A critical perspective on some aspects of GPS development and use

We seek to clarify a few problems associated with GPS use in order to propel their resolution by clearly elucidating the nature of these problems. We express our concerns about (1) certain aspects of prescribed GPS availability augmentation that currently calls for heavy supplemental reliance on (apparently risky) baro-altimeters, (2) the difficulty of ameliorating multipath effects in many civilian applications, (3) GPS's susceptibility to foliage attenuation as an L-band signal, (4) some evolving policy issues relating to agricultural use (and implied development support) of GPS, (5) Receiver Aided Integrity Monitoring (RAIM) validation (specifically its lack of official confirmation), and (6) anticipated obscuring cross effects of (RAIM) [a variant of failure detection in dynamical systems] with heavy (as contrasted with light or medium) integration with inertial navigation as is otherwise recommended for use to achieve the greatest navigation accuracy. These topics, while controversial, cut across almost all applications and so elucidation should be viewed as a positive step forward.