A pre-construction InSAR baseline documents historical ground and building movement before excavation, tunneling, dewatering or other major works begin, often going back years across the entire area of influence. It helps engineers recognize existing trends, plan monitoring around vulnerable assets and establish a reference against which later change can be judged. Attributing later deformation to construction still requires site evidence, engineering analysis and compatible monitoring records.
Set the area of influence early
Start with the proposed works, the likely mechanisms of settlement or heave and the surrounding assets that could be affected. The initial area of interest should cover the expected zone of influence plus a wider area for context. A tight study boundary can hide regional subsidence or movement that predates the project. You can read more about InSAR for civil engineering and infrastructure on SkyGeo's website.
A useful asset list includes buildings, roads, rail lines, utilities, historic structures and any survey control points. Prioritize locations where the consequences could be high or where conventional instruments will be difficult to install.
Reconstruct the history carefully
Historical SAR acquisitions may go back years before the design phase. Review coverage, acquisition frequency, viewing direction, reference points and whether the assets have reliable radar targets. Distinguish a continuous time series from separate periods or datasets processed with different assumptions, and note whether the site has changed through demolition or changes in land cover.
The baseline should identify persistent movement rates, seasonal components, spatial differences and apparent changes in trend. It should also flag structures with insufficient data instead of treating them as stationary.
Compare with engineering surveys
Combine satellite observations with leveling, building condition surveys, geotechnical reports and any existing automated survey instruments. This tests whether the movement is physically plausible and shows which assets need additional pre-construction measurements. Remember that satellite line-of-sight displacement and vertical leveling cannot be compared directly without the right geometric conversion. SkyGeo's research on the reliability of InSAR monitoring of buildings provides related evidence on observing urban structures.
For a historic masonry building, a radar point on the roof can provide valuable context but not a complete picture of the foundation. For an excavation, changes in groundwater or the construction sequence may be important explanations that the satellite does not measure.
Design a baseline that stays useful during the works
Before construction starts, agree on the reference period and method, coordinate conventions, reporting units, quality checks and asset identifiers. Keep an auditable record so future project teams can compare new movement with the same baseline. Define how a change will be assessed and when additional field inspection or more frequent instrumentation will be needed.
The Amsterdam quay wall research examined the reliability of locally optimized PS-InSAR for assessing building deformation and compared it with leveling. It offers relevant evidence for pre-construction monitoring, though coverage and timescale will vary from site to site.
When should the baseline start?
As early as possible in design, before the activities whose influence you need to evaluate. If historical imagery exists, useful retrospective information can sometimes still be recovered after works begin, but its adequacy must be checked rather than assumed.
Frequently asked questions
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Not on its own. It provides strong evidence of detectable movement in the areas and periods observed, but poor coherence, gaps or a short archive limit what can be concluded.
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As early as practical, leaving time to check archive suitability, define the zone of influence and align satellite observations with ground surveys.
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It provides useful context, but major changes to structures or surfaces can alter radar targets and require updated measurement and validation arrangements.
Assess a baseline before works begin
If you are planning excavation or construction near sensitive assets, tell us about the project area and your pre-construction monitoring needs. Contact SkyGeo.
