Jökull - 01.12.1973, Side 7

thermal emission (geothermal or volcanic) re-
mains to be determined. It is interesting, of
course, to consider why the ERTS-1 image re-
veals so much detail in comparison with avail-
able aerial photography. The main reason is
the low illumination angle, less intense bright-
ness of the ice and snow because of the re-
sponse of the detector on the multispectral
scanner, and the synoptic or regional view af-
forded by the image. By comparison, the avail-
able aerial photography covers only a small
area within each frame. Much of the aerial
photography of Vatnajökull has been acquired
in August when snow cover is at a minimum,
but when solar illumination is still high. Also,
much of the aerial photography is concentrat-
ed on the margins of the icecap rather than in
the interior areas. Because of the high reflec-
tivity of the ice and snow during the summer
months the aerial photography, in many cases,
tends to be overexposed with respect to details
tn the snow and ice. Because of the lack of
contrast in the snow-covered surface, many of
the flight lines for the ca. 1960, Air Force aerial
photography extend onto the icecap but then
stop prematurely. Therefore, many parts of
Vatnajökull were never photographed at all
during that series of aerial survey missions.
The ERTS-l image of Vatnajökull gives us a
view of the surface of the icecap which has
never before been seen.
Beyond the present margins of Vatnajökull
are a number of interesting features related to
past positions of Vatnajökull and Hofsjökull
outlet glaciers. Recessional moraines are well
displayed in front of several outlet glaciers of
Vatnajökull: Svínafellsjökull, Skeidarárjökull,
and Sídujökull.The beautiful little outlet glacier
east of Hjartarfell and south of Arnarfell hid
mikla, on the southeast side of the Hofsjökull
^cecap, has a striking series of concentric re-
cessional moraines. Large medial moraines
wtthin the icecap proper also show up well
under the low sun angle. Particularly promi-
nent are the medial moraines of Vedurárrönd,
the two smaller moraines north-northeast of it,
and the medial moraine on the eastern side of
fyngjujökull.
Perhaps the most striking and impressive
aspect of the ERTS-1 image is the regional
portrayal of geologic structure, glaciological
features, volcanic landforms, and particularly
those large structural and volcanic features
which are partly or wholly buried under the
glacial ice of Vatnajökull. An analysis of these
features is the subject of the following article.
REFEREN CES
Eythorsson, Jón, and Sigtryggsson, Hlynur. 1971:
The climate and weather of Iceland: in
The Zoology of Iceland, v. 1, pt. 3, 1—62.
Pálmadóttir, E. 1973a: Islenzkar rannsóknir úr
gervilinetti. Morgunblaðið, 14. febr. 1973,
p. 3.
— 1973b: Gervitungl og gróður. Morgunblað-
ið, 18. marz 1973, 1—3.
Williams, R. S., Jr. 1972: Satellite geological
and geophysical remote sensing of Iceland:
in Proc. Eight Intl. Symp. on Remote Sens-
ing of Environment, Univ. of Mich., Ann
Arbor, Mich., 1465-1466.
Williams, R. S., Agúst Böðvarsson, Sturla Frið-
riksson, Guðmundur Pálmason, Sigurjón
Rist, Hlynur Sigtryggsson, Sigurður Þórar-
insson, and Ingvi Þorsteinsson. 1973: Satel-
lite geological and geophysical remote sens-
ing of Iceland — preliminary results from
analysis of MSS imagery: in Proc. of Symp.
on Significant Results from ERTS-1, NASA,
317-327.
ÁGRIP
MYND AF VATNAJÖKLI
TEKIN AF GERVIHNETTINUM ERTS-1
31. JANÚAR 1973
Hinn 23. júlí 1972 lét bandaríska geimferða-
stofnunin NASA skjóta á loft gervihnetti, sem
hlaut heitið ERTS-1, en ERTS er skammstöf-
un fyrir Earth Resources Technology Satellite.
Gervihnöttur þessi er sem sé eingöngu ætlaður
til vísindalegra rannsókna og myndir þær, er
hann tekur, getur hver sem er fengið með
kostnaðarverði; hérlendis hjá Landmælingum
Islands.
ERTST fer umhverfis jörðina á 103 mínút-
um (14 sinnum á sólarhring) í 920 km fjar-
lægð, og er braut hans næstum frá norðri til
JÖKULL 23. ÁR 5