" Totally i think i have to cover area of more then 20km."

Area of more than 20 sq.km

OK in such an event the only way out (?) would be a high resolution surveillance radar ?

The warehouse may be in a large open area - but I dont think the access doors will not be more than a few meter's wide even assuming you are going to berth a MegaTop 747 inside it ? Then why not keep a vigil on the entry points alone instead of the whole area. But I know, some clients are like that - tough.

Raghu