PHOTOGRAMMETRIC ENGINEERING
Fic. 7. Close-up photo of a sorted polygon, abt.
4 feet (1.1—1.2 m.) across, in the same area and at
the same level as in Fig. 6. (Taken by the author
July 28, 1957).
portance. Similarly to photo interpretation
having been proven of great value for discov-
ering archaeological secrets, e.g. traces of an-
cient settlements, interpretation of photo-
graphs, showing terrain features, may be use-
ful for revealing areas or patches of perma-
nently frozen ground. Especially at high lati-
tudes many geomorphic features stand out in
beautiful relief as patterned ground (see be-
low). If air photos are taken on suitable days
with favorable light conditions in spring or
perhaps early summer, when the snow cover-
age has been melted and foliage does not con-
ceal the features of the terrain, quite a good
result of a careful analysis of the pictures may
be expected.
Vertical air photos as well as obliques
ought to be taken in both color and black-
and-white. Actually, color photos are often
preferable, especially as obliques. In either
case, the photos must be taken at a scale
which is large enough for studying the
ground details.
The interpretation of air photos should be
supported by field observations and checked,
if possible, by analyzing ground photos, taken
at the same season and which show important
details that are easily recognizable in the air
photos. This is a common experience: the an-
alyzing of both air and ground photos will of-
fer the interpreter the best chances of a good
result.
CLASSIFICATION OF PATTERNED GROUND
As regards classification of patterned
ground there are several fine papers published
in different languages, among others by the
pioneer Bertil Hógbom, Sweden (1914) in his
scientific work (for the degree of Doctor of
Philosophy, Uppsala 1914) on the geo-
logical importance of the ground frost, en-
titled "Über die Geologische Bedeutung des
Frostes." Thirty years later another excellent
work was presented in German by Carl Troll,
Bonn (1944), see below.
In English there is an excellent review pre-
sented by Washburn in 1956 (see references),
entitled “Classification of Patterned Ground
and Review of Suggested Origins." The term
Patterned Ground is introduced by Washburn
as a group term for the more or less sym-
metrical forms, such as circles, polygons, nets,
steps, and stripes, that are characteristic of,
but not necessarily confined to, mantle sub-
ject to intensive frost action (Washburn).
The arrangement by the Washburn-classi-
fication of commonly obvious characteristics
of patterned ground is in the direction of the
increasing gradient. Most circles, nets and
polygons occur on essentially horizontal
ground. Steps and stripes, on the other hand,
are limited to slopes. Further, within these
two main groups of characteristics, patterned
ground can be ascertained by the presence or
absence of obvious sorting between stones and
fines. According to this, Washburn classifies
Circles in (a) Sorted (including debris islands)
and (b) Non-sorted (including peat rings,
tussock rings), Nets in (a) Sorted and
(b) Non-sorted (including earth hummocks),
AA
F16. 8. Sorted polygons on a slight slope causing
an extension of the actual polygon into elongated
features which, in the center of the picture, re-
semble sorted stripes. Murchison Bay, North East
Land, at abt. 130 feet (40 m.) above sea level.
(Photo by the author July 27, 1957.)
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