#32 – Mike Roddewig

September 30th, 2026

#32 – Mike Roddewig

{Music}

00:00:10,860 –> 00:00:48,740 [Austin Madson – Host]
All right. Hello, everyone, and welcome to the LIDAR Magazine podcast series. My name is Austin Madson. I’m an associate editor at LIDAR Magazine. Thanks for joining us today as we continue exploring the many different applications of lidar remote sensing. We’re really happy to have the opportunity to chat with Dr. Mike Roddewig, who joins us today from Fairbanks, Alaska. Dr. Roddewig is an assistant professor with appointments in the Electrical and Chemical Engineering Department and the Geophysical Institute, where he’s affiliated with the Space Physics and Remote Sensing groups.

He’s also the chief technology officer of 532 Engineering Incorporated, a novel lidar startup company. Dr. Roddewig received his PhD from Montana State University in 2017, where he built an airborne fisheries lidar system to locate invasive trout in Yellowstone Lake. After his PhD, he stayed in Bozeman to work for a photonics company, building instruments around nonlinear optical crystals. He also worked part-time mapping rivers using acoustic Doppler profiles.

00:01:13,880 –> 00:01:53,600 [Austin Madson – Host]
A few years later, in 2019, he was hired back at Montana State as engineering lead on an undisclosed Air Force lidar project. In 2022, he started his company, 532 Engineering Incorporated, to work on commercializing a drone version of that same fisheries lidar that he developed during his PhD work. Dr. Roddewig’s research interests are in optical oceanography and the development of new lidar and passive optical instruments to solve remote sensing problems. His current work focuses on the development of frequency-modulated coherent lidar, drone-borne water lidar, and upper atmospheric ion lidar. All that said, let’s go ahead and get going. Thanks again for joining us today, Dr. Roddewig.

00:01:54,360 –> 00:01:55,760 [Mike Roddewig – Guest]
Yeah, of course, Austin. Happy to be here.

00:01:56,180 –> 00:02:09,240 [Austin Madson – Host]
Fantastic. Yeah, so why don’t we start a little bit by having you talk about your journey to University of Alaska Fairbanks, or UAF. How did you get here, or there, rather, and what led you to photonics?

00:02:10,860 –> 00:03:18,180 [Mike Roddewig – Guest]
You know, it was all a bit kind of convoluted in a sense. I initially never intended to get into photonics. You know, as an undergrad, I thought optics was just camera lenses, and I didn’t–wasn’t particularly interested in camera lenses. And, uh, I got my undergrad and then went to do my master’s at, uh, School of Mines, where I did, radio astronomy, built a radio telescope and was gonna continue down kind of an RF path. And instead, you know, I was gonna go to UC Boulder for my doctorate and mentioned to the professor there that… I mean, so I really liked the outdoors, and so it was part of the reason I had gone to Colorado, and mentioned to the professor who was gonna pick me up there that, “You know, wouldn’t it be great if there was, you know, some good programs up in Montana?” And she was like, “Oh, you know, you should talk to Joe Shaw at Montana State.”

And I ended up talking to Joe Shaw at Montana State. He was doing some work up in Barrow, Alaska, which is the northernmost city in the US, and I thought that sounded pretty exciting. And so I ended up at Montana State. And so initially we were building infrared cloud imagers, which are basically devices that use thermal cameras. You look up at the sky. The sky itself is colder than clouds, and so that tells you what the cloud cover is doing, um, and what portion of the sky is obscured or is not obscured. And about a year into that, the lab I was in picked up this fisheries lidar project to put on a Cessna, and it was being worked on by one of the staff engineers. I went to Joe and I said, “Hey, you know, that sounds really cool. Can I go work on that?” And he said, “Yeah, sure. Just so you know, there’s no real money in it, and so, you know, you’ll have to find your own funding to do it.” And so I did, and every year I would hunt down fellowships or whatever to, you know, pay for, you know, my tuition and salary and a stipend, and get this lidar out the door, which we did.

And it was a lot of fun because it combines a lot of neat things. You get to be out flying in a plane. We flew over Yellowstone Lake. It was incredibly pretty. And it’s a fun problem to look for fish in the water using lidar. We really have only, I think, as far as research, scratched the surface. And, you know, part of that is it’s kind of this niche topic that, you know, most lidar people are familiar with. Uh, everyone assumes when I say lidar, they’re all like, “Topographical lidar.” And I say, “Oh, no. I don’t do…” I– We would like to have point cloud data from the ocean or a lake one day, but we’re not at that point yet. And there’s just a lot of fun work to be done in it. Uh, and it’s, uh, it’s this neat combination of the outdoors and, you know, doing field work and then also developing some really cool optical instruments. And so I, I think that that’s kind of how I ended up in optics and, so kind of by accident in some sense.

00:05:20,060 –> 00:05:35,620 [Austin Madson – Host]
Yeah, that’s, that’s really great. Let’s… Can we dive in a little bit more to your PhD, your self-funded almost PhD work, right, this special lidar project? How, how did it come about, and, and what really drew you to it? It obviously wasn’t the funding.

00:05:36,320 –> 00:05:40,320 [Mike Roddewig – Guest]
Back then, I did not understand the nuances of funding very much, so I’m not sure how it was initially funded. I think Montana State had a ecology center or something along those lines that was… They, they had paid money to build the instrument, and the pilot that was flying it, I think, was donating his time, his flight hours. And so the need was, and I believe this is still a problem, so Yellowstone Lake, uh, back in the late ’80s had a whole bunch of lake trout introduced to the lake.

