WEBVTT FILE 1 00:00:03.200 --> 00:00:04.200 The shape of what we 2 00:00:04.200 --> 00:00:08.333 build, live, work, study, operate--on whether it be on the Earth, 3 00:00:08.333 --> 00:00:11.300 the Moon, Mars, wherever we're going-- 4 00:00:11.300 --> 00:00:12.266 --matters. 5 00:00:12.266 --> 00:00:16.100 Knowing that at a scale where we can understand what's going to happen, 6 00:00:16.100 --> 00:00:19.733 what has happened and predict what could happen, is really important. 7 00:00:19.900 --> 00:00:24.400 Laser altimetry, as developed here at Goddard, went from an idea 8 00:00:24.400 --> 00:00:26.166 to try to capture that 9 00:00:26.166 --> 00:00:28.200 into something we can actually do. 10 00:00:28.200 --> 00:00:36.766 [music] 11 00:00:36.766 --> 00:00:38.400 In 2018 12 00:00:38.400 --> 00:00:41.200 NASA launched two next-gen lidar missions 13 00:00:41.200 --> 00:00:44.300 specifically to look closely at our changing planet. 14 00:00:44.700 --> 00:00:49.000 But if over three decades of lidar missions has taught us anything, 15 00:00:49.000 --> 00:00:53.666 it's that laser altimetry at Goddard is an evolution of technology, 16 00:00:53.666 --> 00:00:58.700 propelled by scientific curiosity in the face of almost certain setbacks. 17 00:00:58.900 --> 00:01:01.266 Take the story of the tree-measuring lidar: 18 00:01:01.266 --> 00:01:05.066 the Global Ecosystem Dynamics Investigation, 19 00:01:05.066 --> 00:01:06.900 or GEDI. 20 00:01:06.966 --> 00:01:09.600 GEDI had its genesis really 21 00:01:09.600 --> 00:01:13.700 in all the innovative work that had been done with lidar at Goddard. 22 00:01:14.066 --> 00:01:18.366 Some of those innovators, this was Jack Bufton and Bryan Blair at Goddard. 23 00:01:18.366 --> 00:01:21.866 Bryan had an instrument called SLICER that was flying around, 24 00:01:21.900 --> 00:01:24.333 taking these cool lidar transects. 25 00:01:25.500 --> 00:01:30.333 And then they put an instrument up in space, the Shuttle Laser Altimeter. 26 00:01:30.333 --> 00:01:32.333 And I saw some of that data and I thought, 27 00:01:32.333 --> 00:01:33.433 Wow, this is really cool. 28 00:01:33.433 --> 00:01:36.366 We've never been able to look at canopies in three dimensions like this. 29 00:01:36.366 --> 00:01:39.033 There's certainly got to be some applications to this. 30 00:01:39.233 --> 00:01:43.133 The Shuttle Laser Altimeter was the first real test for lidar 31 00:01:43.133 --> 00:01:46.633 and provided the momentum for MOLA to take on Mars. 32 00:01:47.266 --> 00:01:51.733 But it also gave us a glimpse at what lidar could measure on our own planet. 33 00:01:51.733 --> 00:01:57.500 And so the push for the Vegetation Canopy Lidar, or VCL, began. 34 00:01:57.600 --> 00:01:59.100 It was a really innovative mission. 35 00:01:59.100 --> 00:02:00.266 We were trying to do something 36 00:02:00.266 --> 00:02:01.666 that hadn't been done before, 37 00:02:01.666 --> 00:02:04.466 but we were optimizing it for vegetation. 38 00:02:04.800 --> 00:02:07.100 Vegetation is very different than if you're looking at ice, 39 00:02:07.100 --> 00:02:10.766 or if you're looking at Mars, or if you're looking at the Moon, 40 00:02:11.000 --> 00:02:14.400 because you have to have enough laser power to get through the canopy 41 00:02:14.400 --> 00:02:17.200 and get a strong return underneath the ground. 42 00:02:17.633 --> 00:02:21.233 The VCL team could build lasers strong enough, 43 00:02:21.233 --> 00:02:24.000 but they couldn't get them to last very long. 44 00:02:24.000 --> 00:02:28.500 And that proved too risky for very cautious NASA in the nineties. 