Story and Interviews by Chris Howell, with:
Dr. Simon Yueh, JPL SMAP Senior Research Scientist
Dr. Rajat Bindlish, visiting scientist, USDA-ARS Hydrology and Remote Sensing Laboratory
SMAP pre-launch conference excerpts from Dr. Dara Entekhabi / SMAP Science Team Lead, M.I.T.
In a chill, pre-dawn countdown out of Vandenberg Air Force Base Space Launch Complex-2 on California’s central coast, NASA/JPL launched a new Earth Science observatory on the morning of Jan. 31, 2015, known as SMAP (Soil Moisture Active Passive). Flying a United Launch Alliance (ULA) Delta-II 7320 rocket into a precise, Sun-synchronous polar orbit, SMAP holds the promise to become one of our most useful tools in the study of Earth Science. It’s a pathfinder mission in the quest to better understand the dynamic nature of Earth’s water cycle over land and how it interacts with the corresponding cycles of energy and carbon—the three forces that make life possible, that shape our climate.
Three and a half years earlier, a craft also designed to explore Earth’s water cycle, Aquarius, launched from the same pad, flying a ULA Delta-II in the same 7320 configuration. Initially planned as over-ocean only, its mission would soon expand to include soil data as it passed over land. Doubling as a soils laboratory in low-Earth orbit, the science it gathered would also play an important role in preparing for SMAP during the final years leading up to its launch.
The sensors aboard Aquarius, three L-Band radiometers from NASA’s Goddard facility and a unique, active radar scatterometer developed by JPL, had been designed and built for ocean research. But it was known that the low frequency L-Band radiometers at 1.4 GHz could read moisture levels in soil as deep as 2 inches while the craft flew 400 miles above.
Knowing how much, or how little, water is held within the root zone, or top one meter of soil at any given time, is a method long known by science to accurately forecast climate conditions such as drought and floods, crop yield, and weather events. Until recently, soil moisture could only be measured at ground level in selected locations, and gathered mostly by volunteers.
This had been our only way to gather soil moisture data since the late 1940s, and it was known to be inconsistent, with poor sampling distribution often found to have subjective bias. The models produced were speculative with much of the data based on probability.
We needed a better way to gather the data to manage our lands, our water resources, and food supply, until we found how we could do it from space.
Using over-land data from Aquarius as it flew in low-Earth orbit, emerging trends in the soil moisture variation, wet or dry, could be observed and measured. In 2011, just before Aquarius was launched, the U.S. Department of Agriculture became interested and made a proposal to NASA to do just that. SMAP would be operational by 2015. But until then, Aquarius could offer measurements accurate enough to produce more reliable forecast models.
Just above Santa Barbara, a two lane road winds majestically through mountain passes cut into the ancient stone of the Santa Ynez Mountains. Driving north through Gaviota Pass on the way to Lompoc, the countryside is punctuated by dramatic rock formations, thrust up by tectonic movement eons ago. Earlier in the month, a few welcome days of light rain had turned the hillside from a golden brown to verdant green; cattle were grazing. This is the road leading to Vandenberg Air Force Base where SMAP would soon be launched.
Arriving for the pre-flight press conference, two other journalists and myself were escorted by Air Force personnel to a small press center located in the NASA Complex. Aside from the panel of five, and members of the NASA media crew, it was a small gathering. Each speaker presented eloquently, but it was the address by SMAP Science Team Leader, Dara Entekhabi from M.I.T., that changed my perception of the mission.
As he spoke, Entekhabi referred to SMAP as an instrument to “study the metabolism of the environment.” He described its science objective using the metaphor of a clock: “ … three cycles that maintain life on Earth, fundamental cycles of the Earth’s system: The Water Cycle, unique to Earth, The Energy Cycle and The Carbon Cycle.” He spoke of this triad being “linked together through soil moisture and precipitation, like three gears in a clock. If one of them speeds up it affects the others, having a cascading, downstream effect.”
He went on to say: “If it wasn’t for soil moisture, these three gears would act independently and would vary without any synchronization. But, we know that’s not the case. As soil water evaporates, it feeds the clouds and returns that precipitation back to the atmosphere, and you’ve got a water cycle going. Just as humans have adapted to perspire in order to maintain their body temperatures, the Earth does the same.”
JPL Senior Research Scientist Simon Yueh and I met through a phone call in August 2014. When I first heard that Aquarius had been handed a new mission, I needed to know more. Three years earlier, I’d written a story on Aquarius for a marine science magazine out of Southern California. NASA had picked up the interview portion and asked to run it on their FAQ page for Aquarius. Research for the story and my own interest in the project had drawn me into the saga, and now the mission had changed.
