3 Gorges Dam with InSAR Satellite Data

In this video, I provide an independent assessment performed by Value Space of satellite based photos and radar (InSar) data about the condition of the 3 Gorges Dam on the Yangtze River in China. We now have a public source of information that can be obtained for these highly secretive projects that is not dependent on their release by a government. In this video, I summarize the results and provide additional insights into using InSar data.

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[Ezekiel]

I worked for ABB Swiss at the Three Gorges Dam, where we worked on generators. Even then, water ingress was evident in the turbine room. Repair work was being carried out on the wall behind a large wooden panel. Everything was strictly guarded, we were always accompanied by security from the hotel to the dam down to the turbines and back. Photos were prohibited. We could feel that they had to hide something. That was almost 20 years ago. I am sure that this dam does not meet modern safety standards. An Alstom employee told me that the vibrations from the turbines were noticeable. They thought that a turbine was creating an imbalance, but that was not the case. They never found out where the vibrations came from.

[UserNameWasCensored]

Just a few clarifications (as someone who has performed InSAR and PS-Interferrometric analyses for the past 30+ years): The Sentinel satellites generally have had a repeat time of six days. With respect to Sentinel-1, which contains a C-band radar, the repeat time is currently 12 days because the second satellite (1b) is not functioning. But 1c should be up in orbit soon (planned for December).

The nominal resolution of a Sentinel-1 image is 30m (~100 feet). Three scans are combined to create the 10m resolution image that is available to the general public. The vertical resolution of a C-band microwave is about 2.8 cm (slightly more than an inch) or half of one wavelength. So individual measurements cannot be made with an accuracy of better than +/- 2.8 cm.

So one pixel covers an area of 100 m2. The radar response of that entire area dictates how the "movement" (in the line of sight from the satellite), if any, will be measured. That's a pretty big area. For example, if a worker leaves a fairly large metal toolbox on top of the Three Gorges Dam and the S1a satellite passes over, the resulting image will (likely) have a more intense response because of the size, shape and material of said box. The intensity of the response, along with the phase of the microwave, is how movement is measured. So it's really, really difficult to say anything about objects on the ground.... unless one has set up specific reflectors (with known parameters) or are analyzing a mountainous area with no vegetation.


All in all, a very informative discussion on InSAR 👍 - I usually caution people from accepting results that aren't taken over several years (statistically averaged) and backed up by field measurements.

[LiDARs]

I run a laser scanning firm that’s scans a lot of concrete. You would never see pre failure symptoms from satellite let alone low altitude, aerial scans involving the primary structure. You would see aberration in the landscape. Something that size would not be designed to flex. You have affixed or failed. We talking mm to cm of deflection before fail. Not feet to meters.

[dwshank]

I worked for the U.S. Army Corps of Engineers in the final years of the 3GD's construction. The unclassified assessment was that it is a very ambitious project that will require a higher level of active management and maintenance than other big dams (mostly due to where it's located) but that with that maintenance, it would be fine. So, as long as the CCP is devoting the proper resources and listening to the experts, it should hold up.

[rileydj]

Great video! I lived in Tianjin China from 2000-2005. Took a Yangtze River boat tour from Yichang to Chongqing in 2002. We spent hours at the damn site watching workers. All along the week long tour we could see the painted marks on the gorge walls of where the water will be after completion….. as we passed thousands of little towns and homes that would be underwater. That was tough to take.

[RealJeep]

There are a hundred videos out there saying the dam's failure was imminent. Thanks for bringing clarity to this issue.

[ericfielding]

Great explanation about the use of InSAR for monitoring dams and adjacent areas. The Icelandic government and university have a long tradition of using InSAR to monitor the magma movements and volcanic eruptions in Iceland, so you were right to point to that as another application. We use InSAR in the USA to monitor the volcanoes in Hawaii, Alaska, and the Cascade volcanoes also.
One small correction about the InSAR measurements. The SAR systems from Sentinel-1 and other satellites are not looking vertically at the Earth's surface, but at an angle that is typically around 35 degrees away from vertical. The InSAR method measures displacements along the direction between the ground and the satellite, not purely vertical elevation change, so it can include some horizontal motion. The Sentinel-1 SAR satellite is looking westward when it is traveling southward and looks eastward when it is traveling northward. This means it can be possible to separate vertical and horizontal displacements by combining InSAR data with two different directions. You should ask the Value Space folks whether the data you are viewing has an east or west component added to the vertical.

[RealTalkLaughs]

Kudos to you for only observing fact and reality, and not some politically convenient narrative.

[franklinmc]

It's amazing what a little data can do to eliminate some of the hyperbola that is dished out on YouTube. Bravo Sir! As a country we have neglected Infrastructure Maintenance. I hope every Community Civil Engineering Authority will use this type of tool to understand what's happening to our roadways and bridges.

[keithdrower]

I have been monitoring dam stability due to underground mining subsidence, for 40 years. Satellite images and Lidar, L1 and L2 ard very useful, but ground based survey measurements are much more accurate and reliable. I am sure that the Chinese authorities will be monitoring this dam. They would be taking a big risk if they were not doing this.

[JimmyJamesJ]

Thanks for this video. As an engineer myself I was assuming this to be the case after seeing other videos out there crying disaster. Glad to see some real data.

[rb]

Love seeing real data that is not skewed by politics or money.

[StirlingLighthouse]

Yet another outstanding evaluation!
Thank you Casey 🙏

[robertmendlein]

Good job, Casey! Stick to data-driven and being honest.

[hotspur_courier]

I really appreciate the level-headed, non sensational discussion here and the interpretation of the data based on objective observation that proves the null and doesn't try to split hairs on digital/visual perceptive anomalies.

[ADHJkvsNgsMBbTQe]

Science for the win. It’s amazing how useful remote sensing can be.

[labethspain]

Videos such as these are SO interesting! The narrative and seeming knowledgeable comments, I find, are an valuable educational tool for the average layman. Thank You!

[DonaldAtherton-lu]

Casey, facts, facts and nothing but facts.
So tired of politicians and spinning things.
Facts, facts, facts

[ross]

This is great. Giving a clear and concise factual description is great to see. Especially the explanation of the data points that we have access to.

[larryshaw]

that was a cool video. I love the data driven approach and your ability to just focus on the data and not all the BS stories that come out every week.