Transcript:

BRAD NEWBOLD 0:00
Hello, everybody, and welcome to We Measure the World, a podcast produced by scientists for scientists.

TIANXIN “CARLOS” WANG 0:05
I live in California, and we’re constantly faced with the problem of water scarcity. And so being able to manage water effectively is very important, and this is where kind of the VBR comes in. Because, you know, setting up eddy covariance is a practical challenge. It’s very expensive, and in order to have these fluxes everywhere to better understand the spatial pattern of evapotranspiration, we need these type of measurement. But, you know, without eddy covariance, variance Bowen ratio is that kind of a sweet middle ground that offers ET measurements at a much lower price point.

BRAD NEWBOLD 0:48
That’s just a small taste of what we have in store for you today. We Measure the World explores interesting environmental research trends, how scientists are solving research issues, and what tools are helping them better understand measurements across the entire soil plant atmosphere continuum. Today’s guest is Tianxin “Carlos” Wang. Carlos is a postdoctoral researcher in the Department of Environmental Science, Policy, and Management at UC Berkeley, where his work focuses on the exchange processes of energy and trace gas fluxes between the biosphere and atmosphere through the study of biometeorology. His specializations include eddy covariance, surface energy balance, evapotranspiration, and remote sensing. He recently received his PhD from the same department at UC Berkeley, and prior to that, his bachelor’s in environmental science, technology, and policy from Cal State Monterey Bay. And today, he’s here to talk about his doctoral research on making the measurement and estimation of evapotranspiration easier and more cost effective. So Carlos, thanks so much for being here.

TIANXIN “CARLOS” WANG 1:58
Thank you so much for having me here today.

BRAD NEWBOLD 2:02
So today, we definitely wanted to talk about your projects, your research interests. But first, can you tell us a little bit about your background, how you got into the sciences, and how you found your way to biometeorology?

TIANXIN “CARLOS” WANG 2:16
Yeah. It’s kind of like a big serendipity. I moved here around ten years ago, over ten years ago from China, and I did my undergraduate in geology. It has nothing to do with evapotranspiration or biometeorology. But, you know, what’s interesting about that was the serendipity is that right after I graduated, I got a very fortunate internship with NASA Ames Research Center where I worked with OpenET under the supervision of Forrest Melton. And that’s exactly where I kinda got into the zone of land-atmosphere interaction research, you know, with eddy covariance specifically. And I got so into it, and I kinda learned how to operate eddy covariance system just by reading the Campbell Scientific user manuals. But, know, I was able to set up a tower, and I was able to measure some fluxes, but I never really understood the nitty gritty details about what the flux am I measuring. And, you know, that really motivated me to kinda pursue more and which led me to, you know, Dennis Baldocchi’s lab at UC Berkeley to better understand, you know, what eddy covariance measures and what’s the mechanism between the land and atmosphere, which kind of fundamentally pushes me towards the research of biometeorology.

BRAD NEWBOLD 3:48
So in talking about biometeorology, that might be a new term for a lot of folks in our audience. Can you explain a little bit about what that entails? What are the main questions that study covers or aims to answer?

TIANXIN “CARLOS” WANG 4:02
Yeah, absolutely. So we can think about biometeorology as a subdiscipline of meteorology. So in meteorology, we understand, you know, we’re studying the atmospheric dynamics and then how does that affect, you know, certain patterns like weather or climate across different spatial and time scales. And for biometeorology, we’re fundamentally studying how the biosphere is interacting with that meteorological component. You know, for example, it can be agriculture. You know, if we have a nice irrigated alfalfa site, the biometeorology there entails, you know, how much water is leaving the ecosystem or how much carbon the ecosystem is sequestering from the atmosphere. It also relates to human health as well, like a heat wave and how does that create certain problems like environmental injustices, and how do we understand that heat wave across different marginalized communities.

BRAD NEWBOLD 5:00
Interesting. I also heard that METER Group might have had some involvement in you moving from geology and working in the ground to more working in atmospheric sciences.

