Then and Now Part 3: Shedding Light on Navigation

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Post written by LTJG Ryan T. White

Let’s go back in time once more; further back than we’ve ever gone before, to a time before the U.S. Life Saving Service; back even before the U.S. Revenue Cutter Service. It’s August 7, 1789 and we have witnessed the creation of the U.S. Lighthouse Service. Prior to 1789, individual states provided funding for lighthouses on their coasts. These lighthouses aided navigation by acting as points of reference and marking dangerous areas for mariners. Following the various engineering advances of World War II, more lighthouses were constructed in areas that were deemed to be too dangerous decades before. And soon, lighthouses became part of the landscape with keepers like Idawalley Lewis becoming living legends. With even further advances in technology, lighthouses became automated and no longer required the support of a keeper.

“But Ryan, why don’t we see ‘1789’ at the bottom of the Coast Guard crest?” The Coast Guard traces its sea-going heritage to the creation of the Revenue Cutter Service in 1790 instead of the land based Lighthouse Service created a year earlier. In 1915, the Life Saving Service was combined with the Revenue Cutter Service to become U.S. Coast Guard. It wasn’t until 1939 that the Lighthouse Service merged with the Coast Guard.

While nations were already operating radio beacons prior to World War I for navigation purposes, a system with greater range and better precision was needed. With the advent of radar came the Coast Guard Long Range Aid to Navigation (LORAN) Program. LORAN is a land based navigation system that uses at least three towers in “chains” to triangulate positions. Each LORAN chain is made up of one master station and at least two secondary stations. Chains are given four digit identifiers. Add a zero to the chain identifier and you have the duration of the cycle. In an example provided by ET1 Stephen Pearson, “The North East U.S. chain identifier is 9960. Add a zero at the end the cycle for the chain is 99,600 microseconds. The cycle begins and ends with the master station transmitting.” The more secondary stations present does not mean that the LORAN chain is more accurate, but that more area around the master station is covered. Through various improvements, LORAN-C became the final operational product, with an accuracy of about a quarter mile. The United States has 24 LORAN-C stations and shares chains with Russia and Canada.

From the land based concept of LORAN we move to the space age and the United States-owned Global Positioning System (GPS). GPS uses a satellite-based system to triangulate a user’s location. Unlike LORAN-C which uses only three towers, GPS is able to use more than three satellites to increase the accuracy of the position. GPS is managed by the National Executive Committee for Space-Based Positioning, Navigation, and Timing (PNT).

While GPS is much more accurate than all prior systems of navigation, improvements could still be made. Using land-based systems, the United States was able to correct for slight differences in GPS positions, enhancing the overall accuracy of GPS. This enhanced form of GPS is known as the Differential Global Positioning System (dGPS). dGPS consists of 89 remote sites and two control centers providing an accuracy of about 10 meters. These numbers fluctuate but in general the coverage of dGPS continues to grow. Sites within the Nationwide Differential Global Positioning System (NDGPS) are owned by the Department of Transportation, but monitored and managed by the Coast Guard.

Navigation systems have evolved by leaps and bounds in the maritime community over the past two centuries and the Coast Guard has been right in the thick of it. From the days of lighthouses with very limited ranges to the WWII developed LORAN culminating in the implementation of LORAN-C, the changes have been drastic. There is little doubt that mariners would find the 10 meter accuracy of dGPS in 2009 more comforting than the crudely marked shoal water of 1789. Safety and innovation drive the bus as navigation systems continue to evolve and shine new light on the maritime community.

1 comments on “Then and Now Part 3: Shedding Light on Navigation”

  1. It’s sad that ships don’t need lighthouses anymore. With the advent of GPS, that old tradition seems to be setting sail (pardon the pun)

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