#EarthDayAtHome with Optical Engineer Mark Helmlinger

Hi, my name is Mark Helmlinger from the Imaging Spectroscopy Group at JPL. I’m very fortunate to work as a electro-optical engineer there. Our group builds remote sensing instruments and that’s what I’m standing in front of, posters of examples of some of our data that we’ve collected. Our instruments have been sent on interplanetary missions and around Earth and around Earth in airplanes. And I’m fortunate to be able to travel with those instruments, and operate them.

00:38 - In fact, I was in the airplane when this data set was collected. And these data sets are of Death Valley. Our sensor is about as close to Star Trek sensor package as you might find. We can mount it in all sorts of platforms; an airplane’s a platform, a remote sensing platform. And our imaging spectroscopy can be used - spectroscopy is a very powerful tool - and it can be used to make maps of the surface chemistry of planets or of the Earth over Death Valley, for example. This is what we call a RGB image or a true color image, what you’d see if you were looking out the bottom of the plane and then this is a false color image made from other spectral bands.

01:31 - And so I said this was a RGB image and this is an RGB image here, and these are other spectral bands and all these colors every one of these different colors here, that I’ve represented on these posters, is a different surface chemistry: different mineral, mineral type, different amount of water saturation, all kinds of things can be sensed with this kind of technology. And over here are examples of the types of information that’s collected; these are called spectra or spectrum. So I said this was an RGB image here and here, right? Well, really your eye can only see red, green, and blue. In a video camera there’s an array of little squares and each square has a filter over it, either a red green or blue filter over it, and that corresponds to the red green or blue response of your eye. And then if you were to take a magnifying glass to the display you’re probably looking at right now, you’d - blow it up enough and you’d see little red, green, and blue dots and it’s the combined intensity of those dots that fake your brain out into thinking that’s where all the other colors are.

02:41 - So that’s an extraordinary claim, and an extraordinary claim demands extraordinary proof. So what I’ve made here is what’s called an integrating sphere. This is a cake mold from Michaels, comes in two halves and it’s about the volume of one box of cake mix and you can make a soccer ball cake with it or a baseball cake. And it’s actually hollow, and I’ve painted it flat white inside. And I’ve got three LEDs mounted to illuminate the interior.

03:13 - I have a red LED, [switching sound] I have a green LED, [switching sound] and I have a blue LED [switching sound]. Now if I turn them all on at the same time [switching sounds] and adjust them just right, that looks kind of like white light, right? But if you look inside - I hope you can see, yes? There’s just a red, a green, and a blue LED in there. That’s all, there’s no white light bulb so where’s the white light coming from? Now I’m gonna do some really interesting. Gonna turn off the blue one. Isn’t that a pretty color yellow? So if we tip it again you’ll see there’s only red and a green LED in there so where’s the yellow light coming from? Well your brain knows that it can only see red, green, and blue, and that yellow is in between red and green in the rainbow; so whenever your brain sees even amounts of red and green light it says, aha that might be yellow - even though there may not be actually in a yellow light there. You can be fooled. So, if I turn down the green light, I get kind of an orange, and if I turn down the red light, I get kind of chartreuse.

04:27 - And if I turn off the red light and turn on the blue light, Well, I can get all kinds of aquamarine shades of blue. And if I turn off the green light and turn on the red light, wow we can get like deep purple and these pinkish colors. So… you can see that [switching sounds] - oh, and when you turn all of them on, but you change the blue one you can change what’s called the apparent color temperature of the light. I mean, it looks like it’s a white-hot filament or a yellow-hot filament. So this is, again it’s hollow inside, is a demonstration tool.

[switching sounds] 05:11 - It’s powered with three batteries, variable resistors, and switches. The resistors limit the current to the diodes. It’s obviously put together with hot glue, out of scrap wood, so knock yourselves out. So we only see those three colors right? Red, green, and blue and the dyes on these posters are red, green, and blue as well; and we can control the amount of red, green, and blue dye on the poster with either channels from these instruments that really are red, green, and blue light or from wavelengths that you can’t see called near-infrared wavelengths. Now, I’ve made another extraordinary claim that I’m gonna demonstrate as well.

05:58 - Near-infrared, what’s that? It’s light you really can’t see. So what I’ve done here is, I’m gonna generate a rainbow with this overhead projector. If you look I’ve got just a slit exposed here on the platen¬- it’s kind of dusty- that goes up, gets focused by a lens and goes in the mirror and it goes through this prism here. And this prism does something that’s called spectral dispersion where it’ll take that white light, that bar of white light that well, is hitting my hand here and it’s gonna turn it in to a rainbow. Because it bends light and it bends blue light more than it does red light.

