At 3vGeomatics, part of Orica Digital Solutions’ Geosolutions portfolio, we believe informed decisions start with understanding the limits of your tools.
InSAR (Interferometric Synthetic Aperture Radar) is a powerful technology for monitoring ground movement; however, like any tool, it has nuances that can impact accuracy and reliability.
Here we break down 14 common InSAR pitfalls (“gotchas”) and how to avoid them:
- Sensitivity & underestimation.
InSAR provides 1D line measurements along a specific line of sight. The direction of ground displacement will rarely coincide with this line of sight and InSAR will therefore commonly underestimate the total displacement magnitude.
Solution: Monitor from two perspectives, which increases coverage, provides displacement direction and reduces underestimation.
- Phase ambiguity.
Ground-based radars suffer from this speed limit issue; they ‘run out of room’ in their wavelength, analogous to a clock reaching midnight and going back to zero. This issue does not exist for satellite InSAR because data is analysed spatially during post-processing; a luxury not currently available to a real-time ground-based radar. Assuming modern processing techniques (see also 8), the wavelength can be far exceeded by counting the phase cycles as the displacement intensifies across an area.
- Phase aliasing.
This is the real speed limit for satellite InSAR. When the phase cycles mentioned above are too close together, they can no longer be counted. This is analogous to contour lines on a map getting too close together once the ground is sufficiently steep.
Solution: More frequent data or a longer wavelength.
- InSAR doesn’t measure height well.
Unlike LiDAR, InSAR measurements only work when the ground is undisturbed. Excavation, dumping and blasting all ruin this consistency and InSAR is blind to these events.
Solution: Use LiDAR to monitor height change, but don’t expect InSAR-level precision.
- InSAR in Mining.
In addition to 4, mining activity is not a friend of InSAR. However, when the ground surface is disturbed, some InSAR approaches can recover as soon as the activity moves on.
Solution: Use a provider that supports ‘Non-Persistent Scatterers’.
- Precision, not accuracy.
InSAR can offer millimetre precision (a measure of repeatability), but due to issues caused by 1, 3, and 4, InSAR may often not be accurate (a measure of truth). Luckily, gGeotechs mostly use InSAR to track trends though, which precise measurements excel at.
- Uncertainty.
There is no agreed-upon method for estimating InSAR uncertainty, and approaches vary from ignoring the issue completely to sophisticated modelling of the signal-to-noise ratio. Be sure to challenge providers about their approach to handling uncertainty.
Solution: Use well-established InSAR providers.
- Not all InSAR is the same.
The InSAR industry is unregulated and prone to wild claims from enthusiastic beginners. Pay attention to:
– Processing techniques and which scatterer types are supported.
– How quickly results are delivered after an image.
– How consistent the service is.
– How responsive the service is.
Solution: Use well-established InSAR providers.
- Data Quantity.
InSAR processing involves complex modelling in order to remove unwanted effects and isolate displacement. 15 images are is typically the minimum number of images needed to estimate full-time series-based InSAR results.
Solution: Budget for more data than you think you need.
- Early Detection, not Critical Monitoring.
InSAR images are acquired every few days, and results have a delivery lag of hours to days, depending on the provider. Safety-critical alerting is not applicable for this type of data.
Solution: Consider InSAR a strategic tool that informs decisions about what to do with more tactical, critical monitoring tools.
- InSAR Displacement Direction.
Given either ascending (flying north, looking east) or descending (flying south, looking west) data, a single line of sight displacement map can be produced. Given both, in addition to the two line-of-sight maps, an up-down and an east-west map can also be produced. Some vendors may also go further and produce a total magnitude map and a direction layer, which maps the solved direction for each pixel. Because most SAR satellites fly almost exclusively pole to pole, this makes them insensitive to horizontal north-south displacement.
Solution: A new generation of recently launched inclined orbit satellites makes full 3D InSAR possible; this will require a third footprint over a site.
- Vegetation.
This creates extra uncertainty at best and complete noise at worst for standard SAR data in the X and C radar bands.
Key factors: The lushness, size and density of the vegetation.
Solution: Longer-wavelength data in the L-band circumvents this issue, albeit at the expense of some measurement precision (L-band can achieve cm precision, whereas X and C can achieve mm precision). NISAR, launched in October 2025, will provide free, global coverage of L-band data.
Use cases for L-band: closed vegetated sites, forested geohazards that could threaten site access, and very fast displacement (longer wavelength data has a higher speed limit).
- Looking back.
Historical SAR data exists for every site, dating back to 2015 or 2016. Data is patchier prior to that, but still often available. Use cases: historic baseline assessments, past incident investigations, long-term dewatering displacement analyses, and InSAR baseline data for initiating immediate monitoring (see also 9).
- Snow.
Sites that have a reliable and persistent snow season are often not monitorable during these periods and users may choose to pause InSAR each winter.
Key factors include temperature, available sunlight, slope aspect, latitude, altitude, and snow depth. These factors affect how the snowpack changes between images; therefore, InSAR can still be effective even when the snowpack is not changing. Low-precipitation Arctic sites and/or high-altitude sites may be monitorable year-round.
Solution: For intermittent snow, sites that receive occasional snow will retain much more coverage if Non-Persistent Scatterers are supported by the vendor (see also Section 5).
Speak to a 3vGeomatics expert today.
