Posts tagged ‘Water’

Jan 5

Do Funding Agencies Favor Collaboration?

It’s an interesting question, and certainly one scientists need to think about. In a recent conversation a science colleague said, “I think in science right now, all the funding agencies are recognizing that to answer the problems that matter, you need to bring in people from different disciplines and even industry. If you look at the major funding focus of the National Science Foundation, when they consider bio-complexity, they’re not looking for a group of people with the same perspective. Science questions are becoming more complex, so you need to get input from people with varied backgrounds.”

R.J. Cook Agronomy Farm at WSU (http://css.wsu.edu/facilities/cook/)

Examples of this are two projects that METER has collaborated on recently: the Specialty Crops Research Initiative – Managing Irrigation and Nutrients via Distributed Sensing (SCRI- MINDS) and the WSU Cook Farm project, both of which were able to get funding based in part on the use of METER’s technology, and both had a high-level of multidisciplinary involvement.

We got involved in the Cook Farm Project seven years ago because another scientist and I had an idea that fit in the context of a hot topic of the time which was to create a wireless sensor network that was densely populated in a relatively small area. We did this because at that time, scientists were recognizing that many of the processes they were interested in were occurring when they were not out in the field measuring. In order to understand these processes, we needed in situ measurements collected continuously over a long period of time.

What we were trying to do is show that you could create a wireless sensor network in a star pattern, where you have a central point collecting data from a host of nodes surrounding it. Our questions were: can we create a sustainable star network in the field to get consistent and continuous measurements over several seasons, while densely populating the study area with sensors? The measurement network that we designed allowed us to investigate how topography, slope, and aspect interact to determine the hydrology of the soil in this intensely managed agronomic field.

Decagon collaborated with scientists at Washington State University, working with twelve sites across a 37-hectare field. We installed five ECH2O-TE (now 5TE) sensors at 30, 60, 90, 120, and 150 cm below the soil surface.

Wheat field

What we learned was that when wheat plants grow, their roots follow the water down a lot deeper than you might imagine. We observed considerable water loss even 150 cm below the soil surface. Data on soil water potential suggested that, as water was depleted to the point where it was not easily extractable, plant roots at a given level would move deeper into the soil where water was more easily accessible. Soil morphology also came into play as hardpans occurred at several measurement locations and water uptake from layers above and below them showed amazing differences.

It was a really exciting thing scientifically, but also technologically. We learned that the star network was easily possible. It ran autonomously and was very successful, in spite of the fact that the cell phone we used to get the data back to the office never worked very well.

So it was the science question and the technology question together that was able to secure the funding. With those twelve sites WSU was able to secure a grant from the USDA for 4.2 million dollars and the research is still ongoing today. In fact, recently Cook Farm was established as one of the National long-term agroecosystem research sites (LTAR) which will help continue this kind of research well into the future.

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Dec 22

Measuring Osmotic Sap Water Potential

Sometimes networking with new scientists at conferences and workshops can pay dividends in terms of new ideas. Steve Garrity and I recently attended and taught practicum sessions at the PEPg (Plant Environmental Physiology group) Ecophysiology Workshop. The mission of this workshop was twofold: to invite the world experts on plant physiology measurements to come and lecture, and to invite the manufacturers to teach about instrumentation and provide hands-on training.

Workshop participants check the water potential of soil with a UMS T5 mini-tensiometer.

With three sessions per day using METER instrumentation and only two of us, neither Steve nor I could teach about leaf water potential using the WP4C chilled mirror dew point instrument. So, we asked another scientist who is an expert in plant water relations to teach it for us. Not only did he do a great job of teaching about measuring leaf water potential using a hygrometer, but he also inspired us to take another look at how to make this measurement as we learned about its importance to his research (to learn more about how to do this, watch our virtual seminar).

He’s developed a procedure where you can freeze the leaf and break all of the cells so you are left with the cell water (the symplastic water).

Later in the conference, this same scientist gave a talk about the importance of osmotic potential. He’s developed a procedure where you can freeze the leaf and break all of the cells so you are left with the cell water (the symplastic water). He was able to squeeze that sap out and test it in a thermocouple psychrometer, where he established a relationship between how tolerant plants are for drought and what their osmotic sap water potential (turgor loss point) was. We have made many of those sap measurements but had not used them in this manner. That’s really interesting to us at METER because we were unaware of this relationship, and we have now found another use for osmotic potential measurements in leaves.

We would never have realized this new idea without the help of our colleague. Meeting with other scientists at conferences and talking over ideas can be really important. Have you ever struck gold in terms of coming up with new ideas for research, funding, or inventing new research tools at a conference you’ve attended?

