What is InSAR?

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

1 Resolution depends on the beam mode chosen for the monitoring program and can range from approximately 50 cm to 20 m.
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.

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).

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