Reference Systems for the Evaluation of Dead-Reckoning Navigation Equipment,

Aircraft dead-reckoning navigation systems present particular problems in their assessment, and diagnosis in development where a continuous measurement of their error pattern is required. The inherent accuracy of modern inertial and Doppler equipment is such that there are few direct methods of measuring the system errors to the required precision. Need for long range, long duration flights over both land and sea with a continuous high accuracy reference led RAF to develop an integrated navigation system in which the outputs of a number of inertial navigation systems are recorded in parallel with those of Doppler radar, DME, Decca, Loran C and Omega. The recorded data is processed post-flight in a Kalman filter which is used to estimate the inertial system errors. The final reference is formed by compensating the inertial outputs for these errors and has the properties of high accuracy, low noise, and continuous availability. Although simple in concept, implementation of such a scheme is complex. The major problem lies in constructing suitable mathematical models of the various equipments. The second difficult area is that of obtaining the statistical information regarding the performance of the equipments in a form suitable for inclusion in the models. Although the reference is produced off-line the techniques can be implemented on-line.