GPS upended?

[StuM]

Originally Posted by redneckrob

The Coast Guard DGPS system is being shut down (https://www.navcen.uscg.gov/?pageName=dgpsMain) WAAS is alive and well but not typically used (or needed) by cruisers.

Aah, so you are not talking about

"a marine and is an aviation differential GPS system that uses ground stations and satellites to transmit corrections to GPS that are independent from the GPS system itself" .

Unlike WAAS, DGPS doesn't use any satellites other than the standard GPS signals. It is not independdt from the GPS system. The DGPS stations transmit radio signals that report on how accurate the GPS signal is at the station.



WAAS covers a much larger area than USCG DGPS ever did, is as accurate as USCG DGPS and is much more useful for cruisers



From your link:

"Since 2016, the Coast Guard has continued assessments and outreach affirming that the positional accuracy provided by un-augmented GPS and GPS augmented by the U.S. Wide Area Augmentation System (WAAS) is sufficient to meet Coast Guard mission requirements and navigational safety requirements for harbor approach."

[boatpoker]

Originally Posted by BlackHeron

I have noticed a reduction in GPS accuracy across all of my devices as we came up through the ICW dismal swamp route into the Chesapeake the last few days. Was really bad around Norfolk.

Has this started already?

I came through Norfolk about 2 weeks after 911. None of my electronics worked properly through Hampton Roads , GPS, radar, VHF, depth sounder.
I assumed massive military interference as the military went into high gear.

[BlackHeron]

Originally Posted by boatpoker

I came through Norfolk about 2 weeks after 911. None of my electronics worked properly through Hampton Roads , GPS, radar, VHF, depth sounder.
I assumed massive military interference as the military went into high gear.

This is our fourth time through the area and have had no issues there on other transits. There were some scheduled jamming tests a few months back and noticed issues then too, when we were in Florida (if I remember right) but it was announced and we were expecting it. Perhaps warning civilian users is no longer in military vogue.

[a64pilot]

Originally Posted by StuM

Aah, so you are not talking about

"a marine and is an aviation differential GPS system that uses ground stations and satellites to transmit corrections to GPS that are independent from the GPS system itself" .

Unlike WAAS, DGPS doesn't use any satellites other than the standard GPS signals. It is not independdt from the GPS system. The DGPS stations transmit radio signals that report on how accurate the GPS signal is at the station.



WAAS covers a much larger area than USCG DGPS ever did, is as accurate as USCG DGPS and is much more useful for cruisers



From your link:

"Since 2016, the Coast Guard has continued assessments and outreach affirming that the positional accuracy provided by un-augmented GPS and GPS augmented by the U.S. Wide Area Augmentation System (WAAS) is sufficient to meet Coast Guard mission requirements and navigational safety requirements for harbor approach."

While I’m not familiar with the USCG DGPS, DGPS is orders of magnitude more accurate than WAAS, DGPS can and will get you to sub centimeter accuracy, Steering that farm tractor for example, WAAS can’t do that, it’s not good enough.
WAAS is good, better than the old GPS, and surely all that’s need for Marine Nav?
I was never a surveyor, but feel sure that any GPS surveying that’s done, is done with DGPS.

Now boats or cars and most civilian use of GPS doesn’t require centimeter accuracy of course, makes me wonder why the USCG was fielding it?

[a64pilot]

Jamming a civilian GPS is easy, very easy.
A couple of years ago I remember a truck driver that was arrested, he had a jammer so that his boss couldn’t track the truck, problem was he jammed the aircraft at the airport when he drove by.

Found it
https://www.cnet.com/news/truck-driv...ewark-airport/

[StuM]

Originally Posted by a64pilot

While I’m not familiar with the USCG DGPS, DGPS is orders of magnitude more accurate than WAAS, DGPS can and will get you to sub centimeter accuracy, Steering that farm tractor for example, WAAS can’t do that, it’s not good enough.
WAAS is good, better than the old GPS, and surely all that’s need for Marine Nav?
I was never a surveyor, but feel sure that any GPS surveying that’s done, is done with DGPS.

Now boats or cars and most civilian use of GPS doesn’t require centimeter accuracy of course, makes me wonder why the USCG was fielding it?

It's all about how far away you are from the DGPS station. DGPS is only that accurate at short range. The USCG was only ever looking at WAASS levels of accuracy and their solution was set up pre WAAS.

USCG DGPS: 1993
WAAS: 2003
IOW, it's obsolete for intended purpose

(If you are offended by it, please ignore the bold in the following)

https://www.researchgate.net/publica...nt_NDGPS_Recap

The current performance standard for NDGPS dates back to the April 1993 Broadcast Standard, which requires a 10 meter (m) 2DRMS system over the coverage areas. This also is the basis for the U.S. agreeing to Harbor and Harbor Approach requirements found in IALA R-121 and IMO Resolution A.953(23). The specification was derived based on spatial decorrelation, or the degradation of the accuracy of the DGPS correction over increasing baselines between the reference station and rover, as well as in the Horizontal Dilution of Precision (HDOP).

Given the coverage of each base station, there will be very large "spacial decorrelation" over much of the coverge area.


https://www.navcen.uscg.gov/?pageName=dgpsMain
"Users can expect better than 10-meter accuracy throughout all established coverage areas. Typically, the positional error of a DGPS position is 1 to 3 meters. "

[barnakiel]

I do not think gps is important on harbour approaches. There are atons, virtual atons, etc.


