Magnitic North, Compass, GPS, and Maps!

[Siskiyou]

 
Glanceblamm brought the shifting magnetic north to my attention a couple weeks ago regarding its impact on navigation.  I have done a little investigation of the subject regarding land navigation.  I have pulled out USGS Topo Maps going back to 1949 from my collection to find the Variation, or Magnetic North.

I referred to http://www.airnav.com/ for airport information regarding Variation/Magnetic North(MN).   You can go to it by State and find your nearest airport and look up the current posted Variation.  For example the Anniston, AL Metropolitan Airport Variation has not been updated for years but it currently shows 01W in 1990.  It would be interesting to hear from a member in that area with the current MN as shown on a GPS, Garmin or otherwise.

I did a little research and Garmin updates the MN in their gps units, it is unknown if other manufactures do the same.  So I have been stumbling around the woods with my GPS not realizing that MN has shifted over three degrees in the Western U.S. and more in the Eastern U.S.  Apparently the shift has made the news because of changes being made in the signing at Tampa Bay International.

In my early retirement years I was setting up emergency helicopter control tower s at airports around the country.    The weather instruments had to be orientated to the North, and the windows were temporarily labeled for the controllers. 

I was first introduced to the Garmin eTrex at the Forest Service dirt airstrip near Atlanta Idaho years ago.  The area was smoked in so getting a reading off the afternoon sun was impossible because visibility was about 100 yards.  I have to admit to being a little turned around, and I did not trust my compass because magnetic North was set at 19˚E which was the average used in Northern Siskiyou County based on older USGS Quad Sheets. 

In those days I had not heard of the Air Nav website, and even if I had, I did not have access to the internet on the fire I was dispatched from. 

One of the important aspects of the trailer package was the weather station.  It was important the anemometer and weathervane were orientated to the North.  Critical fire weather information was relayed from this location to NOAA Fire Weather in Boise, Idaho.  Current weather reports might prevent the entrapment of fire fighters.  I asked some of the crewmembers if anybody had a local compass/map.  Nope, they were from Arizona.  A Helitack member pulled a Garmin eTrex out of her bag and gave me the MN for the location we were at.

In a day or so a Fire Weather Forecaster from Boise appeared on the scene.  Her job was to prepare fire weather forecast which were part of the morning and afternoon briefing.  She showed up with a truck load of equipment and quickly scrutinized my setup.  Like me, on arrival she thought North was in a different direction, but after checking her compass and the data my instruments were putting out, she did not set up her gear and took data from my equipment.  She had one item I did not, weather balloons. 

Note how the MN is the same in N. California and Idaho.
http://www.ngdc.noaa.gov/geomag/img/us_dec_8x11.pdf

But as a hunter out in the woods I have never had to be down to the exact degree.  I have  two compasses at my computer, the Sylva Ranger, and a similar Brunton.  The value of the marks on both for setting MN/Variation is 2-degrees.  The Sylva Ranger can be fine tuned a little more than the Brunton but for general use it makes little difference.  I keep one in the pickup and the other in my daypack.  I also have a lower priced Sylva Base plate compass in my Go Pack.

Question?   Can a GPS be adjusted to use True North.

Answer.  Yes.  In general when using a Garmin GPS go to MAIN MENU>SETTINGS>HEADINGS>NORTH REFRENCE>THE USER CAN SELECT THE FOLLOWING TRUE, MAGNETIC,GRID, OR USER.
If I had a hand drawn map from the 1940 period for a gold find with notes and bearings for magnetic north I would look for a USGS Topo for that area and period and select the USER option and that opens the Magnetic Variation box allowing me to enter the old Magnetic Variation.  When the Magnetic Variation box opens you get a pop up with a number board from which you select the numbers you need. 

The nice thing about a compass is they do not need a battery.  But they do not provide the user with the different categories of information a GPS does.  Depending on the topography of the country you are in, the landmarks maybe different.  I am from the mountains and I start looking for the sun and mountain tops along with other landmarks to guide me in the outdoors.  Put me in the city and I might never get out.  Admittedly since purchasing my first gps I have made very little use of a compass. 

Recent research in Siskiyou County with a Garmin GPS using the function that displays Magnetic North shows there has been (approximately) a three degree s change in Siskiyou County using USGS Quad sheets from 1954 and 1955.  During that period MN was shown at 19˚.  Currently the Garmin displays 16˚E.

Last week a friend went around to the following airports in Siskiyou County with his Garmin GPS and recorded the magnetic north as shown on his unit.  The Variation shown for the airports was taken from the Air Nav website.  The friend’s earlier USGS quad sheets show a 19 1/2˚ MN.



Siskiyou County Airport
Variation:    19E (1975)
   
Garmin 2011 16E

Montague Airport-Yreka Rohrer Field 
Variation:    18E (1985)
   
Garmin 2011 16E

Weed Airport
Variation:    18E (1985)
Garmin 2011 16E

The Garmin readings were taken at each airport.

Siskiyou County Airport and Rohrer Field are relatively close together as the crow flies and there is a 1˚ variation; the key is there is a ten year difference in the data.

I am thinking the shifting of magnetic north might have a bigger impact on surveys than buck hunters. 

It appears that updated posting at the Tampa airport did not come about with a shift of one or two degrees ,but when the accumulated shift exceeded four (4˚).  The nice thing about using a GPS is that it is simpler then a compass.  (For Some!)

