Abstract: A method determines the atmospheric refraction of a radar beam by utilizing a stabilized optical telescope directed toward a star near the radar target location. This allows measuring the target refraction as observed from ships at sea without a-priori knowledge of the local refraction index or weather conditions in the target area. The telescope may employ an infra-red (IR) sensor and is capable of imaging stars. The atmospheric refraction of the star light is determined by pointing the telescope based on star ephemeris data, and measuring the star image deviation from the center of the telescope's field-of-view (FOV). The corresponding refraction of the radar beam can be determined by employing a conversion factor relating the IR-to-RF atmospheric propagation characteristics. This conversion factor can be obtained by dedicated tracking measurements.

Abstract: A ship includes a star tracker mounted on a platform stabilized in ENU by the inertial navigation system (INS). The line-of-sight (LOS) of the star tracker is directed toward two separated stars, and the LOS difference angles are noted. The angles are processed to generate vector triads representing geodetic (ephemeris) and navigation system attitude. The triads are processed to generate a coordinate transformation matrix. The transformation matrix is separated into systematic error and reference attitude error. The reference attitude error is summed with the inertial navigation system attitude to generate corrected ENU attitude. The corrected attitude is used as a reference for shipboard sensors, to reduce errors when the sensor data is linked to other platforms.

Abstract: A ship includes a star tracker mounted on a platform stabilized in ENU by the inertial navigation system (INS). The line-of-sight (LOS) of the star tracker is directed toward two separated stars, and the LOS difference angles are noted. The angles are processed to generate vector triads representing geodetic (ephemeris) and navigation system attitude. The triads are processed to generate a coordinate transformation matrix. The transformation matrix is separated into systematic error and reference attitude error. The reference attitude error is summed with the inertial navigation system attitude to generate corrected ENU attitude. The corrected attitude is used as a reference for shipboard sensors, to reduce errors when the sensor data is linked to other platforms.