EOSDA LandViewer and Other Free Satellite Imagery Platforms: Features And Benefits
Satellite imagery refers to the pictures of Earth taken by satellites orbiting the planet – a powerful source of information that shapes our understanding of the world in the entirety of its ecosystems. Spaceborne data empowers us to take an inventory of Earth’s surface, track changes, and spot patterns without the need for ground interventions.
The onset of space-based Earth observations roots back to the 1960s, however, it’s today that we’re seeing the highest democratization of satellite imagery driving its widespread adoption. Technology miniaturization and falling launch costs have led to a recent burst of satellite missions of all scales; while the spacecraft grew smaller, the quality and accuracy of collected data have increased. And so has the value of satellite-derived insights. With the current level of detail, satellite revisit frequency, and spectral capabilities, we are able to monitor deforestation across the globe, map natural disasters in near real-time, accurately forecast crop yields months before harvest, and detect specific minerals using hyperspectral data.
Figuring out what data you need: types of satellite imagery
Getting the most out of satellite data for your specific purpose requires more than a list of the best free satellite imagery platforms. Governments and businesses alike have been exploiting the ‘gifts of space’ in a variety of applications – from conducting nationwide cadastral surveys to estimating competitor sales by counting cars at the parking lots – relying on a variety of data that encompasses low, medium, and high-resolution satellite imagery, free (public) and paid (commercial) datasets, the most recent scenes and historical time-series spanning over years. The bottom line is that before diving into the search, it’s necessary to go through a checklist and determine the characteristics of satellite imagery that would provide the most value in the particular scenario.
Without further ado, here are some of the most important parameters to consider.
Temporal resolution. It is the interval between two satellite captures of the same area, also known as a satellite’s revisit period. This parameter can range from several weeks (Landsat 8, Sentinel-2) to several days (MODIS, SPOT 6, 7) to a quarter of an hour (weather satellites).
Spatial resolution. Roughly speaking, it’s the level of detail. Low to medium-resolution imagery will do the work if you need to zoom out to see a bigger picture. However, zooming in to spot minor details, such as a building or a vehicle, requires the highest resolution satellite imagery free from the limitations of lower spatial resolution.
Spectral resolution. The greater the number of spectral bands in the electromagnetic spectrum a satellite sensor can record, the higher its spectral resolution. Based on this, satellite images are divided into multispectral (3-15 bands) and hyperspectral (hundreds of bands). The typical minimum set includes the visible red, green, and blue bands, which make up a natural color composite – it is the closest to the way we see the world from the ground level: vegetation is green, water is blue, and snow is white. Every band contains valuable information and remote sensing analysis is the art of extracting it via mathematical equations (indices) and band combinations.
Scientists and analysts classify satellite images into multiple types based on their use. For instance, the three most widely used types in meteorology and climate studies are:
- Visible imagery
These satellite scenes capture the reflected sunlight in the visible spectrum, which means two things. First, it’s the most intuitive representation of Earth’s surface of all – basically, an ordinary photograph of our planet that’s very much like what the human eye would see from space. Second, such imagery can only be collected during daylight hours, with minimum to no cloud cover obstructing the view. Visible imagery proved its utility in land topography and water body observations; snow cover, fog, and clouds can be easily recognized in such pictures, which makes them a great tool for weather forecasting and early warning for the coming storms.
- Infrared imagery
Infrared cameras mounted on satellites are able to sense and measure the energy emitted by objects in the infrared spectrum, which is invisible to the human eye. This can be compared to the infrared vision of vampire bats or mosquitoes, detecting the infrared heat from their prey at night. Such satellite imagery is free from the limitations of the visible one and can be collected round-the-clock regardless of the cloudiness level. Sensors detect infrared radiation at different wavelengths enabling us to narrow down the best spectral bands depending on what we need to analyze. For example, thermal infrared images are crucial in locating forest fires and active volcanic eruptions, tracking variations in sea surface temperatures, and detecting urban heat islands.
