Have you ever wondered what part of the planet is the most cloud free, or perhaps the most cloudy? It is recognised that the biggest impact on optical Remote Sensing is cloud; even if we can acquire an image everyday, we still cannot do much with it if is full of clouds.
With the free and open data policy adopted by NASA/USGS for the Landsat series, and the ease of which this data is being made available, is it possible to look into the metadata and try to answer where is the cloudiest place on Earth? Of course, I’m going to tell you, but first, where do you think is the most cloud free location on Earth?
The Data
Landsat 8 has now been orbiting and delivering satellite data for the last 4 years. I am stunned at how quickly this time has passed. Amazon conveniently supplies and regularly updates all the scenes. You can access this list at the url below:
http://landsat-pds.s3.amazonaws.com/scene_list.gz
All results shown here are from a download of this list I made on 7th April 2017. My downloaded file contained 1,044,560 records. This is NOT a list of all Landsat 8 acquisitions as the AWS page notes:
Landsat 8 is required to deliver 400 scenes a day but it is doing significantly more – over 700! More proof of the stunning success of this mission.
Distribution
Let’s take a look at the cloud cover distribution. Just under a third of the scenes acquired so far have cloud between >0 and <=10%
Sometimes you get -1.0 cloud cover… and this means bad data
update 12/04/2017 as Anya pointed out in the comments below “LC81572252017093LGN00 is not so much bad data as much as it is night data. The thermal bands are fine, what one would use for night imaging. The cloud cover algorithm uses reflective bands and cannot determine cloud cover on night imagery.”
The most cloud free place on Earth
The least cloudy place is located at path 179 and row 045, with 96 scenes acquired completely cloud free. So far, Landsat 8 has acquired 105 scenes here; a little over 91% of all Landsat 8 scenes are cloud free!
Where is this place? It covers the boarders of Egypt, Libya and Sudan.
Where is the cloudiest place on Earth?
This is a little trickier to define. If we ask what scene has experienced the most acquisitions with 100% cloud cover then the data shows this is path 181 row 075 with 3 scenes 100% covered in cloud. Where is this? Just off the coast of Namibia
Ever wondered what 100% cloud cover looks like 🙂
Top ten cloudiest locations in the world as defined by scenes acquired by Landsat 8*
* count of scenes with >=80% cloud cover between 2013 and April 6th 2017, from the available list on AWS.
Locations approximate!
10th cloudiest place – 185/058 (51 scenes) (South Western Cameroon)
9th cloudiest place – 184/062 (53) (Southern Western Republic of the Congo and the border of Gabon)
joint 5th – 126/042 (54) (Guizhou Province, China)
joint 5th- 126/040 (54) (Guizhou Province, China)
joint 5th – 125/041 (54) (Hunan, Province, China)
joint 5th – 080/023 (54) (Adak, Atka, Nikolski, Bering Sea)
4th cloudiest place – 185/059 (55) (Eastern boarder Equatorial Guinea and Gabon)
Top 3 now… exciting!
joint 2nd cloudiest place – 129/040 (58) (Sichuan Province, China)
joint 2nd cloudiest place – 183/062 (58) (South western Republic of Congo)
and the cloudiest place – 129/039 (59) (Chengdu, China)
Distribution of images, blue top 10 cloudiest locations, Orange is most scenes with 0% cloud cover. Areas have been exaggerated to display on map.
I processed this data using Python, did the graphing in Excel and I looked at the tiles in EarthExplorer, screen shots of maps are from QGIS. With this data it would be possible to work out the cloudiest scene covering the UK, or anywhere for that matter. It should also be possible to look at cloud masks on Sentinel 2 data as well.
If you enjoyed this then perhaps check out cloud appreciation society :).
Update 12/04/2017. I came across this website from CARTO which shows average cloud. Plus Planet managed to image an area often dominated by clouds in this blog.