And it’s a problem because they’re not a native species to Yellowstone Lake and they compete with the cutthroat trout, which is what a lot of the different animals rely on, so the bears and the wolves and so on. And so the, the problem is the, the lake trout, they spawn, and when they do spawn, they spawn in deep water where predators can’t get them. And so they… And then they go and eat cutthroat trout. So they’re, they’re kind of this, uh, this fish that is invulnerable, I guess, in a sense. And so the Park Service for many years, and I don’t know where the project is at, it’s been about 20 years since I worked on this. Um, well, no, 10, thank gosh, has been trying to remove the lake trout by one, you know, one means or another. And one of the things they really wanted to do was locate the spawning sites, uh, where the lake trout were spawning because they typically spawn in the same place every year. Um, or so they t- I’m not a fisheries biologist by any means, so I just know what I’m told and what I remember.

And so the Yellowstone Lake itself is fairly large, and the way they would normally locate spawning sites is they would go out and map with sonar from a boat, or, they at one time tagged fish with ultrasonic markers and they’d track where they went, and then they’d kind of figure out this is probably a spawning site. And so what we did was in some sense complementary to that. I mean, the advantage we… Yeah, and I tell everyone, lidar doesn’t necessarily add a capability that a fisheries biologist or an oceanographer or a limnographer wouldn’t already have. What we do is we fly in a plane, right? And so a plane flies at a hundred miles an hour, and so we can cover very large areas very quickly. And that was the advantage of lidar, in Yellowstone Lake, is we could go survey like the southeast, uh, arm of the lake, which is very remote and would take them, I think they said two or three hours by boat just to get to it, and then they’d have to begin their surveying. So yeah, that was the need.

And so we identified several spawning sites and we published a paper basically showing that where we had identified, you know, probable, you know, congregations of fish and the environment was right. So the biologists, of course, know they like to spawn in this much water and they’re about this far off the bottom and so on. And it matched up really well with some of the other data that they have that those were indeed spawning sites. And so that was the impetus behind that project, was to, you know, locate the spawning sites of lake trout. And then we also did some other fun things just because now we had the lidar and a plane, so we might as well go fly it.

00:08:49,092 –> 00:08:55,252 [Austin Madson – Host]
Well, what, what are some of the other fun things that, that you did that you could utilize that new lidar?

00:08:56,292 –> 00:09:43,512 [Mike Roddewig – Guest]
So one of the neat things about the lidars that we build is they’re what’s called dual polarization. And so everyone’s probably familiar with polarized sunglasses. And the way that works is, you know, your, your light’s an electromagnetic wave, which means it has both an electric and a magnetic component. And that electric field has a directionality associated with it. And so dual polarization means you can detect and separate light based on that directionality. And that’s also how polarized sunglasses work, because light that reflects off the ground tends to reflect with a certain polarization. And so if you build a filter that cuts that out, you, you know, you reduce your glare. You can see, you know, see much further into water and things that I think people are probably familiar with. I wanted to test, ou know, was one (where) there’s different types of polarization.

\And so you could apply one type of polarization to the outgoing beam of your laser and then detect what returned. And so I was looking at was there an advantage to one or the other? That project ended up not going a whole lot because what we ha- I needed a target to hit, right? Some kind of reproducible target. And I was just a, you know, I was just a grad student. And so, you know, what I did was I went and bought a whole bunch of PVC pipe, um, sunk it to where it was about three meters in the water and then put these little marker buoys at the end. And it was, it wasn’t long enough, I think, for the pilot to hit. Like, we would, we made these… He just kept passing and passing over it and we never really got it. And then I think before we were able to come out, some storm blew, and this was in Flathead Lake in Montana, which is in the northwest part of Montana.

So Yellowstone’s kind of, um, south, I guess southwest corner. It’s mostly Wyoming. And a storm came in and destroyed my target. And then I think Joe or someone got an angry call from the director of the Flathead Lake Biological Station saying that, “Your student’s PVC is all over the place and it needs to be gone.” And so, uh, my wife and I went out in a, in a rowboat and actually dove because some of the, some of the pipe had washed up on shore and then some of it had, uh, you know, ended up kind of just scattered throughout the bay where you could see it. And so we dove and retrieved all these pipes, and that was kind of the end of that project.

And so we were also looking for phytoplankton, uh, densities, which is, you know… So basically, we can see anything in the water that you or I could see, except we’re a lot more sensitive, right? So we put out a lot more light, right? So you don’t want to look into the beam. And, um, we have a much more sensitive detector than what our eyes can do. And so… But it’s still just fundamental physics that everyone can understand, right? You know, if light reflects off of something, we can see it. And if it doesn’t, we can’t. So, um, anyways, you know, so that, those were the… We never got a whole lot with phytoplankton.

We did end up detecting, interestingly, in Yellowstone, um- So Yellowstone has a lot of geyser activity, right, which everyone’s probably familiar with. And so the geysers are not only above ground, they’re also under the water. And so we were able to, in our fisheries surveys, you know, we’d usually we’d fly the shoreline because that’s where the lake trout wanted to, to spawn. And so we hit up by the north end of the lake, where I guess there is a lot of hydrothermal activity. And so we were able to see some old hydrothermal vents in the data and some active ones too, which was pretty cool. And so we published that as the, as far as we know, we were the, we the first ones ever to observe that with lidar.

