Source: NASA
Introduction
A sophisticated imaging technique originally developed by engineers at NASA’s Jet Propulsion Laboratory is finding a second life far from the reaches of space exploration. By sharpening contrast in digital photographs, this specialized process—known as decorrelation stretch—is now revealing ancient imagery that has remained hidden in plain sight for centuries.
The NASA technique for manipulating satellite photos now reveals ancient images that were previously dismissed as faded or invisible to the naked eye. From the intricate walls of Cambodia’s Angkor Wat to remote archaeological sites in Norway and Mexico, researchers are utilizing this space-age technology to uncover historical narratives that were once thought lost to time.
What Happened
The application of this technology began in earnest when archaeologists discovered a series of long-forgotten murals within the central tower of the Angkor Wat temple complex. While thousands of tourists walked past these walls daily, the depictions of traditional musical ensembles and horseback riders remained obscured by severe fading.
Between 2010 and 2012, researchers successfully identified these paintings and roughly 200 others throughout the temple grounds by applying the decorrelation stretch method. The algorithm functions by isolating and enhancing color variances within digital files, effectively stripping away the visual "noise" of age and environmental decay to highlight the underlying artistic details.
Background
The origins of this discovery date back to 1996, when Ronald Alley, a researcher at the Jet Propulsion Laboratory, authored a paper regarding the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). This instrument, mounted on NASA’s Terra satellite, was designed to capture high-fidelity Earth imagery. Alley, building on work from a former supervisor who co-invented the decorrelation stretch algorithm, recognized that the technique could extract significantly more data from orbital imagery than standard processing allowed.
The bridge between space exploration and archaeology was built by Jon Harman, a rock art enthusiast and retired professional with a background in medical imaging. Around 2005, Harman observed NASA-released imagery of the Martian surface that had been processed using the algorithm. Recognizing the potential for his own field of study, he utilized his technical expertise to adapt the NASA-derived algorithm into a functional plug-in for ImageJ, an open-source software platform maintained by the National Institutes of Health.
Key Details
The utility of the Dstretch plug-in, as it is now known, has expanded far beyond its initial testing grounds. It has become a vital instrument for historians, anthropologists, and conservators working in diverse environments.
| Feature | Description |
|---|---|
| Algorithm Origin | NASA Jet Propulsion Laboratory (1996) |
| Initial Purpose | Processing ASTER satellite imagery from the Terra satellite |
| Archaeological Adapter | Jon Harman |
| Software Integration | ImageJ (National Institutes of Health) |
| Annual Requests | Approximately 200 |
| Key Application Areas | Rock art, tombs, ancient architecture, and mummified remains |
Impact
The impact of this technology on the field of archaeology has been profound. By providing a non-invasive way to analyze artifacts, researchers can document fragile surfaces without risking physical damage. In addition to its primary use in studying rock art, the technique has been successfully employed to investigate the faded tattoos on ancient mummified remains and to identify the structural foundations of buried Greek buildings.
Harman notes that while the adoption of his tool within the rock art community was expected, the breadth of its secondary applications has been a source of genuine surprise. The ability to clarify imagery in diverse settings—ranging from Egyptian tombs to public parks in Canada—demonstrates the versatility of an algorithm originally intended to study the surface of Mars.
What Happens Next
The demand for this digital tool remains steady, with Harman currently fulfilling approximately 200 requests for the Dstretch plug-in annually. Furthermore, the development of simplified smartphone applications, which began around 2010, has allowed thousands of users to utilize a version of this technology for their own field research.
As academic interest grows, more researchers are publishing papers documenting the efficacy of decorrelation stretch in professional archaeological settings. Moving forward, the continued integration of this NASA-derived technology ensures that experts will have a more robust toolkit for identifying and preserving cultural heritage sites that have been weathered by the elements.
