Satellite spies strange stripes in the desert

3 September 1994

The origins of five long parallel lines which have appeared on satellite
images of Western Australia have left geologists scratching their heads.
The lines, which are up to 600 kilometres long and 15 kilometres wide, were
found on images of the Nullarbor Plain, a vast desert that stretches north
from the Great Australian Bight. But they are not supposed to be there.

‘The Nullarbor is supposed to be a featureless expanse,’ says Ian Tapley
of the CSIRO, the Australian national research organisation. ‘We have no
explanation for the lines yet.’

Even more puzzling is that the lines appear only during the day. This
is odd because they have been detected by infrared sensors, which produce
their best images at night. Infrared radiation gives a measure of temperature,
and temperature differences between, say, rock and sand are greatest at
night. During the day, features of the land are uniformly hot, making them
difficult to identify from thermal images. The lines appear to be about
2 °C cooler than the surrounding plain.

The mystery emerged last week in Sydney at a forum on remote sensing.
Ian Barton, from the CSIRO Division of Atmospheric Research in Melbourne,
said the lines were first noticed last month by his colleague Fred Prata.
Barton sent the images for analysis to Tapley’s group at the CSIRO Division
of Exploration and Mining in Perth.


Prata was studying images taken by Europe’s remote-sensing satellite,
ERS-1, over 10 days in October 1992. Since his discovery, the lines have
also been found on thermal images taken on the same days by a weather
satellite operated by the US National Oceanic and Atmospheric Administration.

One possibility is that the lines reveal fault lines in the limestone
that makes up the plain. But, says Tapley, ‘there are no known fault lines
in the area’. He plans to work out the positions of the lines to see if
they can be related to geological features or drainage patterns.

Another explanation being investigated is that the lines are ‘tracks’
left by a storm as it passed over the desert. The storm would have had
to last a long time to have travelled 600 kilometres. But if it had dropped
rain or hail onto the desert, the water could have percolated slowly into
the ground, cooling the surface for the 10 days over which the lines were