InSAR in Colombia: when it helps monitor subsidence

InSAR helps identify ground-deformation patterns over time and prioritise inspections when surface conditions, satellite geometry and image availability provide an interpretable signal. It does not establish the cause of movement by itself or replace levelling, GNSS, geotechnical work or field verification.

The European Space Agency's Copernicus Sentinel-1 mission uses synthetic aperture radar, which can observe day or night and through clouds. InSAR compares the phase of compatible acquisitions to estimate change along the sensor's line of sight. That definition sets an essential limit: the result is not automatically vertical displacement or a complete three-dimensional vector.

Begin with a measurable question

Avoid requesting a “subsidence map” without a period, area and decision. An operational question might be: is there a persistent signal near a corridor that justifies inspection? Define the relevant velocity or magnitude, minimum extent, review frequency and independent evidence available for comparison.

Feasibility depends on:

• scene coverage and temporal continuity;
• movement orientation relative to the line of sight;
• vegetation, water or rapid surface change that reduces coherence;
• terrain and radar shadow;
• stability of the reference point or area;
• expected magnitude relative to noise and method.

If these conditions are weak, the honest pilot result may be that InSAR is not suitable for the question.

Do not confuse a signal with its cause

Atmosphere, orbit errors, reference changes and coherence loss can produce apparent patterns. Review quality masks, temporal persistence and spatial consistency. Where feasible, compare ascending and descending tracks and independent measurements.

A trend near a mine, construction site or aquifer does not demonstrate causality. Connect the series to geology, operations, precipitation, extraction, works and field observations. Record hypotheses separately from confirmed facts.

Deliver an explainable inspection queue

An operational product includes a scene inventory, method and version, reference, quality masks, time series, attention areas and uncertainty. Each alert should explain persistence, magnitude and priority. Symbology should not hide temporal gaps or areas without enough coherence.

GIS for risk management can connect these signals to assets, events and visits. Every series retains its cutoff and is not silently blended with results from another processing method.

Use a pilot before expanding coverage

Choose an area representative of the expected phenomenon and with some independent evidence. Test whether the series is repeatable and changes an inspection decision. GeoSAT's InSAR subsidence-monitoring assessment can structure this pilot. It does not guarantee detection of all movement, attribution of a cause, prediction of failure or replacement of responsible specialists' judgement.