06:47 - So what I’m going to do to make that a little more obvious - if you’ll excuse me I’ll put up this- this is what we call “increasing the contrast ratio” this is blocking some of the light from our ambient illumination. I’m also going to turn off the interior lights here, here we go, that should make it a little more obvious. Now dispersion is a mechanical thing. It has to do with the way wavelengths of light interact with different materials as the waves go through; it’s called index of refraction. And I made a claim that there’s light you can’t see with your eye but yet exists, right? Seeing is not believing, there’s a lot more to the universe than you can see with your eye, right? So what I’ve made here is a “radiometer” and it has an entrance slit in it and a bar graph, right? And if I expose it to the ambient light, you can see the lights go up and down on it as I let light in to and out of the detector here. This detector can see wavelengths of light that your eye can’t see it’s a silicon solar cell, in fact one from on top of one of those solar-powered daisies.

08:16 - So what I’ve got here is - this is the ambient light, kind of lighting up that detector, giving enough now here, I don’t know if you can see it, but there’s this rainbow is actually shining on the body of the housing of the instrument here. And there’s blue, blue-green light going in see if I put my hand there, it goes off. And so now there’s mostly green light or yellow maybe, right, and then here’s some red light - it likes the red light a lot better - there if I point it the right way it’ll get to the right spots. Okay. And then here it is out in the dark where there isn’t any visible light, but what do you know It still responds. Here I can make it more sensitive. There we go, it’s called a gain adjustment.

09:14 - So again, here we are in the blue, and the green, and the red - really likes red - and then, wow, look at that there’s a lot of something hitting that detector but you can’t see it with your eye. And that’s infrared light in fact, well let’s see how far does it go… well, there’s a lot of infrared, wait, this is the ambient light from the surroundings here but it starts to pick up right around here and then zooom! And then it goes back down again, right. So, a spectrometer is an opto-mechanical device, and here we’ve split up the wavelength of light into its various wavelengths by position here, right. This detector is wavelength agnostic. If the wavelength is between 400 nanometers, which is a measurement, a linear measurement, and a thousand nanometers, which is the wavelength, a billionth of a meter, this detector will pick it up but it doesn’t care what the wavelength is it only shows intensity. [switching sound] So it’s only by position here that we know what wavelength is actually hitting the detector and that intensity by wavelength or by position in a spectrometer.

10:33 - That makes a curvy wiggle, like here, and these curvy wiggles are “spectra.” And it’s like a fingerprint of the light - of the matter that’s interacted with the light. Now our instruments use reflected sunlight, which is basically white, right, it’s got a lot of wavelengths in it. But when sunlight hits the ground, goes through the air, it picks up the color of the sky and the color of the air and it bounces off the ground here, which is done here, picks up the color of the ground, right? It hits my shirt, it picks up the color of my shirt, which is reflecting more green light than blue or red light and so it looks green to your eye. Well the colors that you can’t see, way out in the infrared, are what our instruments can sense.

11:28 - By the way I also have - calibration’s my specialty and so, showing how to calibrate something is always a lot of fun. This is four LEDs of known wavelength. These are wavelengths that you can actually see with your eye. Remember that yellow one really is yellow, it’s just stimulating both your red and your green cones in the retina of your eye so- and it’s a little shaky, batteries not making good contact. So what I’m gonna do is put this - come on, when it works - alright. I’m gonna put this right where the slit is and it’s gonna - the light from this is gonna go up as if it was the slit and then it’s gonna hit this board over here.

12:31 - It’s gonna go through the prism, and get dispersed. Now all those LEDs, trust me, were in a straight line. About as straight as could be. And yet, if you look real close - and your heart is pure you can see that the red light is - I’m just gonna point here - and the red light is in one position and the yellow light another and the green light another and the blue tone in another. In fact, if you remember the rainbow was blue here and red there, so, because I know the wavelength of each one of these LEDs if I made them really tiny points and really really bright like oh, I don’t know a laser, right - now this isn’t working [hitting sound] there we go. Tada! So if I actually put a laser through that system and lasers are very known wavelengths I’d be able to calibrate it and be able to mark off well this is that wavelength, that wavelength, that wavelength that I can with a magic marker here or a wet wet board marker I could make a graph: this is how intense it is and this is what the wavelength is based on the position.

