NAD-83 2011 (epoch 2010.000) gravimetric computations

Isn't that eight years away? (optimistically?)

> Isn't that eight years away? (optimistically?)

Yeah and on top of that, it took many government agencies 15-20 years to adopt NAVD '88 as their official vertical datum.

Just gotta love the NGS adjustments. Keeps us from getting too complacent.

(They do the same thing with SPC's too......)

I dunno what to tell you Deral...

We are actually “seeing“ (or GOING to see) about twice that variance out here (~2.5 feet also “lower”).

Just like the Change from NGVD29 to NAVD88, it is just something that “WE” are going to have to deal with. The transition to a geocentric Datum for North America, and a Gravimetric Geoid, is both inevitable and necessary to maintain technological and scientific consistency.

I'm working today on a project that MUST be “delivered” in NAD27 UTM meters...a PITA, but that's what the client wants (because his GIS is NAD27 UTM meters)!

I have made the comment before, that there are STILL a lot of communities in the West, that are ENTIRELY based on the elevation STAMPED in the 100+ year old Bench Mark set vertically in the wall of the Court House! It AIN'T NGVD29 or NAVD88, BUT it is CORRECT/ACCURATE/PRECISE (if you are working in that town).

Loyal

Don't forget GEOID12 Deral

One thing to bear in mind here Deral...is that when GEOID12 is released later this year, it “should” be pretty consistent with the NAVD88 heights that you are using. I wouldn't get too excited just yet, as Cliff indicated, the Gravimetric Datum is some years down the pike.

Loyal

(because his GIS is NAD27 UTM meters)!

Gotta love that. I thought I put NAD27 to bed back in the 80's, now I keep getting drawn into it just because of some coumpter guys that can't stop using it for some reason (yeah I do know why they do it).

If the elevations drop 2.5' here we will be right on top of NGVD29!

> I did some comparisons this weekend and found a consistent change in the ARROX. ORTHO HGT.
>
> N (USFT) E (USFT) Ellips Ortho
> EM005 W152 4818422.64 1853487.09 1024.97 1109.44
> Lawton 2007 481842.621 1853487.07 1024.95 1109.44
> Opus 2001 481842.58 1853487.05 1024.94 1109.34
> OPUS 2011 481842.64 1853487.15 1024.89 1108.23
>
> That's -1.21 feet from what we have been using elevation wise since 1996.
>
> Some random verticals spaced on the far reaches on town.
> 29B27 -1.16
> Tw0 -1.15
> 09A4 -1.13
>
> Seems pretty consistent and the note on the OPUS reports said when they finsh the grav-d then this elevation will replace NAVD-88.
>
> I need to chew on this a while but NAVD-88 is in the codes of every agency we deal with and of course our entire county is based on this with years and years of data for projects.
>
> We only use OPUS as a vertical blunder check but I guess I'll have to examine a larger data set to come up with some number to apply to match our Lawton system otherwise people will begin to distrust the OPUS reports or our numbers.

I started to post some numbers for my area, but I re-thought this all out. If the gravity field model is being re-fined as a result of Grav-D, why would the ellipsoid model remain the same? I thought NGS was going to make their ellipsoid a truly Earth Centered one. At the same time I'm thinking that "Grav-D is a Global project so wouldn't this create further refinements in the ellipsoid itself (in terms of the best fit and smoothing)".

BTW I submitted some data to OPUS and it returned an approximate ortho height in line with Deral's numbers. About 3 decimeters

Don't forget GEOID12 Deral

Thanks Loyal. I just read the message on the NAD8302001 that says is will soon be not supported. That's doesn't worry me but now if you click on submit using the new NAD83-2011 is does not give you a geoid height but only the "approx" gravimetric height that is supposed to be closer to a true MSL value.

If they are working with a new Geoid 2012 and use that then I'm not going to have any grief. Our area has been pretty stable and consistent.

I'm not to worried as of yet, but you have to start early to stay on top of these things.

Just very interesting that I got about 40 opus results sent to me last week, as did some others who have used OPUS-DB. Maybe they are actually wanting some of our comments and results. I dunno. Nothing on their website that I could find.

Yes, Ralph. All my sheets have pretty much the same ellipsoids heights as we have seen over the years. Only the ortho is radically different. But it does say "Approx" so it's not even beta I suppose at this point.

