What is Optical Imagery data?
Skylight uses Optical Imagery as short form for Electro-Optical Imagery or “EO”. Optical Imagery is one method of imaging the earth from space. There are several major providers of optical data, the European Space Agency (ESA) for Sentinel-2 and the US National Aeronautics and Space Administration (NASA) for Landsat 7/8/9 to name a few. Different providers offer collecting optical imagery with different coverages, resolutions, and add-on services.
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The images come in color
Visibility is impacted by weather (i.e. clouds can hide vessels below)
Many optical satellites do not work at night
What is resolution and why does it matter?
Resolution describes how detailed the image is. The higher the resolution, the better the detail, making it more likely to see vessel features and obtain better size and heading estimates. The lower the resolution, the more blurry the image. There is a tradeoff between resolution and footprint size. While higher resolution images are preferred over lower resolution images, the satellite must image a smaller area in order to capture higher resolution images.
How does Skylight use this data?
Skylight uses Optical Imagery Radar data to display vessels that are ‘dark’ (not carrying AIS) to users. As of May 2024 we use one source of optical imagery, summarized in the table below.
Source | Requires making an order | Collection area (footprint) size | Avg delay from collection to delivery | Coverage areas (where satellite is turned ‘on’) | Detections can be downloaded |
SENTINEL-2 | No | ~200 ~300 km x 250 kmwide | 4-6 hours | Most continental coastlines. Collection areas available for download here: https://sentinel.esa.int/web/sentinel/copernicus/sentinel-2/acquisition-plans | Yes |
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