<font color='black' size='3' face='Georgia, Times New Roman, Times, Serif'><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3">
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<div style="font-family:helvetica,arial;font-size:10pt;color:black"><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3"><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3"><font size="3">J<font size="3">oaquim: Thank you for the expl<font size="3">anation. But I think all you have done is confirm that the region is probably a <font size="3">large sand bar<font size="3">, sometimes <font size="3">su<font size="3">bmerged or partially submerged. The<font size="3">re seems to be two reasons <font size="3">data is so <font size="3">spar<font size="3">se there: f<font size="3">requent cloud cover hindering remote sen<font size="3">s</font>ing, and very shallow water that makes soundings by ship impos<font size="3">sible.<br>
<br>
<font size="3">Here is a representative sample of MODIS data that I culled from USGS’s G<font size="3">lobal Visualization Viewer<font size="3">:<br>
http://commons.wikimedia.org/wiki/File:MODIS-MCD43A4-02-2004.png<br>
<br>
The <font size="3">part<font size="3">icular<font size="3"> MODIS data <font size="3">set is MCD43A4 (MODIS/Terra+Aqua Nadir BRDF-Adjusted Reflectance 16-Day L3 Global 500m SIN Grid<font size="3">). If you cycle <font size="3">through the months and years, you can clearly see that <font size="3">MODIS <font size="3">usually sees something there but sometimes does not. That means (to me) that<font size="3"> sometimes the s<font size="3">and bar is submerged too far <font size="3">for the sa<font size="3">tellite to detect it but usually is shallow enough <font size="3">to yield a <font size="3">signal.<font size="3"> <font size="3">None of the data are consistent with deep water.<br>
<br>
<font size="3">Regards,<br>
<font size="3">— daan Strebe</font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3"><br>
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<div style="font-family:helvetica,arial;font-size:10pt;color:black"><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3">-----Original Message-----<br>
From: J. Luis <jmfluis@gmail.com><br>
To: strebe <strebe@aol.com><br>
Sent: Sat, Nov 24, 2012 6:36 am<br>
Subject: Re: [Proj] Slightly off-topic: The phantom island that is real<br>
<br>
</font>
<div id="AOLMsgPart_1_72d1e401-1ca7-476a-a7fb-b3ed6b3946b1"><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3">
Daan<br>
<br>
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.<br>
<br>
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.<br>
<br>
<a class="moz-txt-link-freetext" target="_blank" href="https://listserv.hawaii.edu/cgi-bin/wa?A2=ind1211&L=GMT-HELP&D=0&T=0&P=116217">https://listserv.hawaii.edu/cgi-bin/wa?A2=ind1211&L=GMT-HELP&D=0&T=0&P=116217</a><br>
<br>
Regrads<br>
<br>
Joaquim<br>
<br>
</font><blockquote type="cite"><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3"><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3">I<font size="3"> don’<font size="3">t
follow your <font size="3">ass<font size="3">ertion. <font size="3">The e-mail you cite states the island DOES
appear in GTOPO30 and SRM30+. I see the same thing. W<font size="3">hen </font>I look at the raw values in
SRTM30 Plus, the entire are<font size="3">a of the
island consists of sea-level DEM values. Plus, NA<font size="3">SA Blue Mar<font size="3">ble satellite
imagery clearly shows shallow water over the
entire 30<font size="3">_k<font size="3">m x 6<font size="3">_km area<font size="3"> that is
called “San<font size="3">dy Island” on
innumerable maps.</font></font></font></font></font></font></font></font></font></font></font></font></font></font></font><br>
<br>
<font size="3">Whe<font size="3">ther or not there is an “island”
there (as opposed to <font size="3">a barely submerged
sandbar<font size="3">) is perh<font size="3">aps open to
debate o<font size="3">r depends on the ti<font size="3">des.
But the<font size="3"> <font size="3">crew of the
res<font size="3">earch ve<font size="3">s<font size="3">sel is claiming 1<font size="3">,400<font size="3">_m <font size="3">soundings,
whi<font size="3">ch <font size="3">just
does not coincide with that area
at all.</font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font></font><br>
<font color="black" face="Georgia, Times New Roman, Times, Serif" size="3">
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<div> Regards,<br>
<font size="3">— daan Strebe<br>
<br>
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<div style="font-family:helvetica,arial;font-size:10pt;color:black">-----Original
Message-----<br>
From: J. Luis <a class="moz-txt-link-rfc2396E" href="mailto:jmfluis@gmail.com"><jmfluis@gmail.com></a><br>
To: PROJ.4 and general Projections Discussions
<a class="moz-txt-link-rfc2396E" href="mailto:proj@lists.maptools.org"><proj@lists.maptools.org></a><br>
Cc: strebe <a class="moz-txt-link-rfc2396E" href="mailto:strebe@aol.com"><strebe@aol.com></a><br>
Sent: Fri, Nov 23, 2012 6:40 pm<br>
Subject: Re: [Proj] Slightly off-topic: The phantom island
that is real<br>
<br>
<div id="AOLMsgPart_1_104064cd-d38a-42bd-bbd0-df388e0c30ae">
We discussed that on the GMT list too and no, the island
does NOT exist in the SRTM+ or GTOPO30 series<br>
<br>
See for example<br>
<a class="moz-txt-link-freetext" target="_blank" href="https://listserv.hawaii.edu/cgi-bin/wa?A2=ind1211&L=GMT-HELP&D=0&T=0&P=107015">https://listserv.hawaii.edu/cgi-bin/wa?A2=ind1211&L=GMT-HELP&D=0&T=0&P=107015</a><br>
<br>
Joaquim<br>
<br>
<blockquote type="cite"><font color="black" face="Georgia, Times New Roman, Times, Serif" size="3"><font size="3">The
crew of a research ship claims to have undiscovered a
large island in the South Pacific’s Coral Sea near New
Caledonia, called Sandy Island. The news feeds have
picked up on this and it’s making its way around the
geeksphere with great rapidity. Here is an example
article:<br>
<a class="moz-txt-link-freetext" target="_blank" href="http://phys.org/news/2012-11-aussie-scientists-un-discover-pacific-island.html">http://phys.org/news/2012-11-aussie-scientists-un-discover-pacific-island.html</a><br>
<br>
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.<br>
<br>
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 don’t think a datum mismatch can account for
this, given the size of the sandbar. <br>
<br>
I have started a thread here:<br>
<a class="moz-txt-link-freetext" target="_blank" href="http://mapthematics.com/forums/viewtopic.php?f=10&t=469">http://mapthematics.com/forums/viewtopic.php?f=10&t=469</a><br>
<br>
Enjoy!<br>
— daan Strebe<br>
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