45 00:02:28.500 --> 00:02:32.966 After that happened, we focused on the airborne lidar program, 46 00:02:32.966 --> 00:02:35.466 and this is again with Bryan Blair 47 00:02:35.466 --> 00:02:37.800 using that really innovative instrument 48 00:02:37.800 --> 00:02:39.333 he had called LVIS, 49 00:02:39.333 --> 00:02:43.200 the Land, Vegetation and Ice Sensor, I believe it's called. 50 00:02:43.200 --> 00:02:47.066 If you really want to get down to really high resolution 51 00:02:47.066 --> 00:02:50.600 and looking at the sort of landscape-scales 52 00:02:50.600 --> 00:02:51.933 changes over the Earth, 53 00:02:51.933 --> 00:02:53.700 you need a swath mapping system. 54 00:02:53.700 --> 00:02:54.366 So, 55 00:02:54.366 --> 00:02:57.300 sort of in the mid nineties we started working on LVIS, and you know, 56 00:02:57.300 --> 00:03:01.033 we really worked on that in large part because people said it couldn't be done, 57 00:03:01.033 --> 00:03:03.466 and you know, it's really kind of drove us to 58 00:03:03.466 --> 00:03:06.100 to see how much we could get out of that system. 59 00:03:06.100 --> 00:03:07.500 [airplane engine sound] Airborne 60 00:03:07.500 --> 00:03:10.500 missions were successful at keeping that momentum going, 61 00:03:10.500 --> 00:03:13.800 especially in the long periods between satellite launches. 62 00:03:14.100 --> 00:03:17.600 Sort of a core of us kept going year after year, 63 00:03:17.600 --> 00:03:21.200 going from one instrument opportunity to another, 64 00:03:21.600 --> 00:03:25.700 and sort of making opportunities if we didn't have any. 65 00:03:26.366 --> 00:03:30.800 The thread that kept us all going was the airborne system. 66 00:03:31.033 --> 00:03:33.933 Airborne lidar really plays a role helping us 67 00:03:33.933 --> 00:03:37.466 understand how things work in real world settings. 68 00:03:37.466 --> 00:03:39.366 Yeah that's definitely, definitely the best way to go 69 00:03:39.366 --> 00:03:41.900 was to build the hardware, get some data over real terrain and 70 00:03:41.900 --> 00:03:43.633 and actually, you know, 71 00:03:43.633 --> 00:03:47.300 show that it meets the requirements, that you can scale it to the space. 72 00:03:47.300 --> 00:03:51.666 But along the way also as we were flying, as we were collecting those data sets, 73 00:03:51.666 --> 00:03:55.600 we were releasing those publicly and letting people experiment with them 74 00:03:55.600 --> 00:03:57.233 and get comfortable with them. 75 00:03:57.233 --> 00:04:01.466 Dubayah, Blair and others leveraged the success of LVIS to propose 76 00:04:01.466 --> 00:04:03.266 a new satellite mission, 77 00:04:03.266 --> 00:04:06.266 DESDynI, a combined radar and lidar mission 78 00:04:06.266 --> 00:04:09.933 that could see through clouds down to tree canopies. 79 00:04:10.233 --> 00:04:14.400 However, NASA's budget cuts sidelined a couple of Earth science missions, 80 00:04:14.400 --> 00:04:17.466 and DESDynI was grounded indefinitely. 81 00:04:17.533 --> 00:04:22.400 And that was a devastating blow because we now been trying from 1995 82 00:04:22.400 --> 00:04:25.833 and now it's 2010, we've been trying to get a lidar 83 00:04:25.833 --> 00:04:29.700 that was meant just for vegetation structure into space, 84 00:04:29.700 --> 00:04:33.466 using the best people in the world who were at NASA Goddard to do this. 85 00:04:33.533 --> 00:04:36.133 And at that point, I've been doing this 15 years. 86 00:04:36.133 --> 00:04:37.200 Maybe I'll just quit. 87 00:04:37.200 --> 00:04:38.500 [music hit] 88 00:04:39.466 --> 00:04:41.233 But of course we really didn't quit. 89 00:04:41.233 --> 00:04:44.466 So we said, Well, let's look for another opportunity. 90 00:04:44.666 --> 00:04:48.000 That opportunity was on board the International Space Station with 91 00:04:48.000 --> 00:04:49.433 the GEDI instrument. 