Former JPL project scientist Yi Chao, who had been on the Aquarius team throughout many of its ten years in development, had left JPL to work in the private sector. And now, I was referred to Dr. Simon Yueh. Yueh had played a key role on the Aquarius team through his work developing the radar scatterometer.
In part one of our story, Yueh shared the excitement of discovery made through Aquarius’ over-ocean mission. Time went quickly, and our talk stayed on the topic of how over-ocean weather events could be driven into a frenzied dance of water cycle, energy cycle interaction.
Still curious about the history of Aquarius’ dual mission, I met with Dr. Yueh once more, on Oct. 10, 2014, in JPL’s viewing gallery above the “clean room,” while technicians below made final adjustments to the instrument, to SMAP, as we spoke.
- Q: Could you tell us how the Aquarius mission first came to include soil moisture?
A: When the Aquarius mission was first being developed by NASA there was some thought given to how the data could be used over land. So, even though Aquarius is an ocean mission, the data acquisition over land has always been in the plan.
- Q: Why soil moisture? Does this new mission have to do with weather patterns, or is it more of a study of fresh water resources? What’s the dynamic involved in soil moisture mapping?
A: Soil moisture is an additional benefit we have with Aquarius data set. Scientists have always realized that Aquarius had that potential. The resolution is not at a highly sufficient level for SMAP (soil moisture active passive) type applications, but even given Aquarius’ lower resolution of a few hundred kilometers, we can still learn quite a bit about the process over the land surface.
- Q: So, with SMAP the swath width will be one thousand kilometers?
A: Right, so a one thousand kilometer swath will allow SMAP to cover everywhere on the Earth’s surface in about three days with a much higher resolution; about forty kilometers for the radiometer and a few kilometers for the radar. SMAP has two types of instruments; one is the radiometer, which measures the passive microwave emission from the surface, and the other, the radar, a high-resolution scatterometer, will allow us to obtain a greater spatial resolution.
- Q: Are there any obstructions that prevent measurement like ice or dense vegetation?
A: Vegetation is a key limiting factor in the ability to measure the soil moisture. But that would be only in very limited places on the Earth, regions having a biomass so great as to prevent SMAP to make a good measurement; say, the Amazon, or a similar region with very dense forest. But for most of the Earth’s surface, vegetation has not much impact on our measurements.
- Q: How do you predict weather from measuring soil moisture?
A: Because the soil moisture represents two important effects. First, it influences the rate of evaporation and precipitation. When the rain falls, we know the soil moisture will increase and the ground become wetter. When there is no rain, the water will start to evaporate. For many regions on Earth, the evaporation of water into the atmosphere will form clouds, which then leads to precipitation events. So, it’s really a measure of the balance between those two. That kind of information will assist in weather prediction.
The other key contribution in the knowing the measure of soil moisture is to help us better understand the amount of energy contained in the soil. Water has a great energy capacity, a heat capacity. And so, the water can retain the memory, what we call the temperature information of the soil, for a few days. If there’s no moisture present, then you know the temperature in the soil can go up and down very quickly, like the desert. But once you put water in the soil, it will modulate the weather. This is how our prediction model works.
- Q: Right now, Aquarius and SMOS (the European Space Agency’s Soil Moisture Ocean Salinity spacecraft) are working similar missions over land. Does each offer unique data or are they working in tandem to provide a double blind study?
A: So for the SMOS mission, the primary focus is really on the soil moisture. The information that we just spoke of has been confirmed by the SMOS measurements; that is, the impact of soil moisture on the weather prediction model. Soon, we’ll be realizing the benefit of measuring soil moisture from remote sensing observations.
- Q: So, understanding the dynamics of the water cycle through soil moisture is a key to predicting weather patterns?
- Q: Aquarius has given us a new understanding of how ocean dynamics and over ocean weather are interrelated. Is the over land data from Aquarius and SMOS bringing us a similar insight into how weather patterns emerge through observing changes in soil moisture?
A: Both data sets are still undergoing what we call the learning phase for the scientists, and also for the application user, to figure out how we can better use both types of information for societal benefit. These are two “pathfinder” kinds of missions. Scientists are still learning quite a bit from these two data sets.
Another lesson that we’ve learned, or information that we’re getting from both SMOS and Aquarius over land missions is more than just soil moisture itself. Recently, it’s been discovered that data from SMOS, and eventually from SMAP, will also allow us to figure out the water content information in the vegetation. This is something we’re very excited about.
- Q: So we’ll be able to observe, in real time, the health of crops in the field anywhere on the planet?
