. UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE REPORT DOCUMENTATION PAGE fOrmApproved (1MRNo 07Q4 01R8 la RFPORT SECURITY CLASSIFICATION lb RESII'ICFIVE MARKINGS UNCLASSIFIED 2a SFCURITY CLASSIFICATION AUTHORITY 3 DISTRIBUTION/AVAILABILITY OF REPORT Approved for public release; distribution 21, DECLASSIFICATION/DOWNGRADING SCHEDULE is unlimited. A PERFORMING ORCANI7AHON RFPORT NUMBFR(S) 5 MONIIORING ORGANIZATION RFPORT rjUMBf P(S) 6a NAME OF PERFORMING ORGANIZATION 6b OFFICE SYMBOL 7a NAME OF MONITORING ORGANIZATION (If applicable) NAVAL POSTGRADUATE SCHOOL NAVAL POSTGRADUATE SCHOOL 6i ADDRESS (City, State, and ZIPCode) 7b ADDRESS(City, Stafe, and 7IPCode) Monterey, CA 93943 Monterey, CA 93943 8a NAME OF FUNDING/SPONSORING 8b OFFICE SYMBOL 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER ORGANIZATION (If applicable) 8c ADDRESS(Cify, State, and ZIPCode) 10 SOURCE OF FUNDING NUMBERS PROGRAM PROJECT TASK WORK UNIT ELEMENT NO NO NO ACCESSION NO 11 TITLE (Include Security Classification) Examination of Three-Dimensional (3-D) Effects on Sound Propagation Through Mesoscale Features Using 3-D Coupled Mode Theory 12 PERSONAL AUTHOR(S) Binhlam, Jacqueline M 13a TYPE OF REPORT 13b TIME COVERED 14 DATE OF REPORT (Year, Month, Day) 15 PAGE COUNT Master's Thesis FROM TO June 199? 22. 16 SUPPLEMENTARY NOTATION 17 COSATI CODES 18 SUBJECT TERMS (Continue on reverse if necessarv and identify bv block number) FIELD GROUP SUB GROUP Underwater sound propagation modeling 19 ABSTRACT (Continue on reverse if necessary and identify bv block number) A study of the three dimensional (3-D) effects of mesoscale variability on underwater sound propagation is conducted by interfacing the Chiu-Ehret 3-D acoustic coupled mode (CM) model with a forecasted sound speed field generated by the Harvard Open Ocean Model (HOOM) This research concentrates on the sensitivity of the acoustic wave field to source depth and location with respect to a core ring in the Gulf Stream system for a 50 Hz sound source, The inclusion of the exact 3-D physics in acoustics modeling requires substantial computer resources. For this reason, it is very desirable to determine when the simpler adiabatic or Nx2-D approximations may be used. To achieve this goal, "exact" 3-D acoustic coupled mode model calculations are compared to results from the adiabatic approximation and Nx2-D approximation in terms of transmission loss and phases and amplitudes of individual mode modulation envelopes. The results show that the accuracy of the adiabatic and Nx2-D approximations depend strongly on the radial and transverse sound speed gradients along the track and the acoustic quality considered. 20 DISTRIBUTION/AVAILABH IIY OF ABSTRAC1 21 ABSTRACT SECURITY CLASSIFICATION @ UNCLASSIFIED/UNLIMITED SAME AS RPT DTIC USERS 22a NAME OF RESPONSIBIE INDIVIDUAL 22b TELEPHONE (Include AieaCode) 22c OFFICE SYMBOL Ching-Sang Chiu 408-646-3239 68 Ci DDForm 1473, JUN 86 Previouseditionsareobsolete SECURITY CLASSIFICATION OF THIS PAGE S/N 0102-LF-014-6603 UNCLASSIFIED T^c;77n/i Approved for public release; distribution is unlimited Examination of Three-Dimensional (3-D) Effects on Sound Propagation Through Mesoscale Features Using 3-D Coupled Mode Theory by Jacqueline M. Binhlam Lieutenant, U.S. Navy B.S., United States Naval Academy, 1982 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN METEOROLOGY AND PHYSICAL OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL June 1992 ABSTRACT A study of the three dimensional (3-D) effects of mesoscale variability on un- derwater sound propagation is conducted by interfacing the Chiu-Ehret 3-D acoustic coupled mode (CM) model with a forecasted sound speed field generated by the Har- vard Open Ocean Model (HOOM). This research concentrates on the sensitivity of the acoustic wave field to source depth and location with respect to a core ring in the