I have a pilot friend and he claims gps is not used on landings, they use visuals and virtual atons cast by the tower.


b.

[redneckrob]

Originally Posted by barnakiel

I do not think gps is important on harbour approaches. There are atons, virtual atons, etc.


I have a pilot friend and he claims gps is not used on landings, they use visuals and virtual atons cast by the tower.


b.

Several of us here spent at least 20 years as professional pilots. I would advise you not to ever fly with your friend!

[redneckrob]

Originally Posted by StuM

Aah, so you are not talking about

"a marine and is an aviation differential GPS system that uses ground stations and satellites to transmit corrections to GPS that are independent from the GPS system itself" .

Unlike WAAS, DGPS doesn't use any satellites other than the standard GPS signals. It is not independdt from the GPS system. The DGPS stations transmit radio signals that report on how accurate the GPS signal is at the station.



WAAS covers a much larger area than USCG DGPS ever did, is as accurate as USCG DGPS and is much more useful for cruisers



From your link:

"Since 2016, the Coast Guard has continued assessments and outreach affirming that the positional accuracy provided by un-augmented GPS and GPS augmented by the U.S. Wide Area Augmentation System (WAAS) is sufficient to meet Coast Guard mission requirements and navigational safety requirements for harbor approach."

Completely agree. The only issue is that WAAS is relatively newer and especially new to the marine market since its initial target audience was aviation. So most of us don't have WAAS capable GPS receivers and there aren't even that many available to buy. I'm sure that will be rectified as time goes on and it becomes standard in the chip sets though, which will be good for all of us.

[Nicholson58]

Certainly important to thousand of boaters. I can’t imagine what the automotive lobby will bring to the table if the interference is real. There must be a thousand times more GPS users on the road. It’s getting difficult to acquire paper road maps presuming one knows how to use then.

[Auspicious]

Originally Posted by redneckrob

Well you're almost there! There are two frequencies. The second requires the codes to use, and it allows the receiver to back out propagation delays.

You’re confusing two different things. All GPS receivers use both L1 and L2. Phase comparison between the frequencies is what allows the calculation of propagation delay. The code for selective availability (SA) still exists and SA could be turned back on if the government decided to do so. SA did not distort either signal. It was all about timing jitter. The code to back out the jitter was transmitted on L1 and L2. Don’t confuse frequency with signal or data payloads.

USCG is indeed turning off their DGPS system in deference to WAAS. WAAS works as well and is a lot cheaper to maintain. It works the same way as DGPS. A signal is transmitted from ground-based reference stations and disseminated through satellite.

M-code also uses L1 and L2 with an orthogonal modulation that does not conflict with C/A and P(Y). M-code is autonomous. It provides anti-jamming and anti-spoofing characteristics through power, signal modulation robustness, and encryption.

See the link I posted above and https://www.everythingrf.com/community/what-is-m-code .

Originally Posted by a64pilot

That never happened either, many, many Commercial GPS receivers were used due to the lack of funding, there were very few Military GPS receivers, none for example in Army Aviation at the time.

I was in government during Desert Storm deploying systems to the field. Commercial GPS units were common. If I remember correctly that is what led to shutting off SA. “My” systems directed spotting teams who called in strikes.

[Auspicious]

Originally Posted by Nicholson58

Certainly important to thousand of boaters. I can’t imagine what the automotive lobby will bring to the table if the interference is real. There must be a thousand times more GPS users on the road. It’s getting difficult to acquire paper road maps presuming one knows how to use then.

Therein really is the key. GPS has become ubiquitous. Auto navigation. Marine. Land surveying. All kinds of deployed sensors. Aviation. Autonomous vehicles.

It will be interesting to read the actual license terms. I'd like to think the FCC put all the risk on the tech company to turn off in the event of interference. I'd like to think that. There was a lot of tense discussion between DoD and USCG (then part of DoT) in the early 90s related to DGPS as an official service. Government agencies don't often see eye-to-eye when missions differ.

[Dockhead]

Originally Posted by barnakiel

. . Gps is not the only system there. Nobody cares if it goes bonkers (Galileo did, and more than once).. .

Yeah, tell that to the U.S. military, and NATO. Smart bombs guided by BeiDou?

[BlackHeron]

Maybe it is time to buy a new GPS receiver with integrated rate compass. I see B&G has one that plugs right into their Zeus and Vulcan chartplotters with NMEA-2k for around $200.

https://www.bandg.com/bg/type/instru...0-module-pack/

[a64pilot]

Originally Posted by Auspicious

I was in government during Desert Storm deploying systems to the field. Commercial GPS units were common. If I remember correctly that is what led to shutting off SA. “My” systems directed spotting teams who called in strikes.

There were many Commercisl systems, but not because the military ones were unreliable or didn’t work, which is what you posted, we didn’t have Military systems because they hadn’t been purchased, so Commercial systems were purchased, because Military systems aren’t sitting on stores shelves waiting to be bought.

Gulf war was 91, Clinton didn’t have Selected Availability turned off until nine years later in 2000, by then GPS was pretty much fully integrated in the Military..
SA never affected the Military, even when Commercial receivers were used because SA is a regional thing, you can enable or disable it by region, it’s not an all on or all off thing, and it’s variable too.

SA can be defeated by a non moving GPS by averaging, my Apollo Precedus for example had a survey mode where it averaged hundreds of position fixes and that took out the SA errors, but wasn’t effective on a moving platform of course.