Lidar on the Star Wars Planets


I recently managed to visit the Nicola Telsa museum in Belgrade, Serbia (on my own dime). One of the demonstrations they had was the use of a Tesla coil to light a 4-foot, or the metric equivalent, fluorescent tube. My wife was quick to volunteer to hold one because the guide told us that this was how they lit the lightsabers in the original Star Wars movies when CGI was still in its infancy. So began my thought of Star Wars planets, light, and what problems lidar would have on each world. If you make it through to the end, there may be a picture of my wife holding a “lightsaber” powered by a 500 kV Tesla coil.

Tatooine

Let’s start with a relatively easy one. Tatooine is the desert planet where we first find Luke Skywalker. You should already know that or you would have already stopped reading. Tatooine has some nice advantages for lidar. None of that pesky vegetation getting in the way of our laser pulses and we can get a nice bare earth sampling without much ambiguity. So, what might be difficult? Well, first are the sand storms. You’ll have to avoid those while surveying or you won’t end up with the lidar you’re looking for. Second is that the dunes are always going to be moving. You might get a great survey, but it is obsolete as soon as you get it. Very similar to our own beaches.

Dagobah

Dagobah is the swamp world where we first meet Yoda. This is a pretty difficult planet for lidar. You’ve got a potentially dense canopy that may have water underneath. If you do manage to get your lidar pulse through a hole in the trees, you’ll likely have a hard time deciding if you’ve hit the ground or the water. However, the water will likely be very still and act as a specular reflector (e.g. mirror), so unless your lidar pulse was straight down, you’ll probably only get returns from the ground (or shrubs or X-wing fighters). This may be similar to what you’d find in areas around the Gulf of Mexico or tropical islands. Note that you could use a green laser to try and penetrate the water, but those looked like black water swamps with plenty of colored dissolved organic matter to absorb in the blue and green.

Hoth

The ice world of Hoth isn’t necessarily difficult for a lidar survey during good weather. It isn’t very useful though, all you’ll get is the snow or ice surface. You will need to use an appropriate wavelength for your laser though. The reflectance of snow drops off outside the visible range and is particularly low around the 1550 nm wavelength commonly used in Europe, so you’d likely get no returns. It’s a bit better for the 1064 nm wavelength typically found on lidar systems in North America, but a green laser would be your best bet. This might be useful to estimate the thickness of the snowpack in the mountains to gauge water supply, but you’d need a good way to estimate snow water equivalence too.

Coruscant

As a city planet, Coruscant provides many difficulties. We’ll just check in on two of them. First is the building shadow. The buildings tend to be built vertically as it makes them considerably more stable, but the lidar systems are usually scanning or imaging at an angle. That means that on any given flight line, you’ll likely have shadows of the buildings. You might have to space your flight lines to match the roads, though Coruscant doesn’t have roads, so there might be nothing regular to use. The second issue is where you have multiple surfaces of interest in the same vertical space. For example, an overpass for us or a walkway between buildings for Coruscant will have multiple surface of interest in the same x,y space. Big cities are not easy to get full coverage and a planet-sized one is particularly difficult.

Alderaan

Alderaan was probably a lot like our Earth and had similar problems. However (spoiler alert!), since it was destroyed in Episode IV, no further dwell on it shall we.

Endor

Finally, let’s look at the forest moon of Endor. This is a forested world covered by giant trees. This probably wouldn’t be too bad for a lidar survey. The tall trees are easy to discern from the ground and would be sufficiently spaced to have gaps for the laser pulses to go through. The slopes might present some accuracy issues since it isn’t clear what the right answer is when part of a pizza-sized laser spot hits a 30 degree slope. Overall, it would be a lot like flying lidar over the Redwood National and State Parks (where the scenes were filmed). Lack of an Ewok removal algorithm would present an additional problem. Some say that should have been developed prior to filming.

Tesla Again

I said if you made it to the bottom, and I hope you didn’t cheat and scroll, there might be a picture with the Tesla coil. Here it is. Unfortunately, using a flash and trying to show that a “lightsaber” is lit are mutually exclusive activities. The tube really was lit up blue. Only blue and green tubes were used, and no red ones, so there wouldn’t be any fights.

tesla coil and light saber
Tesla coil lighting a fluorescent tube at the Tesla Museum.

So that’s it for the main topic, but here’s a little bonus Tesla story you might find amusing at my expense. Feel free to stop reading and carry on with your day.

The Tesla Museum runs a tour every hour but it turns out the English one is only every other hour. We got there at 2:40 and the next English tour was at 4PM. We got to see the end of the last tour from a distance, but the museum isn’t that big and you can only partake in the demonstrations if you’re part of the tour. After we went through all the rooms, we still had plenty of time on our hands before the tour at four. We were about to cut our losses when my wife asked the ticket person if we could go out and come back. She said that was fine as long as we had the tickets, so we headed down the street to find a pub. After a couple beers, as appropriate while on vacation, we paid the paltry tab of 270 Dinars (around $2.50 US). My wife left a percentage-wise large tip of 100 Dinars. It was at that moment that we noticed the 100 Dinar note has Nicola Tesla on it and it has the formula for the SI unit named for him.

Never having seen currency with a scientific formula, we felt that would be a great souvenir. If only we hadn’t just used our only one for tip. I still had a 500 Dinar note and on the walk back I looked for something to buy that would give me a 100 Dinar note in change. This was our only day in Serbia, so there wouldn’t be any further chances. It had to be something of the right price, because I didn’t want change that didn’t include a 100 Dinar note and there are 200 Dinar notes. Finally, I saw a bottle opener for 400 Dinars and I bought it. Completely overpriced in view of two beers, one of them a half liter, costing 270 Dinars, and the poor workmanship.  And the change I got? Two 50 dinar notes. I had to ask if perhaps he had a 100 instead. He did! So, I got my 100 Dinar souvenir note for 500 Dinars. A smarter guy would have just asked someone to change the 500 for five 100s.

100Dinar_note
My 100 dinar note with the bottle opener that cost 400 dinar. Note the rough edges around the opener part. I’ll have to file those down.

Kirk Waters

I’m a physical scientist at the NOAA Office for Coastal Management. In my spare time, when I’m not torturing co-workers, I try to fit in some technical work on lidar processing and distribution. I also try to figure out ways to improve the Digital Coast’s data offerings in general. Somewhere in the back of my head there are still a few brain cells that remember satellite ocean color, oceanographic field work, and something about the ozone hole.

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