A: Yes, the health of the crops; whether there’s sufficient water in the vegetation to sustain the plant life and facilitate its growth. What European scientists have found is that the amount of moisture in the vegetation and the soil has a direct correlation to crop yield.
- Q: How are we doing with international cooperation? Is the scientific community working together to better understand and plan for climate change?
A: Yes, definitely. There are regular, joint Aquarius and SMOS science teams. There are also European scientists serving on the SMAP team. On the European side, they are also very interested in transitioning scientific information into practical application through EUMETSAT (the European equivalent of NOAA). Hopefully in the future we can draw from serious, longtime study. Once the SMOS and SMAP data get into a kind of production system, then this system, the information, will become more readily available.
On the U.S. side, we have a similar arrangement with our two agencies, NASA and NOAA. In the U.S., NOAA is responsible for weather operations, and the data acquired from their weather satellites. So when you see TV news and weather, a lot of the information is from NOAA satellites.
Before any of that can happen, NASA must develop the technology. We figure out what information we need and how to obtain it from the satellite. SMAP is NASA’s first launch of an instrument designed with a primary mission to measure soil moisture. With a spatial resolution of nine kilometers, it will have much higher accuracy than either Aquarius or SMOS. Once scientists figure out how to best utilize the data, the system will transition into an operational setting, the soil moisture data becoming available to all, guiding decisions for many years come.
- Q: Is this latest Earth science research being made available to the general public in ways that can be understood, and how can this information be accessed?
A: The NASA data set, including information we gather from SMAP, will be made available to the public for free. NASA has an open data policy. For SMAP, the data can be obtained through the National Snow and Ice Data Center (NSIDC) and the Alaska Satellite Facility (ASF). NASA has several data archiving centers around the nation. For the dense surface and ice portion, NASA works directly with NSIDC. They’ll be distributing the soil moisture product and the freeze/thaw product for SMAP through the NSIDC web site. ASF will also provide SMAP radar data online through their web site.
- Q: Are there educational programs in place to carry this information to young people, from K-12 through university level?
A: We’re definitely looking for cooperation with the general public. Currently, NASA also has a program called GLOBE involving high school age students throughout the country as well as internationally. Any student wanting to participate in the program is welcome and encouraged to work with the GLOBE program.
- Q: There are some who question whether climate change is occurring at all. What are some of the arguments challenging the latest findings and how are they being addressed?
A: From a scientific point of view, there is a lot of evidence which points to the changing climate. So, from a scientific point of view, I think it’s quite clear, that the evidence is very strong that the climate has been changing. And then there are people who are quite concerned about what we should do about it.
We know, historically, that the climate has been changing over a millennium. We know that the consequences in many regions have not been too positive for many civilizations. So, we know that climate change has historically been shown to have a very serious impact on human life. I think the question in some people’s minds is whether climate change could be affected by the human population, right? There is strong evidence that shows the correlation between global warming, the temperature change, and the start of the industrial age.
Wanting to know more about how the USDA might use Aquarius’ soil moisture data, what drew their interest, and what we might learn from the higher resolution data SMAP would soon provide, I contacted Dr. Rajat Bindlish, visiting scientist with the USDA-ARS Hydrology and Remote Sensing Laboratory located in Beltsville, Md.
Here’s a portion of our conversation from Feb. 12, 2015, regarding Aquarius’ overland mission to map Earth’s soil moisture and the anticipation of SMAP becoming operational.
Dr. Bindlish, with the successful launch of the SMAP observatory last January interest in the mission appears to be growing. People are curious about how the data from SMAP will be used and what benefit it might bring.
- Q: I’ve heard that a request was made by USDA to access Aquarius’ data for soil moisture measurement as it passes over land. How did that come together?
A: USDA submitted a proposal to NASA to do soil moisture research using Aquarius’ observation prior to Aquarius’ launch. We knew the sensor specifications of Aquarius were ideally suited for soil moisture estimation. Aquarius has a L-Band radiometer plus a scatterometer system. We were familiar with using L-Band measurements for soil moisture in work we had done before.
Using that background we submitted a proposal to the Aquarius team with the specific objective to do soil moisture research using Aquarius’ observations.
- Q: How would the USDA be able to utilize the Aquarius soil moisture product?
A: As you know, soil moisture is critical for many applications, starting from water cycle to agricultural applications and crop yield predictions. It is also critical in applications ranging from floods to droughts and any other application related to land surface hydrology. We were able to develop a soil moisture product using Aquarius observations. That product is publically available to the end user from NSIDC (National Snow and Ice Data Center).
- Q: How is this information able to improve crop production, livestock and fresh water resources?
A: The soil moisture for agricultural applications is critical input used to prepare the yield forecast models. So, the data is used to create yield prediction models, which allows us to come up with a more accurate yield estimate.
