29. Advanced InSAR techniques for ground deformation imaging

Precise mapping, analysis, and modeling of ground-surface deformation is a critical element in the assessment and mitigation of natural and anthropogenic hazards (for example, Dzurisin, 2007). By combining two or more radar images of the same area acquired at different times by space-borne sensors, scientists can map ground deformation at an unprecedented level of spatial detail. The technique, called interferometric synthetic aperture radar (InSAR), is being used to map and monitor ground deformation caused by volcanic activity, earthquakes, landslides, and pore-fluid pressure variations in susceptible aquifer systems (Lu and others, 2007). Numerical modeling of InSAR imagery can  help characterize the mechanism(s) responsible for the observed deformation.

Although there have been numerous successes, InSAR applications continue to be limited by two pervasive problems. First is the presence of atmospheric delay anomalies in InSAR observations. Differences in atmospheric temperature, pressure, and water vapor content at the two observation times can cause differing path delays and consequent anomalies in an InSAR deformation image (interferogram). Atmospheric delay anomalies can reduce the accuracy of InSAR-derived deformation measurements from several millimeters under ideal conditions to 2–3 centimeters under more typical conditions, thus obscuring subtle deformation that might hold clues to the cause of the deformation. The second problem is lack of good temporal sampling of InSAR images. In many cases, documenting the transient behavior of deformation is critical for hazard identification and mitigation purposes. However, transient deformation can be short-lived, and many times it cannot be captured with InSAR due to long sensor-revisit times (for example, 35 days for ERS and Envisat, 24 days for Radarsat-1, and 46 days for ALOS).

Building on current USGS capabilities, we invite a remote sensing scientist, physical scientist, or geophysicist with solid training in InSAR data processing or modeling to develop advanced InSAR processing and analysis techniques addressing one of the following frontier research areas.

First, recognizing recent advances in the persistent scatterer InSAR (PSInSAR) technique, this Opportunity calls for further development of PSInSAR to improve the accuracy of deformation mapping. The atmospheric delay anomalies in InSAR images have unique characteristics, i.e., they are highly correlated in space but uncorrelated in time and often exhibit a power law dependence on frequency that is characteristic of elementary (Kolmogorov) turbulence. The behavior of atmospheric delay anomalies contrasts with the characteristics of ground deformation signals, which are both temporally and spatially correlated. Through temporal and spatial filtering and analysis of a sequence of InSAR images, PSInSAR can overcome the difficulties caused by atmospheric path-delay anomalies and loss of coherence. The ultimate objective is to remove the contribution due to the atmosphere and other intrinsic errors associated with individual InSAR images in order to achieve millimeter-scale accuracy in deformation measurements.  

Second, this Opportunity calls for improving the temporal sampling of InSAR monitoring by developing the potential of ScanSAR InSAR. The radars onboard Envisat, Radarsat-1 and ALOS are capable of acquiring images in both strip and scan modes. In strip mode, radar-antenna pointing is fixed along the flight path, and the antenna footprint covers a strip (swath) on the surface beneath the orbital track. As a result, the size of an image is limited in the cross-track direction to about 100 km. Scan-mode SAR (ScanSAR) is achieved by periodically switching the antenna look angle into neighboring subswaths in the cross-track direction, thereby increasing the size of the accessible image swath to 400~500 km. Because ScanSAR can acquire more frequent observations of a given study area than is possible with strip-mode SAR, interferometric ScanSAR images significantly increase the number of interferometric observations in a fixed time frame, improving the temporal resolution of deformation mapping. This makes ScanSAR InSAR a very attractive tool for monitoring transient deformation signals. This Opportunity seeks to realize ScanSAR’s potential for advancing InSAR deformation studies by developing new data processing and analysis techniques and applying them to deforming volcanoes.

If successful, the developments described above will result in more precise InSAR measurements of ground deformation at volcanoes and other targets of interest. Such measurements can be used for time-series analysis to reveal subtle transient deformation signals associated with magmatic intrusions, earthquakes, groundwater withdrawal, and other processes of interest to USGS programs. These precise deformation measurements will improve deformation models, through which we expect to gain insight into such topics as how volcanoes work, how strain accumulates along active faults, and how landslides initiate and develop.

References

Dzurisin, D., 2007, Volcano deformation—Geodetic monitoring techniques: Chichester, UK, Springer-Praxis Publishing Ltd., 441 p.

Lu, Z., Kwoun, O. and Rykhus, R., 2007, Interferometric synthetic aperture radar (InSAR): Its past, present and future: Photogrammetric Engineering and Remote Sensing, v. 73, p. 217–221.

Proposed Duty Station: Vancouver, WA

Areas of Ph.D.: Remote sensing, geophysics, geology, geography, hydrology, electrical engineering

Qualifications: Applicants must meet one of the following qualifications: Research Geophysicist, Research Geologist, Research Physical Scientist, or Research Geographer

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Zhong Lu, (360) 993-8911, lu@usgs.gov; Dan Dzurisin, (360) 993-8909, dzurisin@usgs.gov

Human Resources Office contact: Erica Settlemyer, (916) 278-9383, esettlemyer@usgs.gov

Summary of Opportunities