1 00:00:00,020 --> 00:00:04,030 VO: What we think of snow depends a lot on where it falls. 2 00:00:04,050 --> 00:00:08,070 If you live in the eastern U.S., maybe it's fun. 3 00:00:08,090 --> 00:00:12,120 Or, maybe it's just a pain. 4 00:00:12,140 --> 00:00:16,210 Kim: But if you live in parts of the world where they 5 00:00:16,230 --> 00:00:20,240 depend on the water that's in the snow for a large 6 00:00:20,260 --> 00:00:24,320 fraction of their total water that they use for drinking, agriculture, 7 00:00:24,340 --> 00:00:28,370 for industry or for hydropower, the snow is 8 00:00:28,390 --> 00:00:32,400 a very important natural resource. For example, in the western part of the United States, 9 00:00:32,420 --> 00:00:36,450 80 to 90 percent of their renewable water comes from snow. 10 00:00:36,470 --> 00:00:40,480 [music] 11 00:00:40,500 --> 00:00:44,490 [music] 12 00:00:44,510 --> 00:00:48,500 [music] 13 00:00:48,520 --> 00:00:52,560 [music] 14 00:00:52,580 --> 00:00:56,580 [music] 15 00:00:56,600 --> 00:01:00,630 [music] VO: Snow is one part of the cryosphere that many of us 16 00:01:00,650 --> 00:01:04,680 have actually encountered before. But it also plays a critical role in 17 00:01:04,700 --> 00:01:08,700 regulating the Earth's climate. Through decades of remote sensing, 18 00:01:08,720 --> 00:01:12,720 NASA has kept a close eye on the ebb and flow of snow cover. 19 00:01:12,740 --> 00:01:16,740 Hall: We now have a 52-year record of 20 00:01:16,760 --> 00:01:20,780 snow cover in the Northern Hemisphere, and we can see 21 00:01:20,800 --> 00:01:24,820 changes in the extent of snow cover over the 22 00:01:24,840 --> 00:01:28,840 time period--particularly in the last few decades--where we can see that the snow 23 00:01:28,860 --> 00:01:32,860 cover has been retreating. It's been melting a lot earlier in the springtime. 24 00:01:32,880 --> 00:01:36,880 Osmanoglu: The extent is relatively easy to do and it has been done over the 25 00:01:36,900 --> 00:01:40,950 years. What's tricky is though how thick is that snow. And 26 00:01:40,970 --> 00:01:44,960 it's even trickier how much water is in that snow. 27 00:01:44,980 --> 00:01:49,000 VO: That tricky part is known as the snow water equivalent, or how much water would actually 28 00:01:49,020 --> 00:01:53,050 be in a layer of snow if it melted. NASA and its partners have taken 29 00:01:53,070 --> 00:01:57,080 to the air to help solve this elusive mystery. First there's the 30 00:01:57,100 --> 00:02:01,130 Airborne Snow Observatory, or ASO, a small 31 00:02:01,150 --> 00:02:05,170 plane outfitted with a couple of instruments, one of which measures snow depth using 32 00:02:05,190 --> 00:02:09,200 lidar. Lidar measures distance using light from lasers. Since 33 00:02:09,220 --> 00:02:13,240 2014, ASO has flown over basins in California and 34 00:02:13,260 --> 00:02:17,270 Colorado, taking before and after looks at snow depth. 35 00:02:17,290 --> 00:02:21,300 Scientists subtract the snow-free summer data from the snow-on winter 36 00:02:21,320 --> 00:02:25,350 data to get an idea of the snow depth. There's no single way to 37 00:02:25,370 --> 00:02:29,390 measure all types of snow across the globe, and so NASA's other airborne 38 00:02:29,410 --> 00:02:33,430 campaign, SnowEx, is testing different combinations of sensors. 39 00:02:33,450 --> 00:02:37,460 This winter, SnowEx will test a new instrument, the Snow 40 00:02:37,480 --> 00:02:41,490 Water Equivalent Synthetic Aperture Radar and Radiometer, or SWESARR. 41 00:02:41,510 --> 00:02:45,510 Osmanoglu: SWESARR consists of two main components, 42 00:02:45,530 --> 00:02:49,560 one of them being the radar and the second one being the radiometer. 