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![]() February 20, 2004 Ancient Desert Markings Imaged from OrbitVisible from ESA’s Proba spacecraft 600
kilometers (km) away in space are the largest of
the many Nasca Lines; ancient desert markings now
at risk from human encroachment as well as flood
events feared to be increasing in frequency. They were made simply enough, by moving dark
surface stones to expose pale sand beneath.
However their intended purpose remains a mystery.
It has variously been proposed they were created
as pathways for religious processions and
ceremonies, an astronomical observatory or a
guide to underground water resources. In this image, acquired by the Compact High
Resolution Imaging Spectrometer (CHRIS)
instrument aboard Proba on 26 September 2003, the
18.6 meter resolution is too low to make out the
animal figures although the straight Nasca Lines
can be seen faintly. Clearest of the straight
markings is actually the Pan-American Highway,
built right through the region seen as a dark
marking starting at the irrigated fields beside
the Ingenio River, running from near the image
top to the bottom right hand corner. Associated
dirt track roads are also visible amidst the
Nasca Lines. A team from Edinburgh University and remote
sensing company Vexcel UK has been using data
from another ESA spacecraft to measure damage to
the Nasca Lines, with their results due to be
published in the May Issue of the International
Journal of Remote Sensing. Nicholas Walker of Vexcel UK explained:
“Although the instrument lacks sufficient
resolution to unambiguously distinguish
individual lines and shapes, by combining two
satellite images using a technique known as SAR
interferometric coherence it is possible to
detect erosion and changes to the surface at the
scale of centimeters.” “Some de-correlation comes simply from
the geometry of the area as seen by the
instrument in space, with low coherence around
areas overshadowed by Andean foothills to the
east of the Nasca plain,” said Iain
Woodhouse of Edinburgh University. “The
second major loss is seen in the river valleys,
due primarily to agricultural activity taking
place during the two-year period. The de-correlation observed is most likely
caused by vehicles displacing stones along these
tracks and the sides of the Pan-American Highway.
The de-correlation from the run-off is distinct
from this as it follows the characteristic
drainage patterns down from the foothills. ### Frdric Le Gall This text derived from http://www.esa.int/export/esaSA/SEMO0R1PGQD_earth_0.html Recommend this Article to a Friend Back to: News |
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