TIANXIN “CARLOS” WANG 5:12
Yeah. Absolutely. I wasn’t sure if that’s a story that I’m allowed to tell as a consumer, feedback. Right? So during the first leg of my post bachelor training, I started working with NASA Ames, and one of the main goal was to quantify consumptive water use from an in situ perspective. And back then, you know, the gold standard measurement is using lysimeters. Because deploying weighing lysimeters is very hard, and METER Group offers those drainage lysimeters that allows us to capture, you know, the concept of water use at the field with high accuracy and precision. But it also comes with a heavy labor requirement where you had to dig, you know, a six feet hole in order to put the lysimeters in. I think after putting around maybe forty lysimeters, I think the period that really broke me was at a vineyard site where we put eight lysimeters digging through hardpan layers, and at the end, we couldn’t get the drainage, any drainage out of the system. We didn’t really understand why, and but that really pushed me, you know, towards the side of, okay, I’m gonna do atmospheric research because, you know, I set up a tower and I can measure everything and I can get nice values.

BRAD NEWBOLD 6:35
Well, we’re glad that we could help in some way.

TIANXIN “CARLOS” WANG 6:38
Absolutely. Absolutely.

BRAD NEWBOLD 6:40
Where I’m sure you’re much more comfortable and much more happy. So as we mentioned in the introduction, part of your interest in research centers around measurements and estimation modeling of evapotranspiration. We’ve mentioned and we’ve talked about evapotranspiration before on the podcast, but could you go into a little bit detail, just kind of the overarching definition of evapotranspiration, what it is, how it’s used, why it’s important?

TIANXIN “CARLOS” WANG 7:05
Yeah. Absolutely. So evapotranspiration, kinda in the simplest term, is the combination of evaporation, whether it’s from soil or open water, plus the component from biological parameters like plants, and so they transpire. And so together with the evaporation and transpiration, it forms the term evapotranspiration. And so evapotranspiration is one of the major component of the water cycle. And so if we understand evapotranspiration or ET correctly and accurately, we can predict weather patterns, we can better understand how the energy cycle is linked to the water cycle, and that translates to the carbon cycle as well. And then so in a holistic sense, ET helps us to better understand the land-atmosphere interactions across spatial and temporal gradients.

BRAD NEWBOLD 8:00
Got it. So what have been, I guess, general, or you can talk about your experiences as well, what have been some of the biggest challenges in measuring or estimating evapotranspiration?

TIANXIN “CARLOS” WANG 8:12
Yeah, that’s a really good question. I think one of the things I worked on a lot in my doctoral research is something called advection, which is the horizontal movement of heat or water, that’s carried by the wind. And so ET, in a sense, we understand it as a vertical movement of the water from the land surface to the atmosphere, but horizontal movement can also introduce biases or external factors that can affect this vertical transfer of water. And this is where kind of the measurements of ET comes in very importantly because without accounting for all these different atmospheric processes, we wouldn’t be able to understand evapotranspiration correctly and accurately.

BRAD NEWBOLD 8:58
So one of the primary methods at getting at evapotranspiration is through eddy covariance. Right. Can you talk a little bit about that method, the eddy covariance method, and why it’s the gold standard at getting at evapotranspiration.

TIANXIN “CARLOS” WANG 9:15
Sure. Yeah. I think one of the main selling parts about eddy covariance being the gold standard measurement is that it’s a direct flux measurement, directly capturing the entire vertical exchanges between the surface and the atmosphere. And so this measurement is also continuous, meaning that when you set up a tower, we’re measuring fluxes, you know, twenty four hours per day, three hundred and sixty five days per year, and we measure these fluxes at a sampling frequency of twenty hertz, meaning that we sample twenty data points per second. And so throughout the day, we have millions of data point coming in to, you know, better understand the vertical turbulent exchanges. And it also covers a larger spatial footprint compared to point measurements like a lysimeter, which we call flux footprint, and that allows us to understand the entire, you know, water and energy exchanges within a specific field.

BRAD NEWBOLD 10:18
Right. Can you go into a little bit more detail about, I guess, everything that goes into it, into the eddy covariance method? So what is the setup that you’re looking for? What are the sensors you’re using? The methodologies behind it.

