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Monitoring Landslide Subsistence with ENVI® SARscape

On September 4, 2018, Hokkaido, an island off the coast of Japan, was drenched by a rainstorm that was part of Typhoon Jebi. Two days later, Hokkaido experienced a 6.6 magnitude earthquake. With saturated ground, and slopes already prone to landslides, the earthquake caused large-scale mass wasting.

For rescue and recovery efforts, quickly understanding where landslides occur is vital. Remotely sensed imagery of the affected area can provide critical information, however, during rainstorms or hurricanes, this can become very challenging because of the cloud cover that blocks traditional satellite imagery collects. This is where Synthetic Aperture Radar (SAR) is an unsung hero.

SAR can penetrate clouds and be collected day or night—SAR sensors don't need the sun as a light source because it is an active data collection modality meaning that it emits and measures a signal that the sensor creates. In addition to SAR's ability to see through clouds, SAR can also be used to measure changes in topography and this makes it a great data source for locating and evaluating landslides.

Image Courtesy Kyodo/Reuters, note the clouds in the sky. This picture was taken September 6, 2018.

 

Harris Geospatial Solutions provides the tools to ingest SAR data, which can be quite complex, and extract information like where the land surface slumped and where the debris accumulated. Our Japanese team was able to do just this using PALSAR data from JAXA, the Japanese Space Agency. The data consisted of pre and post event scenes to measure and determine the areas that lost land and where that debris ended up. This type of information is critical for recovery and rescue efforts to understand the impact to infrastructure (i.e. roads and buildings) and the environment (i.e. dammed rivers and future landslide risk areas). The PALSAR-2 images below have been overlaid on an aerial image and highlight the changes that have occurred. Red areas indicate the areas where there was a loss of land and blue areas indicate an increase.

 

PALSAR-2: Image courtesy of JAXA

Aerial Photo: Image courtesy of Geospatial Authority of Japan

 

If you are interested in learning more about SAR data and processing, we’ll be doing a webinar on this topic next month and are also working to get a SAR training class together in our Broomfield, CO office in the spring. In addition, we are trying to get some example models built with the ENVI Modeler up on our GitHub page that work well with popular SAR data sources.

This SAR workflow, quickly created with ENVI Modeler, is used for generating a coherence map and performing change detection to extract the locations where there was change from the earthquake.

 

In the US, the SAR conversation needs to start. For too long SAR has been “around” but not a viable piece of the remote sensing solution because it can be difficult to use. With our new SARscape workflows and upcoming community models, it’s easier than ever for SAR to be a component of your critical decision-making. Get in touch with us and let’s explore how your organization can utilize SAR.

 

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