City Infrastructure

City and local governments around the world face many challenges in monitoring, maintaining, and expanding their critical infrastructure. Rapid population growth and constrained operating budgets can hinder or stop maintenance on aging infrastructure, and slow new development. The first step in identifying problems and prioritizing maintenance is securing/acquiring a dependable, cost-efficient means of monitoring that delivers the information pertinent to decision making and budgeting processes.

MDA uses InSAR as a complementary technology to make traditional monitoring more efficient. It has developed a number of proven, reliable techniques to monitor very large areas and deliver the critical information urban planners and engineers need to understand the state of buildings, bridges, roads, airports, and underground tunnels.

InSAR is a powerful radar technique that exploits the all-weather monitoring capabilities of SAR satellites such as RADARSAT-2. It uses multiple SAR images to generate maps of surface deformation based on small differences in the phase of radar waves returning to the satellite. This proven technique enables the detection and measurement of millimetre-to-centimetre-scale changes in surface elevation. The routine nature of satellite monitoring is useful to detect, track, and visualize growing surface movement hot spots.

 
InSAR
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For civil infrastructure monitoring, MDA is a proponent of the Homogenous Distributed Scatterer (HDS)-InSAR technique, which uses spatially adaptive looking and adaptive filtering to preserve boundaries among different types of scatterers over large areas. This technique preserves the spatial resolution to increase the accuracy and geographic precision of the deformation result. HDS-InSAR provides a holistic view of entire cities, while pinpointing specific areas and assets that warrant further inspection for damage due to both long-term and rapid subsidence.

MDA has successfully applied HDS-InSAR to map surface deformation in several North American cities using RADARSAT-2 and TerraSAR-X data, and detected significant instances of subsidence including long-term seasonal displacement, aquifer depletion, and underground tunneling for road and rail networks.

HDS-InSAR separates temperature-correlated displacement from long-term displacement trends, further improving its accuracy and utility over time. MDA’s operational HDS-InSAR solutions have monitored civil infrastructure in a variety of geographic settings, and have illustrated its ability to capture detailed information over very large areas, and identify threats to the operation and life of the critical elements that make up a city.

 
Permafrost
Permafrost Deformation Image

In the higher latitudes of the northern and southern hemispheres, permafrost, defined as soils that remain at or below 0ºC for more than two years, underlies virtually all human development. An estimated 50% of Canada's land mass has traditionally been classified as permafrost.

The impact of rising temperatures related to climate change, and accelerated economic development in these regions, increases the risk of permafrost related surface deformation to buildings, power, water, and transportation infrastructures as the land on which they are built begins to thaw.

Satellite-based radar and MDA's advanced Multi-Track HDS-InSAR processing techniques provide a means for monitoring large areas in remote locations. Permafrost poses challenges for InSAR monitoring due to the complex temporal deformation patterns caused by both seasonal surface fluctuations and long-term changes in permafrost thickness due to warmer temperatures. Permafrost affected areas experience significant seasonal decorrelation due to winter snow cover and subsequent melt related surface erosion, making accurate monitoring more of a challenge.

To address this issue MDA developed a method that combines and jointly processes two or more same-side geometry InSAR stacks to provide a high-temporal resolution estimate of surface deformation. The method allows for combining stacks from more than a single SAR sensor and for a combination of frequency bands.

Data collected and analyzed for an area near the community of Umiujaq in northern Quebec includes scenes from RADARSAT-2, TerraSAR-X, and COSMO-SkyMed. MDA conducted multiple studies of the area using InSAR stack-based surface deformation estimates, comparing results from the three sensors individually, and all sensors combined. Surface deformation results for each sensor were similar, however, combining data from all three radar sensors produced the best spatial coverage of coherent targets. These studies demonstrate the utility of combining stacks from differing radar sensors and bands for Multi-Track HDS-InSAR deformation monitoring.

InSAR is a cost-effective and accurate means of measuring surface deformation at regular intervals and high spatial resolution on an ongoing basis, over extended areas of 10’s to 1000’s of square kilometres, making it well suited for monitoring remote permafrost affected areas including direct onitoring of affected infrastructure.