Navigation systems utilizing satellites in the field of hydrography
Navsat, or Navigation Satellite Systems, are essential tools in hydrography and offshore surveys, providing precise positioning and navigation. While the specific integration of Navsat with systems like rho-rho Loran-C and Doppler Sonar in current applications is not extensively detailed, general knowledge suggests a widespread use of such integrated systems.
The Transit satellite system, commonly known as Navsat, improves positioning accuracy for stationary receivers to about 20 meters. It operates in three dimensions, but only two coordinates can be obtained from a single pass, with the third being derived from multiple passes at a motionless receiver.
Navsat satellites are in almost circular polar orbits with heights of 1100 km and periods of one hour and forty minutes. They broadcast two stable, harmonically related carrier frequencies at 150 MHz and 400 MHz.
One of the advantages of Navsat is its ability to fix a ship's position with an accuracy of between 60-600 meters, depending on the ship's course and speed measurements. The position errors are generally random from one pass to the next, making it a valuable complementary partner to high resolution, continuous systems with systematic biasses or error accumulation.
Navsat's position is first converted to a geocentric coordinate system, then iteratively to the geodetic coordinate system of the closest country or continent. The matter of datum transformations is one of the most misunderstood aspects of using the Transit system.
Navsat can be integrated with rho-rho Loran-C and Doppler Sonar. The accuracy of a ship's position from a good Navsat pass can be improved from ± 100 m to ± 60 m by breaking Doppler Sonar's ship's track into 20 s intervals for computing the Navsat fix.
Navsat satellites can be received over a circle on the earth's surface of radius 30 degrees. Its accuracy depends strongly on the pass elevation angle. For high elevation passes, the longitude is poorly determined. For low elevation passes, refraction and the shallowness of the Doppler curve degrade the fix accuracy.
Navsat was designed for navigating submarines, but its great power for precise surveying offshore lies in the fact that the position errors, though sizeable, are generally random from one pass to the next. It has many auxiliary applications, such as resolving cycle ambiguity in low frequency radio aids, calibrating marine survey positioning systems, radio aids to navigation, positioning offshore drilling rigs, and serving as a geodetic instrument capable of establishing shore control to 1 meter accuracy.
For a comprehensive understanding of Navsat's role in hydrography and offshore surveys, readers are encouraged to refer to the paper titled "Satellite navigation in hydrography" written by Eaton, Wells, and Stuifbergen in 1973. The manuscript is a reprint of a paper originally published in 1976 in The International Hydrographic Review, and can be found at this URL: https://journals.lib.unb.ca/index.php/ihr/article/view/23736
[1] The search results mainly covered a list of military electronic systems without mention of Navsat or its use in hydrography or offshore contexts.
- Navsat, a valuable tool in hydrography and offshore surveys, improves positioning accuracy for stationary receivers to approximately 20 meters, operating in three dimensions and providing two coordinates from a single pass.
- Despite a lack of extensive details on the specific integration of Navsat with systems like rho-rho Loran-C and Doppler Sonar, Navsat can be integrated with these systems for improved accuracy in a ship's position.
- Navsat's great power for precise surveying offshore lies in the fact that the position errors, though sizeable, are generally random from one pass to the next, making it a useful complement to high-resolution systems.
- The integration of Navsat with advanced gadgets like Doppler Sonar can further improve the accuracy of a ship's position, reducing errors from ± 100 m to ± 60 m.
- Navsat's role in hydrography and offshore surveys goes beyond basic navigation, extending to calibrating marine survey positioning systems, resolving cycle ambiguity in low-frequency radio aids, and even serving as a geodetic instrument for establishing shore control with a 1-meter accuracy.