Gulf Stream system for a 50 Hz sound source. The inclusion of the exact 3-D physics in acoustics modeling requires substan- tial computer resources. For this reason, it is very desirable to determine when the simpler adiabatic or Nx2-D approximations may be used. To achieve this goal, "ex- act" 3-D acoustic coupled mode model calculations are compared to results from the adiabatic approximation and the Nx2-D approximation in terms oftransmission loss and phases and amplitudes of individual mode modulation envelopes. The results show that the accuracy of the adiabatic and Nx2-D approximations depend strongly on the radial and transverse sound speed gradients along the track and the acoustic quality considered. in 7 c TABLE OF CONTENTS INTRODUCTION I. 1 BACKGROUND A. 1 OBJECTIVES B. 2 THEORY II. 5 A. REVIEW OF NORMAL MODE THEORY FOR A HORIZONTALLY STRATIFIED MEDIUM 5 COUPLED MODE THEORY B. 3-D 7 C. INTERFACE WITH THE FORECASTED SOUND SPEED FIELD GENERATED BY THE HOOM 11 III. RESULTS AND ANALYSIS 17 A. CASE 1: SOURCE IS PLACED OUTSIDE A WARM EDDY .... 18 CM 1. Comparison Between the 3-D Adiabatic and 3-D Models . . 18 m a. Source Depth: 1360 18 (1) Amplitude Comparison 18 (2) Phase Comparison 19 m b. Source Depth: 300 20 Amplitude Comparison 20 (1) Phase Comparison 20 (2) m m c. Transmission Loss Comparison at 300 and 1360 Depths 21 CM 2. Comparison Between the 3-D and Nx2-D Models 22 m a. Source Depth: 1360 22 Amplitude Comparison 22 (1) Phase Comparison 22 (2) iv m b. Source Depth: 300 23 (1) Amplitude Comparison 23 (2) Phase Comparison 23 m m c. Transmission Loss Comparison at 300 and 1360 Depth 23 B. CASE 2: SOURCE IS PLACED INSIDE A WARM EDDY 24 CM 1. Comparison Between the 3-D Adiabatic and 3-D Models 24 . . m a. Source Depth: 1360 24 (1) Amplitude Comparison 24 (2) Phase Comparison 25 m b. Source Depth: 300 25 (1) Amplitude Comparison 25 (2) Phase Comparison 26 c. Transmission Loss Comparison at 300 m and 1360m .... 26 CM 2. Comparison Between the 3-D and Nx2-D Models 26 m a. Source Depth: 1360 26 (1) Amplitude Comparison 26 (2) Phase Comparison 27 m b. Source Depth: 300 27 (1) Amplitude Comparison 27 (2) Phase Comparison 27 m m c. Transmission Loss Comparison at 300 and 1360 Depths 27 CONCLUSIONS AND RECOMMENDATIONS IV. 60 APPENDIX A IMPLEMENTATION OF CHIU-EHRET COUPLED MODE MODEL - IN A VAX 8250 63 LIST OF REFERENCES 65 INITIAL DISTRIBUTION LIST 67 v LIST OF FIGURES m 2.1 Sound Speed Contours at a depth of 120 generated by Harvard Uni- versity Open Ocean Model (Robinson, et al.) for a region in the Gulf Stream current (480 km x 960 km). The location of the domain chosen for the case studies is marked 13 2.2 Sound Speed Contours (m/s) at a depth of 120 m for a 240 x 510 km2 region containing a warm eddy north of the Gulf Stream system. ... 14 2.3 CASE 1: Sound source is placed outside the warm eddy region. The acoustic solution domain in a cylindrical coordinate system and six se- lected paths 6 = -2°, 6°, 10°, 44°, and 62° are shown (each tic mark on the pie shaped sector indicates a 2° increment) 15 2.4 CASE 2: Sound source is placed inside the warm eddy region. The acoustic solution domain in a cylindrical coordinate system and three selected paths 6 = -45°, 0°, 45° are shown (each tic mark on the pie shaped sector indicates 2° increment) 16 CM 3.1 Envelope Amplitude of 10 Modes from the 3-D Solution Along the Paths 6 = 2° (Figure 3.1a), = 6° (Figure 3.1b), and = 10° (Figure 3.1c). (Source is placed outside a warm eddy at depth = 1360 m) . . . 29 CM 3.2 Envelope Amplitude of 10 Modes from the 3-D Solution Along the Paths = 4° (Figure 3.2a), = 48° (Figure 3.2b), and 6 = 62° (Figure 3.2c). (Source is placed outside a warm eddy at depth = 1360 m) . . . 30 3.3 Envelope Amplitude of 10 Modes for the 3-D Adiabatic Approximation Solution Along the Path 6 = 6°. (Source is placed outside a warm eddy at depth = 1360 m) 31 vi