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Dr. Rowena Lohman, July featured SAR scirntist
Rod Boyce, July 2022

Rowena Lohman, PhD

Sometime back in the early 2000s, Rowena Lohman attended an Alaska Satellite Facility Working Group meeting as a substitute for someone who couldn’t make it that day.

She’s been connected to the Alaska Satellite Facility ever since.

“So I’ve been interacting with folks there for a long time,” she said.

Now a professor of geophysics and tectonics at Cornell University, Rowena is closely involved with ASF as it prepares to host the enormous amount of data expected from the upcoming NISAR mission, a joint mission of NASA and the Indian Space Research Organization.

She has been involved with NISAR since its early days, even going back to the Deformation, Ecosystem Structure, and Dynamics of Ice, or DESDynI mission, a precursor of NISAR. She was originally on NASA’s solid earth team for the NISAR mission and is now the lead on the mission’s soil moisture team.

“I am heavily involved with helping prepare for the NISAR mission, and ASF will certainly play a very large role in that,” she said. “It’s such a new type of endeavor for NASA, with the large amount of data that will be generated.”

NISAR will enhance the work in her chosen area of research: using satellite-based remote sensing to better understand ground deformation before and during an earthquake.

“As we get more data, we’re able to look in places we couldn’t look before,” she said. “And what we find is that we don’t just see the ground moving up and down, we see the vegetation also affecting the signal, and soil moisture affecting the signal and all sorts of other things contributing to the data in ways that are sometimes hard to separate.

“So that’s what I’ve been most interested in: Can we look at progressively smaller signals if we can correctly account for all of these other types of contributions to the data?”

•••

Rowena was born in Wisconsin and soon became a well-traveled toddler. The Badger State was her home for just a few months until her family moved to Brazil. Then it was back to Wisconsin, back to Brazil, and then to Illinois.

All that before starting kindergarten.

Her father worked for Case tractors, a company nearly two centuries old, and traveled a lot on business.

The family moved to Santa Barbara, California, midway through Rowena’s elementary school years. They lived there through the start of junior high school and then headed about 300 miles north to San Francisco.

That was her final stop before leaving for college.

Rowena received her Bachelor of Science in geology in 1998 and her Ph.D. in geophysics, both from the California Institute of Technology. She was a postdoctoral researcher at Woods Hole Oceanographic Institution and at the Jet Propulsion Laboratory.

Cornell University has been her professional home since 2007. As an instructor, she focuses on teaching active tectonics, remote sensing and the department’s introductory Earth and atmospheric sciences course.

Her primary interests, as listed on her Cornell biography page, are earthquake physics, inverse theory, satellite remote sensing (particularly InSAR), finite element modeling, ground displacements associated with a variety of human and natural causes, and the tectonics of Southern California, Louisiana, the Cascadia subduction zone and Iran.

She also has a growing interest in the effects of land-use changes such as from logging and mining on observations of ground deformation and other remote sensing observations.

•••

The study of ground deformation, where Rowena has been putting much of her attention, has great public benefit.

“When we’re working on problems the public cares about like water resources and landslide hazards, for example, a facility like ASF allows us to manage the large data sets and focus on the science,” she said.
She has authored or co-authored numerous papers about ground deformation at locations across the globe.

In one, from 2017, she was co-author on a paper that presented a partial inventory of human-caused ground deformation in North America. That research, using InSAR data, found 263 areas of likely anthropogenic ground deformation. Groundwater extraction accounted for half of the total, with geothermal sites, hydrocarbon production, mining and other sources accounting for the rest.

That inventory included data from a variety of sources, including from the ALOS-1 satellite of the Japan Aerospace Exploration Agency downloaded from the Alaska Satellite Facility thanks to an agreement between NASA and the Japanese government.

In another example, ASF figured into a February 2021 paper titled “Coherence-guided InSAR deformation analysis in the presence of ongoing land surface changes in the Imperial Valley, California.” The paper noted, in laying out the scientific question, that “vegetation changes and soil moisture variability can degrade data quality or introduce confounding signals.”

She is particularly pleased with a December 2021 paper about an analysis of a three-year time series of SAR imagery covering the southern Arabian Peninsula. Two typhoons struck the region, which usually receives very little rainfall, in 2018.

As devastating as the typhoons were, they afforded a research opportunity. The region has minimal vegetation and precipitation, a combination that allowed Rowena and one of her students, Paula Bürgi, now a Mendenhall postdoctoral fellow at the United States Geological Survey, to clearly separate soil moisture from other factors that also affect microwave imagery. Separating soil moisture changes from other factors allows scientists to better understand the influence of that soil moisture on ground deformation.

The two presented similar research, touching on data from Chile in addition to the Arabian Peninsula, at the 2019 fall meeting of the American Geophysical Union.

The Alaska Satellite Facility had a role in that work: SAR imagery from the European Space Agency’s Sentinel-1 satellite was downloaded through ASF.

“Sometimes you need to step back and say, ‘Where can I look that will let me just study this one part of the problem so that I can then use it to better understand the place where we do have more rainfall and agriculture,’” she said.

•••

She has seen a lot of change at ASF over the years.

“One thing where ASF has been in the vanguard is in trying to figure out how to bring scientists like me, at my own little university, into the cloud,” she said. “We all are trying to learn a million things these days. The software we’re using is constantly changing and the problems are changing.”

Take the cloud credits for use on Amazon Web Services, for example. She says it can be difficult for researchers to find time to also learn how to use that cloud system — not only to use it but also to use it effectively and efficiently. Using it costs money, and that includes the time spent learning it.

“One of the things ASF has done is to basically make a small environment where scientists like me can go in and learn how to use the system under some constraints they have set up,” she said. “And that keeps us from running up a really huge bill.

“It allows us to get to the level where we feel comfortable with it and with putting in a grant application that contains a request for data credits and processing time,” she said.

She has witnessed other changes at ASF over her long years of association with the facility.

“The archive has been made progressively easier to use. One way in which ASF has been really responsive is that they want to give us tools that make our job easier,” she said. “And they give us enough access that we can learn what we might be missing.”

The relationship between ASF personnel and the data users is uncommonly good. Rowena said.

“It’s rare to find people who are both very good at data infrastructure and who are good at talking to the people trying to do the science,” she said “They have put together a team that is good at both of those things.”

Rod Boyce is the Public Information Officer for the UAF Geophysical Institute

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