A Stanford-led team has discovered how to estimate crop yields with more accuracy than ever before with satellites that measure a special form of light emitted by plants. This breakthrough will help scientists study how crops respond to climate change. 

As Earth's population grows toward a projected 9 billion by 2050 and climate change puts growing pressure on the world's agriculture, researchers are turning to technology to help safeguard the global food supply.

A research team, led by Kaiyu Guan, a postdoctoral fellow in Earth system science at Stanford's School of Earth, Energy, & Environmental Sciences, has developed a method to estimate crop yields using satellites that can measure solar-induced fluorescence, a light emitted by growing plants. The team published its results in the journal Global Change Biology.

Scientists have used satellites to collect agricultural data since 1972, when the National Aeronautics and Space Administration (NASA) pioneered the practice of using the color – or "greenness" – of reflected sunlight to map plant cover over the entire globe.

"This was an amazing breakthrough that fundamentally changed the way we view our planet," said Joe Berry, professor of global ecology at the Carnegie Institution for Science and a co-author of the study. "However, these vegetation maps are not ideal predictors of crop productivity. What we need to know is growth rate rather than greenness.

The growth rate can tell researchers what size yield to expect from crops by the end of the growing season. The higher the growth rate of a soybean plant or stalk of corn, for instance, the greater the harvest from a mature plant.

"What we need to measure is flux – the carbon dioxide that is exchanged between plants and the atmosphere – to understand photosynthesis and plant growth," Guan said. "How do you use color to infer flux? That's a big gap."  
 

Solar-induced fluorescence

Recently, researchers at NASA and several European institutes discovered how to measure this flux, called solar-induced fluorescence, from satellites that were originally designed for measuring ozone and other gases in the atmosphere.

A plant uses most of the energy it absorbs from the sun to grow via photosynthesis, and dissipates unused energy as heat. It also passively releases between 1 and 2 percent of the original solar energy absorbed by the plant back into the atmosphere as fluorescent light. Guan's team worked out how to distinguish the tiny flow of specific fluorescence from the abundance of reflected sunlight that also arrives at the satellite.

"I think of it like crumbs falling to the ground as people are eating. It's a very small trail," said co-author David Lobell, associate professor of Earth system science at Stanford's School of Earth, Energy, & Environmental Science. "This glow that plants have seems to be very proportional to how fast they're growing. So the more they're growing, the more photosynthesis they're doing, and the brighter they're fluorescing." Lobell is also deputy director of the Center on Food Security and the Environment.

The research team saw an opportunity to use this new data to close the knowledge gap about crop growth, beginning with a major corn- and soybean-producing region of the U.S. Midwest.

"With the fluorescence breakthrough, we can start to directly measure photosynthesis instead of color," Guan said.

The fact that fluorescence can now be detected from space allows researchers to measure plant growth across much larger areas and over long periods of time, giving a much clearer picture of how yields fluctuate under changing weather conditions.

"One of the really cool things about fluorescence is that it opens up a whole new set of questions that we can ask about vegetation, and often times it's these new measurements that drive the science forward," Lobell said.  
 

Next steps

The research team has already identified a number of potential uses of this approach by agricultural scientists, farmers, crop insurance providers and government agencies concerned with agricultural productivity.

If there is a day when the plant is really stressed, the fluorescence will drop significantly, Lobell said. Capturing these short-term responses to environmental changes will help scientists understand what factors plants are responding to on the daily time scale.

"That helps us, for example, figure out what we need to worry about in terms of stresses that crops are responding to," Lobell said. "What should we really be focusing on in terms of the next generation of cropping systems? What should they be able to withstand that the current crops can't withstand?"

At this early stage, fluorescence measurements are relatively low-resolution (a single measurement covers about 50 square kilometers) and because it is only collected once per day, cloudy skies can interfere with the fluorescence signal. For now, researchers have to supplement the data with other information and with on-the-ground observations to refine the measurements.

"Now that we have demonstrated the concept, we hope to soon be orbiting some new satellites specifically designed to make fluorescence measurements with better spatial and temporal resolution," Berry said.

The team plans to continue its research on U.S. crop yields while expanding measurements to other parts of the world.

"In the future, we hope to directly use this technology to monitor global food production, for example in China or Brazil, or even in your backyard," Guan said.