TIANXIN “CARLOS” WANG 10:35
Yeah. So eddy covariance primarily uses a sonic anemometer, which measures the three-dimensional wind speed and directions alongside of an infrared gas analyzer. And so together, it forms something called the covariance, which is the biggest, you know, the main part of the eddy covariance. And so by understanding the fluctuation of the vertical wind speed and then the fluctuation of a specific scalar like temperature and humidity, we can measure evapotranspiration. And it’s actually really interesting because eddy covariance, you know, goes way beyond just measuring evapotranspiration. If we think about the fundamental equation that goes behind eddy covariance, we’re essentially measuring or we’re essentially having an equation that accounts for the local storage, let’s say, of humidity, horizontal, lateral, and vertical advection of that humidity, and then this equals to the sum of the flux divergence from three dimensions. And with the assumptions of steady state conditions and horizontal homogeneity, we’re able to cancel out the advection terms, storage terms, as well as the horizontal and lateral flux divergence terms, allowing us to, you know, directly capture the entire ecosystem exchanges through the vertical component under the assumption of constant flux layer. And I think this is also where it gets important in terms of the, you know, one of the biggest problem in micrometeorological research is the lack of energy balance closure. And, you know, this is a topic that folks talk a lot about. In our recent publication, I mean, we did look specifically into, you know, what’s something that caused the energy imbalance. And one of the things we found is that energy balance closure is death by a thousand cut, and it’s really a multifaceted component. We have advection, we have storage for heat, we have photochemical storage, we have spectral filtering that could all factor into, you know, the uncertainty in our fluxes, which translates into the uncertainty of evapotranspiration. And across different sites, across ecological and climatic gradients, you know, different sites requires different prescriptions, just like us humans, you know, if we feel sick, we can’t all get antibiotics, and we have to tailor our understanding to better treat the problem.

BRAD NEWBOLD 13:10
And I think this goes into many, especially when you’re dealing with biological or natural systems, where the assumption and when you’re dealing with modeling, you have to make assumptions in a lot of these cases. You’re simplifying the natural world down into a model, right? But those assumptions of steady state, or that it is an essential I mean, it is essentially a closed system, but how large, how far does that system expand? Like you said, there’s different leakages potentially of this potentially closed system, and being able to account for each of those in different ways.

TIANXIN “CARLOS” WANG 13:48
Absolutely. And then to build on that, one of the things or examples we’d like to use is our atmosphere or our ecosystem is like a colander. Even though it looks like an enclosed system, but when you pour a specific quantity in there, it leaks everywhere. And being able to account for, you know, all these terms across different dimensions is very challenging, and so in ecosystem science, we tend to idealize the case scenarios, but this is also where reality meets theory. Know, theory breaks because these are the components we’re not currently accounting for.

BRAD NEWBOLD 14:30
What are some of the other, I guess, practical limitations of the eddy covariance method? So talking about, like, you know, setup or installing a station at a location, what goes into that, and where might some of the pitfalls be in that part of the process?

TIANXIN “CARLOS” WANG 14:50
Yeah. Know, setting up the tower is very difficult. It requires you to have detailed knowledge, and if we wanna boil things down, we usually follow the rule of thumb that the fetch to tower height should be at least at a certain threshold. Let’s say the fetch is the horizontal distance of the tower from the field edge, and then the height is just the sensor height. And so, technically, the fetch to height ratio should be around seventy five to a hundred and fifty. You know, setting up a tower requires you to have, you know, enough labors to clean the sensors, and these sensors, you know, could drift over time, and so it requires us to take good care of them, meaning we we have to calibrate routinely. And post processing the eddy covariance data is really hard, and one of the thing I’m gonna throw in, like, as a jargon is coordinate rotation. So how do we align our measured wind with the mainstream? That’s one of the challenges, you know, if we didn’t know a lot about, you know, the fundamentals of micrometeorology comes in. And I think lastly, the other part, you know, aside from other complicated math, chemistry, and physics that goes into analyzing eddy covariance data is the cost. Right. We mentioned before, eddy covariance relies on a sonic anemometer and an infrared gas analyzer, and the infrared gas analyzer alone can cost around twenty to fifty thousand dollars, not including other equipments. And if you’re setting up a tower in a tall forest, you still need to understand, you know, what’s the what’s how tall does your tower need to be, and do you need to get a crane to set up a tower in there? And then when you go to a wet ecosystem, how do you, you know, deal with the the open water body? Or in in a very salty ecosystem, can you use steel, or should you use aluminum? I think it all all kind of adds up.

