[Proj] Slightly off-topic: The phantom island that is real
support.mn at elisanet.fi
support.mn at elisanet.fi
Tue Nov 27 05:10:20 PST 2012
Hello,
well it might also be a hiding place for a military vessel ..
for example a large aircratft carrier ..
that would explain the reason why it time
to time disappears and comes back?
at least the "sand island" top view is very
much like an aircraft carrier? ;)
http://static.ddmcdn.com/gif/aircraft-carrier-top-view.gif
regards: Janne.
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strebe at aol.com kirjoitti:
>
> Joaquim: Thank you for the explanation. But I think all you have done is confirm that the region is probably a large sand bar, sometimes submerged or partially submerged. There seems to be two reasons data is so sparse there: frequent cloud cover hindering remote sensing, and very shallow water that makes soundings by ship impossible.
>
> Here is a representative sample of MODIS data that I culled from USGSs Global Visualization Viewer:
> http://commons.wikimedia.org/wiki/File:MODIS-MCD43A4-02-2004.png
>
> The particular MODIS data set is MCD43A4 (MODIS/Terra+Aqua Nadir BRDF-Adjusted Reflectance 16-Day L3 Global 500m SIN Grid). If you cycle through the months and years, you can clearly see that MODIS usually sees something there but sometimes does not. That means (to me) that sometimes the sand bar is submerged too far for the satellite to detect it but usually is shallow enough to yield a signal. None of the data are consistent with deep water.
>
> Regards,
> daan Strebe
>
>
>
>
> -----Original Message-----
> From: J. Luis <jmfluis at gmail.com>
> To: strebe <strebe at aol.com>
> Sent: Sat, Nov 24, 2012 6:36 am
> Subject: Re: [Proj] Slightly off-topic: The phantom island that is real
>
>
> Daan
>
> Although we never phrased it out in those mails, it's quite obvious that what appears to an island in the SRTM+ is nothing but an interpolation artifact introduced by a constrain imposed the coastline itself. Notice how close the coastline and the 1 m meter contour lines are. Furthermore the maximum height in the SRTM+ data is 1m meter, which is obviously very suspicious. I'll add it also that the 'Walter' that appears in one of those mails is Walter Smith from the Smith & Sandwell bathymetry.
>
> HOWEVER, that does not rule out the possibility that the island exists. Only says that there is no reliable data to constrain the grid construction at that location. The 1400 m difference also puzzled me a bit and moved by your mail I searched also the MODIS data for Sea Surface Temperature ... and the mystery continues MODIS does not seam to find water over there. See the image that I posted in GMT mailing list.
>
> https://listserv.hawaii.edu/cgi-bin/wa?A2=ind1211&L=GMT-HELP&D=0&T=0&P=116217
>
> Regrads
>
> Joaquim
>
>
> I dont follow your assertion. The e-mail you cite states the island DOES appear in GTOPO30 and SRM30+. I see the same thing. When I look at the raw values in SRTM30 Plus, the entire area of the island consists of sea-level DEM values. Plus, NASA Blue Marble satellite imagery clearly shows shallow water over the entire 30_km x 6_km area that is called
Sandy Island
on innumerable maps.
>
> Whether or not there is an
island
there (as opposed to a barely submerged sandbar) is perhaps open to debate or depends on the tides. But the crew of the research vessel is claiming 1,400_m soundings, which just does not coincide with that area at all.
>
>
>
>
> Regards,
> daan Strebe
>
>
>
>
>
>
> -----Original Message-----
> From: J. Luis <jmfluis at gmail.com>
> To: PROJ.4 and general Projections Discussions <proj at lists.maptools.org>
> Cc: strebe <strebe at aol.com>
> Sent: Fri, Nov 23, 2012 6:40 pm
> Subject: Re: [Proj] Slightly off-topic: The phantom island that is real
>
>
> We discussed that on the GMT list too and no, the island does NOT exist in the SRTM+ or GTOPO30 series
>
> See for example
> https://listserv.hawaii.edu/cgi-bin/wa?A2=ind1211&L=GMT-HELP&D=0&T=0&P=107015
>
> Joaquim
>
>
> The crew of a research ship claims to have undiscovered a large island in the South Pacifics Coral Sea near New Caledonia, called Sandy Island. The news feeds have picked up on this and its making its way around the geeksphere with great rapidity. Here is an example article:
> http://phys.org/news/2012-11-aussie-scientists-un-discover-pacific-island.html
>
> However, it is quite clear from satellite imagery and multiple data sources that the
island
in fact exists, though possibly it is a barely submerged sandbar. Yet the crew claims depths there are around 1,400 meters.
>
> Obviously the ship was not where they say it was. The question is, how did the crew of this research vessel convince themselves they were sailing in the same area? I dont think a datum mismatch can account for this, given the size of the sandbar.
>
> I have started a thread here:
> http://mapthematics.com/forums/viewtopic.php?f=10&t=469
>
> Enjoy!
> daan Strebe
>
>
>
>
>
>
>
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