But some users will send and OPUS-S in and use the new frame and possible take that ortho computation as gosple. That's is the only thing that worries me at this point. Not everyone that uses OPUS is a Land Surveyor or Geodesist.

Don't get me wrong Deral, I had to think this out. I'm not a Geodesist and I probably couldn't play one on T.V. ;0).
The way I see it Grav-d is filling in the voids which in the past were left to interpolation. I think it would stand to reason that if the Geoid gets refined, it would affect the Ellipsoidal Parameters and thus the Ellipsoid would have to follow suit. Just my guess.

Ralph

The “CENTER” of the Earth (geocentric “point” or geocenter) certainly has something to do with gravity, but is currently defined by the IERS/ITRF using a multi-technique solution (VLBI, SLR, DORIS, GNSS).

http://itrf.ign.fr/ITRF_solutions/2008/ITRF2008.php

ITRF2000, NAD83, etc. are related to ITRF2008 (actually IGS08) via a 14 parameter Helmert similarity transformation.

http://www.ngs.noaa.gov/CORS/coords.shtml

The Ellipsoid applied to these Reference Frames and “datums” is currently GRS-80, and it's unlikely that will change. The IERS/ITRF doesn't even publish Latitude, Longitude, Ellipsoid height, it's up to the user to apply a particular Ellipsoid to the geocentric ITRF2008 X,Y,Z values published by the ITRF. There has been talk over the years of refining GRS-80 to better fit the Earth, even using MORE THAN the classic TWO (a & b) parameters, but most folks don't see a lot of value in such an exercise.

Ellipsoid Height is entirely dependent (mathematically) on the “datum” (reference frame), ellipsoid used, AND of course the X,Y,Z coordinate estimates of any given point on the Earth's surface, and is independent of gravity (local or otherwise).

The “NEW” North American Datum coming in about 10 years, will use the SAME geocenter as ITRFxxxx (whatever the current International Reference Frame is that “day”). I would ASSUME that the Gravimetric Datum (and underlying Gravity Model) will ALSO reference the same geodetic reference frame.

Grav_D is an attempt (and a good one too) to get a BETTER handle (model) of the “shorter” wavelength gravity anomaly in and around CONUS (and Alaska etc.), than we currently have, or is obtainable by space based measurements like GRACE, GOCE, etc. GRACE etc. will define the GLOBAL model, Grav_D will refine the "local" model.

A GEOID Model (as we use the term), is a model of the DIFFERENCE between the Ellipsoidal Surface, and the GEOIDAL Surface as a function of geometric position (Lat/Lon).

Or something like that...I need an Oatmeal Stout!
Loyal

> The “CENTER” of the Earth (geocentric “point” or geocenter) certainly has something to do with gravity, but is currently defined by the IERS/ITRF using a multi-technique solution (VLBI, SLR, DORIS, GNSS).
>
>> http://itrf.ign.fr/ITRF_solutions/2008/ITRF2008.php
>
> ITRF2000, NAD83, etc. are related to ITRF2008 (actually IGS08) via a 14 parameter Helmert similarity transformation.
>
>> http://www.ngs.noaa.gov/CORS/coords.shtml
>
> The Ellipsoid applied to these Reference Frames and “datums” is currently GRS-80, and it's unlikely that will change. The IERS/ITRF doesn't even publish Latitude, Longitude, Ellipsoid height, it's up to the user to apply a particular Ellipsoid to the geocentric ITRF2008 X,Y,Z values published by the ITRF. There has been talk over the years of refining GRS-80 to better fit the Earth, even using MORE THAN the classic TWO (a & b) parameters, but most folks don't see a lot of value in exercise.
>
> Ellipsoid Height is entirely dependent (mathematically) on the “datum” (reference frame), ellipsoid used, AND of course the X,Y,Z coordinate estimates of any given point on the Earth's surface, and is independent of gravity (local or otherwise).
>
> The “NEW” North American Datum coming in about 10 years, will use the SAME geocenter as ITRFxxxx (whatever the current International Reference Frame is that “day”). I would ASSUME that the Gravimetric Datum (and underlying Gravity Model) will ALSO reference the same geodetic reference frame.
>
> Grav_D is an attempt (and a good one too) to get a BETTER handle (model) of the “shorter” wavelength gravity anomaly in and around CONUS (and Alaska etc.), than we currently have, or is obtainable by space based measurements like GRACE, GOCE, etc. GRACE etc. will define the GLOBAL model, Grav_D will refine the "local" model.
>
> A GEOID Model (as we use the term), is a model of the DIFFERENCE between the Ellipsoidal Surface, and the GEOIDAL Surface as a function of geometric position (Lat/Lon).
>
> Or something like that...I need an Oatmeal Stout!
> Loyal