So this whole thing has had me bouncing around like a BB in a box because of the amount of information available on the net.  It is tough to make a statement without sticking a foot in one’s mouth.  At the start I thought Air Nav was a Go To site for magnetic variation, but last week friend sent me a better link.
http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp

A lot of folks are advising to get rid of old topo maps because of the changing magnetic north of the maps.  I will save my old maps because they are a treasure of information regarding old mining activity and cabin sites. 

[Glanceblamm]

Very well written Siskiyou,

I would not have cared to try simply because of the "data overload" tends to "Flummoxes" (yeah, I learned a new word) those who study it.

The airports were an excellent place to start and I also knew that you probably either had U.S. Forest service maps or had access to them which would be a wealth of information here.

The problem with the shifting magnetic north was first broadcast by an airport and they went as far as to shut one runway down for at least 15 days so that they could relable the ends along with putting up new signs. There was probably much complaints by pilots that forced them to do this, especially from commercial or the smaller buisness jets. This could even have been quite harrowing for the pilot in a light single engine craft who was unfamilure to the area and making his approach to final in the dark, or fog, or both. Even if that pilot had the localizer specific to the runway tuned in, the difference between it and the heading indicator could provide to be alarming. It would probably cause one to question the guages with the fact being that once those wheels touch down, that is the way the plane is going to go!

Your Gold mine is going to be a little different. I think that you were telling me that the current 3 degree shift threw the reading off by 105' over 6.7 miles. Not too bad for the map n compass navigation because the number can be divided by landmarks or obsticles along the route, (chalk one up for known landmarks and new recorded headings)

I do have a scheme brewing in my feeble brain for the layman to measure magnetic shift. It involves that old lost hiker trick where one places a stick in the ground and places his foot at the end of the shadow (sunny day of course) 30 min later the other foot is placed on the shadow and one is suppose to be facing due south. This experirment would have to take place in an area that is undisturbed and with a compass in hand of course for accurate repeatablity but data overload again rears its ugly head. It would seem that if one placed a couple of red bricks to stand on at a comforatable distance apart at any angle, the initial compass reading would qualify as a base or control to measure "shift" in the future?

Why Does The Mag North Shift?...This is my latest find and even it may be arguable.

Earth's magnetic field, which still flummoxes those who study it, "is thought to be generated deep inside the planet," LiveScience writer Jeanna Bryner explains. "An inner core of solid iron is surrounded by an outer core of molten iron. They rotate at different rates, and the interaction between the regions creates what scientists call a 'hydromagnetic dynamo.' It's something like an electric motor, and it generates a magnetic field akin to a giant bar magnet." 

[Siskiyou]

A little side note on the subject.

I stopped at the daughter’s house when I was in town earlier this week.  She ask me a question that brought me a minute of joy.

“Do, you have a compass I can barrow?”

Apparently something triggered a question to granddaughter #4, what direction is North?

Her answer was in front of her.  Any direction she turned North was to her front.

The daughter wanted the compass to explain the different compass directions to her. 

I e-mailed a number of links regarding the changing Magnetic North and a link Silva on using the type 3 base plate compass. 

In the past when taking #4 out for lunch I would pull the gps from the dash and let her hold it and track or progress while she set in the child seat in back.  The kid caught on real fast.  Granddaughter # 3 and I did some geocaching years back and it amazed me how these high tech kids grab on to them and quickly understand how they work.

Anyway I believe there are real Earth science lessons to be passed on regarding the changing Magnetic Earth.

I “almost” explained to her how I used a compass to located deer I shot in thick brush fields in rough country.  After shooting a buck across drainage, I mark the location I shot from with flagging or hankie, and then I take a compass bearing on the location the deer was when the shot was fired.  After scrambling across a couple of draws, shale faces in thick brush tying down the exact location can be tough.  The first time I tried this I was able to take a back reading and find my red hanky and then line up in the area I was to find a dime size spot of pink, foamy blood. 

Rather than the buck story at this stage, I will tell her how I re-located a fishing spot in the Sea of Cortez.  On a successful fishing trip I record the bearings off two peaks (Cerro Colorado and Cerro Guadalupe).  I believe this put us on top of an underwater ridge.  We were able to return to the location on later dates and repeat the catch.  Before tying down this location fishing a little closer to shore resulted in an empty ice chest.   

Magnetic North was not an issue in these two examples because all I needed to do was shoot a bearing(s).    The Variation for MN was about 4˚ less in Baja then what my compass was set for in N. California.  When shooting a bearing and using the same compass this made no difference when it came to repeatability.  I could have set the Variation at 0˚ and returned to the same spot.

Grandma will be taking a compass and a plotter in to town with her morning.

[LipCa]

What you need to watch out for with compasses is the "local" attraction.   

"local" attraction is just like it sounds.   Could be from the local minerals in the ground to the D8 cat parked behind you.  It can be as much as 5 or more degrees.

In my land surveying experience, I have ran many "staff" compass surveys...probably hundreds of miles.   You always take a reading ahead and back from each station so you can catch the difference in the readings if there is local attraction.

In locating old fences that were run by compass, with modern day equipment, you will see that the fences almost always have an angle in them at the top of the ridge and in draws.  I think that is due to mineralization?

If I use a compass in the woods where I can see from ridge top to ridge top, I'll take a reading on an object on the ridge i'm walking towards and when I get there, I'll take a reading back to where I was to see if the readings are 180 degrees apart.

Lots of those areas in Siskiyou county...

[Siskiyou]

LipCa:  Interesting comment regarding the fences, you will have me straining my neck.

[Winter Hawk]

On the aviation charts in SE Alaska there are spots marked as having strong magnetic deviation.  North end of Prince of Wales Island around Calder Bay has that.  A magnetic compass can be off by 40 degrees in that vicinity.

-Kees-