Self-contained method for correction of an inertial system over a body of water

An on-board method for the correction of the inertial system of an aircraft as it proceeds on a course over a region of a body of water comprising the steps of:

• a) continuously determining the location of a point horizontally along said course by means of said aircraft's inertial navigation system;
• and
• b) measuring the vertical distance of said aircraft, at said point, above an ellipsoidal model of a geoid that includes said region;
• and
• c) measuring the vertical distance of said aircraft, at said point, above the surface of said body of water;
• then
• d) computing the difference between the values measured in steps b and c to determine the measured undulation of said geoid at said point;
• then
• e) comparing said measured undulation of said geoid with the undulation of said geoid at said point as determined by gravitational surveys;
• then
• f) repeating steps a through e;
• then
• g) determining a position correction by correlating said measured undulation values with values pre-determined by said survey;
• and then
• h) adjusting at least one of the aircraft's inertial navigation system variable computations by means of said position correction.