BRAD NEWBOLD 17:00
Right. Right. I would even think of, you know, like you’re talking about setting up at different locations. Are you on, you know, a flat plane? Are you on a slope? Right. What is that movement beneath, you know, going to going to be? Is there gonna be, you know, subsidence? Is there gonna be slippage? You know? Just all these little things, that come in. And, yeah, talking about animals, you know, are you going to have, you know, birds and come.

TIANXIN “CARLOS” WANG 17:35
Right. Yeah. Or spiders, come in between your sampling path, then so you’re essentially just measuring the spider fluxes, not the water fluxes anymore.

BRAD NEWBOLD 17:48
So with all that being said, with that background of evapotranspiration and eddy covariance, let’s dig into this new approach with the variance Bowen ratio method. Alright. What is it? Why is it important? What can it do? Let’s just dig in. Ready? Ready to go.

TIANXIN “CARLOS” WANG 18:08
Alright. Let’s let’s do it. The variance Bowen ratio is a, you know, simple technique that allows us to indirectly estimate the sensible and latent heat flux. And what’s so useful about this is it’s very cheap. Most of the weather station already have the equipments that we need in order to calculate these fluxes. And so it takes the simple statistics of the standard deviation between temperature and specific humidity to form something called a modified Bowen ratio to resolve sensible heat flux and latent heat flux accordingly. One of the main attractive part about the variance Bowen ratio method is that it’s very simple in terms of setting the tower up, maintaining the tower, you don’t need to go out and clean as often compared to other sensors, And lastly, you know, the post processing is a lot simpler than other mainstream measurements like eddy covariance.

BRAD NEWBOLD 19:15
What might be the environments where you might want to use this method over, say, eddy covariance?

TIANXIN “CARLOS” WANG 19:25
Yeah. So for agriculture, let’s say, a lot of farmers and water managers really care about, you know, their crop health as well as how much water we have. I live in California, and we’re constantly faced with the problem of water scarcity. And so being able to manage water effectively is very important, and this is where kind of the VBR comes in. Because, you know, setting up eddy covariance is a practical challenge. It’s very expensive, and in order to have these fluxes everywhere to better understand the spatial pattern of evapotranspiration, we need these type of measurement. But, you know, without eddy covariance, variance Bowen ratio is that kind of a sweet middle ground that offers ET measurements at a much lower price point.

BRAD NEWBOLD 20:20
Let’s let’s take a step back and talk about kind of like the foundation of VBR. So can you talk a little bit more about the Bowen ratio itself and why that’s important, how that fits into into calculating evapotranspiration?

TIANXIN “CARLOS” WANG 20:35
Yeah. So Bowen ratio is kinda like a technique that was developed back in nineteen twenty six or so. It kinda simply takes a gradient method to compute the ratio between sensible heat flux and latent heat flux, which is in terms of temperature and humidity, to allows us to better understand the energy partition, between heat and water. And by understanding the Bowen ratio, we can scale that with the net available energy from the sun and from the land surface, to kind of understand how much water would be evaporating from the surface. And so in a mathematical format, it’s the ratio between net available energy and one plus the Bowen ratio that we’re developing.

BRAD NEWBOLD 21:25
Got it. And so the key components you’re looking at basically, you just need temperature Relative humidity, wind, speed, and and direction, or is it mainly just the the flux between, I mean, two positions in space?

TIANXIN “CARLOS” WANG 21:42
Yeah. It’s the flux gradient between the two positions, and this is kind of where the variance Bowen ratio comes in. Because in order to get these flux gradients, it’s very complicated method in the sensor breaks here and there, and it’s very expensive to get this type of measurement. And by using variance Bowen ratio, you know, we’re taking the simple statistics that most weather stations discard, and so we could get this type of Bowen ratio with the standard deviation of temperature and specific humidity. And so what we kind of construct a ratio between sensible heat and latent heat flux is also the product of different covariance terms. And so in a simple sense, these covariance terms are the ratio between correlation coefficient of, temperature and, water transport alongside of the standard deviation of the vertical wind speed and temperature or specific humidity. And so we assume there’s equal diffusion or equal transport of heat and moisture, which allows us to directly estimate something called the modified Bowen ratio with the standard deviation between temperature and specific humidity.

