'NISAR Can Measure Earth Changes Down To millimeters': Paul Rosen On The Satellite's Precision

0:00 So on 30th of July there was a major significance for ISRO as a major collaboration with NASA and we saw the launch of GSLV M2 with NISAR satellite and we have project scientist Paul Rosen with us. Thank you so much for speaking to us. Would you like to say something about the satellite NISAR in particular because the design itself looked completely different from a conventional satellite? >> Sure. NISAR is a first-of-a-kind satellite. It has two very powerful radars. one built by ISRO, one built by NASA. By virtue of this design, we are able to make unique measurements of the Earth. It because we have that large reflector, uh it allows us to get a very wide swath, cover the Earth every 12

0:46 days from two vantage points and all the land and all the ice covered surfaces. So we are delivering data continuously over the mission effectively making three-dimensional movies of the earth that allow us to see changes of the ice sheets of the sea ice of forests uh and all kinds of natural hazards. It's a really powerful powerful mission. Well, before talking to you, I had the ability I mean we just spoke to a couple of school students who had come to uh ISRO and they were very much keen and interested to know about certain parts of it and one was SAR what is synthetic aperture radar and how does it work? >> You can think of it as a combination between uh a camera and a microwave oven. So we use microwaves the radar

1:32 wavelengths to be able to make these measurements. But because these wavelengths are very long, when you send energy to the ground, it illuminates a very wide area which is quite low resolution and maybe many kilometers. So you can't get a precise sharp view of the earth. We use the fact that the radar is flying along its orbit and sending out pulses of energy many many times. So every point on the ground is imaged many times at this very low resolution. And by taking many of these uh echoes along the track, we can combine them in a computer as though the antenna that we're using is 10 kilometers or 20 km long. And that then means that we can get the resolution

2:19 down to, you know, human scale size, high resolution, 5 to 10 m. It's a it's almost magical technique actually. That's why because like you you're using a 10 or 12 m wide reflector but the distance would be almost 10 to 20 km. >> The the data we use to create a synthetic antenna is over is collected over a 10 km to 20 km uh range along the orbit. So, uh, technically a camera uses a lens to focus energy into a single point, >> reflected energy from Earth, >> reflected energy from the Earth. And this radar is using essentially all of these pulse pulses along the track and adjusting them uh in the computer as

3:04 though it's focusing it through a lens so that we get the sharp resolution. >> And why is it much better than an optical uh imaging of Earth? Well, optical images of course have their uh their function. Uh they are sensitive to the chemical properties of what's going on on the earth. Radar is fundamentally different from that. It can see through the clouds. It can see day and night. So it provides complete reliable coverage at all times. So it's excellent for the cases where you might absolutely require it independent of weather and smoke and that kind of thing. for think of a a forest fire or a natural disaster where there's cloud cover and you absolutely want to have those measurements. It's great for that. In addition, these radar frequencies are sensitive to different

3:50 things. They're sensitive to the uh electrical properties, the water content as well as the detailed shapes at the at the scale of the wavelength. So, we're actually imaging through a completely different set of eyes, an invisible part of the spectrum. >> That's what my next question from another student though. So the question was will we see the image in red, green and blue or will it be like an optical image will there be any difference the image generated? >> So the answer is no and yes. So we don't actually see those frequencies. We're actually measuring invisible frequencies above the red color in the rainbow. So if you imagine a rainbow in the sky, our frequencies are invisible way above that. However, when we display the data,

4:37 what we typically do is take both the L and the Sband, which are two different colors. They're two different frequencies. We also take the polarometric information. Just like polaroid glasses can uh orient certain kinds of light, we can use polarization to understand the structural properties on the ground as well. So by combining the polar and frequency information into a false red and a false green and a false blue, we can create color images that are telling us something different from what an optical image would. >> And why was an Sband and Lband, a dual frequency radar was used in uh NISA? >> Well, it's always great to have more frequency content. uh and for example in

5:24 the optical domain they go from a single uh channel pan chromatic to a multi-spectral with multiple channels to a hyperspectral with thousands of channels. Ideally we would do that with radar as well. Uh typically radars are large instruments and often involve the entire spacecraft. So uh it's more difficult to get lots of frequencies. So we're starting with two. This is the first time that two radars have been flown in space in a free-flying mission for the life of the mission uh and operating simultaneously. So, it's a really unique uh capability. Not just that, the satellite itself is unique considering the boom has to unfold itself and then the antenna has to expand or unfurl almost like an origyami

6:10 uh kind of vertic design that you've used over here. How did you what you know finalize on this particular design and how much work was put on it? >> Uh well we've been working on this project for almost what is it 11 years now. So and before that we were doing many different studies. Uh NISAR derived from previous studies. There was a mission concept called destiny in the United States. And during the Destiny period, which was before NISAR, we went through a set of uh design trades where we looked at the conventional kind of antenna to the kind that we have now with the reflector and then a a feed system on the spacecraft. And we determined that this new design would allow us to get more capability, more

6:56 higher resolution and wider swath at the same time uh over the conventional systems. So we went down this path and once we made that decision that this was the right thing to do then we uh had to figure out how to construct it and that wasn't done in great detail until we had our partnership with ISRO because it was highly dependent on the spacecraft designing the fairing and everything like that. So it it was an the process is highly iterative. We have a concept, we flesh it out on paper, we talk about it, we uh do some analysis and then we say well that doesn't quite work. Let's try something else. And so that process takes a couple of years iterating with

