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Tap into the experiences of NASA’s technical workforce as they develop missions to explore distant worlds—from the Moon to Mars, from Titan to Psyche. Learn how they advance technology to make aviation on Earth faster, quieter and more fuel efficient. Each biweekly episode celebrates program and project managers, engineers, scientists and thought leaders working on multiple fronts to advance aeronautics and space exploration in a bold new era of discovery. New episodes are released bi-weekly on Wednesdays. 

Today, we look at NASA’s PACE mission, which seeks to unravel some of the mysteries of Earth’s atmosphere and the vital role played by aerosols and clouds. Join us as we delve into this fascinating journey with atmospheric scientist Dr. Kirk Knobelspiesse.

In this episode, we explore NASA’s PACE mission, an acronym for Plankton, Aerosol, Cloud, ocean Ecosystem satellite. Our focus narrows to two research targets in this remarkable mission—Aerosols and Clouds. Dr. Kirk Knobelspiesse, an expert in the field, guides us through the intricacies of studying these atmospheric components from space.

Aerosols, tiny airborne particles that include dust, smoke, and sea salt, play a pivotal role in shaping our environment, from influencing climate patterns to air quality. Meanwhile, clouds can be significantly impacted by aerosols. PACE is a satellite that carries state-of-the-art instruments to monitor and analyze these aerosols and clouds. We’ll discuss polarimetry, a technique for studying light’s interaction with these aerosols and clouds. Dr. Knobelspiesse unveils the significance of this research, shedding light on how PACE will contribute to our understanding of Earth’s atmosphere, climate, and air quality.

In this episode, you’ll learn about:

  • The critical role of aerosols and clouds in shaping our planet’s environment.
  • How PACE’s state-of-the-art instruments, including polarimeters, provide invaluable data from space.
  • The potential impact of PACE data on climate modeling and air quality assessment.
  • The interdisciplinary nature of scientific research and the importance of collaboration in missions like PACE.


Related Resources:


NASA Earth Science

NASA’s Transform to Open Science (TOPS)

INSIGHT: New Satellite to Eye Phytoplankton, Aerosols  

Related Courses

Complex Decision Making in Project Management (APPEL-vCDMPM)

Critical Thinking and Problem Solving (APPEL-vCTPS)

Systems Thinking Across the NASA Project Lifecycle (APPEL-vSTNPL)

Strategic Thinking for Project Success (APPEL-vSTPS)


Kirk Knobelspiesse
Credit: Kirk Knobelspiesse

Dr. Kirk Knobelspiesse is a remote sensing specialist working to improve our ability to monitor the Earth’s climate. Specific interests include polarimetric remote sensing of aerosols and clouds, atmospheric correction required for ocean color observations, and the statistical and AI tools useful for both. Dr. Knobelspiesse received an undergraduate degree in Photography and a Master’s degree in Imaging Science from the Rochester Institute of Technology. His Ph.D. is in Applied Mathematics from Columbia University. This work dealt with remote sensing retrievals of atmospheric aerosols from multi-angle polarimeters. He has worked at NASA GISS, NASA Ames, and now NASA GSFC.


Teresa Carey (Host): Welcome to Small Steps, Giant Leaps, your window into the world of knowledge and innovation at NASA. I’m Teresa Carey. Let’s explore together.

Today, we’re diving into the fascinating world of NASA’s PACE mission. Our planet is a complex and dynamic system, and NASA’s PACE mission will help us make sense of many of the critical components. PACE is an acronym for Plankton, Aerosol, Cloud, ocean Ecosystem satellite. Wow, that’s a lot. But today we’re focusing on just two of the main players of PACE, aerosols and clouds. So, what are aerosols?

Dr. Kirk Knobelspiesse: Aerosols is a sort of blanket term that we, meaning we scientists, use to describe particulate matter that’s been suspended in the atmosphere.

