Sea State Measurements Using Terrasar-X/Tandem-X Data
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Sea State measurements using TerraSAR-X/TanDEM-X data Dissertation Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Christian-Albrechts-Universität zu Kiel vorgelegt von Miguel Bruck Kiel, 2015 Referent: Prof. Dr. Roberto Mayerle Koreferent: Dr. Susanne Lehner Datum der Disputation: 11.06.2015 Zum Druck genehmigt: 11.06.2015 Contents Contents……………………………………………………………………………………………………..I List of figures……………………………………………………………………………………………...IV List of tables…………………………………………………………………………………………..…XIII Chapter 1: Introduction …………………………………………………………………….…………..1 1.1 Introduction and motivation…………………………………………………..…………..………...1 1.2 Objectives…………………………………………………………………………….……….….....2 1.3 Outline of the thesis……………………………………………………………..…….………….....4 1.4 Summary of the thesis ……..……………..……………………………………………….….…......5 Chapter 2: Ocean waves ………………………………………………………………...…………….….7 2.1 Linear theory ………………………………………………………………………………….....…7 2.2 Wind generated sea surface ocean waves………………………………………………………......9 2.3 Conversion from time to spatial domain ……………………………………………………….…13 Chapter 3: Radar Remote sensing ……………………………………………………………………...15 3.1 Real Aperture Radar (RAR) ………………………………………………………………….…...15 3.2 Spatial resolution…………………………………………………………………………………..17 3.2 Synthetic Aperture Radar (SAR)…………………………………………………………………......17 3.2.1 Range processing ……………………………………………………………………………...19 3.2.2 Azimuth processing ………………………………………………………………...………... 19 Chapter 4: State of the art ………………………………………………………………………....……20 4.1 Ocean waves imaging mechanism by SAR………………………………………..……….….…20 4.2 Historical SAR data……..……………………………………………………………….…....….22 4.2.1 ERS ½ …………... ………………………………………………………….…….…….….22 4.2.2 ENVISAT …………………………….………………………………………………...…...22 4.3 Ocean wave analysis algorithms for C-band SAR data ………………………………………….23 4.3.1 MPI scheme ……………………………………………….…………………………….……23 4.3.2 SAR cross-spectral algorithm ………………………………………………………………..24 4.3.3 PARSA ………………………………………………………………….……………………24 4.3.4.1 CWAVE and CWAVE_ENV………………………………………………………………25 i Chapter 5: DATA ………………………………………………………………………………………..26 5.1 In-situ buoy wave measurements …………………………………………………………….….….26 5.2 TS-X/TD-X SAR …………………………………………………………………………………...28 5.2.1 Calibration ………………………………………………………………………………….….31 5.3 Numerical Wave model data…………………………………………………………………….…..32 5.4.1 Wave model DWD data……………………………………………………………………..….32 5.4.2 K–model data (coastal wave model) ……………………………….…………………….….....33 Chapter 6: TS-X/TD-X Sea Surface observation …………………………….…..……………………34 6.1 TS-X/TD-X data acquired over the ocean………………………………………………….…….....34 6.2 Phenomena sea surface signatures observed in TS-X/TD-X data…………………………….…….40 Chapter 7: Data Analysis………………………………………………………………………………..43 7.1 The 2D Fourier analysis………………………………………………………………………….…43 7.2 Homogeneous and inhomogeneous wave fields observed TS-X/TD-X SAR……………………....45 7.3 Ocean waves peak wavelength and direction derived from TS-X/TD-X data………………,….….49 7.4 Azimuth cut-off ………………………………………………………………….……………….…52 7.5 Azimuth cut-off effect on TS-X/TD-X data ………………………..……………………………….54 7.6 Dependency of azimuth cut-off wavelength from TS-X/TD-X with significant wave height and wind speed …...…………………………………………………………………………………………….……55 7.7 Dependency of azimuth cut-off wavelength with incidence angle…………………………………60 Chapter 8: Empirical algorithm to estimate from TS-X/TD-X data: XWA……………………...62 8.1 Background ………………………………………………………………………….……….….....62 8.2 Data selection ……………………………………………….………………………………….…..64 8.3 Algorithm discussion…………………………………………….…………………………………68 8.4 Dependencies taken into account in the algorithm …………….……………………………..……69 8.4.1 Incidence angle ……………………………………………………………………………....69 8.4.2 Sea surface wind speed …………………………………………………………….……71 8.4.3 Ocean wave propagation direction in relation to satellite path (azimuth)…………………....73 8.5 Validation of the algorithm …………….……………………………………………………..…....74 Chapter 9: Case studies ………………………………………………………………..……………….76 9.1 Case studies over in-situ wave measurements…………..…………………………………….……76 Chapter 10: Coastal wave field extraction …………………………………………………...………...90 10.1 Coastal wave field extraction using TS-X/TD-X data………………………………...……….......90 10.2 Case studies …………………………………………………………………………………...…...91 Case study I: Coastal wave field extraction in high sea state conditions …………………………..92 ii Case study II: Comparison with numerical wave model data……………………………….…..….98 Case Study III: Analyzing sea state variability in the TS-X derived wave field with in-situ wave measurements........................................................................................................................103 Chapter 11: Summary and Conclusions ……………………..