Inertial Navigation System, A.K.A Inertial Reference Unit

Short Name or Variable Name

Strap-down, ring laser gyro micro inertial systems on each aircraft.

GV: Three units on the aircraft. Data from 2 of the 3 units recorded via ARINC data bus to the standard data files.

C-130: Two units on the aircraft, both recorded. Later model of the system on the GV; SM=special missions for hand selected components

Model: GV: Laseref IV P/N HD2001; C130: Laseref V-SM P/N YG4037AB07

Measurements Provided: Aircraft position (Latitude, longitude, baro-inertial altitude), N-S, E-W ground speeds, baro-inertial (pressure damped) vertical aircraft speed, and aircraft attitude angles (pitch, roll, true heading/yaw).

Measurement Characteristics: Position and ground speed data subject to Shuler Oscillation drift errors until blended with GPS data in post processing. Additionally there are "transport delays" and digital filtering in the IRU computer that are accounted for in post processing to align measurements with other recorded data.

Calibration Methods

Initially "sighted - in" on the leveled aircraft for offsets in attitude angles and reference to (radome) gust probe.