Host: That’s Dr. Kirk Knobelspiesse. He’s going to tell us all about his work with PACE. And those aerosols, well, they’re basically tiny particles in the air. Think dust, smoke, pollutants, or even sea salt. These little guys play a big role in our environment affecting everything from our climate to the air we breathe. But PACE is also keeping a close eye on clouds. Clouds are like Earth’s natural air conditioners. They help regulate our planet’s temperature by reflecting sunlight and trapping heat.

Knobelspiesse: So, aerosol cloud interactions are complicated. They’re complicated because cloud droplets form more easily on something, on an aerosol particle. So, if you change the presence of aerosols in the environments, you change the types of clouds that develop.

Host: But here’s the cool part. The PACE mission is using state-of-the-art technology, basically launching a satellite equipped with specialized instruments into space to track these aerosols and clouds.

Knobelspiesse: The polarimeters on PACE are actually kind of special. Polarimeters are a special kind of camera that is sensitive to properties of light that we can’t see with our eyes. If one had polarization-sensitive eyes and you were looking down on Planet Earth, you would see rainbows everywhere you see clouds, technically cloudbows. The location and the nature of these cloudbows tells us what the droplets at the top of the cloud look like.

Host: And why is all this important?

Knobelspiesse: How absorbing those aerosols are, are they bright or are they dark, affects how much energy from the sun is absorbed at different layers in the atmosphere. That affects the meteorology of the scene. And so, these aerosols can have an impact on regional climate, regional meteorological phenomena that are hard to quantify in terms of climate models right now because there isn’t good information about how absorbing those aerosols are.

Host: Understanding aerosols and clouds helps us tackle some big questions like how do they influence our climate? Or how do they affect air quality? And what can we do to make our planet healthier? So, in a nutshell, PACE is providing us with valuable insights from above. And today, we’re delving into Dr. Kirk, Knobelspiesse’s work with PACE. Kirk is an atmospheric scientist with the PACE and AOS missions. We’ll talk about how his work with PACE offers not only a deeper understanding of our Earth, but also valuable leadership and professional lessons. That’s what’s on the agenda for today’s episode.

Kirk, to kick things off, let’s dive into those intriguing tools that you use to study the atmosphere, the polarimeters. What exactly are those instruments and how do they work to gather this important data about our atmosphere?

Knobelspiesse: So polarimeters are a special kind of camera that is sensitive to properties of light that we can’t see with our eyes. And so, we use that special power that they have to better understand what’s going on our planet, Earth. We also use the term, multi-angle polarimeters and the multi-angle is also important. So, in addition to being able to observe the polarization state of light, and I can describe what that is in a moment, there are also multi-angle instruments. They’re essentially cameras that take a snapshot many times as the spacecraft flies over a cloud or a piece of the ocean or spot on the land. And these multi-angle views also provide information about what is in the scene that we’re looking at.

Host: It sounds like triangulating?

Knobelspiesse: To some extent, yes. Also, different surfaces, different types of particles in the atmosphere of the ocean. They scatter light in different directions in different ways. So generally speaking, if you have particulate pollution in the atmosphere, which we call aerosols, larger size aerosol particles tend to scatter a lot of the light that hits them in one distribution of directions. They like to scatter light in a forward scattering direction, sort of similar to the direction of the light that hit them. Whereas smaller things tend to scatter light more in the backwards direction. And so this multi-angle capability helps us distinguish between the inherent properties of particles in the atmosphere.

Host: Okay. So, let’s get into this a little bit more. You work on the PACE mission. Your work focuses on polarimetry. Can you tell me about the significance of polarimetry that we were just talking about and specifically how it contributes to our understanding of Earth’s atmosphere? I know we just talked about the particles, but maybe a broad picture.