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Dec 17

Dr. Gaylon S. Campbell Author Interview

METER’s founder, Dr. Gaylon S. Campbell was born in Blackfoot, Idaho, and grew up on a dry farm in Juniper, Idaho. He went to school in Logan, Utah, finally attending Utah State University where he received a B. S. in Physics in 1965 and an M. S. in Soil Physics in 1966. He was granted a Ph. D. in Soil Physics from Washington State University in 1968. He became an officer in the U. S. Army in 1969, doing meteorological research at White Sands Missile Range, New Mexico. In 1971 he returned to Washington State University as Assistant Professor of Biophysics and Assistant Soil Scientist. There he taught and did research in Environmental Biophysics and Soil Physics until 1998. Since 1998 he has worked as vice president, engineer, and scientist at Decagon Devices, Inc (now METER). He has written three books, over 100 refereed journal articles and book chapters, and has several patents. Today we are interviewing him about his book, An Introduction to Environmental Biophysics.

Dr. Campbell is the author of An Introduction to Environmental Biophysics

Where did you get the knowledge to write the book?

I was hired to teach Environmental Biophysics at Washington State University in 1971, and when I looked around for a textbook to go with the class, there weren’t any that fit very well. I knew what I wanted to teach in the class, and some of the principles were in books that were available, but a lot weren’t. So I started writing up notes to hand out to the students and then improved them over time.

One of the important sources of knowledge for my book was John Montieth’s book, Principles of Environmental Physics. Its first edition came out in 1973. It’s a wonderful book. I didn’t know about it until one of my students brought it into class and let me borrow it overnight.

I went home and started reading it. I read it all night, and by morning I’d finished it. I have read some novels that could keep me awake all night, but that’s the only science book I ever read that could do it.

I was really excited about his approach because it was perfect for what I wanted to do in the class. However, it was at a different level than I needed, so I went ahead and developed my own notes, but his book certainly was an important source.

I started writing up notes to hand out to the students and then improved them over time.

How difficult was it to understand the theory behind what you were writing about?

When I’d take a class in school, I felt like I never understood what was in that class until I attended the next class. Then when I got a bachelor’s degree, I thought, I hope nobody expects me to know something just because I have this degree, because I don’t feel like I know anything. I hoped when I earned a masters degree that it would be better, but I got there and thought, oh boy, I still don’t know anything. It was probably when I took my prelim exam that I finally felt confident enough that I could be a soil physicist if I had to.

But I was wrong about that. I really didn’t understand physics very well, even then. It was when I had to teach it that the real understanding came. When I understood it well enough to lecture about it was when I felt like I had really mastered the theories and understood them at the level that I wanted to.

I suppose that came one piece at a time. In the beginning, I certainly didn’t understand things as well as I did later on. And that still happens today. I learn things that I hadn’t understood before. So I guess when you ask how hard it was: it was an ongoing process. Even when somebody’s already laid it out for you, it doesn’t mean you’re going to understand it. But when you lecture about it and write about it, those are the processes that help to deepen your knowledge and understanding.

When you lecture about a subject and write about it, those are the processes that help to deepen your knowledge and understanding.

The subject is extremely complicated, but people are always saying how easy it is to understand environmental biophysics from your book. How did you bring it down to the level of the students?

When I was in the Army, the philosophy they had was, “If the student hasn’t learned, the teacher hasn’t taught.” That was not the philosophy that you normally encountered at the university. Many professors complained often about how lousy their students were. I never found it to be that way. I always thought my students were getting better and better.

I think it comes down, to some extent, to the philosophy the teacher has. We often see teachers come in and fill the board with equations and wonder why their students don’t understand them. But it’s likely the teacher hasn’t looked at it from the standpoint of the students. The student is going to gain understanding by the same path the teacher did. Professors work and work to put together a wonderful picture of things, and once they have that wonderful picture, they tend to want to dump the whole thing on the student. But students can’t assimilate the whole picture all at once. They have to go step by step too.

If people wanted to learn from your book, what is the best way to get the principles down?

It’s no accident that there are lots of both worked examples and problems for students to solve. I don’t think you can learn physics without solving problems, and so the best way to do it is to look through the ones that we’ve solved in the book and then look through the problems we give at the end of the chapters and solve them. That, I think, is the best way to get there.

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Dec 3

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TDR versus Capacitance or FDR

When we talk with scientists at conferences they often want to know the difference between TDR versus capacitance or FDR. We’ve written a paper about this in our app guide that has been pretty popular, but it can be difficult to find on our website. Here is an introduction and a link if you are interested in learning more.

