posted 04-20-2012 12:35 AM ET (US)        

With the Obama administration having shut off the LORAN system, there were no LORAN signals available to use, nor did I have a LORAN receiver to get some LORAN time delay numbers for comparison, but I did have some old NOAA charts that were marked with LORAN time delay overlays. I dug out a chart of Lake Erie from a few decades ago. On the chart I located three positions which were at the exact intersection or close to the intersection of time delay overlay lines. I noted the LORAN time delays for those objects, and then I went to the HDS.

On the HDS I enabled Phantom Loran, selected the proper chain, the 9960 group repetition interval, and selected the two stations to use for the delays. Then I moved the cursor over the charted position of the objects as shown on the INSIGHT digital chart cartography of the HDS, and I noted the Phantom Loran predicted time delay values: Here are the results:

Bouy near Chickenolee Reef; 9960-X, 9960-Z
NOAA Chart = 28858.00, 57060.00
Phantom Loran = 28858.91 57061.27

These values were in good agreement. The position of the buoy may have moved from the old paper chart to the new digital chart. The variation was only a matter of a few hundred feet.

Shore object near Bolles Harbor; 9960-W; 9960-Z
NOAA Chart = 16464.00, 56700.00
Phantom Loran =16461.51, 56719

These values were way off. The predicted value is about a mile away. Something has gone wrong here.

Detroit River Light; 9960-W; 9960-Z
NOAA Chart = 16456, 56872.8 (interpolated)
Phantom Loran = 16454.83, 56866.04

The Z-value is close, but the W-value is again rather far off.

My conclusion is that accuracy of these predicted LORAN time delays probably varies quite a bit depending on the location and its relationship to the various stations being used. I did not see any error of the magnitude of "five miles" as was suggested. I think if one had some old LORAN time delay numbers, the Phantom Loran could get you in the vicinity of the original location, but not right on the spot.

posted 04-20-2012 08:57 PM ET (US)            

Flashing Red at SW end of South Bass Island
LORAN TIME DELAY COMPARISON

Charted values----HDS vales
9960-Y = 43670 v. 43670.59
9960-W = 16501 v. 16500.5
9960-Z = 56920 v. 56920.04

posted 04-21-2012 06:24 PM ET (US)            

The LORAN system was approximately 80-percent finished with modernization of the system which would have enhanced its accuracy and usefulness to be on a par with available space-based systems, but with the enormous advantage of almost complete immunity to jamming and the ability to be useful indoors and inside buildings--not to mention a cost that is about one-onehundredth of space-based system and a location of all the resources on our own soil, not in outer space. The Obama administration, against the advice of almost all technical advisory committees, shut down LORAN and began to dismantle the system. The dismantling of the system has cost more than it would have cost to finish the modernization. This ridiculous action is a good example of what happens when non-technical government executive-branch political appointees are allowed to make budgetary decisions about long-term infrastructure technical projects. When a government runs on the basis of how many votes can be bought with each dollar spent, incomprehensible actions like this are the result.

Fortunately, there has been a resurgence of interest in modernization of LORAN, and at the moment there is a test program underway to further explore restoration of LORAN as a position, navigation, and timing service. Our modern technological society cannot live without position, navigation, and timing services with ultra-precise information. An enhanced and modernized LORAN is now seen as a very important alternative to the billion-dollar-per-satellite approach of GPS.

posted 04-22-2012 01:02 PM ET (US)            

Concur. Completely.

There's been comments before comparing the accuracy (both absolute and repeatable) between both systems. What some forget was that in many cases, the comparison was an apples and oranges situation; i.e. the comp's were between an older LORAN unit and a new GPS.

Of course there was going to be a significant variance, favoring the GPS unit!

I also recall that there could be a difference in readings between the manufacturers of the LORAN units of the day depending on which algorithm they embedded in their software (I never realized there was more then one way to convert TD to L/L until reading about it). That may have accounted for some of the absolute errors.

tmann45 - I've seen the repeatability in action with a King (I think...it's been a while!)unit mounted in our Revenge in the mid 1980's. I would find that most of the time the comparison between readings prior to leaving our slip and returning varied no more then .02 of a lat/lon.

And that was over 25 years ago....

So how accurate are the new GPS units? Well, I got assigned to assist our IT department on what is called the Continuous Operating Reference Station (CORS for short) project. It is a grant offering from the fed's to the states and passed on to local counties to improve the accuracy of surveys. Here's how it works:

In our county, we installed five CORS units. They are passive receivers mounted on a solid aluminum pole, encased in a concrete tube. The tube goes down 20ft into the ground, and extends 10 feet about the surface, with the pole extending another five to eight feet terminating with an antenna that looks and is the size of 1/2 a basketball.

Once the system is installed, NOAA's National Geodetic Survey group comes and plots with their equipment, the absolute known L/L to the top of the antenna. They told me that it's plotted to 1/10,000 of L/L. When I asked to give me some sort of reference, the guy said it's about the diameter of a dime (knowing that in the real world, that dime can become oblong depending on distance from the equator). Close enough for me.

The antenna feed goes to a server mounted in a building close by, and data from the server across the 'net to our data center where it's stored and accessible by local survey companies to increase the accuracy either real time in the field, or by post processing their recorded data.

The CORS data gives them the difference between what is the known plotted absolute, and where the CORS antenna thought it was, based on GPS readings.

For those interested in more:

http://www.ngs.noaa.gov/PUBS_LIB/GPS_CORS.html

and

http://www.youtube.com/watch?v=kI1fmJdfsV8

and

http://geodesy.noaa.gov/CORS/