00:12:36,176 –> 00:12:39,776 [Austin Madson – Host]
Oh, that’s really cool. What does an active geyser look like, you know, on the-

00:12:39,876 –> 00:12:58,916 [Mike Roddewig – Guest]
Well, it looks like if you have seen the videos of like the vents that are in the deep sea, right, and they’re just spewing stuff out of them? So in the data, it looks like you’d have a little chimney and then there’d be, you could see the plume coming out of it. And so at first I wasn’t sure what it was because literally the, the way I looked at the data was I would sit down, you know, in the evening with a beer and you just paged through, you know, page of data and be like, “Oh, that’s a fish.” And then I had a little utility error that said, “Okay, in this image there’s a fish. Tell me what the coordinates are.”

And, and so for a long time I didn’t know what it was. It just seemed very odd. And, you know, eventually we figured out because the USGS had gone out and surveyed the location of all these geysers that, wait, we pretty much hit one. Um, it wasn’t 100% because I, I had it… So when we’re doing, when we’re flying a lidar, right, the attitude of the, the position of the plane matters. You get GPS, but also the attitude and the orientation of the plane matters as well, right? Which is, uh, you know, probably compensated for by most lidars. In our case, we didn’t really care because, you know, when you’re mapping fish, they’re there and then they’re gone, right? So if, if you’re within 50 meters, that’s good enough for the biologists. So I had an inertial measurement unit on there that could have given me pitch and yaw and so on, but we, we never used it. And so we weren’t, you know, I mean, we, we, I think we were within like 10 meters of the, the vent and I was like, “That’s pretty much for us, that’s pretty much dead on.”

00:14:15,336 –> 00:14:22,096 [Austin Madson – Host]
Yeah, that’s really cool. I’ll have to send a follow-up message and see if you can dig up one of the old cross-sections and maybe we can post it.

00:14:22,136 –> 00:14:23,236 [Mike Roddewig – Guest]
Oh, yeah.

00:14:23,296 –> 00:14:23,716 [Austin Madson – Host]
Yeah. That’s fantastic.

00:14:23,736 –> 00:14:28,576 [Mike Roddewig – Guest]
Yeah. I’d be happy to send, you know, and photos of what the fish look like too in the data.

00:14:29,596 –> 00:14:57,936 [Austin Madson – Host]
Yeah, that’s great. Thanks, Dr. Roddewig. Let’s talk a little bit more about UAV lidar in Alaska. Alaska is, you know, and I think inherently a special place, and you as a resident know that more than most. And so I, I understand your team just got a new grant through NOAA to work on some really cool projects there. Can you, can you walk us through what the goals are for that project and what in particular your, your team will work on and, and why?

00:14:58,016 –> 00:15:00,416 [Mike Roddewig – Guest]
Oh, yeah. Yeah, for sure, because we’re thrilled.

00:15:01,696 –> 00:15:01,856 [Austin Madson – Host]
Congrats.

00:15:01,856 –> 00:15:03,916 [Mike Roddewig – Guest]
So yeah, thank you. I had built, for my PhD, I graduated 2017, and we had built this, um, uh, basically an oceanographic glider. It flew in a Cessna 185, which for people who aren’t familiar with planes, which I wasn’t, this 185 is notionally a four-seater aircraft, but you’d have to be a really small person to be in the back seats. So your kids could be in the back seats and then two people fit in the front. Um, like you said, I, I went and worked, after I got my PhD, I had to get a real job. Couldn’t be a student anymore, you know? And so I, I went, and Bozeman is kind of unique in that it has a, a big cluster of all these small photonics companies. And so I was picked up by one of those companies. Um, didn’t end up doing lidar.

I ended up just doing more laser and, um, uh, nonlinear optical development and instrument development around that. And three years after that, Montana State got this big Air Force project, and so I was recruited back to Montana State to work on that. And while I was there, I think it was two or three different groups, like folks from the Navy, folks from NOAA kept saying, you know, kept coming to us and saying, “You know, we, we really like your li- your lidar, your ocean- you know, your, the fisheries…” We call it the fisheries lidar. There’s no real, you know, like official name for these things. And so it can kind of vary depending on what crowd I’m talking to, what I call it. But it, at that time it went by the fisheries lidar. And they said, “We really like it. Could you put it on a drone?” And then my initial response was, “No, you’re crazy.”

Because you have to understand that the lidar signal, when you’re dealing with like a, what’s called a volumetric target, so something like water or cloud that’s like a large target that exceeds the size of the beam and scatters, you know, has many little particles that are all scattering, the power falls off as the range squared. And that’s just kind of a geometric, you know, s- because it’s the beam goes out as a, as a spherical wave front. So as the sphere gets bigger, your power in any particular area of said sphere becomes, you know, one over R squared, where R is the range. And so the pilot at the time I was working with said for safety reasons, when he was over water, or I think probably, probably just anywhere, um, I’m not a pilot, so he said he would fly, the lowest he’d fly is 1,000 feet, right? So that’s about 300 meters. So you’re looking at a one over 300 squared loss of power before you even hit the water. And water itself is incredibly attenuating. I mean, we would, our max penetration depth, um, was about nine or 10 meters. So you don’t really go, which is still, it’s still 30 feet.

