Suez Canal Blockage: Queue Backlog with Sentinel-1 SAR

Albert Um
4 min readApr 9, 2021

On March 21, 2021, a massive container ship, Ever Given, was found stuck in the Suez Canal. The Suez Canal is an important trade route as it connects a water path between Europe and Asia without going around Africa. The ship blocked the pathway for six days delaying hundreds of other vessels from crossing.

Suez Canal 2021 Blockage

The Suez Canal is a famous bottleneck due to its narrow waterways and high demand. Ships that want to cross are often required to wait in a queue before entering. I feared for supply chain managers after hearing the news of a complete blockage of the Suez Canal. Ever Given was freed on March 29, 2021, 6 days after being stuck, and I speculate reducing the backlog of ships will be a challenge.

I came across an interesting blog by Megan Gallagher, who classified ships with SAR images on the south side of the canal, right outside of Port Taofik, and in the Gulf of Suez to count the number of ships queue for March 25, 2021. The blog can be found here:

(My blog is an extension of the said blog to see how much of the backlog has cleared.)

Sentinel-1 SAR and Google Earth Engine

Synthetic Aperture Radar(SAR) data are images of the earth’s landscape created by the reflective signals, called back-scatter, that return to the radar. SAR emits its own energy to retrieve later, making it an active sensor. In contrast, passive sensors such as optical images retrieve the information reflected from another source(such as the sun).

Large backscatter values caused by double bounce can happen when the signal hits two flat surfaces such as buildings, cliffs, or in this case, ships.

Radar sensors emit energy in wavelengths greater than the infrared wavelength and less than the radio wavelength. SAR wavelengths can range from 1cm — 100cm and the open-sourced Sentinel-1 SAR operates within 3.8cm — 7.5cm (C Band).

The open-sourced Sentinel- 1 SAR images can be analyzed through the google earth engine(GEE). GEE serves as a two-part cloud computing platform, first storing open-sourced images/collections and second rendering the images to highlight certain topics. The GEE platform ( does require an account and operates with JavaScript.

SAR images on Suez Canal

It’s important to note that the Sentinel-1 SAR satellite cycles around the earth and returns to its original position every 6–7 days. I can find the time of capture from the image property, ‘system:time_start,’ which is in Unix time. In short, the date range of capture for March 2021 was {March: 6, 12, 18, 24, 30; April: 5, 11}, with time capture approximately 5–6 PM EET(Eastern European Time).

The visual backlog of the Suez Canal on April 5 is significantly lower from March 30. However, the queue on April 5 appears to be greater than the visual queues during pre-blockage(March 6, March 12, March 18). It is difficult to be conclusive, as I’m only comparing SAR images pre-blockage vs. post-blockage, and seasonality may be in play. Nonetheless, it is impressive to see how much of the queue has been reduced post-crisis.


I have been informed of an exciting website which, for free, tracks vessels in real-time! Although historical data is not freely accessible, I was ecstatic when someone showed me this website.