Module III of this course introduces you to the advanced radar concepts of Polarimetric SAR (PolSAR) and Interferometric SAR (InSAR). PolSAR processing allows you to perform automatic classifications of an observed area into the canonical scattering types surface scattering, double bounce scattering, and volume. In addition to the principles of PolSAR You will learn how to perform polarimetric decompositions. InSAR is a technique to map both the shape and the cm-scale deformation of the Earth surface. In its essence, InSAR analyses differences between multiple complex SAR acquisitions to gain deeper understanding of an observed object. This class will teach the principles and advanced concepts of InSAR and showcase some of the many examples of this powerful technique.
Lecture 11: The Principles and Applications of Interferometric SAR (InSAR)
Interferometric SAR (InSAR) is analyzing phase differences between two or more SAR acquisitions with the goal to measure surface topography and/or surface deformation. While the quality of derived topographic information depends on the relative observation geometry of the used SAR acquisitions, surface deformation can be measured at a fraction of the signal wavelength and, hence, with millimeter to centimeter accuracy. In this lecture you will hear about the concepts of InSAR and the general processing approaches to arrive at surface topography. Limitations of InSAR as well as advanced processing concepts will be covered in future lectures.
Preparatory Reading in (Woodhouse, 2006):
In preparation for this class, please read Chapter 11 “Interferometry” in (Woodhouse, 2006). If you only have limited time, focus on pages 312 – 331 of this chapter.
Side Topic: Visiting the NASA Goddard SWESARR Sensor during its Deployment in Fairbanks, AK
On March 14, 2023, I and a small group of students had the chance to visit the NASA SWESARR (Snow Water Equivalent Synthetic Aperture Radar and Radiometer) airplane during it’s deployment in Fairbanks, Alaska. SWESARR is a new instrument designed to measure the water content in a snowpack. The instrument, developed at NASA’s Goddard Space Flight Center, uses active and passive microwave sensors to map the radio frequency emissions of the snowpack, which can then be turned into a measurement of snow water equivalent.
SWESARR was in town to support the NASA SnowEx campaign, a multi-year field experiment, which includes extensive surface-based observations to evaluate how to best combine different remote sensing technologies to accurately observe snow throughout the season in various landscapes. The video below is a recording of the excellent tour we received from Goddard’s Dr. Batuhan Osmanoglu.
Side Topic: Guest Lecture by Joe Morrison, VP of Commercial Experience at Umbra Space
On March 21, 2023, the class enjoyed a guest lecture by Joe Morrison, VP of Commercial Experience at Umbra Space. Joe is an outspoken proponent of SAR who’s more than worth a follow on Twitter or LinkedIn. Umbra is an exciting NewSpace company developing and launching next generation SAR systems. You can enjoy Joe’s talk titled “SAR: You’re Not Gonna Get Rich, But You Won’t Worry You Wasted Your Life” below.
Lecture 12: InSAR for Deformation Mapping & Limitations of Traditional InSAR Methods
The first part of this lecture will deal with the use of InSAR for measuring mm-scale deformations of the earth surface, such as those related to glacier motion, volcanic activity, earthquakes and other geodynamic signals. In the second part of this lecture, we will look into the main limitations of the traditional two-image InSAR approach. This identified limitations will set up us for future lectures, which will describe advanced processing techniques such as PS- and SBAS InSAR.
For particularly interested students, the slide deck also includes information on the problem of phase unwrapping. As InSAR phase measurements are initially only available wrapped into [-π &pi[, a phase unwrapping process has to be applied to create an unambiguous phase map ready for topography or deformation analysis. You will be introduced to the general process of phase unwrapping and learn about several popular solutions to this problem.
With this lecture we are slowly leaving the range of topics covered in (Woodhouse, 2006). For more information on InSAR limitations please read pages 338-339 in (Woodhouse, 2006). For information on phase unwrapping please read Section “E. The Phase In Interferometry” in [Rosen et al., (2000)].
In 2023, Lab 5 is an optional lab. Please feel free to exercise the lab on your own time. No formal assignment is connected to this lab.
Side Topic: How to Access and Custom Process SAR Data using ASF’s Search and On-Demand Processing Services
On March 30, 2023, the class learned how to use ASF’s data discovery and on-demand processing services to automatically generate large volumes of RTC and InSAR data products. Please rewatch the Class recording below
Lecture 13: The Concepts of Polarimetric SAR (PolSAR)
Polarization describes the path of the tip of the electric field vector of an electromagnetic wave. Polarimetric radars have the ability to fully control the polarization of both the transmitted and received signal, and are therefore able to use polarization as a source of information. This lecture focuses on the principles of of Polarimetric SAR, the properties of polarimetric signals, and on how polarimetric information relates to the characteristics of an observed surface. We will also talk about polarimetric decomposition, an approach to parameterize information contained in polarimetric radars. Decompositions that will be addressed include the Pauli decomposition, the Freeman-Durden decomposition, as well as the H/Î± and the H/A/Î± decomposition.
Preparatory Reading in (Woodhouse, 2006):
Iain Woodhouse dedicates a fairly elaborate chapter (Chapter 4; pages 65 – 91) to the topic of Polarimetric Radar. Reading this chapter is not a requirement but recommended for students that want to dive a bit deeper into the PolSAR subject. Further reading is also listed in under the “Literature” tab of this website.
Lecture 14: The Role of InSAR in Geophysics
Intrinsically, InSAR is a geodetic discipline, providing accurate measurements of surface deformation. While this is interesting by itself, geoscientists are typically more interested in the geophysical source of a deformation than in the deformation itself. Using volcanic activity as an example, this lecture will provide you with some insight on how geophysical parameters can be determined using InSAR measurements and inverse modeling.
In preparation for this lecture and to gain further insight into the topic of inverse modeling of InSAR data, I recommend [Lohman & Simons, 2005], also to be found in the Further Readings section of this website.