Our objective in terms of the proposal was to provide soil moisture estimates so that any end user can access that data for whichever applications they may need it for, climate, agriculture or anything.
- Q: With Aquarius and SMAP having global capability, is USDA putting together global forecast charts, or is that just in the continental United States?
A: So, there are a couple of different agencies within the USDA that develop crop yield forecasts. National Agricultural and Statistical Services (NASS) has a mandate to do crop forecasts for the U.S. including Alaska and Hawaii. Foreign Agricultural Services (FAS) produces global crop forecasts. It covers everything outside the U.S.
- Q: The verification of soil moisture data for accuracy is very important. I understand that both Aquarius and ESA’s SMOS use in situ, ground monitored locations to calibrate and verify their measurements. How does the accuracy of Aquarius’ soil moisture data compare to that of SMOS?
A: SMAP and SMOS have developed extensive validation plans. The performance of SMOS and Aquarius soil moisture products is comparable when the estimates are validated using in situ observations. Aquarius has some drawbacks, mainly that its spatial resolution is not as high as SMOS or SMAP. That’s just inherent in the design of the radiometer. Aquarius was primarily developed for ocean science applications. Whereas SMOS and SMAP were designed primarily for soil moisture applications, therefore their spatial resolution is much higher.
- Q: Has SMOS data always been available to the USDA? If so, why was the request sent for Aquarius to gather soil moisture? Did it have to do with verifying calibration, using data from one to compare with the other? Did it also have to do with the development of the SMAP instrumentation and software?
Aquarius actually gives you another platform. It helps fill the gap going from SMOS to SMAP giving another platform for observations. It was not necessarily designed as a replacement or a substitute (for SMOS) at all. The greater the number of platforms you have for getting more frequent measurements, the better it would be. We’ll also be comparing soil moisture estimates from SMOS and Aquarius and with future SMAP observations. Aquarius observations have also helped us to develop the SMAP soil moisture software.
- Q: SMOS has a 1000-kilometer swath radius, with Aquarius’ swath closer to 400 km. SMOS, however doesn’t have a radar scatterometer. How does the scatterometer aboard Aquarius influence the data sets?
A: The scatterometer gives you an added value that can be used for soil moisture or any other variable estimates.
- Q: Can you tell me something about the AMSR-E, the Advanced Microwave Scanning Radiometer – Earth Observing System?
A: AMSR-E is a spacecraft operated by NASA using a Japanese instrument on the Aqua platform. We have a soil moisture product using AMSR-E observations also. But SMOS, Aquarius and SMAP have an advantage over AMSR-E soil moisture estimates. AMSR-E soil moisture product uses X-Band observations which is 10 GHz, whereas SMOS, SMAP and Aquarius are all L-Band which is 1.4 GHz. If you have a lower frequency, or longer wavelength, it can penetrate deeper into the vegetation and can give you better accuracy in terms of soil moisture estimates.
- Q: Does that include the measuring of moisture content within plants as well?
A: We correct for the moisture content of the plants. AMSR-E can only measure moderate to low vegetation areas, whereas with SMAP, SMOS and Aquarius, you can estimate soil moisture accurately under relatively dense vegetation.
- Q: Do you think that severe weather, flooding in central U.S., drought in the west, is on the increase, and if so, what might be causing it?
A: We are making this soil data product available, and other agencies, other people can use this information, the data, for coming up with the analysis.
Without Aquarius, SMOS or SMAP soil moisture products, we wouldn’t be able to do a very scientific analysis as to whether this is true or not true. You cannot say either way if you didn’t have the data. But, these data products that we are developing from different missions allow people, researchers, to study these conditions and phenomena to see what’s happening. That’s why these products are important. Without them, you cannot arrive at any scientific conclusions.
If you didn’t have the data, there’d be no way to study this phenomena: what is causing the changes, what ground conditions can influence the cloud formations, whatever it may be.
- Q: So, without accurate soil moisture data you’d be basing your information on probability and best guess?
A: Right, So, what would happen if you didn’t have soil moisture from space? For example, you would have a land surface model based on and driven by meteorological precipitation. Based on that model, you come up with a soil moisture estimate that you presume to be true based on meteorological studies. But you don’t know for sure. There’s no certainty. It might be right for some locations, but you don’t know. That’s the reason it’s critical to have these observations over a period of time, so we can come up with better conclusions.
Soon, we’ll examine the unique design and fabrication of SMAP’s 19.7-foot-long (6-meter) scanning antenna, the challenges presented, its preflight testing, the lightweight, resilient materials used, and how it operates during spaceflight, all through interviews with those who created it.
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