Applications of High-Resolution Satellite Imaging

Table of Contents

Finding the Paths
Walk This Way
The Future of Archeology

Rapu Nui


Right from the time Europeans first disembarked on the island in 1722, the gigantic stone statues of Easter Island, which the inhabitants called Rapu Nui, have baffled people. By then, the tale of the 887 statues—or Moai in the Rapa Nui language — had been erased from the collective memory of the Rapu Nui people.

Rapu Nui

Photo Source: Alamy

Why had the ancestors of the islanders invested so much effort on the Moai? These statues are up to 40 feet tall and 75 tonnes in weight, which is the equivalent of 20 medium-sized cars. How had so few people on a distant island — the nearest occupied land, Pitcairn Island with a population of 50 residents, is 2,075 kilometers away — moved the Moai as far as 18 kilometers over rough territory without the help of even large animals?

Rapu Nui

Source: Thor Heyerdahle, Easter Island: The Mystery Solved; 1989

The first question was simple to answer. Polynesian peoples inhabited Rapu Nui sometime between 700 and 1,100 AD. A prevalent belief of the Polynesian culture at that time was that deceased relatives had an influence on the living. These Moai represent ancestors who watched over their descendants, which is why so much effort and significance was devoted to them, and why almost all statues face inland with their backs towards the sea.

Finding the Paths

A conclusive answer to the second question has been difficult to find—and some suggestions have been downright strange, such as the claim that the Moai are the creation of aliens by the once-popular author Erich von Daniken. Other highly questionable theories include the Moai being created on site by the Rapa Nui people molding clay or being catapulted through the air by eruptions at the volcanic stone quarry where they were sculpted.

One of the difficulties that archeologists encountered was that few roads led from the quarry to the ritual platforms, called ahu, where the Moai were put up. It is possible that natural vegetation regrowth and human activity had covered up many of the Moai transport roads because the last of the Moai were carved around five hundred years ago.

In the year 2005, archeologists Terry L. Hunt and P. Lipo from the University of Hawaii intended to try out this hypothesis using panchromatic images captured by the QuickBird commercial satellite over Rapu Nui in December 2001 and February 2002. Panchromatic images are black-and-white photographs that are sensitive to all the wavelengths of visible light.

At about 17 square kilometers, Rapu Nui — one-quarter the size of Manhattan — is very small. This made it easy to scrupulously inspect these satellite images, which cover 85% of the surface of the island at a resolution pixel size of 70 centimeters.

Dr. Hunt and Dr. Lipo were looking for a number of signs of ancient roads — changes in plant life due to compressed soil, patterns of erosion, built-up banks, depressions filled with beds of gravel and soil from seasonal overflowing brooks, and otherwise unaccountable shadows.

Satellite image of ancient road section

Satellite image of ancient road section (A) with circular patterns (6-8 m) visible on the north side (B).

These characteristics appeared on the images as grayscale variations. Supported by field surveys, the images established nearly 32 kilometers of ancient Moai roads extending like spokes from the Rano Raraku quarry to every part of the island. Latest additional image analysis by archeologist Gabriel Wofford, who is also from the University of Hawaii, has ascertained possibly even more ancient roads, although these still need to be substantiated with surveys in the field.

Walk This Way

The system of newly uncovered ancient roads led Dr. Hunt and Dr. Lipo to consider the assertion among the Rapu Nui — passed down for generations — that the Moai had been “walking giants.” The archeologists came up with a method in which small teams use ropes to rock the Moai from side to side, which moves them forward in movements similar to steps. At the same time, a third team behind the Moai keep them from falling backward. The Moai appear to be built for this method of transport — they lean slightly when stood upright, which makes it relatively easy to keep them moving forward.

The Future of Archeology

Space archeologists are specialists who use remote sensing technology and satellite to discover ancient sites or features not noticeable to the naked eye; the University of Hawaii team is part of this expanding section of specialists.

For instance, Dr. Jason Ur, an archeologist at Harvard University, viewed Iraq and with his colleagues narrowed down nearly 1,200 likely sites using images taken by spy satellites in the 1960s. Sarah Parcak, a professor at the University of Alabama at Birmingham, used satellite data to identify possible sites of 1,000 forgotten tombs, 3,100 lost settlements and 17 Egyptian pyramids.

Remote sensing is particularly handy for territories that are perilous for physical exploration or traditional excavations. William Saturno, an assistant professor of archeology at Boston University, and archeologist Damian Evans, who leads the University of Sydney’s Cambodian research base, used space archeology to survey Lingapura, which is the ancient capital of the Angkorian empire in northwestern Cambodia. The Khmer Rouge buried thousands of landmines throughout this site in the 1970s. As this remote sensing technology progresses, so will humans’ understanding of the long forgotten sites.

Teledyne DALSA

This information has been sourced, reviewed and adapted from materials provided by Teledyne DALSA.

For more information on this source, please visit Teledyne DALSA.

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