"Strezhen" - axis of flow channel) visually illustrate 
direction and velocity of ice movement at given 
glacier areas (Fig. 4). 
Drawing strezhinels is based on the preliminary 
constructed vector field. Beginning from the first 
point selected by operator vectors interpolation and 
automated drawing double line are made. Width of 
the double line is proportional to vector length in 
that point. Moving along flow motion with given step 
a double line of variable width is drawn, that visually 
describes the direction and speed of the 
flow.Velocity vectors and strezhinels are displayed 
on the monitor screen in given scales. A printer may 
be used for imagery printing. 
A stereoscopic model constructed with the help of 
simultaneous photos permits us to obtain 
morphometric parameters of the object of interest, 
for example, to draw profiles, to determine slopes, 
to represent glacier surface in  stereoscopic 
projection, and so on. It is to be noted, for said 
goals high precision exterior model orientation is not 
necessary. 
Accuracy estimation and conclusion 
All measurements carried out at different parts of 
pulsing glacier Medvezhy and at inaccessible icefall 
with height more than 4000m, in particular, have 
confirmed the high efficiency of the method. 
Comparison of two versions of the reported method 
was made to estimate accuracy obtained from 
photoprint measurement results. The first version is 
measurement of negatives on a high precision 
stereocomparator. According lo previous 
investigations the accuracy of this method equal to 
0.02 mm in the scale of the photo. The second 
version is measurement of scanned photo prints at 
the monitor screen. 
in both cases, velocity vectors were measured in 
fact at the same points. Results of comparison have 
shown that discrepancies, as a rule, do not exceed 
a value of 0.04 mm in the scale of the 
photogram.They agree to one pixel for given 
resolution. If we accept that error in the glacier 
velocity calculation does not exceed 10%, the 
method could be considered as reliable when ice 
shift value for period between two aerial surveyings 
is not less than 0.4 mm in the scale of the photos 
when contact photoprints were used. 
Produced experiments allow us to make the 
following conclusions: 
1. Based upon developed technique it is possible to 
carry out aerial photo measurements for studying 
302 
glacier movement and its morphometry using 
contact photoprints from negatives and using 
relatively cheap and widely used equipment without 
expensive photogrammetric working stations. 
2. |t is possible to make  stereoscopic 
measurements on unsynchronized photos with 
sufficient success, however, when glacier has to be 
processed high quality of pseudo-stereoscopic 
effect is provided only with rather small time 
intervals between different surveyings. One-two 
weeks interval may be considered as optimal. To 
carry out aerial surveying at the same time of the 
day, with similar parameters of flight is a very 
important factor. 
  
= 2 9 
! | 4 : 
qe > Ge e 2 : 2 3 e 
oe $4 7 o 
à $ Ÿ 9 9 
Oo oe o o e 
ir ez Gee e 
Sater or m un men pga 
A EU EVER 3 9 
Ba 
UAE dk i og in. 
a. " e es 
&s 
+ d— eo dil. alm 2. $e v 
4 9 — dm fe 
d e ^ 
el au M v Beh e 
deoa te 
A e. AS, o 
. & «uw M 
Pt ~~ A. a, a 
& 
Sv Bs ~ S a, & > à 
A TN 2 5 9, * % 
N & 
3 x 1 & 2 
ii 
1 X & 
¢ 4 5 
T" $ 
Lory UE 
0 5 m/day ? 
| La tad H <Q 
  
  
  
Fig.3. Vectors of the ice movement surficial velocity 
according to icefall part shown at Fig.2. Vectors 
scale in meter /day is shown. 
References: 
Crippen Robert E. 1992 Episodes. Measurement of 
subresolution terrain displacement using SPOT 
panchromatic imagery. 15, Ne1. 56-61. 
Finsterwalder R. 1958. Measurement of ice velocity 
by air photogrammetry. Publ. Assoc. Internat. 
Hydrol. Scient. Ne47 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996