Hi Adam,

Thanks, I will give that a try (emailing them).

Actually, I found that same site before. The problem I'm running into is
that most of this data is given in the format of "height above the Geoid".
As I understand it, they pick some gravitational equipotential surface and
call it the Geoid, and then give you the physical height of each point on
earth above or below this surface. I think this is done because one of the
applications of gravity data is to know exact elevation (or at least, it
seems so from what I've read) and also to allow easy reference to GPS data
(which I believe uses the Geoid as its reference, too).

I don't know how to convert from this data format to local gravitational
acceleration. If I knew what the potential level of the Geoid was then I
guess I could back out the local g by using the 1/r^2 gravity formula and
assume that the extra eight above the Geoid was just added to the radius of
the earth at this latitude and plug that into the r^2 part. However, there
are multiple opportunities for mistakes and assumptions there and so I just
kept looking to see if there was a map or dataset that gave me the data
directly.

Sean

At 07:53 AM 6/10/2003 -0400, you wrote:
>Did a google
>http://www.google.com/search?q=earth's%20gravitational%20field
>
>and found the website of the two satellites used to measure the
>gravitational field
>http://www.csr.utexas.edu/grace/
>
>I couldn't find the actual data online in my cursery search, but you can
>probably find out where to get it by emailing the professors involved in
>the above link.
>
>Since it's NASA, the data should be publicly available.
>
>-Adam
>
>Sean Breheny wrote:
>
>>Hi all,
>>
>>Ready for another of my OT questions? :-)
>>
>>I'm trying to find a map or other data that can tell me the local
>>gravitational acceleration if I know the lat/lon of a point on the earth.
>>In other words, I need to find out the local gravitational acceleration
>>to better than 1 milliG in Ithaca NY. So far in searching the web, I have
>>not found anything that gives this information (at least not directly, I
>>found maps of height above the Geoid but I don't know everything that I
>>need to know in order to convert this to simple local gravitational accel).
>>
>>Any ideas?
>>
>>Thanks,
>>
>>Sean
>>
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