And so I keep, I have to remind myself sometimes because, you know, 10 meters sounds pretty lo- small. And I’m like, “Wait, it’s actually 30 feet.” So that’s not bad. But, you know, so you’ve lost all this power. And so to compensate with that, we have this, um, big what are called neodymium, uh, Nd:YAG. If you ever see Nd:YAG, those are the kinds of lasers we’re using. It stands for neodymium-yttrium-aluminum garnet, I believe. Anyways, that, that’s… If you have a green laser pointer, you have an Nd:YAG laser. And so we just had a much larger version of that, right, that put out a lot of power. And so that required… It had to run off AC, and so we had to put an inverter in the plane. And initially, we hooked up the inverter.

The plane had a cigarette lighter , which I still think is a bit, you know, amusing, but it the plane had a cigarette lighter output. And so we hooked up our inverter to that, and immediately, I, I think we might have blown a fuse or the inverter just screamed that, that, “I can’t do this.” And, uh, so we had to get it… Getting this thing off the ground, like getting it, you know, working was a real, it was a real process of trial and error. So we had to go run to Batteries Plus, and we were just like, “Give us the biggest deep cycle battery you have in a battery box.” And then we ratchet strapped that down in the plane because, of course, you can’t have things loose in case you’re in a crash. You don’t want a, you know, 50-pound battery flying around, right? So anyway, it was a bit of an adventure. I was just like, there, there’s just no way, right?

You know, there’s no way you can do this because you need… And you also need, like, a much fancier detector, you know, that’s really sensitive, because the signals then, it also, you know, comes back really weak. And so you end up, um, needing, you know, fairly large optics to collect the signal and then a fairly sensitive detector, all of which are specialized. And the thing ran on a laptop at the time, and it had these digitizers that are on USB. And so it was just like, how are you ever gonna get this on something like a hex? We… At the time, I was thinking a hexacopter, and I was just like, “It’s impossible.” And then I, I think after the second or third time someone came to us about this, I said…

You know, I was working with Joe Shaw again, and I said, “Hey, Joe, I’m gonna go, like, sit down, work the math on this.” And the enabling factor that makes these things work is the drones can fly really close to the water, right? So instead of one over 300 squared, you can be one over 10 squared, so one over 100, and that’s an enormous difference in power, an enormous difference in signal that you get back. And so I ended up, at the time, you know, we were working with NOAA, and I don’t know if I should say this, but NOAA is typically fairly budget constrained. So, you know, they’re like, “If you had an instrument, we could fly it, but we can’t really…” You know, we tried to get funding to develop it.

And I was like, well, I had come from the company I did, we did a lot of what’s called a SBIR grant work, which stands for Small Business Innovation Research. And I was like, this sounds… This kind of, like, building an instrument was exactly what we were doing at the company I was at. So I was like, “This sounds like an SBIR.” And so that’s how 532 Engineering came around. And so we chased SBIR grants through NOAA, um, you know, got a lot better at grant writing, but, you know, we were never quite successful. I did that until I ended up at UAF. Um, I came up to UAF, and then, uh, maybe some of your audience knows, but when you’re writing, like, a grant, like an SBIR, running a small company, there’s just so much you have to do.

And it’s not just writing the grant. It’s the registrations for the business and, you know, all the government rules, and it, it’s just a lot of work. And the nice thing about being at a university is you have offices full of staff that do these things for you. And so I was a little bit like, “You know, I’m gonna put the SBIRs on a back burner and see if I can get this funded through the university.” And that’s what happened. And so this was… This project was a congressional appropriation, uh, from Senator Murkowski. And in Alaska, there, there’s a few things that it, it’s, it’s a good fit for Alaska. So in Alaska, the fisheries industry is really big. Um, it’s a big part of our economy, and it’s also kind of just a cultural identity thing.

00:22:22,016 –> 00:22:30,796 [Mike Roddewig – Guest]
There are salmon hatcheries who raise, um, you know, rear salmon from eggs and raise them to be juveniles and then release them out in the ocean. And these hatcheries need a way… So people may or may not know, right, salmon, when they come back to spawn, they come back to the same place. So they come back to the hatcheries that they were born. And then the hatchery will sell the rights to harvest the fish to whatever processor. And to do that, they need to be able to have an accurate count of, well, how many salmon are there for you to catch? And so the way that’s been done up until, well, it’s still being done today, is usually it’s just a guy looking and saying, “You know, you know, probably 500,000, probably, you know, this, based off my, you know, 30 years of doing this.” And then the problem is the specific hatchery I’m working with, their guy is retiring.

And so now they’re like, “How do we replace the guy that has 30 years of experience? Wouldn’t it be nice if there was something else?” And so they’re really gung-ho about trying, working out on new technology. And so this NOAA appropriation is to work on proving the salmon counting concept and do it not with a manned aircraft, but do it with a, um, a drone. And part of the reason is that, you know, I, I guess I have nothing against manned aircraft per se, but to do our kind of lidar, you need a fairly, like, a one-foot, you know, one-foot diameter hole in the bottom of a plane. And pretty much no one really does that, right? No one cuts holes in the bottom of their plane. And so, you know, like the original pilot, um, like that we worked with in Montana, you know, he was… When we were trying to… Because we’d flown the fisheries lidar since I left Montana State, and we were trying to get him on board, and he retired and sold the plane to someone else, and that guy doesn’t want to fly. And so then I was hunting around. I finally found a guy in Portland.

