Jökull - 01.12.1983, Síða 9

Fig. 2. Oblique aerial photo-
graph looking south across
the terminus of the surging
glacier, Eyjabakkajökull, as
it appeared on July 25, 1973,
after it had completed a 2.8-
km surge. Photograph by
Richard S. Williams, Jr.
Mynd 2. Eyjabakkajoku.il í lok
hlaups, 25. júlí 1973. Ljósm.
R. S. Williams.
beam vidicon (RBV) images have a similar pixel
resolution, but the Landsat 3 RBV image has a
pixel resolution ofabout 30 m.
Aerial photographs and satellite images of glaci-
ers are considerably more useful than conventional
maps to glaciologists because: (1) they represent
original source material; (2) they are acquired on a
specific date at a specific time, important in studies
of dynamics of glaciers; and (3) they portray con-
siderable detail of areas peripheral to glaciers. Most
maps lack those attributes needed for glaciological
studies. In addition, aerial photographs of Ice-
landic glaciers, unlike Landsat images, can be used
for stereoscopic analysis of glaciological features.
Although aerial photographs provide considerable
detail for most of the glaciers of Iceland, they are
generally only available for 1944-45 and for 1959-
60, the two times of comprehensive aerial surveys.
Supplementary coverage is available of parts of
some glaciers from subsequent aerial surveys by the
Icelandic Geodetic Survey. Landsat images, how-
ever, are readily available to all scientists and
provide a sequential (time-lapse) view of the
glaciers of Iceland. The dynamic aspects of these
glaciers can also be inferred from changes noted on
successive Landsat images (within the resolution
limitations of such images).
The limitation in using aerial photographs to
produce a map of a large ice cap, such as Vatna-
jökull, is in the discontinuous nature of the source
material. Nearly all existing maps of Vatnajökull
are ”composites” ofa variety ofsource material and
do not represent the entire ice cap as it was at a
single time (except for the two U.S. Geological
Survey Landsat image maps (1976 and 1977)). For
an ice cap as dynamic as Vatnajökull, published
line maps have serious deficiencies not only in the
pxtrtrayal of the ice cap margins but in the depiction
of proglacial lakes and surficial changes caused by
subglacial volcanic and geothermal activity.
SATELLITE IMAGERY OF ICELAND
Three types of civilian satellite imagery currently
exist of Iceland. The National Oceanic and At-
mospheric Administration (NOAA) series ofpolar-
orbiting weather satellites image Iceland daily with
a maximum resolution ofabout 1 km, too coarse for
most types of glaciological studies (Williams et al.
1974). During August 1978, The Seasat synthetic
aperture radar (SAR) instrument imaged most of
Iceland except for the south-west comer (Ford et al.
1980). It is the Landsat series ofsatellites, however,
which has produced the most useful, albeit dis-
continuous, coverage of Iceland and its glaciers for
the past 10 years, from 1972 to 1982.* (Wiltiamsetal.
1974; Williams and Thorarinsson 1974).
* Gylfi Már Gudbergsson, Department of Geosciences, University
of Iceland, and the author (Williams) are presently compiiing an
„Index to Landsat Images of Iceland: 1972-82.” The index will list
images archived in the United States, Canada and Italy.
JÖKULL 33. ÁR 7