Using space-based remote sensing for improved global navigation and communication

In an effort to improve global navigation and the availability of radio frequency (RF) communication, the U.S. Department of Defense is deploying a series of experimental and operational ultraviolet remote sensing sensors on satellite platforms. These sensors are used to measure airglow radiances from the upper atmosphere and ionosphere to help specify the global distribution of the densities in the neutral atmosphere and ionosphere. The Earth's ionosphere can affect the propagation of electromagnetic radiation in a number of ways including reflection, refraction, frequency dispersion, time delay and Faraday rotation. These effects are stronger at lower frequencies but variations in ionospheric electron density can be important for RF propagation at frequencies up to about 10 GHz. For quiet ionospheric conditions, refraction, time delay and frequency dispersion provide the dominant source of error for single frequency GPS navigation. Under disturbed conditions, these effects can combine to produce scintillation on GPS and communication signals (HF, UHF) and can cause communication outages, and occasionally, GPS outages. To mitigate these environmental effects and provide advance warning of outages, the Defense Meteorological Satellite Program (DMSP) begins this year to fly a series of ultraviolet limb and nadir imagers and spectrometers for their next Block of polar orbiting satellites. The Office of Naval Research (ONR) is sponsoring the development of a geosynchronous ultraviolet imager to provide real-time ionospheric monitoring with high spatial structure. These and other upcoming remote sensing ionospheric instruments provide improved specification of the global ionosphere and feed a new generation of assimilating ionospheric models to help provide a forecast capability for environmental impacts on global navigation and communication.