00:24:20,628 –> 00:26:25,528 [Mike Roddewig – Guest]
Right? And so to do work in Alaska, I not only have to pay him for his flight time in Alaska, I have to pay him to fly from Portland to Alaska, which is a significant flight, right? And so it just gets very complicated and difficult. And I’m, I think, blessed in some sense that at the University of Alaska Fairbanks, we have what’s called a ACUASI, which is the Alaska Center for Unmanned Aerial Systems Integration. Because Alaska is most, most of it has no roads, and so there, a lot of transportation here is either by boat or by plane, especially if you live in a village, um, off the road system. I mean, those are your only real options to get somewhere. And so there’s been a lot of push to could we use drones to, you know, lower the cost of flying cargo and, you know, supplies and whatever else people need into these villages? Because it’s really expensive to live in one of these villages because literally everything is coming by plane or they barge it in in the summer, and sometimes the barge doesn’t make it and that creates a real crisis. And so a QUASI was founded to work on that.

And also, Alaska’s a nice place to test drones because there’s a lot of, you know, unpopulated land, right? So if your drone crashes, you’re not gonna hurt anyone. And they have a, a pretty big fleet of aircraft now. The one I’m particularly targeting is a fixed-wing vertical takeoff and land, because you get the best of both worlds. ‘Cause I was doing some hexacopter work after I first started my, uh, position here, and the problem with the hexacopters is they would fly out for 500 meters and then they were done and they would fly back. And it’s like you really can’t survey. Like, we wanna do transects, like really survey somewhere, and it just really wasn’t feasible. You know, but the hexacopter’s nice ’cause you don’t need an airstrip.

A lot of fixed-wing, the bigger fixed-wing drones, they actually need an airstrip to, you know, fly off of, and they’re complicated to move around and get to different places. And so thankfully, a ACUASI has these drones that are packable in checked luggage or they can fly air cargo, and then you can transport them to wherever you want. So we could be on the beach of the hatchery and launch the thing, and then it can fly for 500 miles because then it switches to fixed-wing mode. So you really get the best of both worlds, and it’s a big deal. And it’s exciting because I, you know, I don’t know how expensive these drones are, but I imagine they’re quite a lot, right? So, um, so this project, it, it just started and we’re putting together a, a pretty, I’m excited, an engineering team to build this. And we’re gonna work on, you know, target one of these fixed-wing drones with ACUASI.

And it also brings in the company because the idea is that once we have a prototype, and hopefully it becomes a little bit more reliable a prototype, the company could start selling this as a service because we have people that are interested in Alaska, “Could you come count our fish? Could you come locate our plankton?” Because when they place their juvenile pens out in their areas, they wanna place the juvenile salmon where there’s the most food, which is zooplankton. And so the, one of the things the lidar can do is map zooplankton or just plank- It can’t distinguish between zooplankton and phytoplankton, but it can map plankton densities. And so that’s really valuable information to the hatcheries, especially because climate change has been, you know, changing how their, um, their, their terminal areas work as far as water temp and so on and when the, the plankton are at their peak. So it’s just, you know, if you build it, they will come.

And then, of course, there’s a lot of fun research problems to do too. And so it’s, it’s really exciting because, you know, we’ve been trying… It, it’s hard to get people, I think, to fund fisheries lidar because it’s such this kind of oddball kind of topic. And so, you know, it’s, it’s really fortunate that we ended up in Alaska and we were able to, you know, contribute something that’s actually really important to the state. And the other application actually is doing bathymetry. And so bathymetry is measuring the depth of water and mapping it out. And this happens to be quite important to the coastal community in Alaska because they tend to get hit by typhoons every October, and you want to know where to build your house or your school or your community center in places that aren’t gonna flood. And to do that, the, uh, the physical oceanographers need maps of bathymetry.

And the problem is every time a typhoon comes in, the bathymetry changes, right? Because it’s, you know, like it’s basically, well, it’s because it’s basically a hurricane as far as I’m aware. And so right now, the… it’s very expensive. Uh, we fly with… There’s a, a group that’s contracted to do that every summer through, I believe, NOAA again. And if we had a local capability with rapid response, as in we can hop on the next flight out there with our crates of, you know, equipment and go map this out, that would be a big deal to these folks and, you know, help them be a little bit, you know, a little bit more resilient because things are changing as far as, you know, the world goes and they wanna keep their villages where they are. And it’s become a real challenge because of the flooding from typhoons.

00:29:48,328 –> 00:30:06,548 [Austin Madson – Host]
Yeah. Thanks, Dr. Roddewig. It’s a cool project. A couple notes. One, I’m glad that the manual counter is retiring. Otherwise, you might have a target on your back ’cause you’re, you’re taking his job. And two, my guess is that you’re gonna have a pretty nice IMU on this system, unlike your previous fisheries lidar.

00:30:06,608 –> 00:30:22,928 [Mike Roddewig – Guest]
Oh, yeah. For sure. Yeah. I mean, we had one. I just never… It was not a priority. I bought it because it was this little, like, $100 USB gizmo, and so you just plugged it in. I wrote the software to pull the data from it, but I never did anything with it. So, I mean, I guess we probably could now.

00:30:26,128 –> 00:30:26,727 [Austin Madson – Host]
Right, yeah.

00:30:26,748 –> 00:30:31,888 [Mike Roddewig – Guest]
But, you know, I, I haven’t… You know, you, you have, there’s, there’s many things you can do, but only so much time, so.

00:30:31,948 –> 00:30:32,468 [Austin Madson – Host]
Totally.

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00:31:05,188 –> 00:31:32,688 [Austin Madson – Host]
Okay. Well, so let’s switch gears a bit and talk a little bit about atmospheric lidar. In particular, I understand that UAF runs a handful of these at their facilities, and, and there are different, different kinds. Can you talk a little bit about Rayleigh lidar and, and resonant lidar, and what are they and, and how do they differ from each other, and, and what information can you, can you glean from utilizing them?

