ON THE EMPLOYMENT OF AERIAL PHOTOGRAPHY
FOR ICE RESEARCH IN THE BALTIC
by Erkki Palosuo
Institute of Marine Research
Helsinki, Finland.
ABSTRACT
In the Baltic aerial photography is used contempor-
aneously with observations made on the ice. The author
presents some investigations of this kind.
Auf der Ostsee Luftbildaufnahme wird gleichzeitig
mit den auf dem Eis gemachten Observationen gebraucht.
Der Verfasser stellt einige solche. Fälle vor.
* * *
Fhotography has been used for over 30 years in con-
nection with aerial ice reconnaissance in the Baltic.
The material obtained is fairly plentiful, and has been
discussed in a number of papers (BUDEL 1943, PALOSUO
1953, ROHDE 1959). It may be said that the primary tar-
gets set for photography have been attained. The pre-
sent paper does not deal with the historical development
of aerial photography or its achievements, but briefly
discusses its future potential uses.
Information on the occurrence of ice is required
both for scientific research and for practical purposes.
The most important of the latter is that of winter
navigation, aerial reconnaissance being primarily
carried out to serve this end. But as regards naviga-
tion, the conditions in the Baltic differ considerably
from those for instance in the Labrador area and in
Arctic waters in general.
Firstly, in the Baltic, ice is only present in the
winter. There are never to be found any old ice floes
of several years standing, or ice-bergs and growlers
calved by glaciers. The basic form of ice in the
Baltic can be said to be level ice that has
formed on the surface of the water during calm cold
weather. Near the coast, this ice is anchored to is-
lands and rocks, and so remains unbroken. This is
termed "landfast-ice", and its extent depends on the
number of islands off the coast. In the course of the
winter it is covered by snow, and offers & poor target
for photography. On the contrary, ice formed in the
open sea will be moved by the wind, and in it many kinds
of mechanical changes occur, including the formation of
lanes, piling up and pressuring. The final result is
a very uneven ice-field, with parts of varying thickness
and of various ages (Fig. 1). Determination of the
varying character of the open sea ice-field is in fact
the most important task of aerial photography.
In spite of the minor inequalities of the ice-field,
the strong ice-breakers of today are capable of getting
through it. Only thick pressured îce ridges, close to
the coast, can obstruct them. For this reason, ice-
breakers usually follow a fairly straight course, though
they benefit from long lanes running parallel with the
coast, or make their w&y round the worst obstacles.
But it is not necessary in the Baltic for them to thread
through growlers and ice-bergs as is required for navi-
gation in Arctic waters.
As far as the Baltic is concerned, therefore, the
maîn objective of reconnaissance flights is that of ob-
taining a general idea of the ice situation without
entering into any great detail. Consequently, maps
drawn in the aircraft with the aid of the naked eye, or
drawings made up by means of optical instruments
(Betin, etc. 1959) are adequate for ice-breakers. Ac-
cordingly, photography which shows more details is not
required in the Baltic area to the extent that it 1s in
the Arctic regions.
Secondly, the ice situation in the Baltic may undergo
quick changes, especially in windy weather. For this
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reason, the results of aerial reconnaissance are passed
on to those interested as quickly as possible. Often
the aircraft is in direct contact by radio with the ice-
breaker. Development of the results of photography is
time-consuming, and imposes certain restrictions on its
employment. This is obviously the most important reason
why, in aerial reconnaissance, photography has a less
established position than is accorded to drawn ice-
situation maps.
Consequently, aerial photography plays its principal
part in scientific research. In practice, the procedure
to date has been that of having the camera in readiness
during the flight, and, if something of interest is seen,
a photograph is taken. After the picture has been de-
veloped it is provided with explanatory notes which in-
dicate the observations made at the moment of exposure,
or later from a study of the picture. This procedure is
useful in that a large number of pictures is taken of a
varied range of objects. It should be borne in mind that
it is usually impossible to predict what the situation
will próve to be. If the opportunity offered by nature
is not taken advantage of, it is possible that another
similar set of circumstances may lie years ahead.
The present ice picture-collections have been arrived
at by classification of the material obtained in this
way, and this may be termed the first objective of
aerial photography. This method should be continued be-
cause situations of & new kind may occur at any time.
The type of photographic equipment, or the kind of film
material which is most satisfactory in use, the altitude
and the best angle for the taking of photographs are
technical questions which I prefer not to discuss in
this connection.
Present-day ice research has, however, progressed
to the study of details which usually cannot be inter-
preted from aerial photographs alone. Aerial photography
must thus be integrated in a plan which normally includes
observations made on the ice itself. If, for example,
the quality of the ice is involved, it is almost essential
to secure ice samples from the sites photographed. How
this can be done in practice is a question to be solved
on the site.
To illustrate the employment of serial photography in
ice research, I will describe two studies now in progress
in Finland. One of these is concerned with the effect
of wind on ice cover. The plan is to take a series of
aerial photographs outwards from the coastline when the
ice cover is fairly level and unbroken. The photography
is repeated after a few days during which the wind has
blown landwards and has pressed the ice against the
coast. The objective is first of all to discover the
amount of rafting in ice fields of different thick-
nesses. Secondly, the breakage figures are traced from
the pictures. Thin snowless ice is pressured, forming
figures shaped like a dovetail (Fig. 2). The shape of
the figure is a result of vibration in the ice. Near
open water, the swell breeks the ice into rectangular
shapes, which further break into smaller pieces (Fig.3).
The average size and the shape of these pieces have been
determined from aerial photographs. Thicker snow-
covered ice, on the other hand, is pressured into ridges
(Fig. 4). Such "stone fences" are visible in pictures
taken in outer sea areas, and they form surprisingly
regular figures. A research programme of this type
necessitates long waits for suitable circumstances, to-
gether with the availability of an aircraft at a moment's
notice. The Institute of Marine Research seldom has
such facilities.
Another topical object of study is that of establish-
ing the extent of the spring thaw. Under the influence
of sunshine and warm weather, melting mainly begins on