Knobelspiesse: So, a very broad picture of what we’re doing is observing microscopic things from space. I’m not sure a lot of people realize that you can do this with a camera from space. I think we’re all perhaps have a sense of say a Google Maps image of how the Earth looks. And that’s one type of remote sensing, but another kind is looking at very fine scale phenomena. So, one aspect of PACE is ocean focused and it’s looking at phytoplankton and other types of organisms that are very small. They’re microscopic living in the ocean, but there’s also things in our atmosphere that we’ll be observing including atmospheric aerosols.

So aerosols is a blanket term that we scientists use to describe particulate matter that’s been suspended in the atmosphere. If you think of an aerosol spray can, the reason it’s called that is it’s aerosolizing, I guess a liquid. So it’s turning that liquid into small droplets. So aerosols are present in our atmosphere. They have all sorts of different sources. Some of them are natural examples, might be like desert dust that blows off of the Saharan Desert or sea spray from the oceans. Aerosols are also caused by human activities such as combustion.

So aerosols are created due to industrial pollution, related to transportation and so on and so forth. And they have two main impacts on humans. One is that aerosols are very important for our understanding of climate. We have modified our climate by changing greenhouse gases, but there’s another aspect of this. We’ve modified other parts of our climate as well. And aerosols play into that because they affect how clouds develop and if you change how clouds develop, you change how much energy gets to the surface of the Earth in the first place.

So that’s from a climate perspective, but aerosols, generally speaking are also not good to breathe. So air quality issues are also something that we’re very interested in, in these missions. And so being able to characterize what those aerosols are, where they’re coming from. Do we need to warn people about high aerosol conditions? That sort of thing is another focus.

Host: Okay. So you’re working to understand these aerosols and the relationship with light is going to give you some kind of insight into them. Let’s talk about those insights. I know you’re still working on collecting data, but what do you think we can expect? How do you see this data? Maybe an example of how it might reshape the way we look at our planet’s atmospheric systems.

Knobelspiesse: Historically, we have been pretty good from space of characterizing the aerosol, the amount of aerosols around the world where they’re coming from, but we haven’t been as good at determining the specific properties of the aerosols. Is this a dust particle or is this a sea salt particle? Is this due to human combustion? Is this a forest fire smoke particle? So with instruments such as PACE which have more information. We’re making multi-angle measurements. We’re making measurements of polarization. We hope to better characterize the aerosol type. And if we better characterize the aerosol type, we know more about how well they interact with clouds.

That interaction depends on the chemical nature of aerosols. We use the terms hydrophilic and hydrophobic, meaning aerosols react well with water or they don’t react well with water. And so of course different types of aerosols might do that in different ways. So their ability to become seeds, cloud seeds, depends on the characteristics of the aerosols themselves.

Host: So do you think in theory then that your instruments that are looking at these aerosols could maybe say, “Oh, there’s a forest fire here. Here’s what we can expect to happen to the clouds in the atmosphere in that region because we now know what these particles do.”

Knobelspiesse: Yeah, so that’s one way. Another way is really just informing climate modelers. So if you compare the various climate models out there, they’ve got a pretty good understanding of what’s going on. But there’s still a couple of elements that are poorly understood in those models. And for that reason, modelers need to make assumptions. One of the assumptions they make is about how light absorbing aerosols are. Again, this gets back to the chemical composition of the aerosols, but certain types of dust, for example, absorb more or less light.

If they do that, they change how they interact with climate. So I actually came back just recently from a conference where there were a number of climate modelers talking about this inherent uncertainty in what they’re doing and they have ways of accounting for this, but it’d be much better if we had direct measurements of aerosol absorption for one in other properties. I should say also that doing this from space from satellites is very important.

We have many ways of measuring aerosols. We can have instruments on the ground that suck in air and sample some aerosols. We have other types of ways of making measurements. But if we’re doing it from the ground, we’re making measurements at point locations. The advantage of the satellite is that you get a global picture. And so the PACE mission and the AOS missions, both of the missions I’m involved with will be missions that observe large portions of the Earth frequently. So we can make global maps of aerosol properties and we can use that to inform the people developing climate models to make more accurate models.