TDR Sensor Installation (Giulio Curioni, School of Civil Engineering, Univ. of Birmingham)

Capacitance and TDR techniques are often grouped together because they both measure the dielectric permittivity of the surrounding medium. In fact, it is not uncommon for individuals to confuse the two, suggesting that a given probe measures water content based on TDR when it actually uses capacitance.

10HS capacitance sensor

With that in mind, we will try to clarify the difference between the two techniques. The capacitance technique determines the dielectric permittivity of a medium by measuring the charge time of a capacitor, which uses that medium as a dielectric. We first define a relationship between the time, t, it takes to charge a capacitor from a starting voltage, Vi , to a voltage V, with an applied voltage, Vf. Read more….

Watch the webinar

In this webinar, Dr. Colin Campbell discusses the details regarding different ways to measure soil moisture and the theory behind the measurements. In addition, he provides examples of field research and what technology might apply in each situation. The measurement methods covered are gravimetric sampling, dielectric methods including TDR and FDR/capacitance, neutron probe, and dual needle heat pulse.

Take our Soil Moisture Master Class

Six short videos teach you everything you need to know about soil water content and soil water potential—and why you should measure them together. Plus, master the basics of soil hydraulic conductivity.

Watch it now—>

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Nov 20

New Applications in Archeology for TDR Probes Measuring Water Content

Recently, I spent a day at the University of Birmingham in the UK where I talked with Dr. Nicole Metje and researchers in the Civil Engineering department. They are working on a project called, “Mapping the Underworld,” (Curioni G., Chapman D.N., Metje N., Foo K.Y., Cross J.D. (2012) Construction and calibration of a field TDR monitoring station. Near Surface Geophysics, 10, 249-261) where they are using TDR probes to help locate buried objects that require maintenance.

University of Birmingham Clock Tower

Currently, people use rudimentary tools to poke around and figure out where the buried object is. A more effective high-tech solution is GPR (Ground Penetrating Radar) that is pulled over the top of the soil and creates a 2D image of permittivity below the ground surface. The problem is GPR only provides relative depth information and must have ancillary data to produce actual values. To address this issue, their group uses TDR probes (time domain reflectometry) which measure dielectric permittivity to ground truth the GPR. Using this method they hope to be able to predict the depth to anomalies that are observed in the 2D GPR output.

Sensor Installation Pit

After working on this for some time, the engineers at the University of Birmingham continue to deal with challenges related to TDR signal, interpretation, and maintenance. One challenge is that TDR systems are complex and power hungry. Thus, the researchers were interested in learning more about soil moisture sensing and different technologies that would help them meet their project goals. My first inclination was to solve their problem with water potential sensors. Many people who work in environmental applications want to know the fate and distribution of water where water potential is the driver. Interestingly, this is one of the few cases where people actually do need permittivity measurements (the value used to derive volumetric water content, VWC) instead of water potential because they use the actual permittivity signal to ground truth the GPR. This realization spawned a four-hour discussion on the frontiers of permittivity measurement in soil and the use of advanced analysis techniques to tease out important soil properties such as bulk density, electrical conductivity, and mineralogy.

I hadn’t given much thought to using soil science instrumentation to locating buried infrastructure. I’m excited to see what the combination of a new technology like GPR and dielectric measurement can do to help us solve everyday problems like where to start digging.

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Nov 13

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Complex Scientific Questions Yield Better Science in Desert FMP Project

The Desert FMP project originated from a discussion between pretty divergent scientists: Rick Gill, a BYU ecologist, another scientist who works on soil microbes, a plant physiologist, and a mammalogist who researches small mammals.

Tree fire in Rush Valley

In an interview Rick said, “We started talking one day about the transformations that have occurred in the arid West over the past 100 years. One of the things we are really interested in is fire. How do ecosystems recover after fire? What’s the role of water in rangeland recovery? And the unique piece of this is: what’s the role of small mammals in this process? We may never have thought of that question, or the complexity of researching how all of our questions work together in a system, if scientists from different disciplines hadn’t decided to collaborate.”

Rush Valley research site. Five replications with four treatments: burned/unburned and small mammal/no small mammal. What’s interesting for us is that you can see that in the burned plots (the light brown) there are strong differences in the amount of the bright green plant—halogeton—that was present and it is systematically associated with the presence of small mammals. Here is the logic: In the spring, the presence of small mammals suppressed the cheatgrass and to some extent halogeton; in the absence of halogeton, cheatgrass ran wild. The cheatgrass transpired away all of the water and the halogeton that had germinated all died before it could flower.

