Google Earth Blog

The amazing things about Google Earth


sentinel

Avalanches in Tibet

On July 17th, 2016 there was a very large avalanche in the Aru Mountains of Tibet. This was followed by a second avalanche on 21st September, 2016. Planet Labs captured some imagery of the location of the second event and have created an excellent before and after, which you can find here.

For a more detailed analysis of the events see the excellent Landslide Blog Part 1 and Part 2. The Landslide Blog also includes some before and after images of the first event, which come from this page. One is a Sentinel 2 image captured after the first avalanche, and the other is a Landsat 8 image captured before the avalanche.

Now, there is Sentinel imagery available from after the second event we can do a full sequence:


January 23rd, 2016. Copernicus Sentinel Data, 2016
 

July 21st, 2016. Copernicus Sentinel Data, 2016
 

October 16th, 2016. Copernicus Sentinel Data, 2016
 

We have also put the Planet Labs images and the above Sentinel images into Google Earth. To view them download this KML file. The Sentinel imagery is actually slightly higher resolution than what you see above.

The fires of Qayyara, Iraq, with Landsat and Sentinel imagery

We recently came across this interesting article on Bellingcat which is about the use of environmental damage as a weapon of war in Iraq. As the Islamic State (IS) is being pushed back, they are setting light to oil wells, pouring oil on the streets and in trenches and setting light to it and also setting light to other industrial products such as sulphur.

The article features some Landsat imagery showing the plumes of smoke. Landsat imagery is freely available, and we have in the past created a KML file that can make animations with Landsat imagery. If you download the KML file and view the animation for the area around Mosul, Iraq, you can clearly see the smoke in the last few images. Also of note, you can see some smoke from a previous event in an image from August 2014 to the north west of Mosul. We have also created animations using Sentinel 2 imagery, which you can download here.

The animations above are created using low resolution thumbnails provided on Amazon Web Services (AWS). To see some high resolution imagery, we downloaded the most recent Landsat-8 image and processed it with GIMP using a method similar to the one described here and here.

The result can be seen below:


Landsat 8 image from October 20th, 2016. Note the sulphur fire marked with an arrow. The black smoke is from oil fires.

For comparison, we also downloaded a Sentinel 2 image from September 14th 2016.


Sentinel 2 image from September 14th 2016. This is before the sulphur fire was started. Copernicus Sentinel Data, 2016.

See the above images in Google Earth, download this KML file.

The Bellingcat article also features an image of the sulphur fire from Planet Labs.

Landsat and Sentinel-2 data now on Google Cloud

Google has just announced the release of Landsat and Sentinel-2 data on the Google Cloud. Landsat and Sentinel-2 data are public datasets of satellite imagery from earth observation satellites. The Landsat data is from a joint program between US Geological Society (USGS) and NASA and the Sentinel-2 data is from the European Space Agency’s Copernicus program.

Google has long had the datasets in Google Earth Engine, but accessing it required a Google Earth Engine account, which had certain restrictions on usage. The Google cloud version appears to be without restrictions. The data itself is public data and you can do almost anything you like with it although proper attribution may be required.

More about the individual datasets and how to access them can be found here: General instructions, Landsat, Sentinel-2.

The imagery is provided as unprocessed tiles for each of the optical bands that each satellite provides. To see the images in colour requires processing. The easiest way to do this is with commercial tools from GeoSage. Alternatively, see this post for instructions on how to process Sentinel-2 imagery using GIMP. Landsat data can be processed in a similar way, although it an some extra steps are required to get the best resolution.

The resolution of Sentinel-2 imagery is 10 m per pixel and Landsat-8 is 15 m per pixel after pan-sharpening. Do not expect to see the kind of detail we are used to in Google Earth.

Sadly, Google has not provided thumbnails with the data.