92 00:04:50.000 --> 00:04:52.733 GEDI wasn't just another successful lidar. 93 00:04:52.900 --> 00:04:55.566 It was the end of a very long road, 94 00:04:55.566 --> 00:04:58.100 hard fought by scientists and engineers, 95 00:04:58.100 --> 00:05:02.300 dedicated to pushing the limits of what lidar could do. 96 00:05:03.066 --> 00:05:07.866 We've been really pretty happy about the success of GEDI thus far. 97 00:05:07.866 --> 00:05:11.600 GEDI again is the first lidar that's been in space 98 00:05:11.600 --> 00:05:15.100 that was optimized to to measure vegetation structure. 99 00:05:15.566 --> 00:05:19.300 And it has--it's created an enormous amount of data. 100 00:05:19.500 --> 00:05:23.466 We've conservatively done about ten billion estimates, 101 00:05:23.466 --> 00:05:27.033 about getting those tree heights and getting that canopy structure. 102 00:05:27.533 --> 00:05:30.300 But ultimately, we really wanted to get at the carbon content. 103 00:05:30.300 --> 00:05:33.833 What role do forests play in the carbon cycle? 104 00:05:34.600 --> 00:05:36.866 GEDI has been steadily gathering data, 105 00:05:36.900 --> 00:05:41.700 chipping away at the global question of just how much carbon dioxide trees 106 00:05:41.700 --> 00:05:46.000 take out of the atmosphere, a big piece of the climate puzzle. 107 00:05:46.800 --> 00:05:50.400 The current lidar missions are all about building on the past. 108 00:05:50.666 --> 00:05:53.233 Things that we in fact have only just begun 109 00:05:53.233 --> 00:05:55.666 to think about from pictures, now we have the third dimension. 110 00:05:55.666 --> 00:05:57.433 ICESat will add the third dimension. 111 00:05:57.433 --> 00:06:00.133 ICESat-2 will add the third dimension, the elevation. 112 00:06:00.133 --> 00:06:03.700 Pushing the technology to get at deeper science questions. 113 00:06:04.133 --> 00:06:08.400 And so came the next generation of ice-focused laser altimeters, 114 00:06:08.400 --> 00:06:11.300 aptly named ICESat-2. 115 00:06:11.300 --> 00:06:15.400 Its single instrument, ATLAS, was designed to precisely measure 116 00:06:15.400 --> 00:06:19.033 small changes in the shrinking, icy poles of Earth. 117 00:06:19.600 --> 00:06:22.166 To get down to that level of accuracy 118 00:06:22.166 --> 00:06:23.600 from space, 119 00:06:23.600 --> 00:06:26.133 everything had to be much better. 120 00:06:26.333 --> 00:06:29.900 It's this story of these incremental improvements through time, 121 00:06:30.066 --> 00:06:34.833 and with each mission, you're leveraging the lessons of the last mission. 122 00:06:34.833 --> 00:06:36.266 It wasn't a short process 123 00:06:36.266 --> 00:06:39.200 for ICESat-2, even though we knew a lot 124 00:06:39.200 --> 00:06:42.433 and had learned a lot over the last 20 or 30 years. 125 00:06:42.766 --> 00:06:45.166 Each mission, you know, has its own challenges. 126 00:06:45.200 --> 00:06:47.566 All of the easy missions are done, as they say. 127 00:06:49.100 --> 00:06:50.833 The first iteration of the 128 00:06:50.833 --> 00:06:54.100 instrument was going to be very similar to GLAS. 129 00:06:55.200 --> 00:06:58.733 As it turned out, the group that wanted the more complicated instrument won. 130 00:06:58.800 --> 00:07:03.400 So then they came back and said, okay, instead of digitizing, 131 00:07:03.400 --> 00:07:07.200 you know, 40 hertz or 50 hertz laser or whatever, we're going to fire 132 00:07:07.200 --> 00:07:08.100 this beam to the ground. 133 00:07:08.100 --> 00:07:11.566 And then individually time tag 134 00:07:11.566 --> 00:07:13.566 each photon that comes back. 135 00:07:13.566 --> 00:07:15.000 There were so many requirements, 136 00:07:15.000 --> 00:07:16.500 there were so many constraints. 