Avionics Navigation Systems, 2nd Edition

11 Mapping and Multimode Radars

11.1 INTRODUCTION

Airborne ground-mapping radars were originally developed in World War II as a means of bombing through clouds and weather—and at night, when the bombing-aircraft operator could not see his target visually. These radars performed two navigation functions. First, they permitted the aircraft to find its way over enemy terrain, without ground navigation aids or sight of the ground, to the threshold of the bombing run. Second, the radar then provided precise navigation during the bombing run by use of cursors set on the target point in a display. Later, a “beacon” mode was added to enable the radar to make fixes on beacon transponders placed at known ground positions in friendly territory and coded to establish their identity. This permitted much easier and more precise navigation by radar during the early phases of the inbound leg to the target and, more important, on return. It was also found that the radar could be used to see intense storms and navigate around them during times of darkness or flight through clouds.

These early radars illustrate the major themes that have concerned navigation radar designers ever since, namely, general navigation; precision navigation for landing, weapon delivery, air drop of personnel and material; and beacon navigation.

Radar-navigation economics also remain much the same. First, a ground-mapping radar is heavier, more expensive, and complex compared to navigation equipment aided by either ground-based ...