7:44 our uh ISRO partners and then we come up with a design. It gets reviewed and certified that this is the right way to go and we c we can achieve it in a technical sense and then we proceed that way and it's it's a multi-layered uh iteration. It's going to take 8 days for it to turn operational, right? Minimum. >> Uh, so it it depends on what you need. We are turning on various subsystems over the first 30 days. It's going to be 30 days before well 20 to 30 days, somewhere in that range before the radars are actually turned on and operational. The deployment of the boom and the reflector, that's going to be from day 10 to day 18. Yeah. >> So, it's going to be stationed at 747 kilometers from Earth. >> That's right. So coming to the as a launch is a success and it has been

8:31 stationed in the uh right altitude. What is NISAR going to look for? >> Uh scientifically it's NISAR is going to look for uh many things. Uh it has specific requirements on the US side in studying ice sheets and sea ice and their interaction with the ocean and the atmosphere. It's going to be looking at forest cover and forest use uh change as well as uh disturbance, agricultural changes and uh crop health as well as wetland uh and inundation studies. But these radars are very well suited to those kinds of measurements to understand the carbon cycle and understand better applications such as forest and and crop management. We're

9:18 also studying solid earth and natural hazard. As I mentioned before, NISAR has this all-w weather dayight capability. And in the event of disasters, we can uh as soon as we fly over, we can get reliable information, compare that information to what happened before and actually come up with a uh a measurement of where uh destruction or damage may have occurred quite precisely. Past systems that are not quite as capable of NICAR have already demonstrated this capability. Scientifically, we're studying earthquakes, volcanoes, landslides, other natural hazards to understand better their mechanisms and understand potential ways to forecast risk better for the public. >> Does that mean NISAR is going to play a very important role in carbon emission

10:05 and its effect on climate change? >> Yes. One of the larger um one of the larger error sources in the carbon cycle is the above ground biomass variability. So one of our main objectives is to measure that variability, reduce the error bar and help carbon modelers to understand that exchange. >> Earlier you have said that NISAR has the ability to even uh identify millimeter level changes when it comes to the earth's surface. Yes. a micro level which can be used like what unfortunately happened yesterday the 8.2 Rita >> absolutely we have the ability using NISAR has the ability using a technique called radar interferometry to measure changes in the position of

10:51 the earth down to millimeters to centimeter scale depending on the area and other conditions. We do this by using the wavelength of the radar as a yard stick effectively. We fly over once, measure the the distance >> kind of thing. >> It it's actually a direct measurement of the phase change. Uh we we me we measure an image we come back again 12 days later and measure a g an image from the same vantage point and by basically taking the difference of these images which are complex images. We have a magnitude and a phase. That phase change which is very precise can be used to measure the motion of the earth down to you know millimeters. So we do these maps and they are used in

11:36 by scientists to model what happened from before to after an event. Uh in the case of the earthquake yesterday, we would have been able to map the precursor earthquake which was I think an order magnitude 7 or above earthquake before the largest one. we would have seen that earthquake, done some modeling and tried to understand what the potentials for the next earthquake might be and maybe um we could at least understand where the potential for the earthquake would be. Timing of earthquakes forecasting is quite difficult. So, but nonetheless, every piece of information is extremely important when lives are at risk. >> Uh any reason why we have a 12 days interval and uh will these datas be available for the uh global scientific

12:21 community? Yeah. So, the 12-day interval is uh one of these engineering trades that we had to do uh with the scientists and the engineers. Sc if you ask a scientist how often they would like data and at what resolution, they'll tell you give it to me as soon as I can get it uh as quickly as possible sampling every day and give me the finest possible resolution. And when you have uh limits on your uh overall design space, you can't give them always that. So by looking at uh a a number of trades, looking at the science, looking at the requirements for what they needed to push the envelope on uh on understanding the earth one step further, which is generally recommended by the global community. They say these are our big

13:08 challenges. This is what we want to do. So, by looking at those requirements and then let's uh let's think about does that need to be a 12-day repeat or a 24-day repeat or an 8- day repeat. >> You chose >> we choose we choose the one that that optimizes the science for the uh available resources that we have in terms of what we can launch and what the cost is. >> Finally, how was the collaboration with uh ISRO? >> It was fantastic. I I can tell you as a scientist I just had nothing but fun working with our Indian colleagues at all the different centers at ISRO. We uh we could share with each other our science goals and our applications

13:53 goals. The program at ISRO is very highly developed in taking data from science into applications. NASA tends to focus on more global science and doesn't always go all the way to the applications in every case. So we learned a lot from that uh that endto-end capability at Israel and I think ISRO has been uh pleased with the interaction with us where we tend to focus on these global problems. >> Oh, I can vouch for that. We are very happy to have you here actually. And about future collaborations with ISRO? >> Yes, I I welcome it. >> Do you have any plans? >> Uh we have we we don't have any definitive plans at the moment. This is something that NASA and ISRO at the level above me would talk about, not so much me. Uh but you'd be very interested. >> I would be very interested personally as

14:40 a scientist and uh and a team member to continue the collaboration as long as we can. We've only really started the mission right now even though it's taken 11 years to get here. >> Next five years >> the next five years and hopefully beyond we'll be we'll be working with this road to get wonderful data and after the first year or two we may change the minds of everybody in the world that this must be continued into the into the future. Maybe, maybe not, but we'll see. >> Well, thank you so much for talking to us. Very nice meeting you as well. That was Paul Rosen, the science ID behind NISAR, a satellite that was launched with a collaboration from ISRO and NASA and it is definitely going to play a major role in providing data and thereby saving a lot of lives. for Daniel from Mother Point today.