00:31:33,548 –> 00:32:31,248 [Mike Roddewig – Guest]
Sure. And I’ll, I’ll start with the caveat that I’m not an atmospheric physicist. I’m much more of an engineer. I collaborate with, um, atmospheric scientists and physicists who are much more familiar with the measurement than I am. And so I can give a basic overview of what they’re looking for. And so there’s different types of lidar looking up in the atmosphere, and we’re typically interested in measuring things like temperature, wind speed in the atmosphere, and also just the density. And that would be either the density of just what’s called the neutral atmosphere, which is something that’s not charged like an ion, or looking at things like sodium or, um, iron. And iron at least tends to, you know, meteorites hit the Earth all the time, and they burn up and then that releases iron. And if they stay high enough in the atmosphere, they become atomic iron, so just literally the iron element and nothing else with it.

And so we build different lidars to look for these things. The first one you mentioned is called a Rayleigh lidar, and all it does is look at the scattering from the air, and that’s it, right? And so if you put out enough light, you know, I mean, we all understand that we don’t live in a vacuum, right? And so air has particles in it. So if you put out enough light and you’ve got a good enough detector, you’ll see the backscatter from the particles in the air. Even though to you or I it looks perfectly clear, the reality is it isn’t. And of course, everyone knows you put dust up and you can see it, right?

So it’s the same idea. It’s just, you know, we’ve taken it to the next level with, you know, high-power lasers, right? So the, the mechanism that causes that, it depends on the specific particle. Rayleigh scatter occurs when the particles are very small, and, you know, the, the lidar also detects what’s called Mie scatter. Mie is, like, more of, like, when you think of, like, you know, um, molecule-sized things, and so, like, ozone or, um, methane, you know, things of that nature. And you have the, the, the beam goes out and we basically just scatter off whatever there is to scatter off, and we measure that return. And through some really clever, uh, algorithm, retrieve winds from it, and you also just get the density of the air, of the neutral, um, because it’s just looking at just, you know, whatever’s floating around up there in general.

And so those lidars are useful, and we look for things like that are called gravity waves, different from gravitational waves, which people might be familiar with LIGO, you know, the laser, you know, thing that floats in, you know, satellites that looks for, um, gravitational waves. Gravity waves are just waves that are caused by different weather processes, and then gravity is what’s there restoring for us. So we all understand that, you know, water is a liquid, right? And you can make waves in water. Air is a liquid too in some sense, right? Because it’s kind of the same thing, right? Just a lot less dense. And so you can actually make waves in air as well. And so that’s under– It- it’s important. There’s a lot of research into understanding how those waves are formed, what generates them, how they propagate through the atmosphere, and so these lidars can detect that.

I mean, because they only look at one point, and they record that one point in time. And so you can see the variation in time as the wave passes through. You can also see the variation in density. And so the resonance lidars are a little bit more fancy and a little bit more fun. The way they work is we’re looking for a specific element. We have an operational sodium light resonance lidar here, and we’re currently developing an iron resonance lidar. And the way they work is every element has specific lines in wavelength that it wants to absorb on. And, you know, it’s a quantum mechanical effect. Sometimes it will absorb on one line and re-emit at a slightly different wavelength. And so it shifts the color just a little bit, but it does it in a completely, you know, repeatable form. We can excite the sodium elements, uh, at their absorption line and then look for the shifted response.

And that’s only you’re gonna, you know, it– that pinpoints sodium. You know, nothing else is going to do that. And so you know you’re measuring sodium. And so sodium, again, is the tracer for, well, you know, now know the sodium density, but you also know the wind and you know the temperature, and those things can be retrieved. It’s kind of basically the same techniques you would use, um, with Rayleigh. So, I mean, everyone probably understands Doppler shift, right? A siren from a car, you know, police car or firetruck sounds higher when it gets approaching you and then lower when it goes away.

Air particles, or sodium atoms, or iron atoms that are moving will also induce a Doppler shift in the light. And so that will move the wavelength slightly as well. And so if you have a really sensitive filter, you can pick off that shift, and that tells you what the Doppler is. And then temperature is measured by basically as we measure the width of the absorption line that’s actually in the element, and that tells you the temperature of the element. And that’s about as far as I can go there without getting out of my field too much.

00:36:54,764 –> 00:36:55,264 [Speaker 3]
Yeah.

00:36:55,384 –> 00:37:26,524 [Mike Roddewig – Guest]
And the trick to doing this is you have to be locked to that absorption line, right? And sometimes those absorption lines are only a hundred megahertz wide, and you’re talking, we’re working at in frequency like three hundred terahertz, right? Which is three hundred times ten to the fifteenth, right? And a megahertz is a hundred times ten to the sixth. So it’s an enormous– You know, you have to be extremely accurate, right? And not only do you wanna be in the absorption line, but you wanna be able to move around in it by literal megahertz, right? And so the way we do that, I actually did some of this at the company I was at too, is sodium, iodine, uh, rubidium can all be.

You can make them into a gas, um, and that gas can exist in a, a normal room. And so we put, you know, whatever element we’re trying to look for in a gas cell, and then we pass a beam through that, and there’s some fancy locking systems that will find the middle of that absorption line and lock the laser to it. And so we can control the frequency of the laser based on that reference cell. And so that’s how these different, um, most of these resonance lidars work, and it’s a pretty– I mean, it was good enough that the company I was at, we were looking at putting it in space. So it’s a fairly, you know, mature technique.

