As incredible as it might sound, the image on the right is a capture from the Earth’s surface. It is surely difficult to imagine that it depicts the vegetations and the swamps along the Mississippi river, because of the red tonality of the image. However this is a False Color image coming from the ESA’s Sentinel-2A satellite and captures part of the Mississippi river with its swampland. Sentinel-2A was launched on 23 June 2015 and it is the first of two identical polar orbiting satellites that will form the Sentinel-2 constellation, after the launch of Sentinel-2B in the second half of 2016.
This mission has been developed by ESA together with an international industrial consortium, as part of Copernicus, the European programme for Earth Observation, and it will provide high resolution optical imagery for land monitoring. For this reason the main instrument of the payload is the MSI ( MultiSpectral Instrument), an innovative high resolution multispectral imager with 13 spectral bands. The new spectral capabilities offered by this instrument can be exploited with multiple applications in Earth Observation. For example,by analyzing the images from Sentinel-2 it is possible to distinguish among different types of crops or monitor the plant growth for a certain region, . In fact the MSI has 3 spectral bands in the “red edge” region(690-730 nm), the portion of the NIR(Near-Infra-Red) spectrum that is adjacent to the red region in the visible spectrum. At these wavelenghts the vegetation absorbs only a small part of the light because of its chlorophyll concentration, so that the reflected light reaches rapidly a high value in those three bands, sending a lot of information to the MSI. Technically this means that the vegetation has a high spectral reflectance in the red edge range of wavelengths, as shown below, where the reflectance is represented for 3 different kinds of plant canopies
The Red Edge band can replace the visible red in the False Colour mode, that’s why the Mississippi swampland looks so red in the first image.
Sentinel-2 can also be used to monitor changes of the Earth’s surface,caused for example by climate change the human activities. But the whole constellation could even help to manage emergency situations, providing useful information on the ground in a short time.
In these few months Sentinel-2 has already exceeded the expectations about the results it can obtain, thanks to its high spatial resolution that ranges from 10 to 60 m. The following image captures the details of an algal storm in the middle of the Baltic Sea and it is useful to study the biological activity in that particular region, where the ecosystem has to face serious pollution problems. In this case the algal storm is part of a larger bloom of cyanobacteria, that are similar to algae and thrive on phosphorus in the water. Their presence can cause a high level of toxicity affecting the ecosystem, aquaculture and tourisme. That’s why it is so important to monitor the status of the blooms, and satellite imagery can provide a wider view of the current situation.
This example shows a possible marine application of Sentinel-2, going beyond the official mission objectives that do not include the ocean colour monitoring.
Sentinel-2 belongs to the ESA’s satellite family called Sentinels that will provide a unique set of observations and data regarding various fields of the Earth Observation activity, from the measurement of the sea-and-land-surface temperature to the atmosphere monitoring, and probably image and data processing will bring the opportunity to discover even more applications.