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Feasibility of Millimeter-Accuracy Geodetic Positioning and Vehicle Tracking with Repeater Satellites

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Technical rept. for Apr 1986-Jul 1989

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The proposed Geobeacon satellite can detect and locate transmitters of a geodetic positioning system as well as transmitters of an emergency search and rescue SAR system. Simple, low-power transmitters on the earths surface will broadcast code-modulated signals which will be received and rebroadcast to a processing site by a constellation of repeater satellites. A SAR transmitter can transmit at one frequency. For geodetic applications, a transmitter must transmit signals at more than one frequency, including a relatively low e.g. 100 MHz and a relatively high several GHz frequency. The LF signals would aid acquisition and tracking of the higher frequency signals. By virtue of this aiding, the transmitted power required to enable tracking of signals at 10 GHz is about 100 x less than the power needed for tracking such a signal alone. Uplink power requirements both for aided tracking and for unaided acquisition are calculated as functions of frequency from 100 MHz to 50 GHz. The chief uncertainty in the calculations concerns the man-made radio noise environment in earth orbit. An algorithm is developed to select frequencies by which aided tracking of the highest frequency signal can be maintained. This algorithm is based on a stochastic description of the kinematic and ionospheric contributions to the received signal frequencies and phases. Discrete Kalman filter equations are derived for estimating the covariance of phase and frequency estimates. Frequency selections and corresponding power budgets are presented for a vehicle-trackingSAR system and for a geodetic positioning system. Satellite geodesycommunications Repeater satellites Space geodesy Radio positioning Radio trackinginterferometry.

Subject Categories:

  • Geodesy
  • Optical Detection and Detectors
  • Navigation and Guidance
  • Radio Communications

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