nick@lfcs.ed.ac.uk (Nick Rothwell) (01/09/90)
I'm posting this for a friend: please reply to him if possible (as specified in the Reply-To field); otherwise, I'll spot follow-ups in sci.misc and redirect them. Ta... -- Recently I heard of satellite pictures that revealed buried ruins in the Sahara desert. I have a simple question. Is this true ? Can satellite pictures reveal buried ruins ? Has this been done much ? I am posting this to comp.graphics aswell in the hope that an ftp site with such pictures exists. I would be grateful for any mail on this subject, or follow-ups to sci.misc. Thankyou, ----Chris---- -- Nick Rothwell, Laboratory for Foundations of Computer Science, Edinburgh. nick@lfcs.ed.ac.uk <Atlantic Ocean>!mcvax!ukc!lfcs!nick ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ "...all these moments... will be lost in time... like tears in rain."
livesey@solntze.Sun.COM (Jon Livesey) (01/10/90)
In article <1523@castle.ed.ac.uk> ct@lfcs.ed.ac.uk (Chris Thornborrow) writes: > > Can satellite pictures reveal buried ruins ? Has this >been done much ? Not just satellites. Much of the early twentieth century archeological work in the UK was done using airborne photography. Take a look at some of the stuff published by Sir Mortimer Wheeler for details. jon.
sns@erm.oz (Stuart Nixon) (01/11/90)
In article <1523@castle.ed.ac.uk>, nick@lfcs.ed.ac.uk (Nick Rothwell) writes: > Recently I heard of satellite pictures that revealed buried ruins > in the Sahara desert. I have a simple question. Is this true ? > Can satellite pictures reveal buried ruins ? Has this > been done much ? The short answer is yes. Many of the commercial satellites (such as Landsat TM) have a thermal bands, e.g. sensors in the near or far infrared range (2.2 um to 10um). If you have an area with a fairly constant surface (such as desert), then sub-surface variations show up quite clearly. There has also been some research in thermal profile mapping, where the rate at which the surface heats up & cools down is used to guess at what material might be causing the effect (for example sandstone has a different thermal profile to granite). sns -- Stuart Nixon, sns@erm.oz.au Earth Resource Mapping, 130 Hay St, Subiaco, Western Australia 6008 Phone: +61 9 388 2900 Fax: +61 9 388 2901 E-mail: sns@erm.oz.au
eugene@eos.UUCP (Eugene Miya) (01/12/90)
You are getting into the area of remote sensing.
The principal instrument you want is Imaging Radar, also know as
side looking radar (SLAR), Synthetic Aperature Radar (SAR), etc.
(typical air or space borne).
There is also the use of passive microwave. Radar has the
advantage in that is it an active sensor sending a pulse (chirp)
out which has a signal (return) which can then be analyzed.
IR has some advantages and disadvantages. I won't digress.
The bottom line is that you are looking at secondary artfacts typically rather
than primary characteristics to learn about your subject
of interest. Airborne imaging radar has been used to lcate runs in the
jungles of Central America and water ways in the Sahara (spaceborne
systems). The mechanics of the subject are long, big, somewhat complex,
and not well understood (do you have 5 days?). We create images, not photos
or maps, the geometry of creation is completely different from a photo (point
perspective) or a map (orthogonal).
Texts include: The Manual of Remote Sensing (Amer. Soc. of Photogrammetry),
(try 7 inches thick) and radar specifically:
Introduction to Radar Systems by Skolnick. Lots of fun working
in this area, you get to go on field trips, take ground truth.
"What do you do?"
"I make maps." -- Starman
Another gross generalization from
--eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov
resident cynic at the Rock of Ages Home for Retired Hackers:
"You trust the `reply' command with all those different mailers out there?"
"If my mail does not reach you, please accept my apology."
{ncar,decwrl,hplabs,uunet}!ames!eugene
Do you expect anything BUT generalizations on the net?jgk@osc.COM (Joe Keane) (01/12/90)
In article <1523@castle.ed.ac.uk> ct@lfcs.ed.ac.uk (Chris Thornborrow) writes: > Can satellite pictures reveal buried ruins ? Has this >been done much ? I think they may be referring to Synthetic Aperture Radar images; i know these can `see' through a few meters of sand and have found interesting things.
rick@hanauma.stanford.edu (Richard Ottolini) (01/12/90)
In article <556@erm.oz> sns@erm.oz (Stuart Nixon) writes: >In article <1523@castle.ed.ac.uk>, nick@lfcs.ed.ac.uk (Nick Rothwell) writes: >> Recently I heard of satellite pictures that revealed buried ruins >> in the Sahara desert. I have a simple question. Is this true ? Radar can see several meters below below the surface under optimal conditions depending on wavelength, dryness, and soil grain size. I've heard some sites have been imaged directly by radar rather than by secondary visual effects, and I believe the Sahara was one of these successful places.
eugene@eos.UUCP (Eugene Miya) (01/13/90)
In article <7113@lindy.Stanford.EDU> rick@hanauma.UUCP (Richard Ottolini) writes: >In article <556@erm.oz> sns@erm.oz (Stuart Nixon) writes: >>In article <1523@castle.ed.ac.uk>, nick@lfcs.ed.ac.uk (Nick Rothwell) writes: >>> Recently I heard of satellite pictures that revealed buried ruins >>> in the Sahara desert. I have a simple question. Is this true ? > >Radar can see several meters below below the surface under optimal conditions >depending on wavelength, dryness, and soil grain size. >I've heard some sites have been imaged directly by radar rather than by >secondary visual effects, and I believe the Sahara was one of these >successful places. Well, er,... not quite. We are certainly seeing substructure in some images, but.... there is a lot we don't know or understand. How imaging radar works is dependent on lots of things: wavelength (which affect whether or not you can see below a surface be it ground or a forest canopy), a set of concepts like surface roughness and surface length, the dielectric constant of the soil (the presence of water which affect this and the wavelength selected), the power of the system, the structure of the chirp sent out, etc. But it has limits: radar is like working in the dark at night, you only see what you shine your light on. Shadows take on a different meaning. Images take on a quality of false 3-D. This causes problems such as range and azimuth ambiguity. Radar is not a miracle sensing system, but somewhat complex and needs a lot of reasearch to understand how to use it and how it works. Wavelength is important because one works in the region where things like raindrops can make a difference. Too big and you see them, too small, you don't. Same goes for soil particle size, etc. Radar works by taking a small antenna and moving it linearly along a track and synthesizing an image by integrating multiple views (looks) along that track. Motion is an integral part of constructing the image and no two scan lines are taken from the same point. One study on penetration of dense forest canopy was thought be a subsurface example. It turns out that was false, there were subtle variations on vegetation not visible to eyes. The human eye is at times an unreliable means of information transmital. Many people are unable to distinguish a radar image some say a black and white negative enlargement. It takes a bit of training to recognize features thats why images have false depth I worked on the Seasat-1 SAR, the preliminary studies for what is now the Magellan spacecraft. Along side of me were people working on the SIR (Shuttle Imaging Radar) and various airborne radars. Simple little description of imaging radar systems. To learn more, the material is complex enough you should take a class (or pay me to explain it to you). Another gross generalization from --eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov resident cynic at the Rock of Ages Home for Retired Hackers: "You trust the `reply' command with all those different mailers out there?" "If my mail does not reach you, please accept my apology." {ncar,decwrl,hplabs,uunet}!ames!eugene Do you expect anything BUT generalizations on the net?