Discussion 
Prof. Dr. Konchine: In USSR, by using the radio-altimeter RWTD, it is not the 
clearance, but the shortest distance D from the air plane to the ground which 
is measured. Then the pictures of the terrain are put in a stereometer which has 
an additional device: the parralactic grids. When observing the stereomodel, the 
observer views a spatial sphere. He puts this sphere, first in connection with 
the nearest point of the model and then with the plumb-point. This enables him 
to get corrections (A D) to the readings of the radio-altimeter and to determine 
the flying height: H = D -f- A^. 
Le Prof. Konchine indique que le radio-altimètre ne mesure pas la distance de l’avion au point 
du sol situé à la verticale, mais la distance entre l’avion et le point du sol qui en est le plus 
rapproché. Des réseaux de parallaxe permettent ensuite avec un stéréomètre de déterminer le point 
du sol à la verticale. 
Plus personne ne désirant poser de question au Prof. Dr. Konchine, le Prési 
dent poursuit le débat ouvert la veille sur les communications du Dr. L. E. 
Howlett et de Mr. C. Powell. 
M. F. L. Corten: Mr. Verstelle from the Netherlands Hydrographie Office, 
who is ill at the moment and therefore much regrets not to be able to attend 
the Congress, has asked me to make the following remarks with regard to Mr. Po 
well’s paper on Decca: »1 should like to make my compliments to Mr. Powell 
for his excellent and most interesting paper on the use of Decca. Although I 
agree with practically all of Mr. Powell’s conclusions and suggestions for further 
development, I should like to make a few remarks, because — seen in the light 
of recent experience in tropical New Guinea, not known to him at the time of 
writing his paper — some statements seem to be too pessimistic. 
Unfortunately, part of the analysis of these recent trials has still to be carried 
out, but it is hoped that detailed information can be presented to the forth 
coming U.G.G.I. Congress in Toronto 1957. A few general remarks however 
can be made right now. It is admitted that only limited trials in the air were 
carried out, but the conclusions given hereunder, no doubt, will be valid for 
air survey also. It should also be mentioned that the very latest and improved 
Decca survey equipment was used in New Guinea. 
Para. 3.3, page 7. — The effect of radio noise (very high noise level in New 
Guinea) proved to be much less serious than expected. 
Para. 3.4, page 7. — Without any knowledge of ground conductivity constants 
it proved to be possible to limit effects of anomalies in propagation speeds 
to errors of 1 part in 10.000 for propagation over land and 1 part in 40.000 over 
sea; in both cases these figures proved to be valid up to distances of 235 kilo 
meters, and very likely more than that. 
Para. 3.6, page 8. — The actual standard errors appear to be considerably 
smaller than the value of 0.01 of a lane adopted for the computation of the 
accuracy contours in figures 3, 4 and 5 of Mr. Powell’s paper. 
Para. 3.7, page 8. — The land coverage of the present New Guinea chain is 
of the order of 70.000 sq.km, and from the point of view of electrical conduc 
tivity, the terrain is fairly homogeneous. From the results it appears that the 
multiplication factor for this land coverage is of the order of 1.2 instead of 2.5 
as mentioned by Mr. Powell for similar conditions. This would improve his over 
all accuracy figures by a factor 2. 
Para. 5.14, page 16. — As already mentioned, the multiplication factor under 
favourable conditions appears to be of the order of 1.2, which would represent 
250 feet at the outer contours. It is very likely that an accuracy of this order can 
be obtained over very large portions of the earth. 
Para. 6, page 17—19. — Future developments as described, indeed are very 
promising. It cannot strongly enough be stressed that further trials are necessary 
and should be carried out.