Conference 7.286::space

    I believe it is the Great Wall in China.  Seems to me that this
    was observed by one of the members of the Skylab crews.

    I think that is supposed to be the answer, too, but it would depend
    on how you interpret the question: I bet there are plenty of man-made
    bodies of water that are visible from orbit, even if the dams
    themselves are not.

    	What monotony?
    
    	Larry
    

    Yes, I'm sure it's the great wall of China, too!
    
    Ray.

    	That is an old, outdated idea.  *Many* human-made objects can be
    seen from Earth orbit with the naked eye.  It was proven as long
    ago as 1963 (and probably earlier), when MERCURY astronaut Gordon
    Cooper reported seeing boats in the water and houses with smoke
    coming out their chimneys on his space flight, the last and longest
    one in the MERCURY series.
    
    	Larry
                                                       

The Great Wall is an old story, but look at the numbers.
It may be 1500 miles long, but it's only a few tens of feet wide,
and quite broken down in stretches.  A 100 foot object at 100 miles
subtends about 1/100 of a degree, less than the one minute of arc
usually associated with discernability.
I don't know about houses with smoke out the chimneys, but
the pyramids, some canals, airports, and probably sports stadiums
are probably quite visible.

- tom]

  Cooper:

'I could detect individual houses and streets in the low humidity and cloudless
areas such as the Himalayan mountain area, the Tibetan plain, and the
south-western desert area of the U.S.  I saw several individual houses with
smoke coming from the chimneys in the high country around the Himalayas.  The
wind was apparently quite brisk and out of the south.  I could see fields,
streams, lakes.  I saw what I took to be a vehicle along a road in the Himalaya
area and in the Arizona-West Texas area.  I could see the dust blowing off the
road, then could see the road clearly, and when the light was right, an object
that was probably a vehicle, I saw a steam locomotive by seeing the smoke first;
then I noted the object moving along what was apparently a track. This was in
northern India.  I also saw the wake of a boat in a large river in the
Burma-India area.' 

John

  Cooper's capsule, Faith 7, was in an orbit varying from 267 to 161 km.

John

        I'm a little late, as I've been on the road, and just caught up
        with this file, but...
        
        My understanding is that the Fermilab accelerator ring is visible
        from orbit as well. At least the folks at Fermi say it is. The
        Great Wall may be the only man-made object visible from the MOON.
        							    ----

    Certainly the gas flares from the wells around the Persian or
    Arabic Gulf are concestrated, bright and man-made.  They should
    be visable from orbit or even the moon
    
    Tony
    

From:	US1RMC::"[email protected]" "John Magliacane" 28-JUL-1993 12:20:12.54
To:	[email protected]
CC:	
Subj:	* SpaceNews 26-Jul-93 *

SB NEWS @ AMSAT $SPC0726
* SpaceNews 26-Jul-93 *
 
BID: $SPC0726
                               =========
                               SpaceNews
                               =========
 
                          MONDAY JULY 26, 1993
 
SpaceNews originates at KD2BD in Wall Township, New Jersey, USA.  It is
published every week and is made available for unlimited distribution.
 
* EARTHQUAKES VIA SATELLITE *
=============================
Up to now, earthquakes have been poorly defined because pre-quake and post-
quake studies at a large number of sites was simply not possible.  But now
with the advent of the ERS1 satellite, the situation has changed.  ERS1 
orbits at a height of 750 kms and views the world via a side scan synthetic 
aperture radar on a frequency of 5.36 GHz.  The satellite was used to study 
the 28-Jun-92 earthquake centered in Landers, California.
 
ERS1 collected images of the Landers area 4 times in 1992.  Once before the
quake, and 3 times after it.  Each pixel is 4 x 20 meters and the satellite
receiver records both signal range and phase data of the echo returns from
the ground.  Despite the fact that no two orbits follow exactly the same
track, it has proved possible to take the data from runs on 24 April pre-
quake and, 7 August post-quake and put them together with a high degree of
coherence.  
 
To do this the operators reconstruct the phase of each pixel by minimizing 
the number of fringes at the corners of the picture, assuming that far field 
data in the picture corners will be least disturbed by the quake.  They then 
eliminate the stereo path difference using a differential elevation model, 
and then calculate the interferometric fringes of the image at map 
coordinates, before resampling to improve overall signal to noise ratio and 
finally plotting what is basically a ground map covered in color coded 
fringes where the quake has shifted the surface betwee the pre-quake and 
post-quake records.
 
The result is a map of the Landers area overlayed by the "diffraction
pattern" of colored fringes.  Each fringe can reveal a shift as little as
28mm, that is the half wavelength of the radar.  Naturally with such a
precise record the middle of the pattern over the fault itself is blurred
because even with the small pixel size at the ground of 4 x 20 meters,
there has been a much larger ground shift than 28mm.  Nevertheless, the
area near the fault has obvious breaks in the surface so a record at that
point is hardly necessary, and ERS1 provides a beautiful record out to
far beyond the edges of the total affected area.
 
This ERS1 technique has a precision never seen before.  Indeed geologists
are now calling for records to be taken by ERS1 of all the world danger
spots including volcanoes which swell just before erupting, glaciers having
sudden spurts of movement which could foretell large killer landslides as
have occured in South America, and of course other active earthquake
fault lines.
 
ERS1 scans the same patch of ground every 35 days. It does not require
the positioning of ground stations in remote and often dangerous places.
So we should hear more about its successes in the future.  ERS1 was built
and launched by the European Space Agency/ArianeSpace. 
 
[Info via GM4IHJ] 
 
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