GPS Anomoly in Chicago

Background:
When I travel, I utilize a Garmin eTrex Vista GPS receiver to navigate myself point-to-point. In the user manual it indicates that on the Satellite page there are two rings which are used to display the location of the GPS satellites in the area. The center ring indicates those satellites that are found to be within a 45 degree angle from vertical. The outer ring indicates those satellites that are found to be within the surrounding horizon (90 degree angle from vertical.)

Anomoly:
On August 27, 2004 at a little after midnight I was driving through Chicago on I-80. Traffic was nearly at a standstill as a lot of construction was going on at the time. About 5 minutes after coming to my first stop, my GPS lost contact with all satellites and indicated that the signal was too weak. When I paged my GPS receiver over to the Satellite page I found that many satellites were listed as being available, but their graphical indicators were all pushed to the edge of the outer ring (indicating that they were all hovering about the horizon). Shortly after leaving the construction area, all GPS satellites returned to their normal position on the graphical display and I began receiving signal again.

I believe this may indicate that the Chicago area was experiencing a scrambling of GPS signal at that time. Does anyone in the Chicago area have a GPS that could be used to determine if the behavior is continuing? If it is, I believe it to be an indicator of an imminent attack on Chicago using GPS receivers. I cannot think of another reason the signal would be scrambled.

The simplest explanation is that your equipment was functioning perfectly and that the satellites were all in the positions indicated by your display and that the signals were not being broacast. The construction site was merely coincidental. The reason for these anomalies is open to conjecture.

It doesn't explain how they were back in place the moment he left the area.
Those sats don't fly about randomly and that fast you know.

I don't see how the correlation between losing a GPS signal and an imminent attack is made.

It is not uncommon to lose signal. I lose it often. Trees, buildings, even if you were beside a large truck in traffic. All of these can cause you to lose your signal. Once you are clear of the obstruction, the signal will come back.

Was it just in that one area or all throughout Chicago? I used to live there and got some friends who have'em.

I used to work in the marine industry and I've heard many stories of GPS irregularity that coincided with military action.

The primary purpose of GPS,regardless of it's commercial uses,is military.

Many sailors have experienced their GPS suddenly becoming extremely accurate at the same time cruise missile attacks are underway.

This said GPS is widely available and therefore potential terrorist weapons could utilize GPS.

It is possible that GPS could be denied if there was a verified threat.

That said I'd say maintainance or another explanation is more probable.

Originally posted by phreak_of_nature
I don't see how the correlation between losing a GPS signal and an imminent attack is made.

It is not uncommon to lose signal. I lose it often. Trees, buildings, even if you were beside a large truck in traffic. All of these can cause you to lose your signal. Once you are clear of the obstruction, the signal will come back.

It wasn't simply a lost signal. My display showed the 'location' of over 15 satellites, but the graphics representing their location were all pushed to the outer rim of my display. I've lost signal many times and the graphics for the satellites stay in their correct places on the Satellite page, they just turn grey (weak signal) or clear (location of satellite, but no signal). This was different. I've been using this thing in my car for over three years now and I've never seen this before.

Maintenance is a possibility, but that is done one sat at a time.

It's also possible that his unit was downloading a new almanac from the satelites. Almanacs are used to tell the receiver where the sats will be at which time on which day. For those who aren't familar.

It is possible, depending on the model, that it's default behavior while downloading an updated almanac is to drop the sats to the horizon, until it has the newest info.

Now to contridict myself. Usually GPS receivers check their almanac version at initalization, boot up, so it would be unusal behavior for it to do it if the unit had been on for awhile.

I'd still go with ground clutter blocking the view of the sky. How many sats did it have before losing signal?

What part of I-80 were you on? If you would like I can try and corroberate this for you but I need a location or given area not lat and long.

There are three types of signal that the GPS will display:

Clear - Location of satellite in sky only
Grey - Weak GPS signal
Black - Locked GPS signal

Prior to the outage I had 5 black, 4 grey and the rest clear.

As for where on I-80, I'm going to have to plead a bit of ignorance as I had been driving for 16 hours at that point. There is a section of I-80 just south of Chicago where they cut traffic to 1 lane at three points to do bridge construction. It's just west of the Indiana border on the toll area of I-80 (I recall because I thought to myself that I wasn't exactly getting my $$'s worth because it took me about 1.5 hours to clear a 10 mile stretch.) Anyone from the area will know what I'm talking about because the construction there is massive. The outage ocurred for the entire time I was in the area and did not abate until a few miles after I entered Indiana.

