman filter framework is proposed for performing the tasks of vision-based mapping and navigation separately. When GPS is available, multiple observations of a single landmark point from the vision sensor are used to estimate the point’s location in inertial space. When GPS is not available, points that have been sufficiently mapped out can be used for estimating vehicle position and attitude. Simulation and flight test results of a vehicle operating autonomously in a simplified loss-of-GPS scenario verify the presented method.