David Lobell is also deputy director of the Center on Food Security and the Environment, and William Wrigley Senior Fellow at the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment. The study was also co-authored by Youngguan Zhang of the International Institute for Earth System Sciences at Nanjing University and the German Research Center for Geosciences (GFZ); Joanna Joiner of the NASA Goddard Space Flight Center Laboratory for Atmospheric Chemistry and Dynamics; Luis Guanter of GFZ; and Grayson Badgley of Stanford's Department of Earth System Science and Department of Global Ecology at the Carnegie Institution for Science.

CONTACTS:   
 

p> Kaiyu Guan, Stanford School of Earth, Energy, & Environmental Sciences: kaiyug@stanford.edu

Laura Seaman, Stanford's Center on Food Security and the Environment: lseaman@stanford.edu, (650) 723-4920

Pilot program was designed to first ground students in the basics of empirical research, then provide an opportunity to apply that knowledge while conducting fieldwork in an international setting.

The Freeman Spogli Institute for International Studies (FSI) and Office of International Affairs (OIA) launched a pilot collaboration last year to provide a rigorous, immersive teaching and training program for students interested in international fieldwork.  The result was a program that included a quarter-long course in the spring of 2015 followed by three weeks in Mexico during the summer to design and conduct a field research study. OIA spoke with Frank Wolak, the Holbrook Working Professor of Commodity Price Studies in Economics and Senior Fellow at FSI, to learn more about the project, titled International Field Research Training: Energy Reform in Mexico.

What was the impetus for designing a program for students with a field research component?

While students at Stanford have many opportunities to pursue independent research projects, they rarely have the opportunity to receive first-hand training in conducting interviews, research design and field implementation. With that in mind, we set out to design a program that would carry the students through the basics of empirical research and then give them the opportunity to apply that knowledge under close faculty supervision. Taking students out of the classroom and giving them the opportunity to see textbook methods in action is invaluable.

Our hope is that this training equips the students with the academic and logistical skills they need to execute their own robust research, be that for an honors thesis, a capstone project or an advanced degree.

How did the prerequisite course prepare students for working in the field? 

The Stanford course taught the basics of the design, implementation and interpretation of social science field research. Building on a basic knowledge of statistical methods and economics, the course first introduced observational field research and compared it with experimental field research. Significant attention was devoted to explaining what can and cannot be learned through each type of field research.

Topics covered included sample size selection, power and size of statistical hypothesis tests, sample selection bias and methods for accounting for it. Examples of best practice field research studies were presented as well as examples of commonly committed experimental design and implementation errors. Practical aspects of fieldwork were also covered, including efficient and cost-effective data collection, data analysis, teamwork and common ethical considerations.

After completing the quarter-long course on statistical research methods, the students, under the guidance of the Program on Energy and Sustainable Development's research team, adapted an education-based research intervention for the Mexican electricity sector. The purpose was to see if providing individuals with information about how their energy bill was calculated and simple ways to reduce household electricity consumption would cause household energy bills to go down.

What was a typical day for the students gathering research?

Research was carried out in the city of Puebla, a city of 1.5 million people about 150 kilometers (93 miles) southeast of Mexico City. The Stanford students collaborated with students from the Universidad Popular Autónoma del Estado de Puebla (UPAEP). For the first few days, the students all met at an UPAEP classroom space to design and review the survey tool, making revisions and conducting practice interviews.

Once oriented in Puebla, the students set out daily in research teams to interview randomly selected households in middle-income neighborhoods in Puebla. The students branched out from a central meeting place in teams of three, pairing two Stanford students with one UPAEP student.

In the field, the students all wore nametags and UPAEP baseball caps to make themselves identifiable as surveyors to households. They worked in the field for eight to 10 hours a day, taking about an hour break for lunch. In the first few days, they were able to collect 15-20 surveys a day, but as they became more comfortable with their pitch and knocking on doors, they were able to increase their yield to a high of 44 surveys in one day. At the end of two weeks, they completed over 260 surveys in just 10 days of fieldwork.

The students were also active on social media documenting their daily activities. For more on the student perspective, their activities and impressions of the project, check out their blog on the FSI website. 

What are the benefits for getting in-country field research experience?

