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Earth Observation guide

This guide aims to help researchers to work with Earth Observation (EO) data using CSC's computing resources. The purpose of this guide is to give an overview of available options, so it would be easier to decide if CSC has suitable services for your EO reseach. It also helps you find the right data and tools for raster data based EO tasks. This guide focuses on spaceborne platforms. However, many tools and concepts also apply to airborne platforms. If you are interested in the fundamentals of EO, please check the resources and further reading section.

What are the benefits of using EO data?

  • Possibility to observe wide areas at same time
  • Non-intrusive
  • Same sensor for different parts of the world, easy to compare different areas
  • Time series to see changes during different seasons and years
  • Cost-efficient

Raster data format

Most EO data is available in raster format. The most common file formats are GeoTiff and GeoJPEG2000.

Why should I use CSC computing resources for EO?

For working with EO data in general, there are three main options:

1) EO specific services, which provide both data and advanced ready-to-use processing environments. Usually these give better user experience and efficiency, but the services might be limited in computing power, available tools and options for adding own data. Often these have fees for using.

2) Cloud services with access to EO data. Practically, the data is often stored in object-storage and can be accessed as independent service. They also provide general computing services, such as virtual machines, to which EO tools need to be installed by the end-user. These options usually have some fees, mainly for processing. The data download may be free of charge or have a small cost, depending on the amount of data needed.

3) Own computing environment - PC, local cluster. Data needs to be downloaded and all tools must be installed to this system. On the other hand, it gives more freedom to select the tools and set-up. Usually this does not cause any extra costs, but the computing power is usually rather limited.

CSC services do not fit well in this categorization, as they provide some features from all of these. CSC computing services provide a lot of computing power and storage space, and they are free of charge for Finnish researchers for academic or educational use.

At CSC, EO data can be processed and analyzed using a supercomputer, for example supercomputer Puhti, or a virtual machine in the cPouta cloud service. Puhti's computing capacity can hardly be compared to any other EO service, in both available processing power and amount of memory. Both Puhti and cPouta have also GPU resources, which are especially useful for large simulations and deep learning use cases.

Puhti has also a lot of pre-installed applications, so it is an environment ready to use. cPouta virtual machines are similar to commercial cloud services, where all set-up and installations are done by the end-user. In general, both services only support Linux software.

At CSC, some Finnish EO datasets are available for direct use. In many cases, however, downloading EO data from other services (see list of EO data download services) is a required step of the process. Puhti and cPouta provide local storage of ~1-20 Tb. For more storage space, Allas object storage can be used.

Using CSC computing services requires basic Linux skills and ability to use some scripting language or command-line tools. In addition, supercomputers and virtual machines require you to understand some specific concepts, so it takes a few hours to get started. The new Puhti web interface makes the start considerably easier, providing a desktop environment in the web browser, which enables the use of tools with Graphical User Interfaces (GUI) and also tools like R Studio and JupyterLab for an easy start with R, Python and Julia.

What data do I need?

What to consider when chosing data:

  • Sensor
    • Optical
    • Multispectal
    • Hyperspectral
    • RADAR (Radio Detection and Ranging), SAR (Synthetic Aperture Radar)
    • LiDAR (Light Detection and Ranging)
    • Note that depending on the wavelengths observed, clouds, ground conditions and atmospheric artifacts may result in data gaps
  • Resolution
    • Temporal: when and how often a certain area is revisited
    • Spatial: the area on the ground that each pixel covers, determining the size of the smallest possible feature that can be detected
    • Spectral: the area of the electromagnetic spectrum that is observed and spectral width of each band provided
    • Radiometric: number of bits used to represent the energy recorded (bit-depth)
  • Costs:
    • Some EO data is freely available as open data
    • Some commercial datasets might be possible to get for free/less for research
  • Preprocessing level
    • Raw data - can have different levels and often need to be processed before it can be used for reliable analysis
    • Different levels of preprocessed data - make sure you are aware of what kind of preprocessing has been performed on your data
    • Analysis ready data (ARD)
    • Mosaics
  • User experience and knowledge
    • Appropriate background knowledge required for many tasks
    • ARD is "ready to go", but be aware of what preprocessing has been performed on your data

Some widely used EO datasets

Name Max resolution, m Revisit time, days Years of operation Open data
Optical, multispectral
ESA, Sentinel-2 10-60 5 2015-> Yes
NASA, Landsat 15-120 8 1972-> Yes
ESA, Proba-V 100-1000 1-2 2013-> Yes
Airbus, Spot 1.5 - 1986-> No
Planet, several satellites 0.5-5 - 2009-> No
DigitalGlobe, WorldView 0.3-30 - 1997-> No
Airbus, Pleiades 0.3-0.5 - 2012-> No
Hyperspectral
NASA, MODIS 250-100 1-2 1999-> Yes
NASA, EO-1 10-30 - 2000-2017 Yes
Radar, SAR
ESA, Sentinel 1 5 6 2014-> Yes
ESA, Radarsat 1-100 24 1995-> Yes
TanDEM-X/TerraSAR-X 0.25-40 - 2010-> No
ICEYE 0.5-2.5 1 2018-> No
LiDAR Footprint size
NASA, ICESat2 13 91 2019-> Yes
NADA, GEDI 25 - 2018-> Yes

EO database

Database of all EO missions and instrument information can be found in the CEOS EO handbook database

Where can I find the data?