43 00:02:49,580 --> 00:02:53,600 Bonds: So with the radar providing the depth of the snow and the radiometer 44 00:02:53,620 --> 00:02:57,680 providing the density of the snow, we can put those two things together and get the 45 00:02:57,700 --> 00:03:01,700 snow water equivalent. Here in the chamber we're going to measure different radiation 46 00:03:01,720 --> 00:03:05,740 patterns that are different frequencies and do some full system testing, 47 00:03:05,760 --> 00:03:09,800 in this chamber. This chamber kind of enables us to isolate 48 00:03:09,820 --> 00:03:13,840 various types of radiation and interference. In about a month, 49 00:03:13,860 --> 00:03:17,880 we're going to take the instrument and mount it on a Twin Otter in the Grand Mesa in Colorado. 50 00:03:17,900 --> 00:03:21,900 We're going to fly it over the Grand Mesa and take various different measurements. 51 00:03:21,920 --> 00:03:25,950 This is what we call our engineering flight. VO: Making sure the sensors are calibrated 52 00:03:25,970 --> 00:03:29,980 is key in order to face the challenges nature will throw at them. 53 00:03:30,000 --> 00:03:34,000 Kim: Half of the area that gets covered by snow every winter contains trees 54 00:03:34,020 --> 00:03:38,060 and forest. And the trees make it difficult for the sensors to 55 00:03:38,080 --> 00:03:42,090 see the snow that's underneath the trees so it makes it difficult for us to measure 56 00:03:42,110 --> 00:03:46,110 how much snow there is. After the snow has had a chance to sit on the 57 00:03:46,130 --> 00:03:50,160 ground for a while, it gets denser and denser and denser over time and it changes. 58 00:03:50,180 --> 00:03:54,240 Which is another reason why snow is very challenging to remotely sense, 59 00:03:54,260 --> 00:03:58,290 it doesn't stay the same. It's constantly changing. [shovel digging] 60 00:03:58,310 --> 00:04:02,330 Kim: One of the things that we often do in the field is go dig what we call 61 00:04:02,350 --> 00:04:06,360 a snow pit. You literally dig a pit in the snow so we can see all the different 62 00:04:06,380 --> 00:04:10,380 layers. The layering is very important. VO: All this digging is part of ground 63 00:04:10,400 --> 00:04:14,420 truthing SnowEx, a way of matching up what the airborne instruments see and what 64 00:04:14,440 --> 00:04:18,460 is actually sitting on the surface. The ultimate 65 00:04:18,480 --> 00:04:22,500 goal of SnowEx is to figure out what the best combination of instruments 66 00:04:22,520 --> 00:04:26,570 would be for a future satellite mission in order to get a global picture 67 00:04:26,590 --> 00:04:30,610 of snow. Hall: We need to know how much snow is in a 68 00:04:30,630 --> 00:04:34,640 snowpack. Because if we have too much snow and the snow melts 69 00:04:34,660 --> 00:04:38,690 too fast, then you can get flooding. And if you don't 70 00:04:38,710 --> 00:04:42,720 have enough snow or if the snow melts too early, that can lead 71 00:04:42,740 --> 00:04:46,750 to a longer wildfire season, a more 72 00:04:46,770 --> 00:04:50,830 intense drought, and we need to know these things for water resource 73 00:04:50,850 --> 00:04:55,030 planning. [music] 74 00:04:55,050 --> 00:04:59,210 [music] Parkinson: After we 75 00:04:59,230 --> 00:05:03,270 had a record that was about 15, 20 years long, 76 00:05:03,290 --> 00:05:07,460 we started noticing that the extent of 77 00:05:07,480 --> 00:05:11,550 the ice in the Arctic was getting smaller over time. 78 00:05:11,570 --> 00:05:15,620 [music] 79 00:05:15,640 --> 00:05:15,620 [silence] 80 00:05:15,640 --> 00:05:19,399