Model for JPALS/SRGPS Flexure and Attitude Error Allocation

This paper develops a linearized parametric error model for assessing the effects of structural flexure and attitude uncertainties on the shipboard variant of the joint precision approach and landing system (JPALS). The outputs of the error model are position domain error bounds on the estimate of the ship reference point (SRP) coordinates. The model is parameterized in terms of GPS antenna installation geometry and the covariance matrices capturing the statistics of GPS measurement, ship structural flexure, and ship attitude estimation uncertainty. The performance of the model is evaluated via a set of simulation studies. It is shown that when the attitude errors are small and the flexure statistics well characterized, the error model provides an accurate and convenient way of mapping attitude and flexure uncertainties into SRP position uncertainties. Estimation of SRP position errors is a nonlinear problem and when ship attitude uncertainties are large, the nonlinearities can be important. However, the bounds calculated by the error model developed can be inflated to deal with these nonlinearities. Finally, by analyzing data collected from ship trials, it is shown that perhaps a more challenging issue may be the potential for highly correlated, bias-like structural flexure uncertainties.