Sounds like someone's earth bulge corrections are amiss! This is the name
used due to the earth shape being slightly ellipsoid instead of a perfect
sphere. The earth diameter is slightly greater at the equator than higher
or lower latitudes.
If this is the case, then it seems that the elevation of all locations
near the HK area would be in error.
We have to account for earth bulge in our EME az/el calculations so it is
a real effect; not just imagined.
73,
Gerald K5GW
In a message dated 8/19/2011 10:48:12 P.M. Central Standard Time,
hk1kxa@hotmail.com writes:
I would not trust Google-Earth elevation data.To add an example like
Bimini, Bahamas: Check Malpelo Island, HK0TU, 400 km away from the colombian
Pacific coast (4.0 N, 81.6 W) According to Google earth the island is
submerged under the water surface a least 340 ft. In reality, this island has
elevations over 1000 ft ASL.
David
HK1A
EC5KXA
AE5XQ
> From: n6bv@arrl.net
> To: towertalk@contesting.com
> Date: Wed, 17 Aug 2011 11:29:16 -0700
> Subject: [TowerTalk] Terrain data for HFTA
>
> Charlie:
>
> You said recently:
>
> > Date: Tue, 16 Aug 2011 20:12:45 -0500
> > From: Charlie Carroll <k1xx@cfl.rr.com>
> > Subject: Re: [TowerTalk] grabbing terrain data for HFTA
> > To: Grant Saviers <grants2@pacbell.net>, towertalk@contesting.com
> > Message-ID: <wg1l6uo0lqvcmp2rougptbc7.1313543269277@email.android.com>
> > Content-Type: text/plain; charset=utf-8
> >
> > Door's abt to close, so have to be brief. Of late, I have taken
> > to semi-automatically extracting terrain data from Google Earth.
> > I dump this info into an Excel spreadsheet for the number
> > crunching. Pretty painless to do something like ten foot
> > intervals out to 10k feet.
> >
> > 73 charlie, k1xx
>
> N6BV: I'm not sure where Google Earth gets their terrain data, but I am
> suspicious that it is derived at least partially from the SRTM (Shuttle
> Radar Topography Mission) data set. I get nervous when I look at the
terrain
> data for islands surrounded by seawater -- which should, by definition,
be
> at or at least very close to sea level. It is often shown as being
> considerably different from sealevel.
>
> N6BV: For example, in Google Earth zoom into Baileytown, Bimini, Bahamas.
> Just to the west of Baileytown the altitude goes considerably negative.
> Either this is a depthsounder reading (which I doubt) or else something
is
> goofy!
>
> N6BV: I'm curious how you are extracting that data from Google Earth
> semi-automatically, even if I'm nervous about the data itself.
>
> >
> > Grant Saviers <grants2@pacbell.net> wrote:
> >
> > >Can some one share a pointer for up to date instructions for grabbing
> > >the terrain data from the web for HFTA? Every instruction I've found
is
> > >hopelessly out of sync with the current terrain data web site.
> > >
> >
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