As the experiment unfolds it is becoming clear that small mammals play a larger role in ecosystem recovery from fire than originally thought. The scientists have used their observations to hypothesize that small mammals eat the seeds and seedlings of two invasive species. This ends up setting the vegetation along a very different trajectory than when small mammals are absent following fire. Rick says, “We have discovered this complex but interesting interaction between water, fire, and small mammals. The first year after the fire, a really nasty range forb moved in called halogeton, which is toxic to livestock. Halogeton also accumulates salts in the upper soil profile that will cause failure in native plant germination. Cheatgrass has also moved in which makes the area more prone to fire as it connects the sagebrush plants with flammable material. But what’s interesting is in treatments where mammals were present, the densities of both halogeton and cheatgrass were much lower than where small mammals were absent.

Plot water potential comparison using matric potential sensors between Mammal (blue) and no mammal (red) over time. With no mammals to control cheatgrass, it depleted soil water availability below no mammal treatment and consequently halogeten was not able to grow.

“The other really important thing is that cheatgrass and halogeton have different growth patterns. Cheatgrass germinates in the Fall. It reaches peak biomass early in the growing season and then dies off leaving a blanket of dead, highly flammable vegetation. Halogeton germinates early in the growing season and remains relatively small until early Autumn when it bolts. These are things that will be really easy to pick up using NDVI sensors, which are sensitive to the amount of green vegetation within the field of view of the sensor. We are also using a system that we’ve designed to manipulate precipitation input. This will enable us to connect water availability to the success of two invasive plants that have negative impacts on rangelands. And with these same treatments we’re going to be able to tease out when in the year and to what extent small mammals are influencing the ecosystem by eating the seeds or the plant and at what stage.”

“Until I saw it in the field, the question of mammals being influential in rangeland fire recovery had never occurred to me. We only discovered that piece of the puzzle because scientists from differing disciplines are working together.”

Below are two virtual tours of the site:

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Nov 6

Volumetric Water Content: Keeping your Eye on the Goal

Most scientists agree that it’s productive to attend seminars and conferences in order to talk with peers, share ideas, and learn about what other scientists are doing. However, in both academia and industry, we need to be careful that we are not so easily influenced by other scientists’ opinions that we lose sight of the end goals of our own projects. This happened to us recently at Decagon. Here’s the background: our volumetric water content (VWC) sensors actually measure the dielectric permittivity of the soil and use a transfer function to predict VWC from the measured dielectric value. Most of our sensors receive a “dielectric calibration” during the production process where they are calibrated in five dielectric standards to make sure they all measure dielectric permittivity accurately, thus leading to accurate VWC measurements with our standard transfer function.

Volumetric water content (VWC) is determined by measuring the charge storing capacity of the soil using capacitance/frequency domain technology.

We were doing a pretty good job calibrating these sensors in dielectric standards, and our default dielectric-to-VWC transfer function resulted in good VWC accuracy. Then we went to a series of meetings and talked to some of our researcher friends who work on instrumentation. They said, “Look, your water sensors aren’t reading as accurately as they should in dielectric permittivity.” Here’s where the trouble started…

Wanting to make the perfect instrument, we went back and re-evaluated the dielectric calibration standards for these water content sensors and tried to use the book values of dielectric permittivity. This was a bad idea because it fundamentally changed the sensor output. Now, despite the sensors giving a slightly more accurate value for dielectric permittivity, they gave less accurate measurements of VWC. Compounding the problem, we now had a population of sensors that didn’t read the same as earlier sensors of the same type. So when customers started replacing their old sensors they said, “Wait a minute, this sensor reads 4% higher water content than my old water content sensor.” That’s when we realized that we had a real problem.

Our underlying mistake here is that we failed to remember that 99% of the people who buy our VWC sensors don’t even care what dielectric permittivity is. They just want an accurate, repeatable measurement of soil moisture. Essentially, because we were so focused on trying to produce a theoretically perfect sensor for a vocal minority of technically savvy users, we lost sight of the practical matter. Did our sensors produce an accurate water content measurement?

I wonder how often this happens in academia and industry. Scientists are bombarded with input from so many different stakeholders, it’s sometimes difficult to maintain the original focus of their projects. We need to remember to focus on the end goal and filter out things that may distract from that goal.

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Nov 1

Spectral Reflectance and Water Content in the Wasatch Plateau Experiment

We chose to collaborate with Brigham Young University in an experiment on the Wasatch Plateau in 2009 because a scientist friend of ours had been working in that area the previous five years, and he noticed there were big grazing responses. The plants growing in the long-term grazed areas were all drought tolerant, while ungrazed plots had plants that were often found only in wetter areas. The only difference was the fence that kept sheep on one side and not on the other. The big question was: how does water influence plants in this ecosystem that we understand relatively well? The story had always been the influence of grazers, when in fact, maybe the indirect consequence of grazing was mediated by water.

