The European Space Agency has developed a suite of new satellites with radar and multi-spectral imaging instruments to monitor the Earth’s surface, oceans and atmosphere. Data from these satellites will bolster the earth observation record with free and open access data. I am particularly interested in the Sentinel-2 mission which will provide high-resolution multipsectral data for numerous land monitoring applications with a five day revisit time. Sentinel-2A was launched in June 2015; Sentinel-2B is slated for a late 2016 launch. I thought I’d have a look at a new Sentinel-2A image that captured Mount Pinatubo because earlier this month marked 25 years since the massive volcanic eruption on the island of Luzon in the Philippines. It was the second largest terrestrial eruption of the 20th century and its effects were felt on a global scale. As you might imagine, the local landscape changed dramatically along with the livelihoods of people in the Pinatubo area.

before

Landsat TM image of Mount Pinatubo (top center of image) acquired December 3, 1989, six months before the eruption.


after

Landsat TM image of Mount Pinatubo acquired on October 27, 1993; two years after the eruption. Evidence of devastating lahars can be seen radiating from the center of the volcano marked by Crater Lake.


I acquired a Sentinel-2A image from the USGS EarthExplorer archive. The data are delivered in JP2 file format, which unfortunately is not supported in R. There are a number of conversion methods outside of R, but I decided to have a look at the Sentinel-2 Toolbox developed by the European Space Agency. The toolbox is open source and includes a number of data visualization, analysis and processing tools for Sentinel-2 data and a number of other satellite platforms (e.g. Landsat, MODIS, SPOT, etc.). The following images were created using the Sentinel-2 toolbox:

RGB

Sentinel-2A image of Mount Pinatubo acquired on March 3, 2016; 10-meter RGB composite (bands 4, 3, 2).


NDVI

The Normalized Difference Vegetation Index (NDVI) derived from the Sentinel-2A image; 10 meter resolution using bands 8 (near-infrared) and band 4 (red). Green areas indicate high areas of vegetation productivity; deep red indicates barren areas and/or water.


The Sentinel-2 satellites measure reflected radiance through the atmosphere with 13 spectral bands at various spatial resolutions:

  • 4 bands at 10 meter: blue (490 nm), green (560 nm), red (665 nm), and near-infrared (842 nm).
  • 6 bands at 20 meter: 4 narrow bands for vegetation characterization (705 nm, 740 nm, 783 nm, and 865 nm) and 2 larger SWIR bands (1,610 nm and 2,190 nm) for applications such as snow/ice/cloud detection or vegetation moisture stress assessment.
  • 3 bands at 60 meter: mainly for cloud screening and atmospheric corrections (443 nm for aerosols, 945 nm for water vapor, and 1375 nm for cirrus detection).

Top image: Manila Bay, Philippines captured by the Sentinel-2A satellite