00:38:14,404 –> 00:39:18,584 [Mike Roddewig – Guest]
The problem with doing it with iron, well, there’s a lot of iron, A, in the atmosphere, and there’s even more iron now that, you know, people don’t think about it, and the Air Force thinks about it, that, you know, Starlink and all these other satellites are continuously reentering and burning up and depositing different elements into the atmosphere. And so the Air Force is very interested in, well, how is this changing the atmosphere? Because that’s important to understanding satellite drag, for instance. So you wanna fly a satellite really low to the Earth. How low can you get until it, you know, too much drag and it falls out of orbit? Iron is one of those elements that we’d like to understand better.

And the problem with iron is you can’t vaporize it in a normal room, right? It vaporizes at some absurd temperature. And so there’s no way we can have a gas cell, right, with some gaseous iron in it. It’s just not possible. It can happen in the atmosphere, you know, in the middle atmosphere. Um, you know, so we’re talking, you know, eighty to a hundred and twenty kilometers up, but it can’t happen easily, right, on the ground. The trick there is we want to use a what’s called a wave meter, and that tells us where we are within a certain accuracy. And then we have an even better system to get us down to kind of that, you know, tens of megahertz accuracy that we really need. And that uses a reference that’s called an, an etalon, which just basically means it’s a cavity, and that cavity has a very… And so everyone– You know, you, if you go, if you go put a child on a swing, right, you know, if you push the child at the right time, the swinging gets bigger, right?

If you push the child at the wrong time, the swinging stops. The cavity works the same way, except it does it with optics, right? You know, so we know that, you know, if the cavity is tuned… I mean, so light is a wave, right? Just the same as, you know, swinging is like a pendulum. It’s like a wave. And so if you have a cavity that’s exactly the right length, the light will constructively interfere with itself, which is what you’re doing when you’re pushing at the right time in the swing, is you’re doing constructive interference, right? Constructively pushing the child higher up. The light will then pass through. And if you’re off that, the light will be attenuated because it’s at the wrong…

You don’t get that constructive interference anymore. You actually get destruct, what’s called destructive interference. And so by using that and the the etalon is precisely at a precise temperature, and ’cause these things really matter when we’re talking nanometers, right? You you can use that to tell then where you are within about a gigahertz or so, um, which is, you know, ten to the ninth. And so, you know, that’s the system that we’re building. And one of the tricks was the absorption line we want to get to is at three seventy-two nanometers, which is not a standard laser wavelength at all. And it turns out you can still use an Nd:YAG laser because the YAG crystal that serves as the gain medium, um, does have a line at, well, it’s eleven sixteen, which if you then triple, you can get to three seventy-two. And so we work, we partner with a company called Lumibird Photonics, worked with them.

They were the developers of a commercial laser on converting this thing to work at eleven sixteen. And it, it was… None of us were, I think, going into this laser engineers, right? I’ve done lidar, but I’ve never built any of the lasers. I mean, I built a, a, a pretty simple laser when I was at the company I was working at, but nothing like building a whole YAG. And so, you know, it was a real experience, um, in just how difficult this stuff can be. We finally, um, we didn’t end up… The lidar is not completed. It’s still being worked on. A lot of that was, you know, this happened during COVID too, so there were delays due to COVID.

00:42:09,144 –> 00:42:49,024 [Mike Roddewig – Guest]
We do have lasing at three seventy-two, which is a real challenge to get to. And, uh, now it’s just, like I said, the laser has to be very precisely tuned to the right, you know, to hit that absorption line. And so we do that by what’s called seeding the laser. So we use a small lower power laser, um, inject that into the bigger laser cavity, and that basically s- kickstarts the laser, um, at the right frequency, and then it will, um, overwhelm the other potential, um, frequencies that could be generated, um, and so that it becomes the dominant one. Uh, yeah, so I guess dominate would, might be the right verb. But that’s the current status of that.

00:42:49,980 –> 00:42:57,920 [Austin Madson – Host]
That’s really cool, the resonant lidar in particular, how you guys are trying to get to those lines in a really precise way. Can we talk a little bit about your favorite project right now, Dr. Roddewig? In particular, and, and I’ll loosely quote you here, if I may, why, why do you think coherent lidar is cool and incoherent lidar is sad?

00:43:15,300 –> 00:44:37,420 [Mike Roddewig – Guest]
I should probably be a little bit more, you know… It’s not “sad”. It’s just not as exciting. Well, it is exciting. I mean, building this drone lidar for NOAA is exciting, and there is a lot of fun stuff you can do with it. Coherent lidar is not typically that, uh, is not really utilized. I’m trying to think. Um, you know, because it’s a lot more complicated… It is a lot more complicated, but it is better in some ways, and we just didn’t have the sources to make it happen until recently.

I think Lincoln Labs worked with it back in the ’80s, um, at CO2 wavelengths, like 13 microns, and then it kind of went away and now it’s coming back because people wanna take lidar to the next level. And so the way a traditional lidar works is, right, you send out a pulse of green or infrared or whatever have you light, right? And you look for the reflections of that light by basically you have a filter, so you only, your detector only sees that particular color and you look for, you know, that light coming back. Now, what you’re looking for is not specific per se to the light you sent out, right? Because the sun also makes the same color of light. You might get a- another potentially interference if you have, like, two cars driving by each other. And so coherent is not– And so we’re sensitive effectively to the intensity, right?

