Navigation & Flight Path Data Acquisition
for Airborne Surveying

SGL has developed a flexible and simple navigation system, SGNav, specifically designed for the airborne geophysical environment.  The system uses the high accuracy of the GPS system and a navigation computer to allow precise navigation in three dimensions anywhere in the world.

SGL's SGNav system steers the crew from their point of departure to the start of a specific line, directs them along the survey line, and then to the next line or any other specified line.  At the end of the flight, the crew will be guided back to the airport.  While flying along a line the SGNav system shows the pilots the correct x, y location to fly as well as showing them the correct altitude to fly based on a number of altitude sensors.

Sample of flight planning generated by our software and fed into aircraft navigation system

The position information is presented to the pilots on a small flat panel LCD screen mounted in the pilot's line of vision.  The SGNav screen also shows the pilots the altitude profile of the line and their position on this profile.  SGNav can also be used with a pre-planned drape surface providing aircraft altitude guidance in the survey area.

The SGNav system registers the aircraft flight path by recording the raw GPS measurements.  The raw measurements, together with the measurements taken at a ground station, are processed post-mission using the kinematic GPS positioning program GPSoft.  GPSoft uses a robust U-D factorized Kalman filter to process double-differenced observations which provides extremely accurate differentially corrected GPS flight path recovery.

The basic SGNav system consists of the following items:

  1. Airborne GPS Receiver and Aircraft Antenna

    • NovAtel GNSS (Global Navigation Satellite System) which incorporates GPS and other satellite positioning systems, sampling rate of 20 Hz
    • In-flight positional accuracy of better than 5 m
    • Post-processed positional accuracy of better than 1 m
    • Power requirement: nominal 10-35 VDC 10 watts
  2. Airborne Navigation Control and Flight Path Recording Computer

    • Provides three-dimensional steering information on a graphical display
    • Records the position of the aircraft and the raw GPS satellite range data necessary for post-mission differential processing at up to 10 Hz
    • Real-time differential GPS position corrections for 2-5 m accuracy in-flight
    • Send UTC time and/or timing pulses to a camera or data acquisition system
    • Data are recorded on removable storage media which are dependable in high vibration environments
    • The computer, designed for airborne use, operates on 28 VDC, 60 watts
    • RS232, optionally ARINC or RS422 data port
    • Great circle, UTM or rhumb line flying
  3. Post-Flight Software

    • Enables the crew to list or view the recorded GPS
    • This software can be run on any PC computer, including the airborne computer
    • GPSoft - post-mission differential GPS positioning software
  4. GPS Reference Station for Differential GPS Position solutions

    To take the advantage of the maximum accuracy of the GPS System, the following is needed at the ground reference station site.

    • NovAtel GNSS receiver
    • Standard PC computer
    • SGL's ground station recording software to record the data from the receiver

SGL conducted an extensive study to compare actual flight paths flown using raw GPS data, and flight paths flown using real-time corrected GPS data, against the pre-planned track and altitude.  Based on this study, we are convinced that there is no longer any advantage in using real-time differential corrections, and there are many surveys where it will actually hamper the crew's ability to follow the pre-planned flight lines.  We therefore prefer not to use real-time differential corrections for navigation, and we continue to differentially correct all of our GPS post-flight using a local GPS reference station.  Differential GPS receivers can be used to provide real-time differential corrections, if required.

Various GPS receivers were reviewed and the NovAtel GNSS receivers were found to be the most suitable for this application.  These multi-frequency receivers incorporate GPS and other satellite positioning systems.  Real-time differential navigation is also possible with the SGNav system.

The recorded reference GPS measurements, together with measurements recorded on the aircraft, are processed after the flight using SGL's GPSoft kinematic differential GPS processing program.

Navigation and Flight Path Recovery Systems

The SGNav navigation system can be configured to provide pilot guidance in any of the following manners:

  1. Raw GPS data
  2. Real-time DGPS with corrections from a satellite service

All the normal navigation parameters are displayed on the miniterminal, such as:

  distance to waypoint
  track made good
  time to waypoint
  distance from waypoint
  aircraft ground speed
  time to start of line
  distance to start of line
  up/down error
  time to end of line
  distance to end of line
  desired heading
  track error

In addition to this, the number of satellites being used, PDOP and various other parameters of the GPS system are displayed.

SGNav Performance Specifications

Differential Position:

The accuracy achieved by this method is better than 1 m.

Single Receiver Position:

The accuracy achieved without differential correction is better than 5 m.

These specifications are given assuming that the GPS receivers are tracking a minimum of four satellites, with good satellite geometry.