13:32 - Well that’s exactly what this is and these are actually number files files of numbers just a whole list of numbers starting at a low wavelength and going to well we call these short wavelengths and long wavelengths here now if you could see with your eye if you wanted to know what those wavelengths are 400 nanometers to five six 700 nanometers so the rainbow would fall right in here so our instrument can see a whole lot of information out here in the near-infrared that your eye isn’t sensitive to so what I’ve done with these posters for example this …turn this off… [switching sound] so that’s how we calibrate our imaging spectrometers by the way we use known light sources, we shine them in the instrument and see where the light falls and okay you know that position is that wavelength and we do that for several different wavelengths over the entire range of the instrument and it’s calibrated so for this image here what we did is chose three colors and three wavelengths of light and controlled the red green and blue bands or dyes in the poster with those three wavelengths only one of them is one you can see about 508 nanometers, which is kind of a… reddish… a bluish green I think. 550 is green so in this image what happens is, it so happens that the borax down here and the salt flats of Death Valley come out looking this really bright red [banging noises] and I’ll just point out if you’re a geologist and you want to know where’s where’s that borax coming from where is it washing out from because Death Valley is a valley and surrounded by mountains and these structures here are called alluvial fans they’re built up over time as flash floods bring debris out from the mountains and deposit one way or the other depending on how it blocks the flow of the water or not. You can see some of these water flows are really really red and you’d say aha wherever this water came from that made this part of the alluvial fan that’s where in the mountains borax has come from This kind of information is used by geologists all the time. If you’ve ever been to Death Valley: Badwater’s down here, Furnace Creek is here, and The Devil’s Cornfield is up here. I highly recommend visiting if you’ve never been.

16:13 - This was a flight that I was fortunate enough to make. We were investigating the air in-between the airplane and the ground. We wanted to fly from high altitude that was close to a low altitude that was far, back up to a high altitude, and Death Valley’s a really great place to do that. So what we did is we flew an east-west - this was a north-south transect, this is an east-west transect. We flew basically over Telescope Peak, actually we started up here and went down to Telescope.

But this is Dante’s View; 16:43 - this is the bottom of the valley, Badwater, and then to Telescope Peak. So you notice, see when we make our images with our instrument - our instrument is called the liner array imager so it works like a scanner, like a platen scanner that you’d scan a document with. We only see one line at a time, but the forward motion of the plane builds up an image, right? So if things are really - our imaging spectrometer sees things in like a fan, so if something’s close it only sees a little bit of it, if it’s further away it sees more of it. But if it’s close, the pixels projected are smaller so your spatial ground resolution is a little higher, if it’s further away the pixels are bigger and your spatial ground resolution is lower. Those are all terminology of the remote sensing business, which is a tool used to study the environment of planets, in this case the environment of the earth. So…

17:40 - So you’ll notice it’s kind of narrow here, wide here, and narrow there, because of the distance from the plane. The plane flew at a constant altitude over these targets. So what I’ve done here is I’ve got these little boxes that you really can’t see pointing to various places. Well each one of these boxes corresponds to one of these boxes here, with the spectra in it. Here let me take this down. [moving sounds] And what I’ve also done is I’ve used three different bands for each one of these and and changed the contrast to just make them look as dramatic as possible.

18:25 - But each one of these colors is actually a different chemical or a plant or a mineral or water, or water with stuff in it. And you see, by how many gazillions of colors we have here, all kinds of information that’s here and this is all significant information that gets put into a computer. This type of technology is really good at finding Waldo, for example, whereas you’d have to hire an army of people to stare at pictures. You put this into a computer and boom you can find exactly that thing that has the chemistry- the apparent chemistry- that you’re looking for. That’s one application. Another application is environmental and looking at plants.

Whereas up in the mountains, here, 19:11 - you would imagine there’s a lot more plants, and they show up as different types. This type of technology can tell the difference between plant types, plant species, and plant health. It can tell the difference between snow: wet snow, dry snow, dirty snow. It can tell the difference between healthy ocean water and unhealthy polluted ocean water. It can tell the difference, if the water is clear enough and it’s shallow enough, between dead coral and live coral and coral species.

19:44 - The applications for this technology are tremendous, and calibrating it making sure that it’s correct. So that we know we can trust the results that we’re getting in regards to measuring our environment. I’ve been fortunate enough to do that my entire career and that’s what I was talking about with you here today. And thank you for your attention. .