BRAD NEWBOLD 23:00
Got it. And so in this process, where have you where have you been able to test this out? So what are some of the the locations, environments that you’re looking at or that you’ve you’ve worked on already?

TIANXIN “CARLOS” WANG 23:15
Yeah. We tested this method at an irrigated alfalfa site in California, I think, over over six months, and we were able to derive sensible heat flux and latent heat flux using the simple technique that showed very strong agreement with eddy covariance measurement. And one of the thing that allows it to work is the core assumption of equal diffusion. For a homogenous alfalfa site was without the presence of advective fluxes, you know, all these atmospheric processes are being capsulated with the Bowen ratio. And so we’re able to use a, you know, six hundred dollar sensors to provide evapotranspiration that’s comparable with a twenty thousand dollar sensor. And right now, we’re kinda moving the sensor, kinda torture the sensor a little bit more into a challenging ecosystem, across three different wetlands with different tidal influence, with different land surface conditions. And to our surprise, the variance Bowen ratio performed way better than we expected, and so maybe this should be a research question as well in terms of why does that work so well. I think fundamentally, across different time scales, we’re able to capture fluctuation of temperature and specific humidity, which is the core concept that goes into the turbulent transport between the land and atmosphere.

BRAD NEWBOLD 24:45
With, like you said, working in an alfalfa field, homogenous crop. You said there’s no nowhere, not much advection from outside sources. But in the wetlands, I mean, you’ve got a lot of stuff moving around. Right. You know, water coming and going. Did you see differences in how well how well VBR worked in different times of the year, day versus night, you know, on that on that temporal scale as well as spatial?

TIANXIN “CARLOS” WANG 25:15
Yeah. So I think maybe maybe two separate kind of a comment. I think when we deployed the VBR at the irrigated alfalfa site, there was the presence of advection. In fact, it’s kinda a very common problem in agriculture, at least in the semi arid environment, where not all the fields are gonna get irrigated at the same time, meaning your upwind field might might be cultivated already or might just be left bare, and then so that introduced heat into the ecosystem. And so in our analysis, we found that the variance Bowen ratio underperformed a little bit despite the strong agreement as a result of these advective fluxes. And then moving into, you know, wetland ecosystems, what we saw was the discrepancies between variance Bowen ratio and eddy covariance. One thing is the day and night fluxes. You know, we still follows the rule of Monin-Obukhov similarity theory, and so with different stability and thermal stratifications at night, we weren’t really able to capture these fine detailed fluxes compared to eddy covariance, and again, covariance is that gold standard with direct measurement capturing all these fluctuations because of the differences in stability, while variance Bowen ratio still has the assumption of equal diffusion, which is, you know, obviously violated at night because of these thermal stratifications. And across different sites, we also started seeing different emerging properties, you know, just how simply the mechanism works across different wetlands. For example, at the tidal wetland, we set up the variance Bowen ratio method and compare it with eddy covariance, and at that side, it was completely just full on water. It was little to no vegetation, but the tidal action is bringing a lot of uncertainties into our kind of a calculation because the variance Bowen ratio still uses the Bowen ratio kind of formulation to get a sense of the latent heat flux, meaning the net available energy drives a lot of the estimation of the latent heat flux. And so when there’s water coming in, it brings in, you know, not only nutrients, but also properties of heat. And water has high thermal inertia, and if there’s the water just standing there, it’s gonna absorb all the heat. And in our results, we did see, you know, this heat being released at night instead of during the day. And so this is not something we’re capturing with the variance Bowen ratio method. But this is also not something really scary because we know, you know, that’s when the theory breaks. And so in a reality or or in a practical sense, in order to achieve better fluxes, we need to account for these serendipities or uncertainties that we are not accounting for in our measurements, and specifically at the tidal system with the open water body, it will be this heat storage that’s within the water.

BRAD NEWBOLD 28:25
Right. What is the time scale that you’re wanting to, I guess, average the data across? Or is there a need to look at only day values versus only night? Is it something where you’re averaging across days, weeks, months, even a full year?

