Dr. Bruce Wielicki, senior Earth scientist within the Science Directorate at Langley Research Center, works as lead of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission. The Tier-1 earth science decadal survey initiative will anchor a future climate observing system.
NASA Tech Briefs: What is the CLARREO mission?
Dr. Bruce Wielicki: CLARREO is a mission to take us into a new level of accuracy of instruments in orbit. CLARREO takes some of these high-accuracy infrared and reflected solar capabilities that we’ve built in the laboratories and some of the NASA research centers, and gets them up into orbit — seeing the whole Earth, so that we can get really accurate climate change data about where the planet is going. There’s a lot of discussion and arguments about how accurate different data sources are. Instead of targeting accuracy the way we normally do for instantaneous weather measurements, the mission targets that accuracy at decadal change measurements, and those are typically required at almost a factor of 5 or 10 more accurate than weather observations are.
To give you an example: You might need a 1 Kelvin temperature measurement to understand tomorrow’s weather. You need 1/10 of a Kelvin accuracy to get decadal change, as we put greenhouse gases in the atmosphere and have to watch how the planet is responding, and then make our changes relative to that. So that is really CLARREO’s mission: to get that accuracy up in orbit, and then also to do it across the whole spectrum of earth’s energy emitted to space, because that’s what drives climate. So the reflected solar all the way from the ultraviolet into the near infrared, the mid-infrared, and the far-infrared. That far-infrared has never been observed from space, so that’s a new and exciting part of this mission. It allows CLARREO to cover so much of the spectrum so that we can become a standard radiometer in orbit to improve the calibration of other instruments, including weather instruments or Landsat instruments. We can actually match them in time-angle space, calibrate them much more accurately to our standard, and bring the whole observing system up in accuracy and capability.
NTB: How do these tools ensure accurate results?
Dr. Wielicki: When we build instruments normally, we’re trying to see the whole Earth at really high resolutions — see down into pixels where we can get individual clouds, for example, or landscapes for vegetation. [CLARREO] instruments are kind of the opposite mode. We back off in things like spatial resolution to make them simpler, but we hone in in terms of really high accuracy. We’ll have special black bodies — a black body is a deep cavity where you can control very accurately the temperature that the instrument observes, and then know that temperature with accuracy that is down to hundredths of a degree. We reach the temperature accuracy by using phase-change cells. These small cells mounted in the black body allow you to change different materials from solid to liquid, and thereby know exactly where those temperatures are, and then use those across ranges of temperature to determine the temperatures your instrument can sense. We can’t afford to do that kind of accuracy on most of our weather and other instruments, so what we have to go for here is a really different shot of how to do that.
NTB: Where does the CLARREO mission stand currently, and how have budget cuts changed the plans?
Dr. Wielicki: That’s been the bad news for us. The science itself has been extraordinary, and we’ve spent about three years really well determining the science requirements. We have the climate modeling community involved, so we’re actually simulating the CLARREO observations in climate models. We can actually show over 100 years in model simulation what CLARREO would have seen, and what it could have told us about climate change.
Just as we were ready to knock on the door that was going to start this mission formally, that’s when the budget cuts to NASA’s science program came. So we’re now on indefinite hold, and instead of having a launch date in 2017 or 2018, we’re now kind of idling. Instead of marching toward a mission date, what we’re doing is continuing to extend the accuracy of the climate studies, in particular these climate models, and retire some of the risks in technology.
NTB: What are these “risks in technology?”
Dr. Wielicki: All NASA missions are trying to do something new, so the risk is really “Can you take from the laboratory an actual instrument that’s going to go into space, through launch, through contamination in orbit, through all of the other things that it might go through, and then achieve what it is you’re doing?” In our case, it’s pushing accuracy to levels to a factor of 5 beyond what current instruments do, and that really requires more care, detail, and independent verification systems. It’s a lot more like what the metrology world does actually — people like the National Institute of Standards and Technology (NIST), and like the National Physics Lab in the UK. If you think about it, no one accepts an international standard for the meter or the kilogram or watt until multiple independent groups have verified at high accuracy, within certainty determination of every component, what we know and don’t know about the observation.
CLARREO achieves traceability at every possible error source, how it can come unglued in different ways, and then we build up a really rigorous error budget of what’s normally called SI or International Standard traceability, to the accuracy levels we need. And that’s why we engaged people like NIST, who have been doing this in the laboratory for a long time. NASA Goddard [Space Flight Center], JPL [NASA Jet Propulsion Laboratory], and we at NASA Langley are involved, and we even have some of the other national physics labs around the world involved, the UK in particular.
NTB: What are the different instruments that you’re building in the laboratory, and how are they each used in the CLARREO mission?
