Earlier today in the xyHt thread I asked something about "polar tides".
Well, later while searching for what that exactly is, I got into all kinds of tidal theory stuff. Specifically, Laplace equations and higher harmonics.
There are several tables showing values at certain observation stations.
In the column headed as "species" some of these mention "overtides".
What the hell is an "overtide"?
While I'm at what means "principal lunar"/"solar".
What is a "Doodson coefficient".
And, how does different NOAA "orders" get these different values.
So, any taker-uppers on any of this?
E.
Fortunately, I did attend all the NOAA webinars on tidal datums a few years ago [4 or 5 maybe] so I do understand a good bit of it.
As a related aside, I see Galileo's "Principia" is again cited. Seems like several times a week I run across it during my various researches. I guess one of these I'm just going to have to break down and get all 3 volumes.
Not in Latin of course! My Latin vocabulary is limited to a few things I happen to remember from working in the pharmacies.
I can help.
I have not read the article in question, but I have studied
the topic.
"Polar Tide" is more commonly known as "Pole Tide", so Google
hits on the latter will work better.
What happens is that the solid Earth moves slightly in relation
to the Earth's rotation axis. This is called Chandler Wobble.
Thus, a physical "North Pole" shows a circular displacement
of +/- 10m with a period of 433 days about the rotational "North
Pole". If you are not doing Astro, you don't worry, because the
modern geodetic frameworks are tied to the physical, solid Earth.
However, this small Chandler displacement creates a centrifugal
force (like driving fast around a corner). The solid Earth is not
rigid, so it responds to this force. This is called the pole tide.
How big? Max of 2.5 cm vertical, 7mm horizontal maximum. It is
global in it's signature with a 14 month period. For a picture
see:
http://earth.eo.esa.int/brat/html/alti/dataflow/processing/geophys_corr/pole_tides_en.html
The equations are not so bad, just some spherical trig. See:
http://www.navipedia.net/index.php/Pole_Tide
All it takes to compute the result is the Chandler pole displacements.
Needless to say, the pole tide is accounted for in global geodetic
systems and software as part of their tidal reduction subsystem.
The International Earth Rotation and Reference System Service (IERS)
Conventions, describe "best practice" procedures.
So, bottom line, if you use (modern) NAD or ITRF you are covered.
If you do PPP (precise point positioning) then it's worth asking the
software provider.
If anybody wants to dig into solid Earth tides and how they relate
to geodetic networks, check out my page at:
http://home.comcast.net/~dmilbert/softs/solid.htm
Hope this helps. It beats learning Latin 😉 .
Thank you Dr. Dennis! I find this stuff terribly interesting. Not likely I'll ever really use any of it except for pure mathematical enjoyment.
> I have not read the article in question, but I have studied
> the topic.
It's not really an article per se. It's an introduction by Dave Doyle of the changing format of Professional Surveyor magazine to become "xyHt".
> How big? Max of 2.5 cm vertical, 7mm horizontal maximum. It is
> global in it's signature with a 14 month period. For a picture
> see:
I bet you would love to do some tidal studies on Europa!
For that matter most of the [known] moons of Jupiter and Saturn experience some sort of "squishing" (as a lot of astronomers like to refer to it) as they orbit their hosts and get close to each other.
> Hope this helps. It beats learning Latin 😉 .
Roger that! Although it would be rather cool to have re-prints of the original "Principia" as originally published by Newton in the 1600s - which I wrongly attributed to Galileo. I do that often. I also get Ptolemy and Copernicus often confused.
> > Hope this helps. It beats learning Latin 😉 .
>
> Roger that! Although it would be rather cool to have re-prints of the original "Principia" as originally published by Newton in the 1600s - which I wrongly attributed to Galileo. I do that often. I also get Ptolemy and Copernicus often confused.
Not me, I'm in my prime....B-) 😉
[flash width=560 height=315]//www.youtube.com/v/6gSj1G4Vf0w?hl=en_US&version=3[/flash]
One of my favorites! Surprised my tape still plays.
A funnier part of that scene is when Doc follows up that pistol twirling with his mimicked shot-glass twirl - move for move. That was priceless.