Preface. Section 1: Ocean variability. Acoustic effects of environmental variability in the SWARM, PRIMER and ASIAEX experiments (Invited paper); J. Lynch, et al. Acoustic intensity variability in a shallow water environment; B.H. Pasewark, et al. Combination of acoustics with high resolution oceanography (Invited paper); J. Sellschopp, et al. Effect of hurricane Michael on the underwater acoustic environment of the Scotian Shelf; D. Hutt, et al. High-frequency acoustic propagation in the presence of oceanographic variability; M. Badiey, et al. Instrumented tow cable measurements of temperature variability of the water column; A.A. Ruffa, M.T. Sundvik. Mesoscale -- small scale oceanic variability effects on underwater acoustic signal propagation; E. Coelho. Spatial coherence of signals forward scattered from the sea surface in the East China Sea (Invited paper); P.H. Dahl. Variability in high frequency acoustic backscattering in the water column; A.C. Lavery, et al. Section 2: Seabed variability. Intra- and inter-regional geoacoustic variability in the littoral (Invited paper); C.W. Holland. Acoustic and in-situ techniques for measuring the spatial variability of seabed geoacoustic parameters in littoral environments; J.C. Osler, et al. Measurements of bottom variability during SWAT New Jersey Shelf experiment; A. Turgut, et al. Mapping seabed variability using combined echosounder and XBPs for sonar performance prediction; K.M. Kelly, G.J. Heald. Variability of shear wave speed and attenuation in surficial marine sediments; M.D. Richardson. In-situ determination of the variability of seafloor acoustic properties: An example from the ONR Geoclutter area; L.A. Mayer, et al. Calculation of in situ acoustic wave properties in marine sediments; B.J. Kraft, et al. Sub-bottom variability characterization using surface acoustic waves; M.E. Zakharia. The influence of noise and coherence fluctuations on a new geo-acoustic inversion technique; C.H. Harrison. Estimating shallow water bottom geo-acoustic parameters using ambient noise; D. Tang. Effect of environmental variability on model-based signal processing: Review of experimental results in the Mediterranean; J.-P. Hermand. Rapid geoacoustic characterization for limiting environmental uncertainty for sonar system performance prediction; K.D. Heaney, H. Cox. Environmental uncertainty in acoustic inversion; S.E. Dosso, M.J. Wilmut. Measuring the azimuthal variability of acoustic backscatter from littoral seabeds; P.C. Hines, et al. Backscatter from elastic ocean bottoms: Using the small slope model to assess acoustical variability and uncertainty; R.F. Gragg, et al. Spatial and temporal variability in bottom roughness: Implications to high frequency subcritical penetration and backscatter; K.L. Williams, et al. Variability of bottom backscattering strength in the 10-500 kHz band at shallow grazing angles; N.P. Chotiros. Predicting scattered envelope statistics of patchy seafloors; A.P. Lyons, et al. The effect of seabed backscattering variability on the probability of detection and on the performance of seabed classification algorithms; E. Pouliquen, et al. Section 3: Acoustic fluctuations: Measurements. Effects of environmental variability on acoustic propagation loss in shallow water; T. Akal. Broadband acoustic signal variability in two "typical" shallow-water regions; P.L. Nielsen, et al. Variability, coherence and predictability of shallow water acoustic propagation in the Straits of Florida; H.A. DeFerrari, et al. Ambient noise and signal uncertainties during the summer shelfbreak PRIMER exercise; P. Abbot, et al. Variability effect due to shallow sediment gas in acoustic propagation: A case study from the Malta Plateau; K.M. Kelly. Acoustic fluctuations and their harmonic structure; R. Field, et al. Group and phase speed analysis for predicting and mitigating the effects of fluctuations; W.A. Kuperman, et al. High-frequency propagation for acoustic communications; M.B. Porter, et al. Channel impulse response fluctuations at 6 kHz in shallow