Geolocation using guided surface waves

Abstract

Disclosed are various approaches for determining positions of a navigation unit and correcting for errors. The navigation unit can receive a guided surface wave using a guided surface wave receive structure. The navigation unit can then determine a potential location of the guided surface wave receive structure. Finally, the navigation unit can determine an accuracy of the potential location based at least in part on a secondary data source.

Therefore, the following is claimed: 
     
         1 . A navigation unit, comprising:
 a processor;   a memory;   machine readable instructions stored in the memory that, when executed by the processor, cause the navigation unit to at least:
 determine a current location of the navigation unit based at least in part on a plurality of Zenneck surface waves travelling along a terrestrial medium and received by the navigation unit, each of the plurality of Zenneck surface waves launched by a respective wavefront incident at a respective complex Brewster angle of the terrestrial medium; and 
 determine an accuracy of a determination of the current location based at least in part on a secondary data source. 
   
     
     
         2 . The navigation unit of  claim 1 , wherein the secondary data source comprises inertial data stored in the memory, wherein the inertial data comprises navigational data representing a current speed, a current heading, an initial location, a past speed, and a corresponding past heading of the navigation unit. 
     
     
         3 . The navigation unit of  claim 2 , wherein:
 the current location is a first location; and   the machine readable instructions that determine the accuracy of the determination of the current location further cause the computing device to at least:
 calculate an estimated location of the navigation unit based at least in part on the inertial data; and 
 determine that the estimated location is within a predefined distance of the current location. 
   
     
     
         4 . The navigation unit of  claim 1 , wherein the machine readable instructions that determine the accuracy of the determination of the current location further cause the computing device to at least:
 identify when an additional Zenneck surface wave is received from a correction station, wherein the additional Zenneck surface wave carries the secondary data source comprising a position of the correction station, a time that the signal was sent from the correction station, and a propagation speed of the additional Zenneck surface wave;   determine a first distance of the navigation unit from the correction station based at least in part on the position of the correction station, the propagation speed of the additional Zenneck surface wave, and the time that the additional Zenneck surface wave was sent from the correction station;   calculate a second distance of the navigation unit from the correction station based at least in part on the position of the correction station and the current location of the navigation unit; and   determine that the first distance and the second distance are within a defined margin of error.   
     
     
         5 . The navigation unit of  claim 1  wherein the machine readable instructions, when executed by the processor, further cause the navigation unit to at least correct the current location of the navigation unit in response to a determination that the accuracy of the current location fails to fall within a previously defined margin of error. 
     
     
         6 . The navigation unit of  claim 5 , wherein the machine readable instructions, when executed by the processor, further cause the navigation unit to at least adjust a circumference of a circle centered on a ground station that generated at least one of the plurality of Zenneck surface waves. 
     
     
         7 . The navigation unit of  claim 6 , wherein the application further comprises machine readable instructions stored in the memory that, when executed by the processor, cause the navigation unit to at least recalculate the current location of the navigation unit based at least in part on the adjusted circumference of the circle centered on the ground station. 
     
     
         8 . A navigation unit, comprising:
 a receiver network having a phase delay)) that matches a wave tilt angle (W) for launching a Zenneck surface wave with a wave front incident at a complex Brewster angle of a terrestrial medium, the wave tilt angle defined by the local characteristics of the terrestrial medium;   a processor;   a memory;   machine readable instructions stored in the memory that, when executed by the processor, cause the navigation unit to at least:
 determine a current location of the navigation unit based at least in part on the guided surface wave; and 
 determine an accuracy of a determination of the current location based at least in part on a secondary data source. 
   
     
     
         9 . The navigation unit of  claim 8 , wherein the secondary data source comprises inertial data stored in the memory, wherein the inertial data comprises navigational data representing a current speed, a current heading, an initial location, a past speed and a corresponding past heading of the navigation unit. 
     
     
         10 . The navigation unit of  claim 9 , wherein
 the current location is a first location; and   the machine readable instructions that determine the accuracy of the determination of the current location further cause the computing device to at least:
 calculate an estimated location of the navigation unit based at least in part on the inertial data; and 
 determine that the estimated location is within a predefined distance of the current location. 
   
     
     
         11 . The navigation unit of  claim 8 , wherein the machine readable instructions that determine the accuracy of the determination of the current location further cause the computing device to at least:
 identify when an additional Zenneck surface wave is received from a correction station, wherein the additional Zenneck surface wave carries the secondary data source comprising a position of the correction station, a time that the signal was sent from the correction station, and a propagation speed of the additional Zenneck surface wave;   determine a first distance of the navigation unit from the correction station based at least in part on the position of the correction station, the propagation speed of the additional Zenneck surface wave, and the time that the additional Zenneck surface wave was sent from the correction station;   calculate a second distance of the navigation unit from the correction station based at least in part on the position of the correction station and the current location of the navigation unit; and   determine that the first distance and the second distance are within a defined margin of error.   
     
     
         12 . The navigation unit of  claim 8 , wherein the machine readable instructions, when executed by the processor, further cause the navigation unit to at least correct the current location of the navigation unit in response to a determination that the accuracy of the current location fails to fall within a previously defined margin of error. 
     
     
         13 . The navigation unit of  claim 12 , wherein the machine readable instructions, when executed by the processor, further cause the navigation unit to at least adjust a circumference of a circle centered on a ground station that generated the Zenneck surface wave to correct the current location of the navigation unit. 
     
     
         14 . The navigation unit of  claim 13 , wherein the machine readable instructions, when executed by the processor, further cause the navigation unit to at least recalculate the current location of the navigation unit based at least in part on the adjusted circumference of the circle centered on the ground station. 
     
     
         15 . A method for determining a geographic location, comprising:
 receiving with a receive structure a Zenneck surface wave traversing a terrestrial medium, the Zenneck surface wave launched by a wave front incident at a complex Brewster angle of the terrestrial medium;   determining a current location of the receive structure based at least in part on the Zenneck surface wave; and   determining an accuracy of a determination of the current location based at least in part on a secondary data source.   
     
     
         16 . The method of  claim 15 , wherein the secondary data source comprises inertial data that represents a current speed, a current heading, an initial location, a past speed, and a corresponding past heading of the navigation unit and further comprising:
 calculating an estimated location based at least in part on the inertial data; and   determining whether the estimated location is within a predefined acceptable margin of error to determine the accuracy of the current location.   
     
     
         17 . The method of  claim 15 , wherein determining the accuracy of the determination of the current location based at least in part on the secondary data source further comprises:
 identifying when an additional Zenneck surface wave is received from a correction station, wherein the additional Zenneck surface wave carries the secondary data source comprising a position of the correction station, a time that the signal was sent from the correction station, and a propagation speed of the additional Zenneck surface wave;   determining a first distance of the navigation unit from the correction station based at least in part on the position of the correction station, the propagation speed of the additional Zenneck surface wave, and the time that the additional Zenneck surface wave was sent from the correction station;   calculating a second distance of the navigation unit from the correction station based at least in part on the position of the correction station and the current location of the navigation unit; and   determining that the first distance and the second distance are within a defined margin of error.   
     
     
         18 . The method of  claim 15 , further comprising correcting the current location of the receive structure in response to a determination that the accuracy of the current location fails to fall within a previously defined acceptable margin of error. 
     
     
         19 . The method of  claim 18 , further comprising adjusting a circumference of a circle centered on a ground station that generated the Zenneck surface wave. 
     
     
         20 . The method of  claim 19 , further comprising recalculating the current location based at least in part on the adjusted circumference of the circle centered on the ground station.