There are four variables that must be defined in order to determine the location of a target on Earth. There is azimuth (or bearing), distance (range), vertical angle (elevation), and self-position (latitude, longitude, and altitude above sea level) to the target. The largest source of Target Location Error (TLE) in existing Far Target Location (FTL) systems is accurately determining azimuth. In most cases, azimuth errors in the guidance of man-portable weapon systems would lead to failure of target acquisition and destruction, and possibly endanger friendly forces. Currently available high accuracy (1-4 mil, where mil is a milliradian or 0.56°) azimuth sensors are expensive, bulky, heavy and power hungry; require up to 4 minutes for set up; and/or have availability issues. Digital magnetic compasses have long been an inexpensive means for azimuth determination, but they are hindered by magnetic interference and offer only marginal accuracy.
The Sky Polarization Azimuth Sensing System (SkyPASSTM) is a high accuracy, low SWaP-C solution for determining azimuth within 1-2 mills for any platform requiring accurate heading information including man-portable weapon systems. SkyPASS is not hindered by many of the operational limitations seen in the current azimuth sensing methodologies. SkyPASS provides accurate azimuth in real-time, does not require leveling, and can even assist in determining orientation when GPS is unavailable.
SkyPASS observes a natural phenomenon that is observable from any point on Earth (including from air vehicles). In the upper atmosphere, there is a defined polarization pattern which is dependent on the absolute location and orientation of the observer and the date/time. This polarization map, undetectable by the naked eye, is imaged by SkyPASS which, using the known date/time, calculates the user’s orientation relative to world coordinates. The x-y position and orientation of the map on the SkyPASS image corresponds to the roll, pitch, and heading of the SkyPASS sensor.
It is important to note that sky polarization sensing is not affected by magnetic disturbances, does not require leveling or field calibration, and can provide an instantaneous answer. When compared to celestial sensing methods, like Sun or Star trackers, SkyPASS outperforms in that it can operate in a variety of cloud conditions, at solar noon, and around sunrise/sunset.
The SkyPASS sensor can be produced at a much lower cost than competing technologies, thus, enhancing a military capability while reducing overall cost. A celestial method that can operate at sunrise/sunset, at solar noon, and in a variety of cloud conditions, SkyPASS is the next step forward in orientation sensing.
SkyPASS has been tested as an add on to the Far Target Location (FTL) systems that enable the warfighter to determine target position with a very high degree of accuracy. The system has also been flown attached to the exterior of aircraft to determine heading accuracy.