Commercial datasets are usually available from data provider, while open datasets may be available in different processing stages from different services. Where possible, it might be a good idea to check processing options close to the data, for direct access or faster download. While graphical browse and download services can provide a good overview of the data and are easy to use, the download of huge amounts of data gets considerably easier using a bulk downloader or download API (Application Programming Interface).

STAC

Many data providers provide a Spatio Temporal Asset Catalog (STAC) of their datasets. These catalogs help in finding available data based on time and location with the possibility for multiple additional filters, such as cloud cover and resolution. The STAC Index provides a nice overview of available catalogs from all over the world. The STAC Index page also includes many resources for learning and utilizing STAC. Check out also CSC's examples for utilizing STAC from Python.

EO data at CSC

Some Finnish EO datasets are available locally at CSC. A STAC catalog for all spatial data available at CSC is coming in 2023.

  • Sentinel and Landsat mosaics of Finland in Puhti. Accessing data in Puhti requires CSC user account with a project where Puhti service is enabled. All Puhti users have read access to these datasets. You do not need to move the files: they can be used directly, unless you need to modify them, which requires you to make your own copy.
  • Sentinel-2 L2A data of Finland in Allas. These files are public, so anybody can download them, also from own computer or other services.
  • More information and list of all spatial datasets in CSC computing environment

EO data download services

SYKE/FMI, Finnish image mosaics : Sentinel-1, Sentinel-2 and Landsat mosaics, for several time periods per year. Some of them are available in Puhti, but not all. FMI provides also a STAC catalog for these mosaics

European Space Agency's SciHub provides worldwide main products for Sentinel-1, -2 and -3. It requires free registration. Big part of the data is in the "Long term archive" and cannot be downloaded directly, but needs to be requested first. Download is limited to 2 concurrent processes per user. Please note that between end of January and July 2023 this system is being updated to become the Copernicus Space Ecosystem.

FinHub is the Finnish national mirror of SciHub; other national mirrors also exist. It covers Finland and the Baltics and offers Sentinel-2 L1C (but not L2A) and Sentinel 1 SLC, GRD and OCN products and requires own registration. Finhub does not have concurrent download limitations nor a "Long term archive".

Both of the above provide a similar Graphical User Interface (GUI) and Application Programming Interface (API) to access the data. You can also use for example the sentinelsat tool for downloading data from ESA open access hubs. See also CSC examples for SciHub and FinHub data download.

USGS EarthExplorer provides among others US related datasets, also worldwide Landsat mission datasets. It requires free registration. Data can be browsed and downloaded via web interface and bulk download. USGS is the main provider of the new Landsat Collection 2 data.

NASA Earthdata provides among many others harmonized Landsat 8 and Sentinel-2 dataset. It requires free registration and download is possible via web interface and bulk download.

Amazon Web Service (AWS) open EO data is a collection of worldwide EO datasets provided by different organizations, including Landsat and Sentinel. Some of the data can be downloaded only on "requestor pays" basis. Currently, Sentinel-2 L2A Cloud-optimized Geotiffs are available for free, also via STAC.

Microsoft planetary computer provides a STAC of all available data, which includes Sentinel, Landsat, MODIS. It is currently available in preview.

Google Cloud Storage open EO data, including Sentinel-2 L1C and Landsat Collection 1 data. Data can be downloaded for example with FORCE.

Terramonitor provides pre-prosessed, analysis ready Sentinel-2 data from Finland available between 2018-2020. It is a commercial service.

Other geospatial datasets

To find other geospatial datasets, check out CSC open spatial dataset list.

How can I process EO data at CSC?

You can find information about geocomputing using CSC resources and how to get started on CSC geocomputing pages, including links to creating user accounts and all other practical information.

What to consider when choosing a software?

  • Functionality
  • Interaction type:
    • Graphical User Interface (GUI)
    • Command Line Interface (CLI)
    • Scripting
  • Technical aspects:
    • Reproducibility
    • Supported operating systems
    • Automation possibility
    • Combination possibility
    • Computational efficiency
    • Support for parallel computing or batch processing
  • Open source vs proprietary
    • Proprietary tools need licenses which may be expensive and/or limiting the use of the tool
    • FOSS (free and open source software) allows the user to inspect the source code and provide high level insights in its functionality

What applications are available on Puhti?