TIANXIN “CARLOS” WANG 28:45
Yeah. I I think it depending it depends on the audiences or or the consumers. And for, you know, researchers and scientists, I think folks are mostly interested in half hourly data, and this is where it kinda gets a little bit complicated in terms of using a cheap method to, you know, achieve the accuracy of a of a, you know, expensive sensor. But then, you know, moving beyond that side for a water manager or a rancher, they really care about, you know, a coarser temporal scale. And in a way, what we saw is our daily values were comparable with eddy covariance, and this is very important for a farmer. And they wanna know how much water is leaving the ecosystem so they can better schedule their irrigation. And, this is kinda where the daily value shines. And then, you know, even for wetlands with different, you know, uncertainties with variance Bowen ratio underperformed here and there. At a annual time scale, we were able to achieve, you know, uncertainty or differences within five percent of eddy covariance. And this is where it comes in for water managers, and if they wanna report how much consumptive water use is from that specific wetland throughout the year, they can use the variance Bowen ratio to kind of get that sense of the rough estimates. I think this kind of opens up maybe the separate realm of having a pros and cons list. And I think, you know, what we think about ecosystem is that it’s very chaotic. There’s no one size that fits all solution no matter your gold standard measurements, and we gotta be able to account for all these externalities in order to better understand the mechanism behind our ecosystem. And that similar concept goes for the variance Bowen ratio. For an ecosystem like an agriculture land, it’s relatively homogenous. You might be suffering from advection or not. Over the periods of long term, we were able to provide good results compared to other ecosystems that might be suffering from heat storage problems or advective fluxes.

BRAD NEWBOLD 31:00
I mean, you’ve mentioned some I mean, I don’t know if I’m gonna call them issues or whatever, but some of roadblocks or speed bumps dealing with measuring evapotranspiration via the VBR method. What are the next steps in fine tuning or refining that model and that method?

TIANXIN “CARLOS” WANG 31:20
Yeah, so I think one of the most important thing that we’re working on is does VBR perform uniformly across different landscapes? And the simple answer is probably not. And so depending on your specific site, we might need to reassess and reevaluate the accuracy of variance Bowen ratio. What we found from our agricultural studies is that the variance Bowen ratio performs really well compared to eddy covariance, but then from our wetland ecosystems, it doesn’t necessarily add up, and we’re still currently investigating, you know, what’s the root cause behind it. But in order to go to the next step, we’re still setting up additional variance Bowen ratio kind of sensors on AmeriFlux and FLUXNET towers because, you know, all these towers have what we need. They have the sensors, and what we need to do is just to update the logger programs to include a subroutine to get the variance Bowen ratio derived fluxes. And so right now, we got collaborators across the United States and in Spain, Brazil, Australia, Estonia, and South Korea to really test, you know, the performance and accuracy of variance Bowen ratio across ecological and climatic gradients. And with, you know, understanding from that, we can better assess what we need to do next. And one of the simplest term is that there needs to be a correction factor, you know, but depends on what. That’s something we don’t know about. One of the thing for wetlands, it might be, you know, okay, the violation of equal diffusion, the necessity of adding the heat storage. But for a tall forest, and that’s something I’m not quite certain about, and that’s why we’re setting up more towers. And I think the immediate impact of that is that VBR does, you know, offer that cost effective estimates of ET. And for the first time, it allows farmers, you know, the potential to get a lot of sensors in their field. And this is very important because, you know, if we open up our phone and we’re like, okay, you know, what’s the chance of rain today? Nowadays, it’s pretty accurate most of the times, you know, glitches here and there, but I think this is the, you know, the advantage of having VBR sensors everywhere too. Because for these weather reports, they have precipitation satellites, and they’re being calibrated by weather stations across the world in order to provide, you know, better results. And one of the things with the VBR is that the setup is very simple. You can just have a pole and then add the sensor on there, meaning that you can stick it everywhere. And for the first time, we could provide a regional scale of in situ evapotranspiration measurements that can be calibrated for remote sensing models. And so in a way, it kind of aligns with our lab philosophy that we want fluxes everywhere all the time, but what’s the price point? And this is something that we can use to achieve that for water fluxes.

