Jökull - 01.12.1973, Blaðsíða 4

images of Iceland will find their way into the
science curricula of different grade levels.
METHOD OF DATA ACQUISITION
The ERTS-1 satellite circles the earth every
103 minutes (14 times each day) in a near polar
(up to 80° N and S latitudes), circular orbit,
920 km above the Earth’s surface. From this
altitude the satellite sensors acquire global in-
formation on agriculture and forest resources,
mineral and land resources, water resources,
marine resources, land use, and environmental
quality and ecology. The experiment in Ice-
land (Williams, 1972) is but one of 327 experi-
ments currently being directly supported by the
National Aeronautics and Space Administration
under the ERTS-1 program.
Eaclt ERTS-1 orbit acquires imagery from
north to south, encompasses a swath 185 km
wide, and crosses the equator at 0942 hrs. local
time. Preceding and succeeding passes overlap
each other (more so at higher latitudes than at
the equator) and after 18 days or about 252
passes the satellite returns to the same position.
That is, the entire globe is covered repeatedly
on 18-day cycles. At the latitude of Iceland,
the satellite passes by about 12 noon or slightly
thereafter universal time. The sidelap of succes-
sive orbits is such that each point in Iceland
can be imaged 3 days in a row. In fact, in every
18-day period, the satellite takes 10 days (10
orbits) to move from east (Gerpir) to west
(Látrabjarg) across Iceland.
The multispectral scanner (MSS) lias been
used to acquire all of the satellite imagery of
Iceland. MSS imagery is acquired in four
spectral bands: green (500 to 600 nm), red (600
to 700 nm), and two bands in the near-infra-
red (700 to 800 nm and 800 to 1100 nm).
Images from each band can be studied separ-
ately or combined in various ways. For ex-
ample, the green, red, and one of the near-
infrared bands can be combined into a “false-
color composite’’, a most useful color image for
studying vegetation distribution, type, and
vigor (Pálmadóttir, 1973b).
The satellite is equipped with two wide-band
video tape recorders to record imagery of areas
outside the range of U.S. ground stations for
later playback. One tape recorder, however,
2 JÖKULL 23. ÁR
failed soon after launch, and the second tape
recorder has seen more limited use since late
March 1973, when an electronic malfunction
occurred. The three return-beam vidicon cam-
eras, because of a malfunction, saw only limited
use in the first few weeks. This system has not
been used since then.
Another part of the ERTS-1 satellite is the
data collection system (DCS). It serves as a
relay between remote, unattended, instrument-
ed ground platforms and NASA ground stations.
Two types of platforms have been used in Ice-
land, one to measure the number of small
earthquakes on the Reykjanes Peninsula, the
other to measure heat flow by thermistors on the
Surtsey volcano. Future use in Iceland’s hydro-
meteorological network also appears probable.
ERTS-1 imagery of Iceland is available at
nominal cost from either of two sources: Land-
mælingar Islands, Laugavegi 178, Reykjavík,
Iceland, or from the EROS Data Center, Sioux
Falls, South Dakota 57198. Scientists or the
general public should contact either of these
organizations for further information.
VATNAJÖKULL IMAGE
On 31 January 1973, the ERTS-1 satellite,
during a northeast to southwest pass over Ice-
land, acquired a 185 km image of the Vatna-
jökull area (Fig. 1) when much of the area was
unobscured by clouds. The image was acquired
at 1208 hrs. local Icelandic time (same as uni-
versal time), when the angle of the sun above
the horizon was only 7°. Also, except for the
coastal and glacial outwash plains, Skeidarár-
sandur, Brunasandur, and Medallandssandur,
all of the area encompassed by the image is
snow-covered.
The snow cover, when combined with the
low sun angle, markedly enhances the glacio-
logical and topographic features within Vatna-
jökull as well as in the terrain and other
glaciers adjacent to the icecap. Clouds obscure
the Mýrdalsjökull and Torfajökull areas, some
of tlie area west-northwest and northeast of
Tungnafellsjökull, part of the area north of
Dyngjujökull (the summit of Trölladyngja is
poking through the clouds), part of the area
north of Kverkfjöll, the northeastern part of
Vatnajökull (Brúarjökull, Eyjabakkajökull, etc.),