I started to look at landslides in satellite images when I saw this tweet by @RemotePixel:
July 11th 2016 Sentinel-2 Image over Glacier Bay, AK massive landslide! pic.twitter.com/pTnHQ7el8G
— Remote Pixel (@RemotePixel) July 14, 2016
Like floods, landslides can be quickly identified using a before/after image comparison. In the case of the Glacier Bay landslide I used this method with Sentinel-1 and Sentinel-2 to compute the area of the debris tongue (about 20 km², 10 km long).
— Simon Gascoin (@sgascoin) July 19, 2016
But Sentinel-1 was not particularly useful since the Glacier Bay landslide was a dark slide on a snow covered glacier, so it was easy to map it using natural color Sentinel-2 images. These kind of landslides are called "supraglacial landslides" and can be found in Landsat or Planet images too. Hashtag #lessbears 😀
— Simon Gascoin (@sgascoin) December 3, 2017
Although the Glacier Bay landslide was one of the most impressive landslide of the decade, it did not cause any damage. The most devastating landslides in the recent years occurred in Palu, Indonesia after an earthquake.
Two articles show that rice irrigation caused the Palu landslide in Sep 2018 https://t.co/vPizerqHWy
We showed images of the fault line and landslides here https://t.co/NWs8JtWs4S pic.twitter.com/WujBIL4OiG
— Simon Gascoin (@sgascoin) October 11, 2019
Palu's shallow earthquake left a scar in the city which was visible from space
— Simon Gascoin (@sgascoin) October 2, 2018
This animation astonished me but other
grumpy sharped-eye scientists noticed the poor muti-temporal registration of the images..
— Olivier Hagolle (@OHagolle) October 2, 2018
... and even fixed it!
Because geolocation inaccuracy makes it difficult to compare the two raw images, this animation stabilises the west side of the image to highlight the 5m+ relative shift along the fault: pic.twitter.com/Sa3aDKJNv4
— Dr Robbi Bishop-Taylor 🛰️🌎🌊 (@SatelliteSci) October 2, 2018
Only a couple of days after the disaster, a surface displacement map made from Planet images was tweeted by @SotisValkan:
This is the most sharp and linear earthquake surface displacement I've seen since 20130Balochistan eq! More than 20km of major strike-slip displacement for Palu fault segment, Sep 28 M7.5 #earthquake. Optical correlation w/MicMac & @planetlabs imagery pic.twitter.com/23ItZnQUNQ
— Sotiris Valkaniotis (@SotisValkan) October 1, 2018
After the Kaikoura earthquake in New Zealand, it was also possible to see both the ground displacement and the landslides caused by the earthquake in the same Sentinel-2 image:
— Simon Gascoin (@sgascoin) November 16, 2016
— Simon Gascoin (@sgascoin) September 17, 2018
In the images above I used a false color band combination with the near-infrared band of Sentinel-2 to highlight the contrast between the detachment zone and the vegetation. Otherwise landslides in temperate regions can be difficult to see in natural colors:
— Simon Gascoin (@sgascoin) July 15, 2017
Whereas, with the near infrared band even small landslides can be identified:
— Simon Gascoin (@sgascoin) May 15, 2019
Most of my landslides tweets were inspired by the landslide blog, where the author Dave Petley often comments Planet images. However, Sentinel-2 is also very useful to make quick landslide analyses because of these characteristics:
- 10 m spatial resolution enable to detect most landslides
- near-infrared band enable to distinguish bare earth and mud from vegetation
- systematic acquisitions with a short revisit time enable to create before/after image comparison even in cloudy regions
Planet provide images with similar characteristics and even a better spatial resolution (albeit with a lower image quality). But a very important aspect of the Sentinel-2 mission is the open data policy of the Copernicus program and the availability of efficient tools like the EO-Browser to explore the data with an Internet Browser.
Next part will be about glacier hazards! In the meantime here are more landslides..
"The landslide crossed the river Hítará, damming the river and causing a lake to form above the debris tongue" pic.twitter.com/RMV2uub6c5
— Simon Gascoin (@sgascoin) January 30, 2020
— Simon Gascoin (@sgascoin) August 26, 2017
— Simon Gascoin (@sgascoin) May 18, 2017
— Simon Gascoin (@sgascoin) May 23, 2017
— Simon Gascoin (@sgascoin) June 6, 2020