311 
i ? v < *» 5 a 7 fl V 1/i tl 1? 13 1* 15 16 17 IB 19 iV V\. 27 ?3 5>4 ?5 ?f> 27 ?9 3? 7.1 
Fig* 6 : Frequency count of ERTS-1 imagery in Canada with 25% cloud 
cover or less taken between July ’72 and October *74. 
Because of the overlap between passes (45% in the south 
increasing to 80% in the north) effective coverage frequency 
can be 2 x greater (in the south) or more than the number 
indicated.