Amazon provided Landsat data via its cloud infrastructure Amazon Web Services (AWS) in 2015 and more recently added Sentinel-2 data. We did a series of posts featuring KML tools to allow you to preview the latest images and make animations from provided thumbnails. The Landsat data on AWS is somewhat limited compared to the Google Cloud offering. Google is providing all Landsat images from Landsats 4,5,6,7 and 8 from 1982 to present. AWS only has Landsat 8 data and even that is only complete data for 2015 and select images from 2013 and 2014.

The image below is a Sentinel-2 image downloaded from the Google Cloud and processed with GIMP. It shows a small part of the Soberanes Fire, California, on September 12th, 2016. To see it in Google Earth (and covering a larger area) download this KML file


Copernicus Sentinel data, 2016.

Animating Sentinel-2 imagery in Google Earth

We have recently been doing a series of posts about Sentinel and Landsat imagery on Amazon Web Services (AWS). We created tools to let you quickly preview the latest Sentinel and Landsat imagery in Google Earth. We also looked at the coverage pattern for the Sentinel and Landsat imagery and created a way to animate the Landsat imagery. Today we are releasing similar animations for the Sentinel imagery.

To see the animations, simply download this KML file, open it in Google Earth and click on any tile.

There are several differences between this one and the Landsat animations. The sentinel thumbnails are much lower resolution than the Landsat thumbnails, so we don’t provide a link to a larger version. Also, the sentinel images often do not cover the complete tile, so we have provided an extra slider to allow you to filter out tiles based on how much of the tile they cover.

The KML file also shows with colour coding how much sentinel imagery there is, with a range from green to red for 1 to 120 images per tile and white for tiles that have over 120 images. The highest numbers can be found over Europe, which is understandable given that it is a European satellite. The amount of imagery also increases towards the north of Europe, we believe this is because the paths the satellite takes overlap more near the poles, allowing more imagery to be captured. There are also hotspots over deserts suggesting that the images are selected for low cloud cover.

The Sentinel-2A satellite that is gathering the imagery was launched in June 2015. In comparison, Landsat 8 has been around since 2013. However, the Sentinel-2A satellite covers the globe roughly every 10 days, whereas Landsat 8 takes 16 days. In addition, the Landsat 8 archive on AWS only includes selected images from 2013 and 2014 (with significantly more of the US than other parts of the world) and only has the complete set of images from 2015 onwards.

We also find the clouds look whiter and obstruct the picture more in the Sentinel imagery than they do in the Landsat imagery. This may relate to how the imagery was processed for the thumbnail or it could reflect differences in the exact wavelengths the respective satellites use to capture the colour bands.

We came across a few errors in the data, such as mislabelled tiles or missing thumbnails, but they were not significant enough to seriously affect the operation of the animations.

As with the Landsat imagery, it is important to note that this is very low resolution imagery, so expect to only see very large scale phenomena. Also, with only a year’s worth of data there is not a lot of change to see. However, it is a continuously updated service and with the expected launch of Sentinel-2B sometime next year doubling the frequency of imagery, we can expect some spectacular animations in years to come.

Sentinel imagery coverage

Yesterday we created a KML file that allows you to preview the latest sentinel imagery using a KML file of all the sentinel tiles. We noticed that some tiles do not have any images available, so we thought it would be interesting to do a map of Sentinel coverage. There are 56,686 tiles, so it took a little while to check all of them to see whether they have imagery and what the date of the latest image is. It turned out that only about half the tiles (27,256) actually have imagery.

We have colour-coded the tiles based on the age (in weeks) of the most recent imagery. As you can see, there is a distinct stripy pattern and the shape of the sun-synchronous orbit is clearly visible. Also of note is that imagery off the coasts and of Antarctica is not as recent as that over the continents.

To see it in Google Earth, download this KML file. Click on any tile to see the date of the latest image available (as of August 15th, 2016).

While creating the above KML we identified a few bugs in yesterday’s KML file, most notably that tiles starting with ‘0’ were incorrectly reporting no imagery. We have fixed the bug, so if you plan to use it then please re-download it from yesterday’s post.