Dr. Wielicki: One of them is a reflected solar spectrometer, and that one will have about a ½ kilometer field of view. It’s a 2D detecting array, so it’s kind of a push-broom in orbit. As you sweep along the ground, one linear dimension is mapping the earth in a 100 kilometer swath. The other dimension is doing the spectrum of reflected solar radiation. We’re getting that direction from about 350 nanometers out to 2300 nanometers. That includes about 98 percent of the reflected solar energy that the earth puts back out to space. We need it to achieve that high accuracy and the total earth’s reflectance of sunlight, which is a critical climate component. A normal imager, like a Moderate Resolution Imaging Spectroradiometer (MODIS), may have sensitivity to polarization of about 1 or two percent, or as much as 4 percent with some slow drifts in orbit. The CLARREO instrument is going to have a polarization sensitivity that’s closer to a quarter percent.
One of the other big differences is that we're able to look directly at the sun and the moon. Using precision apertures, filters, or other instruments to bring the solar radiance down into an earth radiance dynamic range, we are able to test, for example, the subtle nonlinearities that you might get in an instrument viewing the Earth. These nonlinearities might only be a few percent, but knowing their magnitude is critical for achieving the accuracy we need to observe climate change over decades. Again, there are things that aren’t critical for a weather observation, but we’re going for accuracy for that solar instrument in CLARREO.
NTB: How are the work and the responsibilities divided up? What’s it like to work in that coordinated approach?
Dr. Wielicki: That has really been a fantastic collaboration for us, because NIST, of course, is really interested in pushing metrology, in terms of accurate standards that really can benefit the world. When we brought CLARREO to them, the real advantage was we needed improved standards out into some wavelength ranges that they had done in some original explorations. They were slowly moving into that direction, but we gave them a lot more impetus for why it was important to get there now.
So, in particular, the far infrared wavelengths beyond about 15 or 20 microns out to 100 microns, and then in the near infrared. They had things really well understood out to 1100 or 1200 nanometers, but as you started to get out to 2300 or 2400 nanometers, they still needed some work to do. We have regular meetings with them. We have a formal agreement with NIST, we also have formal agreements with the United Kingdom with their National Physical Lab, with their climate modeling center, and also with some of their universities that are involved as well.
NTB: What is your specific role in the program? What is your day-to-day work?
Dr. Wielicki: I’m the cat herder. The scientists in the room are all very bright, determined, strongly motivated people, so you could imagine a room of 50 of those people arguing about the relative importance of different science topics.
I’m a science team lead on a science team for CLARREO that is especially diverse, where we have teams of scientists involved in reflected solar, in the infrared, and teams in radio occultation. You have to take those diverse teams and get them to agree on science requirements across the whole mission, so we’ve really worked hard on not just saying that we need really accurate data, but defining when do you reach the point of diminishing returns.
For example, you don’t need perfect data. Somewhere you have to define the real level of accuracy that you need, and what we were really able to achieve was to very rigorously define that what really was needed was to get under the natural variability or noise of the climate system itself, because we only have one earth. We use natural variability – things like El Niño – as a floor, and then get our accuracy by the factor of 2 under that, and then once you’re below that, then you’re at the point of diminishing return.
NTB: You mentioned infrared spectra. What kind of work is being done there?
Dr. Wielicki: One of the more exciting things with the infrared is we’re getting into about half of the whole infrared radiation that the Earth is emitting out to space, seeing it for the first time in a spectrum, out there beyond 15- to 50-micron wavelengths. It’s called the far infrared. It’s where most of the water vapor greenhouse is. The atmosphere holds more water vapor. That itself is a greenhouse gas, and it therefore amplifies the carbon dioxide warming we get almost by a factor of 2.
This will be the first time we really see this globally everywhere in spectra as well at high accuracy. The transform spectrometer has about a 25 kilometer field of view at nadir. One of CLARREO’s visions here is to not only work as a sort of a transfer radiometer in orbit to calibrate other instruments, but also our own spectra by themselves. Unlike our normal remote sensing instruments, where we might try very accurately to get our instrument noise down to do a retrieval at a single point, this is a very different way of going at it. You go for a very high-accuracy spectra, averaged over very large time and space scales, and then you’re looking at climate change anomalies over years to decades and pulling climate change signals out of those spectra. We typically call it spectral fingerprinting or spectral benchmarking.
NTB: What are the radio occultation teams working on?
Dr. Wielicki: Current GNSS (global navigation satellite system) radio occultation meets CLARREO accuracy goals for temperature changes at altitudes between 5 and 20 km. Improvements that the CLARREO team is studying are advances in sampling by adding receivers for not only the U.S. GPS system, but also for the European and Russian GPS systems. Second, we are studying ways to reach the CLARREO accuracy at both lower altitudes below 5 km and higher altitudes above 20 km. The lower atmosphere issues are signal attenuation by water vapor, horizontal inhomogeneity, as well as sharp vertical temperature inversions. Upper atmosphere issues include the ionosphere, local multipath, and upper boundary condition.
