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Statoscope (Hypsometer) 
This equipment registers - "by the application of various physical principles - 
changes in air pressure. These changes can be converted to height differences 
with reference to an arbitrary isobaric surface, which correspond to the 
bz values of the exposure stations in a restitution instrument. 
Isobaric surfaces are, however, not parallel to the geoid. Over short 
distances, the deformations of the isobaric surface can be sufficiently 
corrected by linear interpolation to known values at both ends of a strip. 
If statoscope data are used over longer distances, the application of the 
so-called Henry correction becomes necessary, which has originally been 
developed for the reduction of APE data, for just the same reason. 
By rendering an independent control of the bz-values in a triangulation 
procedure,statoscope data serves to suppress the unfavourable influence of 
the accumulation of 9 -errors, the most effective error influence in longer 
strips. They do not, however, control the influence of scale transfer errors 
or the accumulated effect of lateral tilt errors. 
In equating corresponding statoscope and bz values of the exposure stations, 
allowance has to be made for the influence of earth curvature on the bz-values 
and for a possible shift and slope of the isobaric surface. This shift 
corresponds to an unknown index-error which has to be determined indirectly 
using ground control. 
The additional slope correction would eliminate any residual slope error not 
accounted for by the Henry correction. 
The accuracy of statoscope (hypsometer)-data has been established as being 
about +_ 1-2 m (standard deviation). Undulations of the isobaric surface over 
longer distances are not included in this value. The accuracy of statoscope 
data depends to a certain extent on the flying height, being better for lower 
flying heights. On the other hand, unfavourable influences of air turbulences 
have to be expected at extremely low flying heights and under certain 
meteorological conditions. 
A recent analysis of low altitude statoscope data (flying height 2000 m), 
obtained from over 1000 models distributed over isolated projects in Saudi 
Arabia, resulted in a standard deviation of O.64 m. 
The statoscope (hypsometer) is a relatively inexpensive piece of instrument, 
rendering very valuable information in return for little extra effort. 
Its application to a photogrammetric project - if no other auxiliary data are 
considered -is strongly recommended in all cases where contour intervals of 
5 m or larger are required. 
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