Host: This sounds really cool. In regarding these instruments, can you just tell me what they look like? If I were to hold one in my hands right now, what would I be looking at?

Knobelspiesse: So on PACE, there’s three instruments. The primary instrument OCI, the Ocean Color Instrument is pretty big. I think it’s about the size of let’s say a small refrigerator.

Host: Like a mini fridge, like a college fridge?

Knobelspiesse: It’s more than that because it’s actually on a moving… It’s on a gimbal, so it moves and it has a big sunshade around it, so it has a shade to prevent light from hitting it. I’d say the whole thing is maybe more like, actually the entire spacecraft, I think a good way of describing the size is ice cream truck. My daughter went with me to visit the facilities. That’s the size that she said about it. The polarimeters on PACE are actually kind of special. They were originally designed as CubeSats.

So CubeSats are these microsatellites, but they’re things you could hold in your hands. They were originally designed to fly by themselves as CubeSats, but at some point, we found a way to collaborate, so they’re essentially attached to the side. They’re going along for a ride on PACE. And that’s advantageous for a couple of reasons. The two things that really limit use of CubeSat data is how well they can maintain themselves in orbit. They don’t have fuel on board to keep themselves at a certain orbit and how big their antennas are to transmit data down to Earth. So by attaching two small CubeSats to PACE, we’ve managed to make use of what a full-size spacecraft can.

Host: When we think about your work and its impact on climate and pollution, I think it’s exciting to consider how it could directly benefit people and improve their day-to-day lives. Understanding these aerosols and how they behave over time seems like it could really be a game changer in helping decision-makers come up with ways to tackle air pollution or just generally to make our environment healthier. So I get that there’s a lot of ground to cover there, but could you paint a picture for us with an example of how this might work in a real-world situation?

Knobelspiesse: So we expect to have many different types of users of PACE data, and this might span the range from scientists who look at large scale measurements, long-term measurements, and understand something about Earth that we didn’t understand previously. At the other end of the spectrum, we do expect to have people who look at PACE data to better inform their activities as stakeholders. So this might be people who are looking at forest fire emissions and seeing where those forest fire plumes are going.

Now, I don’t want to say that one spacecraft is the single solution. This is part of a larger effort that incorporates observations for surface-based measurements and other things. But I think what’s really important is really just to make our data accessible to as many people as possible. And so there’s different ways that we release data. There’s different ways that we make it available to the public. I think most people know this, but all of our data are publicly available to the entire world. And NASA Earth Science has been doing that for quite some time. But we’re really doubling down on this more recently with the Open Science TOPS program. And that’s an important part of incorporating what we would call applications, say a regional air quality government official into the use of our data.

Host: And that TOPS program that you mentioned is something we’re actually going to be talking about in this podcast in a couple episodes from now, which I’m really excited about that one too. And so for you, on a personal level, how does the idea of making a positive impact in people’s lives through your research, through your work, how does that drive your passion for the work that you do?

Knobelspiesse: Everything about this is really enabling others to do things in a way. So this is what I would call science enabling work. We’re collecting the data that scientists can use to better understand climate. We’re collecting data that members of the community can use to help better understand air quality. And so I just am very pleased to be a part of something that even if I am not directly involved in how the data are used, they’re generally positive things for everybody in the world.

I think about other scientists in the past who have made some great discovery, and once that happens, they no longer have control of it. And generally that can be a positive thing, whatever contribution that I make to the world, it’s something that is inherently useful and positive for people, and that’s what I like about what I’m doing.

Host: Yeah, definitely. I know that PACE is a collaborative effort. Can you share some insights into the challenges and the rewards perhaps, of working on a project of this scale that has this diverse teams and partners?

Knobelspiesse: We spend a lot of time thinking about how we define things, how we communicate with each other, and how we document what we’re doing. Documenting what you’re doing and why becomes very important because it’s something that you might put aside for months or years and have to come back to again or somebody else has to come back to again. In the beginning it seems a little bit bureaucratic.

