Abstract: An inertial navigation system includes a first inertial measurement unit with at least a first sensor and a second inertial measurement unit with at least a second sensor corresponding in type to the first sensor. The first inertial measurement unit is rotatably mounted relative to the second inertial measurement unit, The inertial navigation system further include a controller arranged to: acquire a first set of measurements simultaneously from both the first inertial measurement unit and the second inertial measurement unit; rotate the first inertial measurement unit relative to the second inertial measurement unit; acquire a second set of measurements simultaneously from both the first inertial measurement unit and the second inertial measurement unit; and calculate from the first set of measurements and the second set of measurements at least one error characteristic of the first sensor and/or the second sensor.

Abstract: A terrain-based navigation system include at least three laser range finders, each fixedly mounted to a vehicle body, each pointing in a different direction and arranged such that they can be used to calculate terrain gradient in two dimensions. Existing terrain-based navigation systems for aircraft that use a radar altimeter to determine the distance of the vehicle from the ground make use of the large field of view of the radar altimeter. The first return signal from the radar altimeter may not be from directly below the aircraft, but will be interpreted as being directly below the aircraft, thereby impairing the chances of obtaining a terrain match, or impairing the accuracy of a terrain match. The use of a plurality of laser range finders each fixedly mounted to the vehicle body allows more terrain information to be obtained as the terrain can be detected from the plurality of different directions.

Abstract: A terrain-based navigation system include at least three laser range finders, each fixedly mounted to a vehicle body, each pointing in a different direction and arranged such that they can be used to calculate terrain gradient in two dimensions. Existing terrain-based navigation systems for aircraft that use a radar altimeter to determine the distance of the vehicle from the ground make use of the large field of view of the radar altimeter. The first return signal from the radar altimeter may not be from directly below the aircraft, but will be interpreted as being directly below the aircraft, thereby impairing the chances of obtaining a terrain match, or impairing the accuracy of a terrain match. The use of a plurality of laser range finders each fixedly mounted to the vehicle body allows more terrain information to be obtained as the terrain can be detected from the plurality of different directions.

Abstract: An inertial navigation system includes a first inertial measurement unit with at least a first sensor and a second inertial measurement unit with at least a second sensor corresponding in type to the first sensor. The first inertial measurement unit is rotatably mounted relative to the second inertial measurement unit, The inertial navigation system further include a controller arranged to: acquire a first set of measurements simultaneously from both the first inertial measurement unit and the second inertial measurement unit; rotate the first inertial measurement unit relative to the second inertial measurement unit; acquire a second set of measurements simultaneously from both the first inertial measurement unit and the second inertial measurement unit; and calculate from the first set of measurements and the second set of measurements at least one error characteristic of the first sensor and/or the second sensor.