137 00:07:16.766 --> 00:07:19.833 We had constraints on the software capability. 138 00:07:19.833 --> 00:07:23.000 We had constraints on the storage space. 139 00:07:23.000 --> 00:07:25.000 We had constraints on the memory. 140 00:07:25.000 --> 00:07:29.200 By photon tagging--I mean they'd built a detector system and detector electronics, 141 00:07:29.200 --> 00:07:31.500 they were just--it was like 142 00:07:31.500 --> 00:07:34.733 a firehose of data coming into us. 143 00:07:34.766 --> 00:07:38.100 ATLAS has six beams, and it records elevations 144 00:07:38.100 --> 00:07:43.166 for each of those six beams, 10,000 times a second, as long as there is reasonably 145 00:07:43.166 --> 00:07:46.300 clear skies that the laser light can go from the spacecraft to the ground 146 00:07:46.300 --> 00:07:47.066 and back again. 147 00:07:47.066 --> 00:07:49.833 The Earth is much more complicated to work with 148 00:07:49.833 --> 00:07:51.566 because of the clouds. 149 00:07:51.566 --> 00:07:55.133 The algorithm could easily be confused 150 00:07:55.133 --> 00:07:58.133 and start following, you know, the cloud surface. 151 00:07:58.733 --> 00:08:02.000 I was the lead for the receiver algorithms team. 152 00:08:02.000 --> 00:08:06.166 The responsibility of making this work fell on my shoulders. 153 00:08:06.600 --> 00:08:08.300 I had sleepless nights. 154 00:08:08.300 --> 00:08:10.100 I have to tell you, 155 00:08:10.433 --> 00:08:13.066 thinking that I wasn't going to be able 156 00:08:13.066 --> 00:08:14.800 to make this work. 157 00:08:16.333 --> 00:08:19.366 In order to maximize the return from these data, 158 00:08:19.366 --> 00:08:22.366 a key component was determining the location on Earth 159 00:08:22.366 --> 00:08:24.133 of the laser bounce point, 160 00:08:24.133 --> 00:08:26.766 a process called geolocation. 161 00:08:27.033 --> 00:08:29.566 So what we do and geolocation, we get the 162 00:08:29.566 --> 00:08:31.666 we get the position of the satellite 163 00:08:31.666 --> 00:08:32.933 really accurately. 164 00:08:32.933 --> 00:08:37.100 We get the pointing of the laser beam very accurately, 165 00:08:37.100 --> 00:08:41.533 and then we have the range from the altimeter, and we add all those together 166 00:08:41.533 --> 00:08:44.900 to give us where that bounce point came from. 167 00:08:45.400 --> 00:08:51.366 Without the geolocation, you have lots and lots of error and you wouldn't be able 168 00:08:51.366 --> 00:08:55.133 to measure the change in the height of the ice sheets. 169 00:08:55.966 --> 00:08:58.400 We overcame what I think was 170 00:08:58.400 --> 00:09:00.733 fairly insurmountable problems, 171 00:09:00.733 --> 00:09:04.266 but everybody took their own piece of the puzzle and everybody worked it. 172 00:09:04.266 --> 00:09:05.533 [rocket launching] 173 00:09:05.533 --> 00:09:10.366 ICESat-2 launched in 2018 and months later began gathering data 174 00:09:10.366 --> 00:09:14.333 that shed new light on how fast the ice sheets are changing, 175 00:09:14.333 --> 00:09:17.200 how thick the sea ice cover was in the Arctic, 176 00:09:17.200 --> 00:09:20.166 and even measured beneath the surface of the water, 177 00:09:20.166 --> 00:09:23.466 up to 30 meters, a kind of bonus science result 178 00:09:23.466 --> 00:09:26.533 for a team that worked tirelessly to push the limits 179 00:09:26.533 --> 00:09:29.333 of the ATLAS instrument. 180 00:09:32.400 --> 00:09:35.366 So you cannot just build just one lidar. 181 00:09:35.366 --> 00:09:38.200 You need a sustained team 182 00:09:38.200 --> 00:09:41.633 who's been building lidar for some time.