Publications and News
Papers
Fine-Resolution Measurement of Soil Moisture from Cumulative InSAR Closure Phase.Soil moisture can vary spatially at the scale of agricultural fields (~10 -100 m), which is generally too fine to resolve using passive radiometric methods. Active radar provides an opportunity for finer resolution measurements; in particular, the interferometric synthetic aperture radar (InSAR) closure phase parameter is sensitive to changing soil moisture. We have developed a model showing that systematic non-zero closure phase can result from scattering from objects at different depths in a medium of time-varying dielectric, such as from changes in soil moisture. The model predicts that interference between surface and subsurface reflections are needed for closure phase to be non-zero. We find that, under certain circumstances, we can estimate soil moisture from closure phase using a data reduction approach that includes a cumulative sum of closure phase over time and removal of a trend. The correlation between cumulative closure phase and soil moisture suggests that the closure phase is related to the change in soil moisture. We examined a large test region in Oklahoma, where the detrended cumulative closure phase from Sentinel-1 data demonstrates some agreement with in situ soil moisture measurements. In other areas, the match is weaker, implying a terrain dependence for the quality of fit. Cumulative InSAR closure phase promises to provide a valuable new method to remotely estimate soil moisture.
In permafrost regions, active layer thickness (ALT) observations measure the effects of climate change and predict hydrologic and elemental cycling. Often, ALT is measured through direct ground-based measurements. Recently, synthetic aperture radar (SAR) measurements from airborne platforms have emerged as a method for observing seasonal thaw subsidence, soil moisture, and ALT in permafrost regions. This study validates airborne SAR-derived ALT estimates in three regions of Alaska, USA using calibrated ground penetrating radar (GPR) geophysical data. The remotely sensed ALT estimates matched the field observations within uncertainty for 79% of locations. The average uncertainty for the GPR-derived ALT validation dataset was 0.14 m while the average uncertainty for the SAR-derived ALT in pixels coincident with GPR data was 0.19 m. In the region near Utqiaġvik, the remotely sensed ALT appeared slightly larger than field observations while in the Yukon-Kuskokwim Delta region, the remotely sensed ALT appeared slightly smaller than field observations. In the northern foothills of the Brooks Range, near Toolik Lake, there was minimal bias between the field data and remotely sensed estimates. These findings suggest that airborne SAR-derived ALT estimates compare well with in situ probing and GPR, making SAR an effective tool to monitor permafrost measurements.
Seasonal subsidence induced by ground ice melt can be measured by interferometric synthetic aperture radar (InSAR) techniques to infer active layer thickness (ALT) in permafrost regions. The magnitude of subsidence depends on both how deep the soil thawed and how much ice/water content existed in the active layer soil. To provide the later, P-band polarimetric synthetic aperture radar (PolSAR) backscatter is used due to its sensitivity to subsurface soil moisture and freeze/thaw conditions. In this study, which is the second in a two-part series of Permafrost Dynamics Observatory (PDO), we exploit L-band InSAR subsidence and P-band PolSAR backscatter in a joint retrieval scheme to simultaneously estimate ALT and soil moisture profile of permafrost active layer. Both subsidence and backscatter are explicitly characterized by physics-based models and share a common set of soil parameters including porosity and water saturation profiles. The PDO joint retrieval has been applied to the L- and P-band SAR data acquired by National Aeronautics and Space Administration/Jet Propulsion Laboratory's Uninhabited Aerial Vehicle Synthetic Aperture Radar over Alaska and western Canada during the 2017 Arctic-Boreal Vulnerability Experiment (ABoVE) airborne campaign. This high-resolution (30 m) regional estimates of ALT and soil moisture profile spanning over the ABoVE study domain can help link the ground-based field surveys with satellite observations to further understand the permafrost and active layer soil process dynamics to disturbances and climate change occurring across the northern circumpolar region.
This paper details a model for a weak dielectric object on the human body with a small gap between the dielectric and body, as detected by a CW millimeter-wave security scanning system. This model is a refinement of the Virtual Source Model, focusing on the possibility that the dielectric is not directly against the skin. Seven primary scattering phenomena are considered in this model, more than in the Virtual Source model; later phenomena have negligible amplitude. Even a small gap can cause a significant difference in the return.
The efficiency and effectiveness of airport security can be improved through fast and high-fidelity detection of concealed threat objects. If detected objects can be accurately characterized, the number of false alarms will be reduced, while terrorist threats could be more quickly noticed and apprehended. This study aims to accurately characterize the physical properties of weak dielectric objects (like explosive threats) covering a conductive plane (like the human body), using a single frequency mm-wave radar system with a Fresnel aperture. While the conventional synthetic aperture radar (SAR) method requires data over a broad bandwidth, our proposed method works even at a single frequency and is particularly suitable for focused-beam CW mm-wave sensing systems. This method is validated with experimental data.
