Persistent scatterer interferometry, usually shortened to PSI, is a family of InSAR time series techniques. It identifies radar targets whose signal stays stable across many satellite images and tracks their movement over time. Instead of relying on a single pair of images, PSI uses the whole stack, which makes it one of the most precise ways to measure slow, subtle ground and structure movement.
What makes a persistent scatterer?
A persistent scatterer might be part of a roof, a metal structure, exposed rock or another stable radar-reflecting feature. What matters is that its signal remains consistent throughout the image stack. The method estimates each point's displacement relative to a reference, while correcting for effects such as atmospheric delay and orbital errors.
The USGS overview of InSAR explains the relationship between radar phase and surface displacement. Moving from single interferograms to time series analysis like PSI is what made InSAR so useful for operational monitoring.
PSI and PSInSAR
"PSInSAR" is often used loosely to describe persistent scatterer methods. Strictly, PSInSAR™ is the trademarked name of one specific proprietary implementation. PSI is the general technical term for the whole family of approaches, and it is the term used in most scientific literature.
What PSI delivers
With a suitable image stack, PSI reveals slow, subtle movement at stable targets with millimeter-scale sensitivity over time. It is particularly effective in cities, along infrastructure and at industrial sites, where stable reflectors are plentiful. Slopes in radar shadow or heavily vegetated areas may need other approaches, such as additional viewing geometries or distributed scatterer methods.
For infrastructure monitoring, PSI results support screening and investigation once they are linked to the right asset and interpreted alongside other measurements. SkyGeo's introduction to InSAR explains how processing is tuned to balance measurement density and quality.
Frequently asked questions
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PSI is one family of time series InSAR methods within the wider field of radar interferometry.
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It is often used informally, but PSInSAR™ is a trademarked name. PSI is the generic technical term.
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Many do, especially in built-up areas. Geometry, target stability, image resolution and acquisition history determine which ones give reliable points.
See PSI in action on your assets
SkyGeo can show what persistent scatterer analysis reveals at your site. Contact SkyGeo.