We have a lot of reviews and specific types of documentation, but in retrospect, having been at it for a couple of years, you realize just how important this is.

Host: You have a really interesting background from a Bachelor of Arts and photography to a NASA scientist. That’s pretty amazing. So looking at your career trajectory, what advice do you have for aspiring scientists who may be interested in interdisciplinary work or transitioning between fields to pursue their passions?

Knobelspiesse: Well, I call myself an atmospheric scientist, but I sit in an ocean ecology laboratory. That’s where I am. So my job by definition is interdisciplinary, but my recommendation would be not to pigeonhole oneself into a particular discipline. I’ve encountered other people who say, “Oh, I studied such and such and such a thing, and that’s what I do. That’s who I am. And this other thing that’s adjacent to it is not me.” I found at least some level of success in trying to learn a lot about or a little bit about a lot of things because really the different disciplines that we have, atmospheric science, ocean science, chemistry, physics, all of these things are human created groups.

What’s actually happening on our planet, or nature in general is not rigidly constrained to those different groups. So it’s important to learn different ones. Another thing that’s also interesting is not necessarily working with other disciplines of science, but other disciplines of maybe technology. So I spent a lot of time working with computer scientists and computer science, machine learning in particular, has really been a key aspect of what we do.

Host: Transitioning from being a research scientist to a key role in a mission-like PACE must come with unique challenges. What are some of the crucial insights or lessons that people might not find in a playbook when they find themselves needing to understand the life cycle of a mission? What’s your advice for those that are stepping into this role?

Knobelspiesse: Well, NASA is a very large institution as we know, and it has different types of people involved and they have different groups. And the way those groups work has some variability. Scientists are a little bit… Well, I don’t mean unique to mean that we’re special, but we’re a little bit different in a couple of ways in other parts of NASA. So for example, we are expected to be self-supporting, to some extent, in terms of funding. Many of us are civil servants, so that does define how our salaries and that sort of thing, but we’re supposed to find support for the research that we do. What it means is that we tend to have very long-time scale approaches to what we’re working on. We work on multiple things over long periods of time, but when we get to a level of working on a mission, it’s a bit different. A mission has a very defined structure for how it works or for who’s involved. And for me, I became the instrument scientist for the polarimeter on AOS about two years ago.

And learning how systems engineers work, how project managers work, all the details of what’s important for scheduling and all of these sorts of things that have to happen if we want to do the science. That was something that was really a learning experience for me personally, which I had not encountered in say, graduate school before. At the same time, I find myself talking a lot about just why we’re doing the science to everybody else in the project who’s not directly involved in the science.

Host: Looking ahead to 2024, Kirk, what exciting developments can we expect from the PACE mission? Are there any significant milestones on the horizon that you particularly are looking forward to as the mission continues?

Knobelspiesse: So small number of us have been making a list of important science papers we want to write with PACE data. Now, this doesn’t mean that we personally would write them, but we would hope that somebody would use PACE data to write those papers. And so a lot of it is at the very beginning is just looking at the global distribution of various things that we will be measuring that haven’t been measured before or haven’t been measured as accurately before.

And seeing if those distributions of conditions align with how they’re being used in models or aligned with our understanding of aerosols, or clouds, or the ocean.

Host: Yeah. Okay. Well, this is really cool. I mean, I’ve learned a lot. Thank you so much for sharing.

Knobelspiesse: Well, thank you.

Host: Thank you for tuning in to Small Steps, Giant Leaps. For transcript of the show and more information on Kirk Knobelspiesse and these topics, simply head over to our resources page at That’s spelled And while you’re there, if you’re curious to learn more about what APPEL Knowledge Services has to offer, don’t forget to explore our publications and courses. This is Teresa Carey, your crewmate in the world of learning. May your steps towards knowledge be both small and mighty.