Analysis Ready: Technical documentation

Overview

The Terramonitor analysis-ready mosaic is a product designed for GIS professionals. The input required by the customer is the area and time period of interest. The output is the best possible Sentinel-2 mosaic available with these criteria.The mosaic is generated by collecting all available Sentinel-2 images from a given area, and combining any cloud, cloud shadow, snow, haze and smoke free parts of those images to form a uniform mosaic. The images are atmospherically corrected and radiometrically calibrated.

Input

The Sentinel-2 Analysis Ready Data works best with large areas of at least 100 square kilometres, and time frames of at least three months. As a rule of thumb, it is usually possible to produce an analysis ready data product of any country given a time period of one year.

Optical satellite images are not available for every area and time period, mainly due to cloudy weather. The resulting mosaic is thus a best effort with the given restrictions.

Delivery

Files

The resulting product is a number of GeoTIFF files, and a VRT file. A Terramonitor account and related API access token is required to access these files.

For practical purposes, the product is separated into files both spatially and with respect to the different resolutions available. The spatial separation means each file will cover a rectangular area of approximately 100 by 100 kilometres using EPSG:3857. The separation by resolution means each file will only contain pixels in resolution. VRT files are provided as an index to organize the files.

The filenames are of the format <tile index>_<resolution>.tif, for instance 0_10.tif for the first file in the product with data with 10 meter resolution, 1_10.tif for the next one, and so on.

Downloading the files

We will provide a direct URL to each downloadable output file. The recommended method of downloading many files is using the download manager FlareGet.

  1. Download the software here https://flareget.com/. For the purposes of this delivery, the free version of FlareGet is sufficient.

  2. Install the software. You will be prompted to install browser extensions upon installation. However, they are not necessary in this case.

  3. After installation, run FlareGet. From the menu, choose File -> Import -> From http link. Input the URL you got in the delivery confirmation email. Click “Get”.

  4. You will see a list of all the files for your product, around 20 to 50, depending on the size of your area of interest. Click “Start” to begin downloading them. Make sure you are not excluding any files, i.e. you have “All files” selected in Filters.

  5. By default, the files will be output to a folder named FlareGet in the user directory. If you want to change the default output path for the files, this can be done in Settings -> Categories

  6. Wait for FlareGet to download all the files. This will take around 5-10 minutes per file with a standard broadband connection, and several hours in total.

Alternative method for technical users

For tech-savvy users, we provide a curl command to download the files from command line in the delivery confirmation email. With minor adjustments, this is easily integrable to a Python script or existing automated pipeline.

Data

The GeoTIFF files contain all the band data of the Sentinel-2 sensors for every pixel. Having the full band data means these GeoTIFF files are directly usable in further automated processing, as well as visual inspection with any band combination and without any loss of information. In addition to the Sentinel-2 bands, the files contain the acquisition date of the images in 20 meter resolution.

The Sentinel-2 data for 10 meter bands are in files with the _10 suffix. They are ordered B04, B03, B02, B08, or R, G, B, NIR. The 20 meter bands are in files with _20 suffix, and they are ordered B05, B06, B07, B8A, B11, B12, acquisition year, acquisition day of year (DOY).

A detailed description of band characteristics can be found on the Sentinel-2 mission site: https://sentinel.esa.int/web/sentinel/user-guides/sentinel-2-msi/resolutions/spatial

Troubleshooting :

Feel free to send us any questions regarding data quality or how to access it. Our tech team will respond within one work day.