From: mikkelhaaheim@gmail.com   
      
   Le mercredi 27 juillet 2016 19:48:05 UTC+2, Sea Wasp (Ryk E. Spoor) a écrit :   
   > On 7/27/16 3:19 AM, Mikkel Haaheim wrote:   
   > > Le dimanche 24 juillet 2016 19:57:11 UTC+2, Sea Wasp (Ryk E. Spoor) a   
   écrit :   
   >    
   > >> 	Oh, the hell it doesn't. On the Arenaverse scale, even more so, because   
   > >> instead of the trick we can use today -- put up a satellite and look   
   > >> down through what amounts to only a couple miles of sea-level density   
   > >> air -- you'd have to look through effectively infinite amounts of such   
   > >> air, with accompanying dust, humidity, clouds, etc.   
   > >>   
   > >   
   > > Which limits EM range a little (depending on frequency,   
   >    
   > 	Not "a little". With a good telescope in space, I can pick up details    
   > on planets millions of miles away.   
      
   Depends upon the scales. In your fantasy scenario (NOT SciFi, because a   
   "universe" filled with atmosphere will rather quickly collapse on itself),   
   perhaps (it is fairly easy to quantify the actual range, as "rule of thumb"   
   absorbtion of gamma radiation -   
   photons- is 9/10ths absorbtion per arial density of 500g/cm^2... this varies a   
   little depending upon actual photon wavelength and atomic structure, but not   
   too much). OTOH, this just determines the interval of sensor platforms, and/or   
   the area of the    
   platforms required to collect enough of a signal. However, in the REAL   
   universe, especially in the given context of planetary observation from orbit,   
   atmosphere is going to provide very little hindrance. Any polutant capable of   
   blocking out detection    
   completely will also pretty much prevent any field operations in the first   
   place.   
      
      
   >    
   > 	Look through a hundred-plus miles of atmosphere, even pure    
   > nitrogen/oxygen and trace gases without a bit of dust in it, you'll be    
   > losing definition already noticeably. With humidity, worse. With dust,    
   > worse.   
   >    
   > 	Space is easy. Air is hard.   
      
   Vacuum is easy. Space also means distance, and you are ignoring the effects of   
   radiative dispersion over distance (every time you multiply distance,   
   intensity is reduced exponentially), which makes space rather hard.    
      
   >    
   >    
   > > but vastly improves sonar.   
   >    
   >    
   > 	Welll... yes, compared to VACUUM where the range of sonar is zero, yes.    
   > But in the air? No. There's a good reason we don't generally use sonar    
   > in air; it dissipates at relatively short ranges. Underwater, that's a    
   > different thing, but there you've got water, vastly more dense than air,    
   > to transmit the signals.   
   >    
   > 	In air? No, not even at a few kilometers.   
      
   Depends upon intensity of the source and the sensitivity of the sensor.   
   Construct parabolic microphones with 100 m collector dishes, and you will have   
   a pretty good signal for any heavy equipment. Or, an array with a larger   
   number of 1m dishes in scan    
   mode. Jet engines produce enough noise to be heard fairly well over dozens of   
   km, in good conditions. They can detected with parabolic microphones at   
   hundreds of km or more (depending, again, on the size of the dish).   
      
   >    
   > 	And even underwater, sonar's severely limited by all sorts of effects    
   > -- boundary layers, multipath, etc. -- which are much less an issue with    
   > EM sensing in space.   
      
   The effects you mention are all processing issues, not detection issues. The   
   processing issues are VERY MUCH a concern with detection and identification of   
   objects in space.   
      
      
   >    
   > >>   
   > >> 	For any particular case with unlimited monetary expenditure, perhaps,   
   > >> but you're dismissing stuff that we KNOW is a problem as though it   
   > >> isn't, which really makes me question how much you know about the   
   > >> *practical* limitations and not the theoretical. I work, as I said, with   
   > >> multispectral imaging and sensors, some for the military, and our   
   > >> experience with such imaging is more a matter of seeing more of its   
   > >> limitations than its awesomeness.   
   > >   
   > > NOW you are beginning to see what I have been talking about.   
   >    
   >    
   > 	Not really. Because in space, my cheapo IR camera can sense you so    
   > easily that you'll have to spend many orders of magnitude more trying to    
   > hide from it. The person trying to see you will ALWAYS have an advantage    
   > in space, while on Earth often the person trying to HIDE has the advantage.   
   >    
   >    
      
   Be very careful with absolutes. If you happen to be near a hot planet, your IR   
   camera is going to have some serious difficulties. Also, you are again   
   ignoring the effects of distance on emission radiation.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)