[meteorite-list] Sand Dunes and Meteorites

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From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 09:50:21 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C8698E5B35_at_US-Torrance.mail.saic.com>

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On the subject of remote sensing of meteorites from above, Jim Hartman
wrote:

> I know that I am not the rocket scientist here & this may be an
oversimplified
> theory but I have a picture of my house & my fathers house taken from a
> satellite in orbit. Now I may be wrong but I kinda think that if someone
is
> going to go to the trouble of putting millions of dollars of equipment
into
> orbit that they would include thermal imaging as part of that inventory.

Rocket scientist chiming in: many thermal imaging sensors are currently in
orbit (e.g. Landsat, EOS, Spot). But the trouble with all of them is
insufficient resolution. Even if you could get 2-meter resolution data in
a waveband of interest, a meteorite with a 10-cm x 10-cm "footprint" would
only fill one 400th of a pixel. In order to detect such a meteorite with
a signal-to-clutter ratio of 3:1, the difference between your target
radiance and background radiance would need to be 800 times the standard
deviation of the scene gradient. It's not completely impossible, but
you're going to need a very benign background and a significant
emissivity difference between the background and the meteorite.

Temperature difference ends up buying you very little in this case because
the target represents such a small fraction of the area of a pixel. For
instance, to double the radiance output of a 300 K object in the 3-5 micron
band, you'd need to increase its temperature to 320 K -- 36 deg F warmer.

What this all boils down to is that you need a sensor flying at low
altitude in order to get the footprint size down to something more
comparable to the size of the meteorites you expect to find... --Rob

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<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>On the subject of remote sensing of meteorites from
above, Jim Hartman wrote:</SPAN></FONT></DIV>
<DIV> </DIV>
<DIV><FONT face="Courier New"><FONT size=2><SPAN class=090581421-01042002>>
</SPAN>I know that I am not the rocket scientist here & this may be an
oversimplified<SPAN class=090581421-01042002><FONT
color=#0000ff> </FONT></SPAN></FONT></FONT></DIV>
<DIV><FONT face="Courier New"><FONT size=2><SPAN class=090581421-01042002><FONT
color=#0000ff>></FONT></SPAN> theory but I have a picture of my house &
my fathers house taken from a<SPAN class=090581421-01042002><FONT
color=#0000ff> </FONT></SPAN></FONT></FONT></DIV>
<DIV><FONT face="Courier New"><FONT size=2><SPAN class=090581421-01042002><FONT
color=#0000ff>></FONT></SPAN> satellite in orbit. Now I may be wrong but I
kinda think that if someone is<SPAN class=090581421-01042002><FONT
color=#0000ff> </FONT></SPAN></FONT></FONT></DIV>
<DIV><FONT face="Courier New"><FONT size=2><SPAN class=090581421-01042002><FONT
color=#0000ff>></FONT></SPAN> going to go to the trouble of putting millions
of dollars of equipment into<SPAN class=090581421-01042002><FONT
color=#0000ff> </FONT></SPAN></FONT></FONT></DIV>
<DIV><FONT face="Courier New"><FONT size=2><SPAN class=090581421-01042002><FONT
color=#0000ff>></FONT></SPAN> orbit that they would include thermal imaging
as part of that inventory.<SPAN class=090581421-01042002><FONT
color=#0000ff> </FONT></SPAN></FONT></FONT></DIV>
<DIV><SPAN class=090581421-01042002></SPAN> </DIV>
<DIV><SPAN class=090581421-01042002><FONT color=#0000ff face="Courier New"
size=2>Rocket scientist chiming in:  many thermal imaging sensors
are currently in</FONT></SPAN></DIV>
<DIV><SPAN class=090581421-01042002><FONT color=#0000ff face="Courier New"
size=2>orbit (e.g. Landsat, EOS, Spot).  But the trouble with all of them
is</FONT></SPAN></DIV>
<DIV><SPAN class=090581421-01042002><FONT color=#0000ff face="Courier New"
size=2>insufficient </FONT></SPAN><SPAN class=090581421-01042002><FONT
color=#0000ff face="Courier New" size=2>resolution.  </FONT></SPAN><FONT
face="Courier New"><FONT size=2><FONT color=#0000ff><SPAN
class=090581421-01042002>Even if you could get 2-meter resolution data
in</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face="Courier New"><FONT size=2><FONT color=#0000ff><SPAN
class=090581421-01042002>a waveband of interest, a meteorite
</SPAN></FONT></FONT></FONT><FONT face="Courier New"><FONT size=2><FONT
color=#0000ff><SPAN class=090581421-01042002>with a 10-cm</SPAN><SPAN
class=090581421-01042002> x</SPAN></FONT></FONT></FONT><FONT color=#0000ff
face="Courier New" size=2><SPAN class=090581421-01042002> 10-cm "footprint"
would</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>only fill one 400th of a pixel. 
</SPAN></FONT><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>In order to detect </SPAN></FONT><FONT color=#0000ff
face="Courier New" size=2><SPAN class=090581421-01042002>such a meteorite
with</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>a signal-to-clutter ratio of </SPAN></FONT><FONT
color=#0000ff face="Courier New" size=2><SPAN class=090581421-01042002>3:1, the
difference between </SPAN></FONT><FONT color=#0000ff face="Courier New"
size=2><SPAN class=090581421-01042002>your target</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>radiance and background radiance </SPAN></FONT><FONT
color=#0000ff face="Courier New" size=2><SPAN class=090581421-01042002>would
need to be 800 times </SPAN></FONT><FONT color=#0000ff face="Courier New"
size=2><SPAN class=090581421-01042002>the standard</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>deviation of the scene gradient. 
</SPAN></FONT><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>It's not completely impossible, but</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>you're going to need a very benign </SPAN></FONT><FONT
color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>background and a significant</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>emissivity difference between the background
</SPAN></FONT><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>and the meteorite.</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>Temperature difference ends up buying you very little
in this case because</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>the targe</SPAN></FONT><FONT color=#0000ff
face="Courier New" size=2><SPAN class=090581421-01042002>t </SPAN></FONT><FONT
color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>represents such a small fraction of the area of a
pixel.  For</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>instance, </SPAN></FONT><FONT color=#0000ff
face="Courier New" size=2><SPAN class=090581421-01042002>to double the
</SPAN></FONT><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>radiance output of a 300 K object in the 3-5
micron</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>band, you'd need to </SPAN></FONT><FONT color=#0000ff
face="Courier New" size=2><SPAN class=090581421-01042002>increase
</SPAN></FONT><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>its temperature </SPAN></FONT><FONT color=#0000ff
face="Courier New" size=2><SPAN class=090581421-01042002>to 320 K -- 36 deg F
warmer.</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>What this all boils down to is that
y</SPAN></FONT><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>ou need a sensor flying at low</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>altitude </SPAN></FONT><FONT color=#0000ff
face="Courier New" size=2><SPAN class=090581421-01042002>in order to get the
footprint size down to something more</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff face="Courier New" size=2><SPAN
class=090581421-01042002>comparable to the size of the meteorites you expect to
find... --Rob</SPAN></FONT></DIV></BODY></HTML>

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Received on Mon 01 Apr 2002 06:04:17 PM PST

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