There are a variety of situation-specific problems that are hard for any researcher to know fully without being immersed in the field. For example, one of the students' recommendations to improve energy efficiency was to switch household light bulbs from incandescent to compact fluorescents (CFL). This is a valid recommendation in the United States where most people still use incandescent bulbs in their homes, but – surprisingly to the team – most of the people interviewed had already converted to all CFLs in their home.

I was amazed with the students; the level of intellectual curiosity and engagement was impressive with ongoing discussions into the evening at times. The students were not only getting an in-country immersive experience while conducting research, but they were also developing critical thinking skills along the way.

Research aside, the in-country experience gave the students a keen understanding of how local residents live. The methodology employed for gathering data allowed the students to connect with many types of families, ranging from senior citizens living alone to multi-generational families living under one roof. Through direct contact with the community, the students developed an understanding of the local culture and learned local customs. 

Conducting international research at Stanford can be challenging. Where did you turn to for advice on how to structure your activity?

At FSI, we have a great wealth of experiential knowledge on conducting field research all over the world. In addition to consulting with faculty and research managers at FSI, OIA had been enormously helpful in connecting us with resources across campus and facilitating some of the trickier logistics, such as processing stipend payments to our international collaborators and navigating the human subjects approval process. OIA was also able to discern that Puebla was a viable option as a research site.

How would you characterize the success of the pilot program? 

The pilot program exceeded our expectations in the best possible ways. Much of its success was due to the work of Elena Cryst ,'10, program manager for FSI's Global Student Fellows Program, who also accompanied us on our trip. She was an invaluable team leader and organizer and worked tirelessly to ensure that both the research and logistical aspects of the trip ran smoothly.

We will definitely be offering the field research course and research project again. We hope to go to another part of Latin America next, such as Chile or Colombia. We are also still active in Mexico, with three of the students that went on the trip working for us as research assistants this academic year, analyzing the data as it comes in and developing a self-administered online version of the survey instrument with which we hope to reach thousands of households in Puebla.

In addition, Elena will be using our experiences from the Mexico pilot to inform other FSI field research programs in China, Guatemala, India and potentially new sites for next year.

This article was originally published in The Stanford Report on October 27, 2015.

Speaking at the Stanford Center at Peking University (SCPKU) on September 22, Condoleezza Rice, the Denning Professor in Global Business and the Economy at the Stanford Graduate School of Business; the Thomas and Barbara Stephenson Senior Fellow on Public Policy at the Hoover Institution; and a professor of Political Science at Stanford University, said that technology and education are key drivers in achieving sustainable urban development and cited opportunities for China and other developing countries to harness this innovation and mobilize human potential.

Rice’s remarks were part of her keynote address during SCPKU’s inaugural Lee Shau Kee World Leaders Forum.  Welcome remarks were given by Jean C. Oi, the Lee Shau Kee Director of SCPKU and Senior Fellow at Stanford University’s Freeman Spogli Institute for International Studies (FSI), and Peking University (PKU) Prof. Min Weifang and former PKU Chairman.  Michael McFaul, Director and FSI Senior Fellow and former U.S. Ambassador to Russia, introduced Rice who highlighted the opportunities of technology and innovation as well as the governance challenges they can bring.

“If we remember technology is the application of knowledge to a problem, we can begin to address some of the problems of governing with the application of technology.” Rice said. “It is really a question of whether we can marry human potential and technological possibilities to solve our problems. Human potential is key to innovation, and in that regard, the most urgent tasks are around education.”

Rice spoke before an audience of 150 government and academic leaders, scholars, and students at SCPKU.  Following her keynote address, she participated in a roundtable discussion with policy and thought leaders. The discussion was chaired by Karl Eikenberry, Director of the U.S.-Asia Security Initiative at Stanford’s Asia-Pacific Research Center and former U.S. Ambassador to Afghanistan.  Panelists also included Dr. Wang Yiming, Deputy Director General and Senior Research Fellow at China’s State Council Development and Research Center, and Prof. Tong Zhu, Dean of the College of Environmental Science and Engineering at PKU.

“This was a unique opportunity to convene thought leaders on a topic of significant importance to China and the world,” said  Prof. Oi.  “China’s urbanization has been one of the most rapid in history. Technology innovation can help address the challenges of urban governance where people’s lives have changed in one generation.”