BRAD NEWBOLD 34:15
So that flows right into my next question, which is kind of, yeah, more on the application side of things. So you’re talking about agriculture, you’re talking about farmers and water balances. What are, yeah, some of those added benefits for being able to have an easier, more cost effective measure of evapotranspiration for those folks?

TIANXIN “CARLOS” WANG 34:38
Yeah. The main selling point is saving water. Water is, you know, something we kind of overlooked a little bit. I mean, we rely on water to survive, and water costs a lot of money. And California doesn’t rain a lot. Nowadays, we’re facing the unfortunate consequences of, I think storms from politics, from the climate, and we aren’t certain what’s the next step in order to better understand land-atmosphere interactions, understanding evapotranspiration. But one thing we can offer is we have a cheaper and cost effective measurement that help us understand the entire distributions of the water and, you know, saving saving water, being able to manage water, and helping people, you know, to secure food and jobs. I think that comes maybe aside from science. I don’t know. Maybe I’m right way ahead of it.

BRAD NEWBOLD 35:35
So with that being said, what do you see I mean, you’ve talked about some of the next steps for improving the methodology. What do you see there in the future? Like, where do you see this going in the next five, ten years?

TIANXIN “CARLOS” WANG 35:50
Oh, I if if if funding is not a problem, if nothing is a problem, everything is nice, and then I would love to set up these sensors everywhere, like, let’s say, the Sacramento-San Joaquin River Delta region throughout California, to better understand what’s the regional distribution of water. How does that, you know, being useful for other models or hydrological models to better understand the runoff, to better understand the groundwater storage. Are we over pumping? Where’s the water coming from? And maybe, you know, in a derivative format, measuring open water systems like a lake or a reservoir, or even applying it for natural systems like a beaver habitat, and how the presence of beaver can affect the fluxes of water.

BRAD NEWBOLD 36:42
One of your other specialties is remote sensing as well. Is there any interplay between remote sensing and the VBR method? Is there is there any way that they can work together to improve measurement of evapotranspiration?

TIANXIN “CARLOS” WANG 37:00
Right. Yeah. And then that kind of goes into the calibration route we kind of briefly touched based on earlier. Setting up, you know, in situ measurements allows us to understand the energy and water exchanges for a field, let’s say agriculture, but we also need to set these towers, you know, everywhere in order to better understand these fluxes and the spatial temporal patterns of these fluxes. Remote sensing is one tools that allows that to happen. But, you know, satellite passes once every so often, you know, like with the Landsat science team, you know, with Landsat 8, Landsat 9, it passes once every seven days, but it doesn’t capture, you know, what’s going on in between. And so what VBR fills in is that having these dense network of towers, it can not only calibrate the evapotranspiration for remote sensing, it can also gap fill in between where satellite data is not there. And additionally, it also offers additional validation kind of a strategy for these remote sensing models in order to further expand, let’s say, from the West Coast to the East Coast, where there’s more clouds, more humid, more extreme weather.

BRAD NEWBOLD 38:20
Is there anything else that you’d like to add, anything we didn’t cover that you wanna make sure our audience knows about?

TIANXIN “CARLOS” WANG 38:30
I love Lady Gaga. That’s a that’s a maybe non science part.

I’m really excited for her new album to come out this Friday, and that’s it.

BRAD NEWBOLD 38:42
That’s awesome. Where can folks in our audience learn more about VBR and about the work that you’re doing?

TIANXIN “CARLOS” WANG 38:52
So we back in twenty twenty three, we published the paper on VBR where we tested the variance Bowen ratio at the irrigated alfalfa site. And then so if you search Google Scholar on Tianxin “Carlos” Wang, it will show up.

BRAD NEWBOLD 39:12
Yeah. Awesome. Great. Well, I think our time is up for today. Thanks again, Carlos. We appreciate you taking the time to come visit us here at METER Group and be able to talk and chat. Super interesting conversation and best of luck in your research.

TIANXIN “CARLOS” WANG 39:30
Thank you. And thank you again for having me. It’s really been a pleasure.

BRAD NEWBOLD 39:38
Yeah. Thank you. And if you in the audience have any questions about this topic or want to hear more, feel free to contact us at METER Group dot com, or reach out to us on X at meter_env. And you can also view the full transcript from today in the podcast description. That’s all for now. Stay safe, and we’ll catch you next time on We Measure the World.