Good Post Loyal,
But I still need to re-think this and absorb it. From my knowledge GRS80 is defined by 4 parameters not 2, ( a, GM, J₂, and the funky greek w). I need to think about the rest of this. Because maybe I'm confusing this with the GRACE project.

Edit: You are correct I was confusing this with GRACE.

Ralph

Wasn't NAVD88 the mandated vertical datum for CONUS in 95 or 96?

Technically you are CORRECT!

GRS-80 (Geodetic Reference Frame of 1980) is MORE than just an ellipsoid, but the GRS-80 REFERENCE Ellipsoid is defined by the semi-major and semi-minor radii.

I should have been more specfic in what I was typing.

I should have said...The GRS-80 [reference] ELLIPSOID!

(a, b, f, 1/f, e, e²)

🙂
Loyal

> Technically you are CORRECT!
>
> GRS-80 (Geodetic Reference Frame of 1980) is MORE than just an ellipsoid, but the GRS-80 REFERENCE Ellipsoid is defined by the semi-major and semi-minor radii.
>
> I should have been more specfic in what I was typing.
>
> I should have said...The GRS-80 [reference] ELLIPSOID!
>
> (a, b, f, 1/f, e, e²)
>
> 🙂
> Loyal

No worries Loyal, you're still one of the Best in my book!
🙂
We're talking about the same thing only you're defining it Geometrically and I'm defining it Geo-physically.

I'm still busy trying to absorb all your links.

Cheers,
Ralph

Howdy,

Perhaps I misunderstand but isn't this consistent with the tilt in NAVD88 across CONUS? The link here:
http://geodesyattamucc.pbworks.com/f/Lab9answers.pdf is the solution to a lab involving the determination of orthometric heights using ITRF ellipsoid heights, USGG09 ellipsoid-geoid separations and a comparison with published NAVD 88 values at the same points.

As for the issue of whether GRS80 is purely geometric or geophysical, I like the description at: http://earth-info.nga.mil/GandG/publications/tr8350.2/tr8350.2-a/Chapter%203.pdf

Cheers,

DMM

> Howdy,
>
> Perhaps I misunderstand but isn't this consistent with the tilt in NAVD88 across CONUS? The link here:
>> http://geodesyattamucc.pbworks.com/f/Lab9answers.pdf is the solution to a lab involving the determination of orthometric heights using ITRF ellipsoid heights, USGG09 ellipsoid-geoid separations and a comparison with published NAVD 88 values at the same points.
>
> As for the issue of whether GRS80 is purely geometric or geophysical, I like the description at: http://earth-info.nga.mil/GandG/publications/tr8350.2/tr8350.2-a/Chapter%203.pdf
>
> Cheers,
>
> DMM

Thanks Mike,
That was my logic earlier, that based on Geophysical Parameters the Ellipsoid should be affected. Apparently the effects are negligible. The way I see it the Geoid and the Ellipsoid are inexorably tied together, without a Geoid model you cannot formulate an Ellipsoid model but you don't need an Ellipsoid to come up with a Geoid. (say that 10 x fast lol). Where's Mr. G when you need him.

Also your lab made some important points that I wasn't aware of:

The previous class presentation included the statement that NAVD88 “Has
been proven to be ~ 1 meter tilted across CONUS (again, based on the
independently computed geoid from the GRACE satellite).”

3-This height will not be consistent with NAVD88

This is along the lines with what I was thinking.

Thank You for sharing that with us.

Cheers,
Ralph

My suggestion is that our next or future ellipsoid model be based on three dimensional measurements using current technology rather than the centuries-old methods of C. F. Gauss which inexorably link the ellipsoid to the equipotential surface of gravity.

That is the only way I know of to eliminate the gravity bias in historic ellipsoids, as you say, and free them from the geoid permanently.