We propose a fast and accurate method of finding the thickness and dielectric permittivity of weak dielectric objects using a focused continuous-wave radar security scanning system, to characterize objects that may be explosive threats. Building on the previously developed ray-based Virtual Source model for sensing scattering from slabs, this work presents an inversion algorithm using two observable CW millimeter wave probe parameters by considering expected small variations of dielectric slab thickness over its surface. The determination works reasonably well with a simulated dielectric covered conductive ground plane as a representation of body worn explosives.
In my academic research at Northeastern, I worked on creating mathematical models for millimeter-wave security scanners to improve detection of foreign objects on people's bodies. This paper outlines the model we created for a dielectric (insulating) slab on a person's body, and the signal we expect to result from it.
In the News
I was interviewed on CBS New York for the April 8, 2024 eclipse in Lake Placid! We chatted about Baily's beads, my graduate school work, and the general excitement about the eclipse! Also featured is my family's basset hound, Brig.
Alumna Jessica Watkins answers questions from International Space Station
I got the chance to ask a question on a call to the International Space Station with Stanford alum Jessica Watkins! I asked her what part of the broad scientific training to be an astronaut she found most interesting, and she answered she enjoyed learning about marine biology for NEEMO, an underwater research mission simulating the environment of space.
Stanford EE Admit News, May 2020
I was featured in Stanford's electrical engineering admitted student news for the month of May!
National Science Foundation Graduate Research Fellowship Program
I earned the National Science Foundation Graduate Research Fellowship in spring of 2020! This will provide funding for 3 years of graduate study in my Ph.D. program.
Northeastern College of Engineering announcement about NSF GRFP
An article from Northeastern's College of Engineering about this year's National Science Foundation Graduate Research Fellowship Program recipients
Northeastern College of Engineering Class of 2020 Graduates Webpage
Since Northeastern's graduation was online this year, this webpage lists all the 2020 graduates! I earned a Bachelor of Science in Electrical Engineering and a Master of Science in Electrical and Computer Engineering, with a concentration in electromagnetics, plasma, and optics.
Northeastern President's Award
I earned Northeastern's President's Award, awarded to the top 10 students in each graduating class by GPA. I won this award in 2018, 2019, and 2020.
Variety Defined Elizabeth Wig's Northeastern Experience (Northeastern Honors Program News)
I talked to Northeastern's Honors program about my various Northeastern experiences!
News@Northeastern: Mars and Beyond
I was quoted in a News at Northeastern article about the 50th anniversary of the moon landing. I discussed trends in the space industry and my hopes for the future of space exploration!
Huntington 100
I was selected as a member of the Huntington 100 in 2019! Sponsored by the Office of Student Life, the Huntington 100 honors outstanding students for achievements which are commensurate with the university’s mission, ideals, values, and Academic Plan. These students represent what Northeastern is today – a selective institution with rigorous academic programs and a sharp focus on the global experience. Recipients are chosen for their:
- Impact on the campus community
- Record of service, be it within the university or another community
- Global engagement, in the form of international co-op, study abroad, or other experiential learning outside the United States
- Demonstrated leadership
- Entrepreneurial or innovative spirit
- Commitment to a high level of ideals and ability to positively represent the values of Northeastern
An article from Northeastern's College of Engineering about the 2019 cohort of the Huntington 100
Four Undergraduate Researchers Earn Goldwater Scholarship
I, along with three other Northeastern undergraduates, earned the United States’ premier award for outstanding young researchers in STEM fields. The Goldwater Scholarship is a highly competitive, merit-based award for students majoring in mathematics, the natural sciences, and engineering who are interested in pursuing careers in research. It was established by Congress in 1986 to honor Senator Barry Goldwater, who showed a keen interest in science and technology during his 30 years in the U.S. Senate.
Outstanding Student Researchers Nominated for Goldwater Scholarship
I am honored to be one of Northeastern's four nominees for the 2018 Barry Goldwater scholarship, which supports students interested in pursuing research careers.
ALERT Student Spotlight
Hear about my research creating mathematical models for airport security scanners at ALERT!
Inspiring Women Engineers Article
I am thankful to the Society of Women engineers and GE for the GE Women's Network Scholarship that I earned in 2017, which you can read about here.
Northeastern COE Magazine: Breaking the Stereotype
Turn to page 27 of Northeastern's 2018 College of Engineering Magazine to read about my experience as a woman in engineering.
2017 Electrical and Computer Engineering Undergraduate Award Winners
Announcement of undergraduate awards at Northeastern's department of Electrical and Computer engineering. I won the Rochefort award.