NTB: What has the CLARREO been able to determine about how the Earth is changing?
Dr. Wielicki: The very process of deriving more rigorous observing requirements for a diverse set of high-accuracy decadal climate change observations has led to new methods of understanding climate observing system requirements and how to derive them.
CLARREO has pioneered new ways to use climate models to simulate future observing system simulations. We call these climate OSSEs: Observing System Simulation Experiments. This concept has been common in weather prediction observations, but rare in climate observations. The reason is that the problems are very different. Weather is a challenge of observing an instant of time to start the weather model: what is called an "initial value" problem. Climate is almost independent of initial value, and is instead a "boundary condition" problem. So climate OSSEs take very different approaches than weather OSSEs.
We ran a climate model for 100-year climate simulations to understand what CLARREO could provide to test climate predictions. This gets us closer to more rigorous hypothesis testing for climate change. The climate model is the hypothesis, and the climate OSSE shows us how CLARREO can make that test in the future, including what tests might take 5 years, 10 years, or 20 years. These lessons developed in defining the CLARREO mission are being written up now in journal papers and will be applicable to all climate observations in the future. So yes, CLARREO is already discovering new things and we haven't even launched. Science is not about knowing the answers, but is about finding the right questions to ask.
NTB: Are there similar missions that are providing complimentary data?
Dr. Wielicki: Not right now. This is really a new concept. There are other groups that have tried to propose similar things. For example, there’s a UK group, led by Nigel Fox, at their National Physical Lab, and we proposed one called TRUTHS, and that was to do pretty much the reflective solar part of our CLARREO mission. That was proposed to the European Space Agency (ESA) about 4 or 5 years ago, and so we’ve been working actively with them. And ultimately what you want really want is for the US to put up one of these, and then the international community to put up their own version of it, and then just like metrology labs for international standards, you “shoot it out” between those different laboratories for who really has the accuracy on climate change. And given the critical nature of climate change accuracy, this is just kind of fundamental, basic scientific practice to do this.
NTB: What would you say is the biggest challenge from a technical perspective when you’re developing these instruments in the lab?
Dr. Wielicki: The biggest challenge is not to get too fancy on the technology, so in general we are not using cutting-edge detectors or other things that you might have, like huge optics. The optics on our instruments are about an inch — they’re tiny. So what you do instead is focus on crossing the t’s, dotting the i’s, and putting independent verification methods on everything that can change on an instrument in orbit. With instruments like CLARREO, when you’re looking at your calibration sources, you want the entire optical path to be identical to when you look at the earth. Otherwise now you’ve got all these things you haven’t calibrated out that are kind of sitting there in uncertainty; that’s really the challenge.
NTB: Given the budget cuts, do you ever get impatient with getting these projects off the ground?
Dr. Wielicki: Yeah, we get frustrated all the time. It was a year ago when we did our mission concept review, and we just got rave reviews. The engineers said they’d never seen a mission with the engineering and science melded together that rigorously before, and we were all just glowing until we knocked on the door: “There’s not any money to do this right now.” But this is not new. This happens to satellite missions all the time. The cost is high. You can’t get to space cheap. Inevitable glitches in funding profiles will delay you. The global precipitation mission has been going through this for years. They’re finally getting their mission together. You can’t get too depressed by it. If you do, you’re not going to last in this business. You have to be a master of delayed gratification.
NTB: In an ideal world, with all the funding necessary, what would be accomplishing with CLARREO?
Dr. Wielicki: We would’ve launched about 2017 or 2018, serving as that anchor of much of the climate observing system and taking it to a new accuracy.
Another way to explain what we do: If you have observation and climate change over decades, you have error sources in those observations, and those error sources have to be compared to natural variability. So you can actually ask yourself: If I had a perfect observing system, how quickly could I have seen climate change and understood what it was over natural variability? CLARREO is designed to be so accurate that those observations would flow down that perfect system by only about 10 or 15 percent. So let’s say you needed 10 or 20 years to see that trend above natural variability. If it was 20, with CLARREO, you could see that in 22. With a normal observing system, it might take you easily 30 years to see the same trend. As we advance toward trying to control climate change, we’re going to want to see as soon as possible the response of the climate system to those changes, and CLARREO is one of the steps we can take to get that information, not 30 years out but 20 years out, or not 20 years out, but 10 years out.
NTB: What would you say is your favorite part of the job?
Dr. Wielicki:I guess it’s just working with such a talented team: the scientists and engineers. We really have had an almost magical group on CLARREO. It’s not that it has been easy, but the dedication and talent on that team has just been extraordinary. The biggest charge for me is to watch us, over the last three years, evolve a very solid understanding of what this mission ought to be – and even what it shouldn’t be.