FORCE - Framework for Operational Radiometric Correction for Environmental monitoring. All-in-one processing engine with CLI for EO image archives. FORCE example for Puhti

GDAL (OGR) - Geospatial Data Abstraction Library. Collection of command-line tools for accessing and transforming geospatial data. It is relatively fast and requires little computational resources. GDAL supports reading data directly from the Internet or object storage. GDAL is included in many other tools for data reading and writing. GDAL example for Puhti

Julia - Puhtis Julia installation does not include any geospatial packages, but they can be installed by the user. JuliaGeo provides an overview of packages for geospatial data.

Matlab - you can run Matlab jobs on Puhti conveniently from your own computers Matlab installation.

Orfeo Toolbox (OTB) - offers a wide variety of applications from ortho-rectification or pansharpening, all the way to classification, SAR processing, and much more. Orfeo Toolbox is available as CLI, GUI and via Python interface.

Python

  • The geoconda module provides many useful Python packages for raster data processing and analysis, such as rasterio, rasterstats, scimage, sentinelsat, xarray and tools for working with STAC.
  • Machine learning modules provide some common machine learning frameworks, also for deep learning..

QGIS - open source tool with GUI for working with spatial data including limited multispectral image processing capabilities. GUI with batch processing possibility and Python interface. Used for example for visualization, map algebra and other raster processing. Many plug-ins available, for EO data processing, check out the QGIS Semi-automatic classification plugin.

R - Puhti R installation includes a lot of geospatial packages, includeing serveral useful for EO data processing, such as terra, CAST, raster and spacetime, also rstac for working with STAC catalogs.

Sen2Cor - a command-line tool for Sentinel-2 Level 2A product generation and formatting.

Sen2mosaic - a command-line tool to download, preprocess and mosaic Sentinel-2 data.

SNAP - ESA Sentinel Application Platform. Tool for processing of Sentinel data (+ support for other data sources). GUI, CLI (Graph Processing Tool, GPT) and Python interfaces. SNAP GPT example for Puhti.

If you need further applications, you can ask CSC to install them for you.

Machine Learning with EO data

One example of the advanced usage of EO data is for machine learning. If you are interested in the topic, you can find a lot of examples from CSC machine learning with spatial data course materials. For practical guidelines, see also CSC machine learning guide

Alternative processing services

Below is a list of alternative EO processing services that might be useful, when a lot of data is required and downloading it all to CSC might not be feasible.

Google Earth Engine is a processing platform, which requires registration, but is currently free of charge for research users. It can be accessed via browser and has worldwide analysis ready data available (browse the catalog). In general, JavaScript is used on the platform, but also Python and R support exists. Check out GEE's tutorials. Note that Google Cloud Storage might be needed to export large datasets.

Microsoft planetary computer offers JupyterHub together with Dask Gateway, both CPUs and GPUs are available. It is currently available in preview.

Data and Information Access Services (DIAS) offer cloud based Virtual Machines (VMs), dedicated baremetal servers, containers, operating system and software images. These services are specialized in EO and have user support available. All of them are commercial services.

Sentinelhub is a commercial service that offers several different APIs.

Commercial clouds: Amazon, Google Cloud and Microsoft Azure, all provide virtual machines and other processing services, all of them have some local data, see links above.

Where can I get help?

If you are interested in using CSC services for your EO research, please make yourself familiar with the services:

You can find all the ways that you can get help from CSC specialists via CSC contact page. We are happy to help with technical problems around our services and are open for suggestions on which software should be installed to Puhti, or what kind of courses should be offered or materials/examples should be prepared. Please also let us know, if you would like to add a service to this page or find anything unclear.

Acknowledgement

This guide was developed in cooperation with the Finnish Environment Institute, SYKE, as part of the Geoportti project.

Resources and further reading

If you are interested in the fundamentals of EO, take a look at these excellent resources:

  • Fundamentals of remote sensing tutorial by Canada Centre for Mapping and Earth Observation , Natural Resources Canada; an "interactive module is intended as an overview at a senior high school or early university level and touches on physics, environmental sciences, mathematics, computer sciences and geography."
  • Echoes in space - Introduction to RADAR remote sensing by the European Space Agency; "a detailed insight into the history of Radar technology, including all the basics that are needed to understand how electromagnetic waves work and a unique hands-on experience to work with Radar data in diverse application scenarios."
  • Newcomers guide to Earth Observation by the European Space Agency, "a guide to help non-experts in providing a starting point in the decision process for selecting an appropriate Earth Observation (EO) solution."
  • Earthdatascience intro to multispectral data

Further reading:


Last update: January 18, 2023