New Applications of Satellite-Measured Tropical Cyclone Wind Speeds by David R. Mayers A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Applied Physics) in the University of Michigan 2021 Doctoral Committee: Professor Christopher Ruf, Chair Associate Professor Jeremy N. Bassis Associate Research Scientist Darren McKague Dr. Lucrezia Ricciardulli, Remote Sensing Systems Professor Kamal Sarabandi David R. Mayers [email protected] ORCID iD: 0000-0001-8935-1867 © David R. Mayers 2021 Acknowledgements I am grateful to have had Chris Ruf as a research advisor. He taught me how to approach research and scientific writing. He was always very supportive of my projects and ideas, while also promptly providing feedback and helpful suggestions of his own. I am thankful Chris took me on despite coming from another department and that he introduced me to remote sensing. I am indebted to my committee members, Drs. McKague, Sarabandi, Ricciardulli, and Bassis, for their insights and support. I am thankful that my parents provided a solid educational foundation and that they supported my decision to pursue a PhD despite being unfamiliar with the concept. I am blessed to have Meredith’s loving support throughout graduate school. Thank you for dealing with my irregular work schedule and for sacrificing kitchen space for my dual- monitor workstation. I am thankful that the Applied Physics Program provided an excellent learning experience and opened the doors to so many research opportunities throughout the University. The Climate and Space Sciences and Engineering Department accepted me as an honorary member; I am grateful for the support I received in education, logistics, and IT. I am happy to have had Tianlin, Raji, Rachel, Mohammad, and Charlie as coworkers. I learned much from all of you and you all made my graduate school experience more enjoyable. And, finally, I thank anyone who has contributed to my passion for science and learning. ii Table of Contents Acknowledgements ..................................................................................................................................... ii List of Tables ............................................................................................................................................... v List of Figures ............................................................................................................................................. vi Abstract ...................................................................................................................................................... xii Chapter 1 Introduction ............................................................................................................................... 1 1.1 Earth-Based Measurements of Tropical Cyclones ............................................................................. 7 1.2 Satellite Measurements of Tropical Cyclones .................................................................................... 9 1.3 CYGNSS .......................................................................................................................................... 11 Chapter 2 Estimating the True Maximum Sustained Wind Speed of a Tropical Cyclone from Spatially Averaged Observations ............................................................................................................ 20 2.1 Motivation ........................................................................................................................................ 20 2.2 Dataset and Processing Methods ...................................................................................................... 23 2.3 Scale Factor Dependencies ............................................................................................................... 26 2.4 Hurricane Sergio Example................................................................................................................ 34 2.5 Discussion and Implications ............................................................................................................. 36 Chapter 3 Parametric Wind Speed Model: Complete Tropical Cyclone Wind Field from Sparse Measurements ........................................................................................................................................... 39 3.1 Overview of Existing Parametric Wind Models ............................................................................... 41 3.2 Improving the Model ........................................................................................................................ 42 3.3 Error Sources .................................................................................................................................... 48 Chapter 4 MTrack: Tropical Cyclone Center Fix from Satellite Wind Speed Observations ............ 51 4.1 MTrack with SMAP ......................................................................................................................... 53 4.2 MTrack with CYGNSS .................................................................................................................... 61 4.3 MTrack Performance Analysis ......................................................................................................... 69 4.4 Future Use of MTrack ...................................................................................................................... 75 Chapter 5 New CYGNSS Level 3 Gridded Wind Speed Product with Storm-Centric Averaging ... 77 iii 5.1 Establishing a Storm-Centric Grid ................................................................................................... 79 5.2 Inter-Track Comparisons and Averaging ......................................................................................... 82 5.3 Performance Assessment .................................................................................................................. 87 Chapter 6 Summary and Future Work .................................................................................................. 97 Bibliography ............................................................................................................................................ 103 iv List of Tables Table 2-1: Examples of instruments that measure wind speeds at varying spatial resolutions. ... 22 Table 2-2: The root-mean-square difference in wind speed (m/s) between true and measured Vm with varying types of correction applied to the measured Vm, for different spatial resolution of the measurements. Cases considered are no correction, a constant SF for a particular spatial resolution, and SF corrections that depend on Vm, Rm, and both Vm and Rm. The ‘‘LMS Rm, Vm’’ row shows the results with Vm dependence for three different sizes of Rm: large, medium, and small. ...................................................................................................................................... 31 Table 4-1: Comparison between Best Track and MTrack uncertainties (using SMAP input) ..... 70 Table 4-2: The MTrack uncertainty and uncertainty reduction factor (compared with Best Track) for each of the ensembles in Figure 4-17. As the perturbations grow larger, the MTrack uncertainty also becomes larger. However, MTrack produces a consistent improvement in confidence compared with Best Track for even the largest perturbations. ................................... 72 Table 4-3: MTrack performance metrics with CYGNSS wind speeds as input for five cases. The hurricane category, according to the Saffir Simpson scale, is included because there is a correlation between storm intensity and center fix accuracy. The uncertainty reduction factor is much greater than 1 in all cases, meaning that MTrack always has a much lower uncertainty than Best Track. .................................................................................................................................... 73 Table 4-4: Comparison of cross-path and along-path uncertainty. The cross-path uncertainty is greater than the along-path uncertainty in all cases. This seems to stem from a similar eccentricity in the residual surface ................................................................................................ 74 Table 4-5: MTrack uncertainties due to CYGNSS wind speed errors for a few cases. The CYGNSS wind speeds were randomly perturbed over many trials, and the average error which propagated to MTrack is in this table. .......................................................................................... 74 v List of Figures Figure 1-1: Historic TC tracks (Rohde 2006) ................................................................................. 3 Figure 1-2: Typical TC structure in a model’s wind field (left) and the clouds as seen from space (right). Note, these images represent different, arbitrary storms. ................................................... 5 Figure 1-3: NOAA Hurricane Hunter WP-3D Orion "Kermit" (Photo by David R. Mayers, 2020, Lakeland, FL) .................................................................................................................................. 7 Figure 1-4: Bragg resonance mechanism which dominates the backscatter of scatterometers .... 11 Figure 1-5: Bistatic geometry with iso-delay ellipses and iso-Doppler parabolas on the surface (Clarizia and Ruf 2016) ...............................................................................................................