One of InSAR's most powerful features is that it can look back in time. Satellite radar archives go back to the early 1990s, so it is often possible to measure how the ground moved years before anyone started monitoring an asset. That history can be invaluable for understanding long-term trends, setting baselines and answering questions about when movement began.
The start of the satellite record
ESA's ERS-1 satellite launched in July 1991, followed by ERS-2 in 1995. Their radar observations helped establish satellite interferometry as a practical technique. ESA's ERS mission overview documents those missions, and later satellites such as Envisat, TerraSAR-X and Sentinel-1 added further periods and capabilities.
What makes an archive usable
To build a time series, a satellite must have imaged the site repeatedly from suitable geometries, and the images must contain usable phase information. Differences in orbit, wavelength and imaging mode between satellite generations are handled during processing. Buildings and rock usually provide excellent historical reflectors, while forests and earthworks are more variable.
For a construction project, a historical record can show whether movement existed before work began. For an abandoned mine, even intermittent imagery can provide valuable context about how the area has behaved over decades.
How to scope a historical study
A good request states the asset boundary, the earliest relevant event, the suspected movement mechanism and the minimum useful timescale. SkyGeo then reviews which observations exist, which points can be measured, how the time series is referenced and how quality varies across satellite generations.
Historical monitoring is especially useful in civil engineering and energy, where knowing when movement began can shape the engineering interpretation. See also our guide to establishing a pre-construction baseline.
Frequently asked questions
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In many places, yes, where suitable archived radar observations exist. Some locations have later or less frequent coverage.
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Often, with careful harmonization and uncertainty analysis by experienced analysts.
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It can show when surface movement started, which is valuable evidence. Establishing damage and its cause also requires structural and site evidence.
Discover what the archive holds for your site
SkyGeo can check how far back reliable data goes for your assets. Contact SkyGeo.
