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Student Spotlight Summer 2022

Andrew Fore

The L3Harris Geospatial Summer Student Spotlight is Nanar Jacobs, a part-time PhD student who works for the Wetern Arctic Centre for Geomatics in Inuvik, NWT, Canada, which is part of the Northwest Territories (NWT) Centre for Geomatics, Governemnt of Northwest Territories (GNWT), Canada. Jacobs is pursuing her PhD at Wilfrid Laurier University where she is studying remote sensing methods that use both high-resolution Synthetic Aperture Radar (SAR) and optical remote sensing data to detect, monitor and analyze permafrost thaw impacts in the Dehcho region and in the Northwest Territories. 

“I hope my PhD research helps deepen knowledge about permafrost thaw and its effects on the ecology, environment and community,” says Jacobs. Permafrost thaw is one of the more serious, yet lesser focused on impacts of climate change. Permafrost degradation is creating geological challenges in the Northwest Territories such as landslides and permafrost thaw slumps that impact the region economically and socially.

“I’d like to promote geomatics education by building a bridge between high-tech advancements in remote sensing and its practical applications in the Northwest Territories with the aim to develop remote sensing and outreach projects that engage community leaders, elders and all interested indigenous community members in the Northwest Territories,” said Jacobs.

Her Research Study: Monitoring Hay River Airport Using ENVI SARscape®

Jacobs’ study focused on monitoring the Hay River Merlyn Carter Airport for permafrost degradation due to climate change. The Hay River airport serves as an important distribution for the communities on the Mackenzie River and the Arctic Coast, with about 6,000 aircraft flights per year. The airport was built on an old river channel (Snye) and the location of the building site is one of the primary causes of its history of terrain instability. Other factors contributing to stability issues include underlying permafrost degradation, climate change and freeze-thaw frequency within the active layers in permafrost soils.

Monitoring and identifying the location of pavement failures, particularly on runways, is of paramount importance for the safety of moving aircraft and the overall safety of the airport. Jacobs’ research hypothesized that failure of infrastructure built on the permafrost can be predicted by understanding and assessing the mechanism of the permafrost degradation and its impact on the ground surface. Furthermore, Jacobs believes that understanding the long-term behavior of the ground-movements will help mitigate issues caused by permafrost degradation.

Fig.1: Illustrates the location of the airport within Northwest Territories, Canada, and outlines the research study area of the airport. (a) The location of Hay River Airport shown on a map of Canada; (b) Radarsat-2 image of Hay River Merlyn Carter Airport. The red arrow points to the old river channel (Snye).

One of the methods to derive ground deformation measurements includes remote sensing methods for risk assessment, deformation estimation and quantification of structural instabilities and ground motions. Currently, remote sensing interferometric data processing techniques are used to examine the spatial and temporal evolution of surface motion using microwave sensors.

In this study, Radarsat-2 and Sentinel-1 datasets were used to investigate Hay River Airport ground-displacement patterns and analyze the temporal evolution of the detected displacements. Radarsat-2 datasets make it possible to evaluate the ground surface dynamics with an interval of 24 days over the location of Hay River Airport. Datasets from the Sentinel-1A and Sentinel-1B satellites make it possible to evaluate the ground surface dynamics with an interval of 12 days over the location of Hay River Airport.

The data processing and analysis was done using ENVI SARscape. “I use ENVI SARscape in my work and in my research,” says Jacobs. “I have found ENVI SARscape to be an invaluable tool that is incredibly powerful for processing and analyzing SAR data. Because the software is the industry standard, it keeps you up to date with developments and at the same time helps you to learn and develop to achieve your research goals.”

Dataset Information:

Radarsat-2 datasets are Single Look Complex (SLC) products, with HH polarization, for the period March 16, 2014, to July 7, 2020, Beam U10, Descending, and for the period April 5, 2017, to June 24, 2020, Beam U1W2, Ascending, are provided by NWT Centre for Geomatics, GNWT https://www.geomatics.gov.nt.ca. RADARSAT-2 Data and Product© MDA Geospatial Services Inc. 2022 All rights reserved. RADARSAT is an offical mark of the Canadian Space Agency.  

Sentinel-1 datasets are Single Look Complex (SLC) products in Interferometric Wide Swath (IW) mode, with VV polarization, for the period February 6, 2017, to March 11, 2021, Path 42, Descending, are downloaded from Alaska Satellite Facility https://asf.alaska.edu/.

Fig.2: Shows the SBAS processing steps [adopted from L3Harris ENVI SARscape, Interferometric Stacking - SBAS – Overview - © sarmap SA 2021, SARscape In this study, the small baseline subset (SBAS) interferometric SAR method was applied to obtain surface deformation at the Hay River airport. The SBAS approach permits the utilization of extended targets, which increases the number of ground points that can be monitored. Therefore, to decrease the decorrelation phenomena in time and space that influences extended targets, SBAS technique uses appropriate combination of differential interferograms produced by data pairs that have small time and space thresholds

Fig.3: Shows an example of baseline plot of total 318 interferograms for Sentinel-1 (Track 42, Descending). Time-position plot for Sentinel-1 (Track Number 42, descending) interferometric pairs. Some of the data processing results are shown in Figures 4, 5, and 6.

Fig. 4: The line-of-sight velocity derived from Sentinel-1 (Track Number 42), and overlaid on Google Earth. Each pixel covers an area of approximately 15m×15m on the ground.

Figure 4 Shows the map of Hay River Airport ground surface deformation velocity in the line-of-sight direction derived from Sentinel-1 (Track 42) datasets. Each pixel covers an area of approximately 15m×15m on the ground. The most noticeable area that is successfully observed, is around the taxiway and it is reported to have water accumulation throughout the year due to the underlying permafrost thaw, which created a settlement. Although the sub-drainage system was installed, it was not working for several years. Past the taxiway intersection, the pavement changes to gravel, where the work was carried out in leveling the gravel coverage, therefore, this section is observed to have low coherence.

Fig. 5: Vertical velocity component derived from Radarsat-2 datasets. Each pixel covers an area of approximately 2m×2m on the ground.

Figure 5 shows the vertical velocity component derived from Radarsat-2 datasets, which are using both ascending and descending geometry measurements in order to obtain the vertical component where the positive values indicate upward movement, and the negative values indicate downward movement.

Fig. 6: Estimated vertical (upward-and-downward movement) velocity time-series for two selected Points (A, B).

Figure 6 shows a time-series plot for two selected points (A and B) from the area where the Snye river channel underlies the airport airstrip pavement, and both points show the same displacement patterns. In general, the section of the airport that is located on the Snye river channel is experiencing surface subsidence at higher rates than the surrounding area.

Conclusion:

Using SAR and ENVI SARscape to assess and monitor critical infrastructure built on permafrost such as airports will ensure the greatest possible safety for the communities in the Northwest Territories. The use of radar remote sensing technology will improve the ability to operationalize an efficient method to monitor permafrost thaw and its impacts in the Northwest Territories.

 

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