Using thermal imaging equipment which can sense at long ranges. You should be able to see the heating effects easily on thermal imaging equipment.
During the day time. The naked eye should be able to view these craft making the decent. As they will attain their own desired altitude at a very high altitude. So, the cloud tubes that they create will appear short from our perspective on the ground.
What you will see if your fortunate enough to be directly under them. Is small cloud tubes which are long. There will be clear sky through the center until the venturi effect clogs up the middle. Which will turn the center into a darker cloud then the outer ring of the tube. Those upper level winds will also quickly destroy the cloud tubes. The space of five or more craft which are safely distanced apart should be no larger than 2-3 inches in diameter with your arm outstretched. Depending on atmospheric conditions. Do not expect them to last longer than a minute.
These Disc shaped craft may even hide themselves in the middle of a cloud layer. They may even be able to create their own clouds. When these craft slowly lumber through our atmosphere. They may leave behind in their wake a long cloud. Using simple video cameras. You should be able to see the cloud growing length wise in a singular direction. Using thermal imaging may or may not work at this point. Because the exterior of the disc shaped ship may have already cooled to ambient temperature.
Unless, It is using a heating method to create the clouds. Thus, The thermal imaging camera should be able to see only the heated outline of the craft.
When a disc shaped cloud is hiding within any cloud. It matters not if it is natural, man made or made by them (Aliens not from Mexico). If them is really from elsewhere. If a disc craft which is hiding from view decides to leave earth. No matter the speed of their ascent. A venturi will be created. Air mass above will be pushed out to the leading edges of the disc shaped craft. Creating a positive air pressure. Below the disc shaped craft. There will be a negative air pressure. Even an updraft of winds. The thermal variances of the winds should create interesting sites/effects and visual artifacts.
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http://en.wikipedia.org/wiki/Venturi_effect
http://en.wikipedia.org/wiki/Venturi
http://en.wikipedia.org/wiki/Robert_Venturi
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http://en.wikipedia.org/wiki/Thermodynamics
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The videos used are only for visual examples. I do not claim they are real in any way.
http://www.youtube.com/watch?v=SAmPoccq1NUhttp://www.youtube.com/watch?v=3iKZy9ujfJM
http://www.youtube.com/watch?v=V8C0_D49gPk&feature=related
http://www.youtube.com/watch?v=OawJSIjWpP0
