AN EXPERIMENT WITH THE USE OF THE AIRBORNE PROFILE 
      
     
   
  
   
  
    
    
   
    
     
    
   
    
   
   
   
    
   
      
     
    
    
     
   
    
   
   
    
   
    
   
    
   
   
    
RECORDER FOR MULTIPLEX HEIGHTING 
Jd. A, Eden 
m 
Précis 
The paper describes an experinent using Multiplex to determine 
whether height control to an accuracy suitable for 50 foot contouring 
of 1/37,000 scale photographs could be obtained by means of the 
Airborne Profile Recorder flown at the same time as the survey photog- 
raphy. The experimental material consisted of a block of four strips 
of photography run over a distance of about seventy miles between the 
Bristol and English Channels. Only one ground height control point 
was used, and no plan control points. Heights were determined to a 
standard mean square error of 11.9 feet. 81% of the 260 points 
heighted were in error by less than fifteen feet. The maximum error 
was twenty-eight feet, These results were considered sufficiently 
good as a basis for 50ft. contouring. 
  
The Material 
A block of photography, four strips wide was flown across Devon 
and Somerset between the Bristol and English Channels, the distance 
being about seventy niles, The Airborne Profile Recorder was operating 
at the time of the flight. The strips averaged thirty-six photographs 
long, the total number of photographs being 438. The photographs 
were exposed from a height of 18,500 feet with a six inch Wild RC5 
camera. In addition, three tie strips were flown aeross the main 
direction of the stripping from a height of 10,000 feot. (See Figure). 
Ihe Object of the "xperiment 
With this material an experiment was undertaken to determine 
whether it was possible to use the recordings of the Airborne Profile 
Recorder to establish sufficient spot heights to an accuracy suitable 
for 50 foot contouring, Multiplex was Go be used for this work. In 
order to check the accuracy of the experimental results 260 height 
controls were available well distributed about the area to an accuracy 
of + 1 foot. Only one of these points was used in the experiment. 
General Exper iment: nl Proc cedure 
To perform the experiment the record of the hypsometer in the 
A.P.R. was corrected by app tion of Henry's formula. This purports 
to effect a correction such that the datum Of. these measures is with 
reference to à horizon instead of with reference to an isobaric 
surface, 
This corrected record was used for the purpose of levelling the 
machine air bases in the direction of flight and for establishing a 
continuous elevated horizontal datum below which depths were measured 
down to the ground. The distances down to the ground beneath this 
he | 
elevated datum were determined from the recordings of the radar alti- 
meter which constitutes another part of the Airborne Profile Recorder.