Alaska scientists use satellite to detect open water on otherwise frozen rivers

A river mostly covered in ice on a sunny day with a bridge in the distance.
A photo of the Tanana River from Salcha contributed to Fresh Eyes on Ice. (Tori Brannan)

Scientists at the University of Alaska Fairbanks have developed a way to use satellites to detect open water on otherwise frozen rivers.

Open water can be dangerous for Alaskans who depend on river ice to get around, and having reliable information about such hazards could make it safer for those traveling on the ice.

Enter Synthetic Aperture Radar. That’s when a satellite bounces a radar beam off the Earth’s surface and measures what comes back. UAF researchers figured out how to look at that data and classify the ice conditions on all sorts of different Alaska rivers from roughly October to January.

Remote Sensing Specialist Melanie Engram with the Water and Environmental Research Center at UAF was lead author on the study, published in March in the journal Remote Sensing of the Environment. Engram says Synthetic Aperture Radar, or SAR, is a great tool for Alaska, because it doesn’t depend on daylight and can penetrate cloud cover.


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This interview has been lightly edited for length and clarity.

Melanie Engram: We have long, dark winters where optical imagery is rare or or not available at all. So having an active instrument, such as SAR, that can provide its own illumination is really useful in especially in northern earth science studies.

Casey Grove: Does it paint a picture? Does it tell you the depth or the quality of the ice? How does it work?

ME: We looked at a small area of the river that we had. We also took a photo that was pointed down on the ice with shore-based cameras to train the classification. So we could we could see, “Oh, that’s open water in the photo.” And then, “What do we have in SAR?” And then we would see, “Oh, there’s ice and ice cover. It’s rough ice covered or smooth ice covered.” So it was pretty much, “Let’s look and see.” Look and see what is, when the river is open, this is what the SAR values are. When the river has ice on it, this is what the SAR values are. We used shore-based cameras. We used citizen science photos that were uploaded to the Fresh Eyes on Ice photo portal. And then we also went out on the ice in January of 2021, on a stretch of the Tanana River close here to Fairbanks.

CG: Yeah, for the fieldwork that you actually had to go do, it wasn’t like you were just sitting in an office and looking at what the satellite told you, right? You actually had to go out in some fairly cold temperatures, right?

ME: Yeah, it was. It was more than 20 below, 26 below was the coldest, I think. We went out on snowmachine. You could see the, you know, the steam coming up from the from open water. So there were open water zones, even in late January. That was helpful for us. We went down as far as we could until there was open water toward Nenana that we couldn’t we couldn’t go any farther.

CG: I mean, that’s kind of the point, right? To help people understand what the river is doing, you know, who may be out there traveling by snowmachine? Did it kind of drive home that point for you and kind of take it out of the theoretical realm into the real world where you were actually like seeing the open water?

ME: Yes. And that’s why they they brought me along. So I’m a senior citizen, but I thought it was really important to get out there and see it myself and say, “Well, oh, OK, this is this is what the river ice is like. These are some other things we might want to consider.” We pulled up big blocks of ice, and we looked to see if it was clear ice or if there was sediment that was frozen in the ice, and I never would have thought of that sitting in the office. So I think it’s really important to get out there and actually put your boots on the ground of what you’re studying

a portrait of a man outside

Casey Grove is host of Alaska News Nightly, a general assignment reporter and an editor at Alaska Public Media. Reach him Read more about Caseyhere

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