The Wasatch Plateau above Ephraim Canyon, UT, USA.

METER donated some sensors in order to set up an experiment where we changed the amount of water in various plots of land. We had rain exclusion plots, and we had treatments where we collected all incoming rainfall and reapplied it either once a week or every three weeks. This allowed us to say to what extent this system was controlled by water during the growing season. To do this, we took measurements with our prototype NDVI Spectral Reflectance Sensor to measure canopy greenness. We also used our prototype volumetric water content sensors to measure soil moisture (this was a few years ago and the sensors were prototypes at the time). Using these sensors, we found that water is critical in a system people have dismissed as being climate-controlled because it’s at the top of a mountain.

A very early prototype of a NDVI sensor measuring canopy greenness in experimental plots on the Wasatch Plateau.

It turns out the amount and timing of precipitation makes a big difference. We were able to directly connect plant survival, not just to the grazing treatment, but to the actual amount of water that was in the soil. Also, using continuous NDVI data, we were able to look closely at the role of grazing on plant canopies. When we looked at our NDVI data, we were able to see a seasonal signal, not just a single snapshot sample in time. So by having the richer data from the data loggers, we obtained a more nuanced understanding of the impact of land use on these important ecological processes.

One of the mistakes we made was failure to include redundancy in the system. We only had two replicates, so when one of them went down we ended up having just one little case study. However, that mistake gave us new ideas on how to set up a better system using the right sensors for the job, and it generated a new idea on how to get real-time analysis of data. In our new Desert FMP project, we have a much better-replicated system where more is invested in the number of sensors that we’re putting out. Each treatment combination will have five to ten water potential sensors. We are also developing a system where we can analyze data in real-time, so this time we will know when a sensor goes out if a student accidentally kicks it.

For more details on the Wasatch Plateau Experiment, watch for our published paper that we’ll link to when it comes out.

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Dec 11

Burn victim research leads to new method for measuring stomatal conductance

Measuring the stomatal conductance of a leaf should be a pretty straightforward problem. The conductance is just the flux density of water vapor divided by the concentration difference between the leaf and its surroundings. Common approaches to this problem involve either flowing air of known vapor concentration over the leaf and measuring how much water vapor is picked up, or sealing a cup of known capacity to the leaf surface and measuring how quickly the vapor concentration in the cup increases. Both of these, though simple in concept, require quite a bit of expensive equipment to pull off. We wanted a simpler approach. We put a humidity sensor in a small tube, the end of which could be pressed against the leaf. As vapor diffused through the tube the humidity in the tube increased. The conductance of the tube is easily calculated. It is the diffusivity for water vapor divided by the tube length. The leaf conductance could be computed from the tube length, the humidity in the tube and the ambient humidity. That worked, but it turned out that ambient humidity variations introduced too much error, so we later added a second humidity sensor toward the distill end of the tube. Our approach was very simple, and works well, but it wasn’t a new idea.

Cross section of METER’s Leaf Porometer

I read of a similar device in a conference proceedings (I don’t recall the name of the conference) in 1977 when I was on sabbatical at University of Nottingham in England. The device wasn’t for leaves. It was developed by a medical researcher to assess severity of burn injuries, and for use on neonatal infants. The skin of a non-sweating human is pretty impermeable to water. A typical conductance is around 5 mmol m^-2 s^-1. This is about half the value for a leaf with stomates closed, and about two orders of magnitude lower than leaves with open stomates. Burned skin, however, is much more permeable, and the permeability is related to the severity of the burn. A device that could measure the permeability of skin would therefore give information on the severity of the burn. The researcher built an apparatus, similar to our porometer, with two closely spaced humidity sensors in a diffusion tube. As I recall, it was somewhat successful, but I’m not aware of it ever having been commercialized or used much after that. The application for infants is also interesting. Full-term babies have low skin conductances. I haven’t seen measurements, but assume they are similar to adult conductances. The skin of premature infants, though, has a much higher conductance. I don’t know typical conductance values, but do know that, without intervention, the conductance can be so high that evaporative water loss from the baby will reduce body temperature to dangerously low levels, even in an incubator. I don’t know if later work has been done to measure skin conductance, but it is interesting that the first applications of the technology we now use in our porometer was for measuring conductance of the human epidermis, not the epidermis of leaves.

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