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Sentinel 3 for beginners

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“As the most complex of all the Sentinel satellites, Sentinel-3A carries a suite of cutting-edge instruments to measure oceans, land, ice and atmosphere.”

I haven’t used Sentinel 3 before; my preferred workhorse is Sentinel 2 and its multispectral data. I’m interested in the surface of the earth and its characteristics. Mapping features, classifying terrains and monitoring change all at a 10m resolution (not all the Sentinel2a bands are at this resolution) is a very attractive, and not to mention free, data source. I want to take a busman’s holiday and explore the other satellite data, especially ones that are delivering data to everyone for free. Maybe there are complementary images to be used. Maybe I can get some information that I haven’t previously considered but would give value to work I do today or in the future. In short, I want to be curious!

Poke the box

As Seth Godin writes in ‘Poke the box’

“We have little choice, but to move beyond quality and seek remarkable, connected and new”

So let’s have a beginners look at Sentinel 3 data.

How will it be used?

Sea

  • Ocean Monitoring
  • Forecasting
  • Water Quality & Pollution
  • Sea ice charting
  • Ship routing and climate monitoring

Land

  • Land used
  • Vegetation state
  • Height of rivers and lakes(!)
  • Monitor wildfire

Phew! that is a lot of intended applications.

Sea ice

https://twitter.com/simon_rp84/status/824643955186929664

 

Fires in northern Italy

 

Galapogos Islands (stunning!)

 

So what are you going to do with it?

https://twitter.com/nick_appleyard/status/808261331514167296

 

Sentinel 3 also carries the following instruments

  • Ocean and Land Colour Instrument (OLCI) covering 21 spectral bands with a swath width of 1270 km
  • Sea and Land Surface Temperature Radiometer (SLSTR) covering 9 spectral bands, dual-view scan with swath widths of 1420 km (nadir) and 750 km (backwards)
  • Synthetic Aperture Radar Altimeter (SRAL) Ku-band and C-band
  • Microwave Radiometer (MWR) dual frequency

Getting the data

Data is available from the Sentinel hub. Enter search criteria, bounding boxes and download data from the sensors listed above.

And download the data that best fits what you need; I chose data from the OLCI sensor. Zipped up, it’s about 650mb. Once you have your data and have unzipped it you will get a directory full of files. This is perhaps the point where you might say “how can I open this?” or, “how can I use this?” Don’t give up because the clever folk at ESA have built STEP (Science Toolbox Exploitation Platform) and within it they have made available SNAP which is a desktop tool to process Sentinel 1, Sentinel 2 and Sentinel 3. It even has a github page

Above is the SNAP toolbox with my downloaded Sentinel 3 OLCI dataset. Open the bands, right click on one and open the image window

Great; I have an image. Lets create an RGB now – that is easy as well. Click window, open RGB image and choose a 3 band combination.

and boom! Southern Australia in all its glory

Amazingly you can do all sorts of operations using the SNAP program, classifications (including random forest), image stretching, analysis – the list goes on.

I still remain a beginner; I am not sure what commercial applications can be made from this data, but there is definitely potential. Maybe going forward this data can be used to visualise and add information to important work such as this:

https://data.giss.nasa.gov/gistemp/graphs_v3/

 

I am always keen to derive information and gain knowledge. The rapid pace of new data being acquired from Earth Observation should challenge us all to learn more about the Earth.

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