So how much of light do we see? But we have no way to distinguish it from any other light that’s at the same color. And so coherent gets you, um, you can be sensitive to the, the exact, um, wave you sent out. And the way it does that is by when you send out your laser pulse, or you can do it with a continuous beam, you split off a tiny part of that that gets, um, combined together with the incoming beam and if the two of them are matched, you’ll get, um, interference, a constructive interference actually. So you can– And, and you get a lot more information that way too. Um, you can modify the beam you transmit in interesting ways, which what I mean by is, so the radar community has been doing what I just described since basically 1945, right? And no one in– I mean, there are isolated examples, like there’s an incoherent meteor scatter radar out at the rocket range here, but by and large, every radar that’s on the market today that’s in any aircraft is gonna be a coherent system.

And you can get a lot better ranging information out of that. You are no longer sensitive to sunlight because sunlight is not the same as the beam you sent out. It doesn’t have the same frequency and phase characteristics, which you are now sensitive to, so you can discriminate against that. Um, you can also apply different coatings, um, so you can modify the wave you send out in different ways so that you can improve your ranging accuracy. Because right now with an incoherent lidar, you do time of flight, right? And so you’re limited to how fast can you measure time, right? And that’s, that’s kind of it, right? How short, how narrow can you make your pulse? How fast can you measure time? And that’s it. Um, but with a coherent system, you can do things a lot more accurately because you can apply a specific pattern to the beam and then you look for that specific pattern in the received signal and when you pick that up, you can really narrow down, um, in range where you’re at.

And I mean, so this is the way GPS works. This is the way, um, I mean, communications works, the way your phone works. You know, so it’s, it’s just, you know, to me being originally kind of a radar RF guy, um, it’s fun because it’s like you’re playing with RF, but you’re doing it at 300 terahertz, right? So the, the concepts are actually fairly similar, right? And we can use all these neat ideas that have come out of the radar community over the past, what, 70 years, and apply them to lidar. And so the things that enable this are we now have sources, like the source I have in my lab, because I, I really, I like oceans. You know, it’s kind of become my thing.

I wanted to–can I build a coherent lidar in the ocean? And so, I used some of the startup money. So when you start as a professor, you, you get a, a sum of money that you can buy whatever you want with. And so I bought the parts to build this lidar, and doing it in the ocean is more fun too because you’re not just– People have done coherent lidar in the air where you… And so topographic, um, your general what people think of as lidar, right? You don’t really get a signal until you hit a hard target, right? Hard being like a tree, the ground, you know, not the air. And so the problem with the ocean is the ocean itself becomes a target, right? Because you, you immediately get a reflection. As we all know, when you look at the ocean, you can see it, right? So, um, it’s a highly, highly scattering environment, which makes it exciting and interesting to work with. And, you know, so you, you get to investigate, you know, are there appropriate codes to work for that?

Are there, you know, and like I’ve been working on just modeling, like is this going to work? Because there’s, you know, reasonable questions of, you know, do things get too muddled, right, in the water because water has a lot of scatterers in it. If you’re just looking for the color green, who really cares if the phase of the green has been scrambled because we’re not sensitive to that. But if you’re looking for a specific phase relationship between what you sent out and what’s, you know, the laser’s currently doing, um, you need to have that phase relationship. And so understanding how, you know, how turbid things can be before you lose that, um, to me is a lot of fun. You know, it’s a lot of probability and statistics, which I really love.

And you also get to play with some really neat sources. So like the source I have has a five kilohertz line width, which is almost unimaginably precise, right? It does that at ten sixty-four nanometers, which again is, uh, you know, I don’t… I say three hundred terahertz. I’d have to sit down and do the math, but it’s, it’s up in the hundreds of terahertz, right? And we’re talking that it’s accurate to within five kilohertz, right? So that’s what? Ten to the three, ten to the fifteenth. So that’s a, an accuracy of like one over ten to the twelfth. I mean, it’s just insane, right? But they’re that good now. And so you can do these things because you need a source that’s going to maintain a stable, um, frequency and phase for when you’re trying to make your measurement, ’cause otherwise the stuff doesn’t work. I think that’s why I think it’s fun. It’s, it’s neat. It’s mathematically challenging, um, and you get to… It’s frustrates me that I can’t use all the fun things the radar people have been doing forever, and so now I can.

00:50:19,308 –> 00:50:26,308 [Austin Madson – Host]
Yeah, it’s fantastic. I think we’ll all be on the lookout for when you finish your cool, coherent lidar.

00:50:26,408 –> 00:50:27,088 [Mike Roddewig – Guest]
Yeah.

00:50:27,088 –> 00:50:45,188 [Austin Madson – Host]
You sold me. Um, yeah, this has, this has been really refreshing, Dr. Roddewig. We heard a lot about the really cool projects that you’re working on there in, in Fairbanks. That’s really all we have for today’s episode. I wanna thank you again, Dr. Roddewig, for chatting with us today.

00:50:46,168 –> 00:50:48,168 [Mike Roddewig – Guest]
Yeah, you’re very welcome. Thank you for having me, Austin.

00:50:48,467 –> 00:51:07,528 [Austin Madson – Host]
Of course, yeah. And thanks to everyone for listening in. As always, I hope you were able to learn something new. If you haven’t already, make sure to subscribe to receive episodes automatically via our website, Spotify, Apple Podcasts, whatever your, your poison is, and stay tuned for other exciting podcast episodes in the coming week. All right, take care out there.

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