Downloading, Visualizing and Preprocessing Sentinel-2 Data in SNAP
Contents
Introduction
Getting Started
Install Required Software
Why do we need to take these steps
explanation of why it is being done to the data and what is being done
Getting Sentinel-2 Data
There are three ways we will outline in this tutorial to access Sentinel-2 data, through two Copernicus data servers, Scihub and SNAP Product Library, and Google Earth Explorer.
Copernicus account
1. Navigate to the Copernicus open access hub through this link 2. click the person icon with a question mark located in the upper right hand corner of your screen. 3. In the lower left corner of the drop down, click Sign Up and fill out all the necessary fields of the corresponding forms, being sure to enter a valid email address. 4. once your account has been created and validated, sign in using the same dropdown in step 3.
We now have access to our Copernicus and therefore Sentinel data. For more help, this link provides a comprehensive overview of the steps necessary https://scihub.copernicus.eu/userguide/SelfRegistration
Scihub
In Figure 1 we see the default Scihub display. depending on the data we are looking for, we are able to filter our search by location, sensor, and in Sentinel-2's case, even satellite.
Below the login icon there are three Icons (figure 2)
the first or top one show the map layers. Click through the options and note the Sentinel-2 Cloudless + Overlay. the second and third icons are in a slider format. the upper icon allows for navigation around the globe. Use this to find your area of interest. Once found switch the slider to the lower icon. This setting allows you to select an area of interest (AOI) which is your first filter for Sentinel data.
Next, navigate to the three horizontal lines icon, found on upper left corner of figure 1. this opens the advanced search dropdown, which allows for the filtering of available data by metrics of sensing and ingestion period, mission and the associated characteristics of each. After filtering, click the search icon to search the repository for images that meet both your included location and advanced search criteria.
If any images match your criteria the advance search dropdown will be replaced with the results.
SNAP Product Library
Google Earth Explorer
Subsetting to AOI
It is beneficial to subset the downloaded Sentinel data package if your AOI is only a portion of the downloaded image. This will increase efficiency, reduce processing time as well as increase clarity of intent.
The simplest method is to navigate to Raster toolbar then the Subset option. In the popup window (FIGURE) a blue bounding box will appear, this represents the extent of your image or view. Move the edges of the box to your desired location to resize, then press OK. If your desired AOI has exact coordinates or measurements, this option is not the most ideal.
A few other ways to accomplish a subset are discussed in the Subset section of the [1] Basic Processing of Radarsat-1 data in Snap ESA tutorial found on the main Wiki page.
Exploring Data in SNAP
Colour Manipulation Tab
RGB Exploration
RGB image profiles
Resampling to increase Usefulness
Image Classification Exploration
Spectrum View
Pin Manager
Sentinel-2 Toolbox
References
Geospatial Ecology and Remote Sensing. (2018a, March 13). Exploring Sentinel-2 multi-spectral band combinations in SNAP. https://www.youtube.com/watch?v=vtlN5MXYGaY
Geospatial Ecology and Remote Sensing. (2018b, March 13). Exploring spectral response curves from Sentinel-2 in SNAP. https://www.youtube.com/watch?v=E8Tu_IaJl6c&list=PLf6lu3bePWHCOUjTDZRNx5N07otDM8iUq&index=2
SNAP - Explore Sentinel-2 products (Old version). (2016, January 16). https://www.youtube.com/watch?v=tR_7Oq80TkA