Satellite Imagery: Near-Realtime Sources

Several public agencies collect daily/weekly imagery that can be very helpful for trip planning. These resources are particularly valuable in the fall and spring, when trying to get a sense for snow cover, frozen lakes, etc. I use three satellite sources: MODIS, Landsat, and Sentinel.

MODIS

MODIS Aqua and Terra satellites collect imagery daily, but the resolution is not great. I use this imagery to get a quick sense for conditions.

NASA Worldview is my go-to. The site is well-designed with a powerful time-slider to compare seasonal images. For Alaska, you will need to change to polar projection and rotate to north.

Change Projection

Rotate to North

Landsat

Landsat has less frequent imagery, but with slightly higher resolution than MODIS.

Sentinel Hub Playground provides an elegant interface to view Landsat imagery, as well as MODIS and Sentinel. Unfortunately, the MODIS resolution is not as high as provided by NASA Worldview, and Sentinel not as high as via EO Browser (see below).

Select Dataset

Select Landsat 8 from satellite dropdown

Click the calendar icon to view available acquisition dates (takes some time to render)

Available dates are highlighted

Choose cloud cover

Cloud cover slider, 0% filters to cloud-free imagery

If you choose a low cloud cover percentage, an older image will load, regardless of the calendar date selected. For this reason I prefer to view the acquisition date on the image. Select Show acquisition dates from the Effects tab

Show acquisition dates

Sentinel

Sentinel imagery is available several times per week, and, at least in Alaska, has incredible resolution.

There are two versions of Sentinel-2 imagery, L2A and L1C. For some reason, Sentinel Hub Playground (above) only offers L1C, the lower resolution option. For higher resolution, you want Sentinel Hub EO Browser.

EO Browser is a more complex site than the Playground, but the payoff is worth it.

From the Search panel, select Sentinel-2, L2A

Search panel

From the Results panel, either select Visualize from the tabular results, or click on a blue ‘coverage’ region.

Results panel

Note the cloud cover percentage in the results… you might want to scroll back to a date with less cloud cover.

Proof of Concept

These tools, particularly MODIS and Sentinel-2, were critical in pulling off a remote ice skating trip to Katmai National Park and Preserve.

This edit includes a demonstration of MODIS and Sentinel
I just want to see the skating!

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