Sentinel Satellite Imagery
Note: due to the costs of accessing this data, it may be restricted to paid CalTopo accounts at some point in the future – we’re going to leave it public as a trial run and see how that goes.
It’s been a long, heads-down grind here at CalTopo as we work on the app, and new desktop features have been put on hold for now. Occasionally, however, something crosses our desk that’s so exciting that we can’t not work on it. Sentinel imagery is one of those features, and I haven’t been able to put it down since discovering it yesterday.
Thanks to the Copernicus program, its Sentinel satellites, and the Sentinel Hub aggregation site, CalTopo’s low-resolution MODIS daily satellite imagery is now supplemented by high-resolution Sentinel imagery on a weekly update cycle (Sentinel-2 images the globe every 5 days, but to keep things simple, the CalTopo UI uses weekly blocks). For now, the layer is named “Weekly High-Res”.
As with MODIS, once you select the layer, there are some configuration dropdowns:
When it comes to pre-trip planning, I truly believe this is a game changer – and that’s not a term that’s thrown around lightly at CalTopo. How good is it?
A major use case is checking snow coverage for spring or summer trips, for example Mt Whitney. MODIS can often give you a rough sense of the snow level to +/- 1000′, but here’s what it looks like zoomed in:
By comparison, here’s a Sentinel image taken sometime in the past 5 days:
Dialing the clock back two weeks (+/- the 5-day acquisition window) gives a sense of the melt rate. For exact dates, you’d need to consult Sentinel Hub’s playground.
Say you want to know how 2017 (another high-snow year) compares to 2019? Setting the timeline to “2 years ago” shows slightly less snow than the most recent shot from this year, but given the melt rate and uncertainty around exact acquisition dates, I don’t think you can draw any conclusions other than the years being roughly comparable:
If you’re not familiar with the Whitney area, a satellite image alone isn’t going to help orient yourself. Here’s MapBuilder Topo blended with false color Sentinel imagery, giving a good visual of snow coverage without obscuring the map features:
Beyond snow coverage, here’s a pair of images showing how Lake Powell’s changing elevation over the past two months has impacted a canyon (show in false color so that the water is easier to identify):