water; W.S. Hodgkiss, et al. High resolution analysis of eigenray gain perturbations in ultra-shallow water; S.M. Simmons, et al. Impact of flow variability on fixed side-looking 100 kHz sonar performance in a shallow channel; M. Trevorrow. Correlation between sonar echoes and sea bottom topography; J. Wegge. Section 4: Acoustic fluctuations: Models. Acoustic scattering in wave-covered shallow water. The coherent field; B.J. Uscinski. Simulations of temporal and spatial variability in shallow water propagation; E.I. Thorsos, et al. Assessing the variability of near-boundary surface and volume reverberation using physics-based scattering models; R.C. Gauss, et al. Modeling propagation and reverberation sensitivity to oceanographic and seabed variability; K.D. LePage. Uncertainty in reverberation modelling and a related experiment; C.H. Harrison, et al. Statistics of the waveguide invariant distribution in a random ocean; D. Rouseff. Effects of environmental variability on focused acoustic fields; B.E. McDonald, et al. Effects of sound speed fluctuations due to internal waves in shallow water on horizontal wavenumber estimation; K.M. Becker, G.V. Frisk. Relative influences of various environment factors on 50-100 Hz sound propagation in shelf and slope areas; T.F. Duda. Sub-mesoscale modelling of environmental variability in a shelf-slope region and the effect on acoustic fluctuations; S. Finette, et al. Yellow Sea internal solitary wave variability; A. Warn-Varnas, et al. Four-dimensional data assimilation for coupled physical-acoustical fields; P.F.J. Lermusiaux, C.-S. Chiu. Source localization in a highly variable shallow water environment: Results from ASCOT-01; M. Siderius, et al. Experimental testing of the blind ocean acoustic tomography concept; S.M. Jesus, et al. Benchmarking geoacoustic inversion methods for range dependent waveguides; N.R. Chapman, et al. Adjoint-assisted inversion for shallow water environment parameters; P. Hursky, et al. Tidal Effects on MFP via the INTIMATE96 test; A. Tolstoy, et al. Multipath effect on DPCA micronavigation of a synthetic aperture sonar; L. Wang, et al. Sea surface simulator for testing a synthetic aperture sonar; B. Davis, et al. Using a faceted rough surface environmental model to simulate shallow-water SAS imagery; A.J. Hunter, et al. A study of ping-to-ping coherence of the seabed response; L. Pautet, et al.Variability of the acoustic response from spherical shells buried in the seabed by model-based analysis of the at-sea data; A. Tesei, et al. Section 5: Sonar signal processing and performance predictions. Performance bounds on the detection and localization in a stochastic ocean; A.B. Baggeroer, H. Schmidt. Robust adaptive processing in littoral regions with environmental uncertainty; L.M. Zurk, et al. A robust model-based algorithm for localizing marine mammal transients; C.O. Tiemann, et al. Assessment of the impact of uncertainty in seabed geoacoustic parameters on predicted sonar performance; M.K. Prior, et al. Reverberation envelope statistics and their dependence on sonar beamwidth and bandwidth; D.A. Abraham, A.P. Lyons. The role of nowcast and forecast input parameters for range dependent transmission models; J.S. Sendt, et al. Are current environmental databases adequate for sonar predictions in shallow water? C.M. Ferla, F.B. Jensen. Yellow Sea acoustic uncertainty caused by hydrographic data error; P.C. Chu, et al. Detection of sonar induced measurement uncertainties in environmental sensing: A case study with the toroidal volume search sonar; C. de Moustier, T.C. Gallaudet. Environmental variability of the LBVDS sea tests; S. Sutherland-Pietrzak, E. McCarthy. AREA: Adaptive Rapid Environmental Assessment; H. Schmidt. Environmental adaptive sonar control in a tactical setting; W.L.J. Fox, et al. Transfer of uncertainties through physical-acoustical-sonar and end-to-end systems: A conceptual basis; A.R. Robinson, et al. Sonar performance predictions incorporating environmental variability; P. Abbot, I. Dyer. Author Index.