Did a few minutes of research, as this intrigued me. Looks like mean average sea level on either side of the canal is very similar, but the tides can vary by feet. That and the changes in elevation through the Canal Zone are why the locks are necessary.
Jeff Broadwick CTIconnect 312-205-2519 Office 574-220-7826 Cell jbroadw...@cticonnect.com > On May 25, 2020, at 9:24 PM, ch...@wbmfg.com wrote: > > > Here is another explanation: “mean sea level” aka the geiod, is an oddly > irregular surface where the force of gravity is exactly the same everywhere. > So you hold gravity constant, the distance from the center of mass of the > earth changes. And as water does seek its own level, it is where the water > would flow if everything would stop turning, tides would stop happening etc. > > <image[1].png> > > > From: Mathew Howard > Sent: Monday, May 25, 2020 7:07 PM > To: AnimalFarm Microwave Users Group > Subject: Re: [AFMUG] Light reading > > I figured it was fairly obvious that "sea level" wasn't a real thing because > of the Panama Canal situation, but I kind of wondered what "sea level" > actually was... I guess this explains that. > > On Mon, May 25, 2020 at 8:01 PM <ch...@wbmfg.com> wrote: >> In areas of the globe of high gravity, the water piles up. >> >> -----Original Message----- >> From: Ken Hohhof >> Sent: Monday, May 25, 2020 6:55 PM >> To: 'AnimalFarm Microwave Users Group' >> Subject: Re: [AFMUG] Light reading >> >> I've always been puzzled how the Atlantic and Pacific oceans can be >> different heights at the Panama Canal. What about "seal level" and "water >> seeks its own level" and all that? Apparently they're the same height down >> by Tierra del Fuego. Very confusing. >> >> -----Original Message----- >> From: AF <af-boun...@af.afmug.com> On Behalf Of ch...@wbmfg.com >> Sent: Monday, May 25, 2020 7:37 PM >> To: af@af.afmug.com >> Subject: [AFMUG] Light reading >> >> So, being confused at ellipsoid heights vs geoid heights and what I am >> looking at in my fancy GPS system, etc I bought a book about the subject and >> got smelf smarted. For a terribly dry subject and a book full of equations, >> I really enjoyed the crap out of reading it. >> >> Several notable thing I learned: >> The ellipsoid is a mathematical representation of the planet. That is >> referred to as WGS84. At least that is the model we are all currently using >> until they tweak it at some point in the future. >> The ellipsoid is a smooth shape calculated from the center of the earth. >> They claim it is within 2cm of being accurate. >> >> The actual axis of rotation of the earth wobbles in about 6 different >> directions all with periods from tens of thousands of years to days. So, >> the elipsoid (WGS84) is defined by actual earth bound landmarks and an >> artificial/derived/ false/imaginary axis of rotation. >> >> It is like a grid cage pinned at a few locations to a beating heart. Not >> only does the earth's real axis of rotation meander around, so do continents >> and plates. >> >> The Geoid (EGM 96) is a list of points in a grid the covers the planet. A >> correction table for elevations. >> Each point defines a distance from the geoid to the ellipsoid in the >> vertical/elevation direction. >> It is generally +/- 100 meters or so of the ellipsoid. >> >> The geoid (EGM 96) is an artificial representation or model of mean sea >> level. As it turns out, water can indeed run up hill. The Atlantic and >> Pacific oceans both slope upward going north. This is due to the variations >> of gravity. If gravity is stronger up the hill than at the base, the water >> will run up the hill. This is seen in the great lakes. Not likely to be >> seen in short distances. >> >> In any event, the geoid gives us some offsets in altitude/elevation so we >> can figure out where mean sea level is at any point on the globe. You can >> calculate the ellipsoid with just math, but then MSL/elevation will be >> offset from that spheroid in a vertical direction. No calculations involved >> >> in the geoid, just a bunch of correction data points. Mostly created by >> satellite and aerial radar and laser surveys. >> >> Down is not down. A plumb bob seeks the center of mass of the planet. Down >> is an angle normal to the tangent of the ellipsoid. If you are in an area >> where the center of the mass of the planet is not aligned with gravity there >> will be an angle between the two downs and ups. Just an odd factoid. Only >> used if you are involved in long baseline survey work the old fashioned way. >> >> When we talk about antenna elevations, we are really talking about height >> above (or below, I guess, death valley etc) the geoid. There really is no >> such thing as mean sea level. The sea has considerable elevation >> differences around the globe. So, with lots of averaging and some laws >> being written and international consortiums of folks that study this stuff, >> the geoid was created. In some areas the geoid is below the ellipsoid and >> in some areas it is above. >> >> We are currently using geoid EGM96 (Earth Gravitational Model 1996) It was >> defined along with WGS84 datum which is the ellipsoid. It is a 15' x 15' >> grid, so pretty accurate. >> >> There is a new one, EGM2008 which will have a grid of 2.5' x 2.5' Seems >> funny to me that they are using feet instead of meters to define these >> grids. >> >> >> >> -- >> AF mailing list >> AF@af.afmug.com >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> >> -- >> AF mailing list >> AF@af.afmug.com >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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