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What is InSAR?

Interferometric synthetic aperture radar (InSAR) is a satellite remote sensing technology for mapping ground displacement. SAR satellites emit radar pulses towards the Earth’s surface and record the reflections. The data recorded includes the intensity of the reflection, and the phase information for each pixel, measured in radians.

After subsequent images are acquired, pairs of images are processed using the phase component, which reveals ground and infrastructure displacement. Image processing involves differencing the relative phase measurements between images, removing unwanted signals, and converting the result into metric and imperial standard values. The precision of the resulting values is associated with the wavelength chosen for imaging. The intensity portion of the data isn’t used for InSAR processing but can be used for very rapid displacement tracking, beyond the limits of InSAR.

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Benefits of using InSAR:

  • High precision: ability to detect 1–2 mm of displacement per year
  • Large area coverage: images (areas of analysis) that are 1500+ km² each
  • Dense data coverage: typically generate tens of millions of data points per area of interest
  • Remote sensing: no ground instruments or in-person inspections required
  • Full site monitoring: often detects displacement in areas of unknown risk

InSAR Monitoring Considerations

Synthetic aperture radar (SAR) satellites are built for a variety of purposes from measuring sea ice, military applications, agricultural monitoring, ground displacement monitoring, and more. The primary mission of each satellite dictates the characteristics of the radar. Each sensor has different parameters balanced to achieve the ideal observation scenario. These include spatial resolution, wavelength, and revisit time. Typically, resolution has the most impact on pricing. By choosing the right parameters at the outset of a project, a balance between resolution, wavelength, and budget can be achieved.

Spatial Resolution

Spatial resolution dictates the density of measurements in an area. However, high spatial resolution isn’t always necessary for a project. Spatial resolution is inversely proportional to the overall dimensions of the footprint; the higher the resolution, the smaller the area of land covered by the footprint. For large areas of interest, such as counties, municipalities, or provinces, a lower resolution option may be more suitable. Conversely, a higher resolution may be better suited if the asset or overall area of interest is small. For example, pipelines, roadways, and dams may only measure a few metres across. In these cases, higher resolution imagery may be more appropriate.

Wavelength

Unlike spatial resolution, the operating wavelength of each SAR is fixed. Some satellites may carry multiple SAR sensors onboard to offer multiple options. Similar to picking the image resolution, a thoughtfully planned InSAR project includes the selection of the most suitable wavelength. Shorter wavelengths can offer higher displacement precision and vice versa. However, longer wavelength data is more able to penetrate vegetation cover and may offer the only viable monitoring solution. For assets that traverse vegetated areas, such as pipelines and utilities, the longer L-Band wavelength is often recommended. For arid or cleared areas shorter X-Band wavelength is typically chosen. 3vG recommends the shortest wavelength that ground conditions will allow to achieve viable measurements.

Revisit Frequency

The last and equally important parameter to consider is the satellite revisit time. This is the amount of time taken to revisit the same area of interest from the same perspective. A quicker revisit time means more frequent updates, higher temporal resolution in products, and a better chance of detecting risks early. Typically, the revisit time varies from one day to two weeks. Increasingly, satellites operate as a constellation of identical SAR sensors that can decrease the revisit time. As constellations are updated, the revisit time reduces. If ground conditions allow, some clients may opt for less frequent data than the maximum available, which can still provide valuable monitoring but at a lower price.

Multi-Perspective Monitoring

Satellites have the opportunity to acquire data over an area while travelling North and looking East (ascending mode), and while travelling South and looking West (descending mode). Acquiring data from two (or more) perspectives provides several advantages, most importantly better coverage, especially for sites with significant topography. Other advantages include an independent check, denser time series, more accurate displacement magnitudes, and the opportunity to determine the direction of displacement.

If a single footprint is used, measurements, and resulting InSAR products, remain in the satellite’s line-of-sight (LOS). While this can provide good value, many areas may be obscured from view. For example, only half of a circular mining pit will be visible from a single perspective. In almost all cases, 3vG recommends multi-perspective monitoring.

 

Satellite Options

SatelliteBandPrecisionVegetationResolutionImage Footprint (WxL)2Image Footprint (WxL)2
TerraSAR-X (TSX)X2 mmPoor3 m30 km x 50 km4–11
Cosmo (CSK)X3 mmPoor3 m40 km x 40 km4–16
SentinelC4 mmModerate20 m250 km x 250 km6–12
Radarsat-2C4 mmModerate3 m20 km x 20 km24
ALOS-2L2 cmExcellent3 m55 km x 70 km14
SAOCOML2 cmExcellent10 m55 km x 70 km8

1 Resolution depends on the beam mode chosen for the monitoring program and can range from 50cm to 20m.
2 Footprint size depends on the beam mode chosen for the monitoring project and may differ from those listed.