……………………………………….105 Outlook…………………………………………………………………………………………………..108 Appendix A …………………………………………………………………………...………………...110 Appendix B ……………………………………………………………………………………………..116 Appendix C …………………………………………………………………………………………......129 Appendix D …………………………………………………………………………………………......132 References ……………………………………………………………………………………………....138 List of Symbols ………………………………………………………………………………………....143 List of acronyms ……………………………………………………………………………………......145 iii List of Figures Figure 2.1: Representation of a linear ocean wave propagating with speed , wavelength , amplitude and modulating the sea surface at height ..…………………………………………………….….7 Figure 2.2: Frequency and period of the vertical motions of the ocean surface (after Munk., 1950)……...9 Figure 2.3: Diagram showing the predicted H s according to the wind speed duration of the wind speed and the fetch distance (adapted from Van Dorn, W.G, Oceanography and Seamanship, 1974)……….....10 Figure 2.4: The sea surface , is composed of a large sum of wave components which propagate at different periods, directions, amplitudes and phases.( after [Pierson et al., 1955], in Holthuijsen, L.H., Waves in Oceanic and Coastal Waters, 2007)……………………………………………….…..11 Figure 2.5: Two dimensional wave number spectrum…………………………………………………….11 Figure 2.6: Representation of the one dimensional (1D) wave spectrum. It corresponds to the distribution of the energy density of ocean waves with frequency……………………………………………….……12 Figure 3.1: The electromagnetic spectrum (in ASAR Product Handbook, 2007 © ESA)……………..15 Figure 3.2: Representation of the SAR imaging system. The SAR is moving with velocity V along the x – axis; azimuth direction, and the sensor is looking into the y-axis; range direction……………………….18 Figure 3.3: Representation of how the SAR system achieves its high resolution coverage by synthetizing a virtual longer antenna: During the flight of the satellite the echoes of the illuminated area by the radar are stored, by analysing the Doppler shift (the change in the frequency/wavelength of the echo is comparison to the original remitted radar pulse, the location of each echo is computed (Figure © ESA).…………………………………………………………………………………………………..….18 Figure 4.1: Representation of a simplified view of the sea surface imaging mechanism by SAR. The radar cross section peak value does not correspond to the sea surface elevation peak but rather to the surface perpendicular to the radar signal…………………………………………………………………20 Figure 5.1: Ocean waves (sea surface elevation) measurements devices commonly known as buoys: 6 meter NOMAD aluminium hulled boat shaped buoy (left). 3-meter aluminium hulled discus buoy (center). Data well Directional Waverider buoy (left)…………………………………………………….26 Figure 5.2: Visualization of standard one dimensional wave spectra provided by ocean wave measurement buoys .In this case the energy density is located in the lower frequencies, which corresponds to long wavelength waves, probably swell conditions. Significant wave height calculated from the spectrum is for this case 3.1 m and a wave peak period of 12.9s………………………………27 Figure 5.3: The TerraSAR-X and his twin Tandem-X satellite. …………………………………………28 iv Figure 5.4: Representation of the different modes imaged by the TS-X/TD-X ©DLR…………………..29 Figure 5.5: TS-X VV polarized StripMap acquired on February 26, 2013 at 19:48 UTC over the Dixon Entrance, west coast of Canada………………………………………………………………………...….31 Figure 5.6: field (left) and the Swell wave height field (right) given by the DWD wave model on November 21, 2008 at 17:01 UTC……………………………………………………………………...…33 Figure 6.1:TS-X VV pol. StripMap acquired on April 9th 2012 at 1:51 UTC. Inlet: TS-X SpotLight acquired on June 13, 2013 at 1:51 UTC on the west coast of USA. ……………………………………....35 Figure 6.2: TS-X VV pol. SpotLight data image acquired on June 12, 2013 at 1:51 UTC (inlet Fig.6.1)……………………………………………………………………………………………………..35 Figure 6.3: TS-X VV polarized ScanSAR data taken on 3th Oktober, 2012 at 8:22 UTC over the Tropical Storm Nadine on the North Atlantic Ocean (left) Sub-scenes taken form different postions on the data image (right). ……………………………………………………………..……………………………….36 Figure 6.4: TS-X VV polarized StripMap data taken on the Oktober 31, 2012 at 11:28 UTC near the Gulf of Mexico. The image data is taken under low sea state and .moderate wind conditions (left) TS-X VV polarized StripMap data taken on the 18 Dezember 2012 at 22:20 UTC. The image data is taken under low sea state conditions with influence of wind, which created signatures visible in the data (right)…....37 Figure 6.5: TS-X VV polarized StripMap data taken on October 20, 2012 at 15:55 UTC. The data is acquired under high sea state conditions.………………………………………………………….....……38 Figure 6.6: TS-X HH polarized StripMap image acquired over