- Water vapor imagery
To generate this imagery type, a special band within the near-infrared spectrum is used as it’s very sensitive to the presence of moisture in the atmosphere. Water vapor images help differentiate between regions with moist and dry air, which is instrumental in forecasting weather and predicting rainfall locations. It can also be utilized to identify the speed and direction of the wind whenever other imagery types fail to detect the presence of clouds in the sky.
Where to find free satellite imagery: top online sources
Once you’ve set your eyes on the specific imagery type, it’s time to learn where you can find it. Nowadays, there is a sea of online platforms providing access to public data and select high-resolution satellite imagery free of charge. Let’s take a look at the three most popular ones.
USGS Earth Explorer
It is a free in-browser platform offering 40+ years’ worth of data from Landsat, the longest-running Earth observation mission operated by USGS and NASA. An extensive library of satellite imagery available in Earth Explorer features Terra and Aqua MODIS, ASTER, VIIRS, as well as fragments of Sentinel-2 datasets and high-resolution imagery from SPOT, OrbView-3, and IKONOS. What makes this tool stand out is the opportunity to browse declassified images from old spy satellites and download hyperspectral imagery from NASA’s experimental Hyperion mission that can’t be found anywhere else.
Sentinel Hub
As the name suggests, this platform is the number one stop for ESA’s Sentinel products, including the only available free SAR satellite imagery from Sentinel-1 and, perhaps, the most widely used free multispectral optical data from Sentinel-2 with 10 m/pixel resolution, 5-day revisit period, and global coverage. Sentinel Hub also contains Landsats, MODIS, Envisat Meris, and several other datasets. On top of the image search, the platform can be used to visualize, analyze, and download data.
NASA Earthdata Search
A playground for Earth scientists, this online platform offers an overwhelming selection of the best free real-time satellite images as well as historical data, in particular, from the EOSDIS program (Earth Observing System Data and Information System). The highlights of an impressive list of available data include Terra and Aqua MODIS, Landsat, ENVISAT, NOAA, Suomi-NPP, and METEOSAT. Unlike the previous tools, it is not specifically focused on land use and land cover analysis. In fact, it encompasses a broad range of Earth science data that can also be effective in studies of the atmosphere, hydrosphere, biosphere, and cryosphere. It’s important to note that there are no in-built tools for image analysis.
EOSDA LandViewer – a one-stop platform for working with satellite imagery
EOSDA LandViewer is another digital platform that is worth mentioning. Developed by a trusted global provider of satellite imagery analytics, EOS Data Analytics, it provides access to a host of the most sought-for public data and allows previewing high-resolution satellite imagery free of charge for further purchasing.
The best thing about this service is that it enables on-the-fly search, visualization, analysis, and downloading of data, saving time and effort that would otherwise be spent on getting all of this done in separate tools. Users can select their area of interest on a global map and choose from a list of both optical and radar pictures available to visualize the territory. It features the latest and historical free satellite imagery from Landsats, Sentinels, MODIS, CBERS-4, and NAIP missions that can be analyzed and downloaded for further use. Besides, users are free to preview and purchase data of high to very high resolution provided by KOMPSAT-2, 3, 3A, SuperView, Gaofen 1 and 2, Ziyuan-3, and TripleSat satellites. The best resolution available is 0.4 m/pixel.
To reveal actionable information locked in spaceborne imagery, EOSDA LandViewer offers an extensive set of tools. Over 10 remote sensing indices and an ability to create custom indices and spectral band combinations within seconds are a staple of this online platform. Changes in land cover, water bodies, and other Earth features can be conveniently highlighted using split view or change detection. And to delve deeper into the dynamics of changes, the platform allows to construct a spatiotemporal time series graph based on a particular index.
All in all, EOSDA LandViewer is an example of a cutting-edge digital product that simplifies the search, analysis, and downloading of data acquired from space, leading to numerous advances on the ground in both science and daily life.