Archive Data

Most SAR satellites are owned and operated by government space agencies. InSAR vendors task satellites to collect data over project sites. Background imagery is also collected by space agencies, and data is available as far back as 1991 in some cases. Archive imagery back to 2014 or 2015 is available for anywhere on Earth. Large cities, major infrastructure projects, mine sites, and energy projects commonly have data extending prior to that. Historical imagery can be purchased economically or free of charge and used to retroactively investigate areas of interest or to establish a baseline for ongoing projects.

Building a Dataset

InSAR requires repeated images taken using the same acquisition parameters and perspective to resolve displacement measurements. Once the ideal parameters for InSAR monitoring have been chosen for a dataset, they should remain unchanged.

Clients can incorporate additional datasets into their monitoring campaigns at any time.

How 3vG can help and what you’ll get

The power of monitoring data is its utility. 3vG’s specialized InSAR monitoring technology maps risk-prone areas so clients can act with the best information.

3vG’s focus is to develop the best satellite-based remote monitoring technology to provide actionable information. We deliver near-real-time displacement data results for wide-area geohazard detection, combined with expert support.

Displacement DataStream

Over time, Displacement DataStream provides an early warning that can indicate progressive, regressive, and steady-state phenomena. Along with a time series for every measurable pixel, products incorporate displacement heatmaps, displacement extents, and a metadata report summarizing the data inputs and deliverables. This includes new displacement detection, acceleration detection, and statistically driven displacement contouring.

3vG offers better monitoring with:

  • Higher precision
  • Greater coverage
  • Faster response times

Web-based InSAR results delivered on the web

All of 3vG’s InSAR monitoring plans include displacement time series derived from a couple of months of data or more delivered to Motionary via the Displacement DataStream. Along with a time series for every measurable pixel, products incorporate displacement heatmaps, displacement extents, and a summary sheet of all data inputs and deliverables. For multi-perspective monitoring, points can also include the direction of displacement and can be visualized in 3D.

Monitoring programs can include:

  • Emergency InSAR Response Plan
  • Rapid Displacement Monitoring
  • An InSAR-specific web portal Motionary
  • Training and support 365 days a year

If your team uses other software to combine and analyze displacement results, the DataStream can be connected to those systems via our API. Results from Motionary can be exported to third-party data visualization software designed for GIS, Google Earth, and Microsoft Excel (csv).

Working with 3vG

3vG’s monitoring philosophy is to work together with our clients to build a custom InSAR monitoring plan for every project. We leverage unique relationships with space agencies to bring a wider range of options and data availability to our clients over our competitors.

Our services are built on a foundation of trust, positive impact, and client success. Our operations team and project managers are in constant communication with our clients. We routinely incorporate client feedback to improve our models to ensure that we continue to deliver the most effective information to our clients when and where they need it.

Frequently Asked Questions
How does InSAR work?

Interferometric synthetic aperture radar (InSAR) is a satellite remote sensing technology used for mapping ground displacement. SAR satellites emit a pulse of radar energy towards the Earth’s surface. The recorded energy forms an image of the ground surface. Pairs of images are processed to reveal ground and infrastructure displacement.

What does InSAR stand for?

Interferometric synthetic aperture radar (InSAR) is one application for SAR data. SAR Satellites are built for a variety of purposes from measuring sea ice, to military applications, agricultural monitoring, ground deformation, and more.

What is InSAR coherence?

Coherence is a measure of the repeatability of a surface over time. Coherence ranges between zero and one; the density and quality of InSAR measurements over a given area is directly proportional to its coherence.

What does InSAR measure?

InSAR measures the amount of displacement occurring over an area. Both the spatial extent and the magnitude of displacement are measured. InSAR can measure ground and infrastructure displacement associated with mining, pipelines, dams, utilities, and more.

How accurate is InSAR?

InSAR’s accuracy depends on the operating wavelength and the noise (coherence) observed between image pairs. Atmosphere, vegetation, snow, heavy rain, vehicular traffic, all contribute to the noise level. With low noise, measurement precision can be up to the millimetre.

What is the coverage of InSAR?

Most SAR satellites are owned and operated by government space agencies and must be tasked to collect new and ongoing data. Imagery has been collected and stored in archives since 1992. In most cases, the coverage of InSAR can be customised for each project.

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