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U.S.FOREST SERVICE RESEARCH NOTE VVO-3 



U.S.DEPARTMENT OF AGRICULTURE. ..WASHINGTON. DC. 3£ MARCH ISt4 



Two Plot Transfer Devices Developed For Aerial 

 Photographic Forest Insect Trend Surveys 



By R. C. Aldrich, 1 Research Forester 



Forest Insect Laboratory, Forest Service 



U.S. Department of Agriculture, Beltsville, Md. 



Aerial color photographic surveys, made periodically when in- 

 sect feeding causes maximum tree foliage discoloration, offer 

 promise as a means to record infestation changes from one such 

 time to the next. A problem unique to this type of survey is the 

 slow, tedious task of transferring locations of permanent trend 

 plots from one set of photographs to the next. If the transfer is not 

 accurate, the sometimes subtle change in the forest from one period 

 to the next cannot be accurately determined. To aid photo-in- 

 terpreters in making these transfers, two devices have been 

 developed and tested as part of a current study to determine whether 

 aerial color photography can be used to follow the trend of a balsam 

 woolly aphid, Chermes piceae Ratz., infestation in Fraser fir, 

 Abies fraseri (Pursh) Poir., near Mt. Mitchell, N.C. The purpose 

 of this note is to describe these devices and how they function. They 

 will be referred to as the "Old Delft" device and the "Ryker" de- 

 vice, 2 thus identifying them with the stereoscope with which they 



THE OLD DELFT DEVICE 



This device is made up of four components (fig. 1 A) in addition 

 to an Old Delft Scanning Stereoscope and a 16-tube fluorescent 



| The author wishes to thank John N. Sauls. Aircraft Mechanic, for his many 

 helpful suggestions and assistance in fabricating these devices. 



Mention of commercial products does not imply endorsement by the U S De- 

 partment of Agriculture, Forest Service. 



U S DEFT. OF MWnmiBE 

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JU L 2 3 1364 



