ULF SITE SELECTION CRITERIA

Low frequency ULF monitoring requiires an electromasgnetically quiret location.

In addition to the desired ground induced ULF signals ... disturbances 
are also caused by:

	1) movement of electrically conductive objects:     minimum distance to:
		moving animal tissue (waving your arms)	  	 20 feet
		metal objects ... a door, a swing on a chain 	100 feet
		a metal fence ... blowing in the wind		100 feet	
		air-conditioning ducts				200 feet
		vehicles ... busses, cars 		    	500 feet	

	2) things that cause the earth to move:
		footsteps					 50 feet
		wind moving and stressing tree roots		 50 feet
		vehicles (depends on speed,size,road roughness)	500 feet
		thunder	... depends on intensity		  3 miles
		sonic-booms ... intensity & duration 		 20 miles
		earthquakes					200 miles

	3) direct electrical events:
		rotating car tire				100 feet
		power-lines and their transients		200 feet
		movement of charged air masses (low humidity       1 mile	
		lightning					  10 miles
		aurora						4000 miles
		

These "ranges" are only an approximation.
However,  they do indicate some of the things to be considered in site selection.

The antenna oritentation can be adjusted to reduce some noises ...
... but at the cost of losing standardizatrion with other observers, 
whose antennas are mounted north/south and east-west.