94 SURVEY NAVIGATION, DISCUSSION 
douin et dont je vous présente le schéma. L'élé- 
ment statoscope différentiel, l'élément de me- 
sure, est constitué par le déplacement d'un 
noyau de transformateur relié à l'enregistreur et 
solidaire de la membrane qui sépare une cham- 
bre à pression constante d'une chambre liée à 
l’extérieur. Ici vous avez l'enregistrement des 
variations de pression. Ces figures ayant été 
projetées, je demande à Monsieur de Masson 
d'Autume s'il a quelque chose à dire quant à 
l'emploi de ce statoscope. 
J'attire l'attention sur la discussion donnée 
dans la méme communication de I'l GN dont 
jai parlé tout à l'heure, de l'appareil pour l'en- 
registrement de l'orientation de l'axe de la cham- 
bre obtenue par l'association d'un giroscope et 
d'un niveau pendulaire. Je ne projette pas l'ap- 
pareil, il est photographié dans la notice. 
Monsieur G. DE MASSON D'AUTUME: Je suis 
plutót intéressé par la facon dont les données du 
statoscope vont étre utilisées par la suite. Je vais 
quand-méme dire un mot de la maniére dont 
nous apprécions — je ne dis pas que nous me- 
surons — dont nous apprécions la qualité d'un 
statoscope. Nous prenons une bande comportant 
par exemple une trentaine de photos et nous 
traitons cette bande en aérotriangulation soit 
instrumentale, soit analytique. Ensuite nous com- 
parons les altitudes calculées par enchainement 
aux altitudes telles qu'elles sont données par le 
statoscope. La comparaison de ces deux figures 
indique immédiatement quelle valeur il faut at- 
tribuer au statoscope. Un calcul plus précis — 
étant donné qu'on connait les erreurs probables 
de convergence ou l'erreur quadratique moyen- 
ne de convergence permet d'en déduire l'erreur 
quadratique moyenne de l'altitude statoscopi- 
que. Cette erreur, avec le statoscope à l'I G N, 
s'est révélée étre comprise entre 1 m et 2 m. 
C'est tout. 
Mr F. L. CORTEN: Thank you very much Mr 
Masson D’Autume. Has anyone from the floor 
anything to say? 
Mr J. A. EDEN: With regard to the statos- 
cope, it is not perhaps realised to what extent 
the statoscope can be used for levelling a model. 
If you take two aerial photographs they may 
be put in a relative orientation with each other, 
and then if we know the base inclination the 
model may be levelled in the fore and aft di- 
rection. The statoscope only gives you height 
with respect to the constant pressure surface, 
but the application of the Henry correction to 
the constant pressure surface gives you very 
good horizontal datum. Therefore, if after put- 
ting a couple of photographs in relative orien- 
tation you incline the air base according to the 
difference of level indicated by the statoscope, 
you can level the model in the fore and aft di- 
rection. Similarly, in the lateral direction by in- 
direct methods, by use of tie strips, you can le- 
vel the model in the lateral direction also. Of 
course, this does not give you heights on the 
ground by any means, and you must come down 
from your elevated station to the ground in or- 
der to get the heights. There you want to know 
the scale of the model in order to know how 
far to come down. That you can get from the 
radar depth measurements, or clearance. How- 
ever, the point that I think is rather overlooked 
in some applications of the A P R is that it is 
not necessary to come down in order to level 
the model up at the top, and you can level the 
model up at the top from a statoscope. That 
puts rather a different slant I think on the A P R, 
because the use of the radar then is concerned 
with the scale. As you go on down the strip you 
will get a scale error, and you must know the 
scale in order to know how much to come down 
from the elevated horizontal to the ground. 
Therefore, you require occasional measurements 
down to the ground of clearance of the radar 
in order to prevent the scale error from accu- 
mulating. But you do not require it necessarily 
in order to level the photograph. Therefore, you 
may use a statoscope to obtain this level. 
Mr. T. J. BLACHUT: In addition to what has 
been said about the use of A P R, I would like 
to say that there is also one field of application 
of the Doppler, because for the reduction of the 
A P R data it is necessary to reduce the obser- 
vation to the isobaric surface and we must in- 
troduce corrections which require knowledge 
of the drift. Doppler can be used in a simple 
way to determine the changes in the drift angle. 
You may be interested to know that in Ca- 
nada we carried out some limited investigations 
on the accuracy of Doppler in view of its direct 
use for mapping purposes, and we found that 
air bases can be determined with quite high de- 
grees of accuracy. We reached figures of about 
four per mile of the air base, so it is quite good. 
However, as you realise, the Doppler system is 
a sort of integration system which accumulates 
errors. As a result, over the longer distances 
the errors would accumulate. We find, for in- 
stance, that over the distances of the order of 
120 kilometres, or so, the errors in distances 
amounted to up to 200 metres. Comparing with 
that the A P R, which also can be used for the 
same [ 
ten tin 
there ©: 
thods, 
think t 
as far 
cerned 
tion of 
I de 
the ap 
direct 
would 
Eden. 
Hei 
bemer 
Radar 
Hôhen 
nierter 
punkt. 
gedess 
einem 
eingest 
kannte 
hóheni 
Boden 
die M: 
aber a 
man e 
bei de 
Fehler 
Profil 
mal w 
filgerä 
Gelän( 
gen d 
Messb 
die a 
kann 
tion di 
oder c 
Radar 
sentlic 
Einba 
Bezug 
Mr 
otherw 
about 
system 
from 1 
NOW — 
flight 
practi 
must » 
Th 
lem c