Using Satellite-Based Geotech Reports to Track Land Subsidence

Gaining 10-year historical land movement insights in New Zealand via InSAR Satellite.

If you're tackling ground stability head‑on as an engineer, landowner, or decision‑maker... you've likely used conventional tools like level‑surveys, monitoring wells, GNSS benchmarks, extensometers etc.

The biggest limitatioin is that geotechs can only report on what they see now. Historical data has tradionally limited, but InSAR satellite data is now available in New Zealand (With Avant).

A rural home in New Zealand sits precariously close to a large erosion scar.

What Satellite-Based Geotech Reporting Techniques Deliver

1. Rich historical context at scale

• Archival SAR records: Lets you reconstruct decades of land movement. In NZ, historical InSAR maps highlight subtle coastal or geothermal subsidence dating back to 2003–2011.

  
  

• Time‑series analysis frameworks like SBAS-InSAR and PS-InSAR extract consistent motion trends over large areas, offering full spatial coverage—not just at discrete instrument points. They routinely reveal subsidence/uplift rates in the  ±mm–cm per annum range.

  
  

2. Robust accuracy & cross‑validation

• Benchmarks comparing satellite results against GNSS, ground‑levelling and geotechnical models often show close agreement (e.g. R² ~0.77). Average subsidence rates around 3–4 cm/year were similarly recorded in ground models vs InSAR outputs.

A geotech engineer surveys an active property development construction site in New Zealand, monitoring land stability before foundation work begins.

3. Environmental & subsurface correlation analysis

• Integration with meteorological, hydrological, soil moisture and geological datasets allows identification of drivers. Deep learning (eg LSTM‑TCN) models fuse environmental factors to improve subsidence forecasting, identifying seasonal or climatic triggers.

  
  

• GNSS-reflectometry and thermal infrared sensors further support soil moisture and freeze–thaw assessment, revealing mechanisms behind deformation.

Why InSAR Boosts Traditional Methods

Challenge	Traditional Approach	Satellite Advantage
Tracking historical subsidence	Benchmarks/levelling limited in spatial and temporal density	Comprehensive historical InSAR record (2000s to now) covers all ground with mm precision
Scaling monitoring	Labour‑intensive sensor placement	Wall‑to‑wall satellite coverage enables city‑wide or regional studies
Capturing slow/seasonal trends	Gaps between periodic visits	Weekly revisit captures slow seasonal deformation cycles
Comprehensive insight	Geo-instruments detect only local conditions	Combines surface motion, groundwater drawdown, precipitation, soil volume signals

A New Zealand geotechnical engineer reviewing InSAR satellite data to identify historical land subsidence patterns across rural terrain.

How to Integrate Satellites into Geotech Programmes

1. Baseline assessment

   • Use Sentinel‑1 SBAS to map subsidence/uplift rates across your project area.

   • Compare with ground benchmarks or GNSS – re‑anchor any discrepancies.

     
     

2. Ongoing monitoring

   • Set up a cadence—quarterly, monthly or event‑triggered (e.g. after heavy rain or extra pumping).

   • Identify hotspots of localized deformation early.

     
     

3. Driver analysis

   • Overlay soil moisture/precipitation and groundwater data to detect correlations.

   • Use advanced models (LSTM‑TCN) to forecast hot‑spots based on environmental trends.

     
     

4. Targeted ground investigations

   • Let satellite maps inform where to drill extensometers or densify monitoring.

   • Refining geotech models with satellite-identified anomalies improves predictive strength.

Avant is New Zealand's leading provider of InSAR satellite geotech reports to both the residential and B2B markets. Speak to our technical team to discuss your next project. - The team at AVANT