Hope that helps.

Oh, and I've lost signal before for many reasons. Typically due to being stopped at a light under a bridge, having my hand over the top of the unit while moving through menus, or if I'm in a city surrounded by huge buildings. Occasionally, I've lost signal out in the middle of nowhere, and, I get a bit nervous when there's no clouds, trees, buildings or trucks causing it. To be certain...this is the first time in over three years my Satellite page displayed almost 15 separate satellite icons pushed out to the horizon. They do go from black to grey to clear all the time, but remain in the correct locations in the sky.

[edit on 1-9-2004 by chaosrain]

Here's what I found for the time period of 12AM 28 Aug 04 through 1 AM 28 Aug 04.


There would have been 9 sats available to you in the Chicago area within that hour.
4 Descending,
5 Ascending.
5 at some point within the hour would have been passing the 15 degree elevation line that is standard for an elevation threshold.

Even at worst you should have had 4 sats available to you for that whole hour.

???

I wouldn't worry about it too much. I work in the marine field and we have signal problems all the time. Interference from other radio sources can affect your signal, GPS is a line of sight instrument. The military could have recycled the system at that time or retasked a satelite for better coverage of another area.


Right before the 1st Gulf War, the military retasked a bunch of satelites for better coverage of the Middle East. They didn't tell anyone because they don't have to. All of a sudden, sailors around the world were getting positions that were 10 miles off.

Get a DGPS receiver and you won't have to worry about military SA(Selective Availability). It's a programed error so as to not give users full accuracy.

Originally posted by phreak_of_nature

Even at worst you should have had 4 sats available to you for that whole hour.

???

I agree...that's why I suggested that the signal was scrambled for the Chicago area.

I live near Chicago and I go there quite often. As for construction its pure coincidence. I mean theres all most always road work going on somewhere in Chicago. But don't worry about it. Theres a lot of things in major cities that could cause interference. Could have been a solar flare for all we know.

Electronics never mess up. People never make up theories to explain things their mind is incapable of understanding. Sheeez! Get a life.

Originally posted by doc2
Electronics never mess up. People never make up theories to explain things their mind is incapable of understanding. Sheeez! Get a life.

Being a technophile, I understand your contention that electrical equipment messes up all the time. Frankly, though, I don't see how any lack of technological understanding on my part has led me to raise this issue. Actually far from the case. It is my understanding of the equipment I was using combined with an understanding of continued efforts on the part of the GPS minders to alter signals in certain areas for security reasons that led me to wonder if something is up in Chi-town.

Please, doc2, enlighten me as to the true nature of the anomoly I experienced for I am not the Nobel laureate you seem to be. Apparently, you know exactly what caused this issue and are simply too far above the rest of us here at ATS to share.

An AWST article this week mentioned tha tthey are scrambling GPS signasl around Nuke plants for security. Maybe you were near one at the time?

I already started a thread on that one:
www.abovetopsecret.com...

Originally posted by FredT
An AWST article this week mentioned tha tthey are scrambling GPS signasl around Nuke plants for security. Maybe you were near one at the time?

I already started a thread on that one:
www.abovetopsecret.com...

After looking into the location of Nuclear Reactors in Illinois, there are three within about 30-40 miles of where I experienced the anomoly. Now, that's a bit farther away than I might expect they would jam signals, but after looking at the reactors available in Illinois, there are a few located in a fairly small area which could pose a greater risk of attack and result in a larger area of signal scrambling. Who knows?

My GPS has had one wierd glitch that i have never been able to explain (short of alien abduction).
i was driving thru NM and had my GPS on the page that shows location and speed.
I looked over to verify that i was going the speedlimit, and saw that i was doing 1640MPH according to my GPS... it also said that i was at over 10,000 ft above sealevel. In reality, It was more like 75MPH and 6,000 ft above sea level.
sometimes GPS have computer voodoo to
(or i am really hooked into a pod somewhere thinking i am typing)

Just FYI, I am a Chicagoan who travels a great deal. I know that stretch of 80 well and the construction is constant. I have lived here for 38 years and I swear there has been construction on 80 the entire time. But construction or not, 80 is always gridlocked. This stretch starts where 294 turns into 80 and if you lucky it eases up after you cross 65. If your not lucky the back-up goes on for several miles after that. And coming from the east it can be even worse that heading out of Chicago.

But as far as GPS goes - sorry, I can't help you. I don't have it.