Free remote sensing data sources

EarthExplorer

EarthExplorer is a multi-source query and download tool operated by the US Geological Survey. It gives access to most US federally produced optical remote sensing data from aerial sources and from satellites with less than daily revisit. As a rule of thumb, it has more archival and high to medium resolution data, while WorldView has more realtime and low resolution data.

Access requirements

Public with a (free) Earthdata account.

Example workflow

1. Create an Earthdata account and log in.
2. In the Search Criteria tab, drop a pin on your site of interest.
3. Select something in the Data Sets tab, for example Landsat → Landsat Collection 2 Level-1 → Landsat 8-9 OLI/TIRS C2 L1.
4. Click the Results tab. In the listing there, next to a scene that you like, click the footprint icon to see it previewed at low resolution on the map, or click the download icon next to it.

Highlights

• The whole Landsat archive: near-global medium resolution multispectral imagery back to 1972.
• Sentinel-2 access: while it’s not the best S2 browser, it’s handy to have available for comparison to Landsat, etc.
• ISRO Resourcesat data – rarely the best available data in terms of resolution, but often overlooked, and sometimes able to fill a crucial gap in better-known sources.
• Excellent aerial (high resolution) coverage of the continental US, for example with NAIP.
• A scattershot, relatively small, yet occasionally useful collection of commercial imagery licensed for open redistribution. For example, coverage of the Korean Peninsula in the mid-2000s with OrbView-3 data.

Limits

• Most data is US-only – can be tedious to wade through if you’re looking for something else.
• Download speeds are often low (a few MiB/second). If you’re fetching large datasets, it’s often best to use EE as a browse tool to find image IDs, then pull them from a faster endpoint (for example, Landsat on AWS).
• Frequently down for maintenance: typically several days/year.

Tips

• For advanced search queries, use the Additional Criteria, which uses metadata as available per dataset. For example, you might construct a query like “Landsat scenes that are less then 50% cloudy and from either June or July of any year between 1990 and 2010”.
• In the nested directory in the Data Sets tab, click the “i” icon to get a dataset description. Click the map icon to display the dataset’s footprint on the map, so you can tell whether it covers your general region of interest (though this may take a minute for a dataset with a complex footprint).

Worldview

Worldview is a multi-source visualization, query, and download tool operated by NASA EOSDIS. (It should not be confused with WorldView, a series of commercial high-resolution satellites from Maxar.) It gives access to most US federally produced remote sensing data from polar satellites with daily revisits. In general these are low-resolution sensors (on the order of 1 km/px) that are focused on topics related to the weather, climate, and environment, for example creating fire maps.

Access requirements

Public; some features may require a (free) Earthdata account.

Example workflow

1. Click the orange + Add Layers button on the left sidebar.
2. Navigate to Air Quality → Fires and Thermal Anomalies and click it.
3. Click the checkbox by Aqua and Terra/MODIS → Fires and Thermal Anomalies (Day and Night).
4. Close the dataset chooser overlay (returning to the map view).
5. Move the date playhead (arrow) at the bottom of the window to yesterday or before (to allow time for data processing).

Highlights

• “Earth at Night” data: Suomi NPP/VIIRS Day/Night Band and its derivatives, which are low-res but allow quick insight into events like power outages, gas field operations, etc.
• Some access to geostationary imagery.

Limits

• Although it has significant download capability, it’s generally more oriented toward in-browser visualization.
• Very little data available through Worldview is sharper than about 250 m/pixel.

Tips

• The main polar imaging instruments, MODIS on the Aqua and Terra satellites and VIIRS on Suomi NPP and NOAA-20, provide a richly multispectral 4-frame animation over midday for basically everywhere that is not in polar night or the gap between swaths. Although it’s low-res, it can be valuable for, e.g., using cloud configurations to pin down times of images.