To celebrate the 10'000th snow product in Theia, here is the latest snow map over the Vicdessos area in the french Pyrenees near Andorra. The snow is in blue and the clouds are in white! Pan and explore the map below..
Big up to the Muscate team!
On March 9th, 2018, a tailings dam has failed at Cadia, a large open pit gold mine in Australia. Dave Petley for the AGU landslide blog collected aerial and satellite (Planet) images of the dam before and after the event. The Newcrest mining company also published a report on the failure.
About 80 people participated either on the 13th or 14th, and nearly 70 participants attended each day of this workshop, whose object was to collect feedback and share experiences on the quality, use and applications of the L2A surface reflectance products delivered by Theia from Sentinel-2 data.
Until V0.9, only a small proportion of Venµs L1C data were available at L1C level on Theia's website. Now, with the version V1.0, a greater proportion of products will be distributed to users, but we advise users to check their geometric quality in the metadata, as explained below.
Distribution of V1.0 products should start very soon !
The figure below shows the evolution of the Normalized Difference Vegetation Index (NDVI) in the pitches of all the 2018 World Cup stadiums.
I retrieved these data from Sentinel-2 observations using the new time series plotter in the EO Browser. I just drew a polygon in each of the 12 stadiums to get the average NDVI values on every available cloud-free date.
Because the NDVI is a proxy of the vegetation health (here the grass on the pitch), these charts allow us to identify which stadiums were built for the 2018 World Cup (Volgograd Arena, Cosmos Arena). On the other hand, the Fisht stadium in Sotchi looks well maintained since 2016. It "served as the venue for the opening and closing ceremonies of the 2014 Winter Olympics (...) was originally built as an enclosed facility; it was re-opened in 2016" (wikipedia). Also it should be noted that the Krestovsky Stadium in Saint Petersburg is a retractable roof stadium. "As of May 2017, the stadium was 518% late and 548% over budget (...) At a cost of $1.1 billion at current exchange rates, it is considered one of the most expensive stadiums ever built." (wikipedia). Hopefully the grass will remain green in the next months, unlike some stadiums in Brazil after the Olympics.
In the meantime, as you can see by yourself, the grass is blue in the Kazan Arena!
A new feature in the EO Browser enables to plot the evolution of the mean NDVI within a polygon. I drew a rough polygon of Saint Barthélemy to check the evolution of the vegetation after Irma from Sentinel-2 data.
On June 23 we will celebrate the third anniversary of Sentinel-2A in orbit. With three years of data we can start looking at the inter-annual variability of biophysical variables, like.. (random example), the snow cover.
This is what I attempted to do for the Theia workshop. I downloaded all available snow cover products from Theia over the Central Pyrenees (tile 31TCH) and I generated additional snow maps from the Theia Landsat-8 level-2A products using let-it-snow processor. Landsat-8 images enable to increase the frequency of observations when only Sentinel-2A was operational between 2015 to 2017.
I resampled the Landsat-8 snow maps to the same reference grid as Sentinel-2 at 20 m resolution using the nearest neighbor method. I cropped all snow maps to the intersection of the Sentinel-2 tile (green polygon) and Landsat-8 tile (red polygon).
When there was a snow map from Sentinel-2 (S2) and Landsat-8 (L8) on the same day, I merged them into a composite using a simple pixel-based rule:
We have just updated the MAJA/THEIA workshop website to add a draft program. The workshop will be held in Toulouse, from 13th to 14th of June, and will be hosted by the ENSEEIHT engineering school in Toulouse historical center. Registrations are still open, until the third of June.
The aim of this workshop is to collect feedback and share experiences on the quality, use and applications of the L2A surface reflectance products delivered by Theia from Sentinel-2 data.
The meeting objectives are as follows :
We look forward to meeting you soon !
The organising Comittee (Arnaud Sellé, Olivier Hagolle, Céline Arnal)
The Global Imagery Browse Services (GIBS) is a great new API provided by the NASA to access its vast collection of Earth Observation products. For example the following URL allows you to download a jpeg picture of the Terra MODIS NDVI on 2018 Jan 01 over Africa:
By looping on the "TIME" parameter (in a bash script using wget) I could get all the available products from 2016-07-30 until yesterday, and make this animation (using ffmpeg).
— Simon Gascoin (@sgascoin) May 24, 2018
Sentinel-2B has two channels centered on water vapour absorption bands: channel 9 (940 nm) and channel 10 (1380 nm). Band 10 corresponds to a very strong absorption, strong enough to prevent any photon to reach ground from the Sun without being absorbed in the atmosphere. This band is intensively used to detect and correct high clouds.
In this blog, we discussed much less band 9 (940 nm) yet. Here, water vapour absorption is not strong enough to catch all the photons which reach the surface. The proportion of absorbed photons depends on the water vapour atmospheric content, and also on the viewing and solar zenith angles. We use band 9 for atmospheric correction, but it could be useful to study convection phenomena within the atmosphere too.