Sonar: empire, media and the politics of underground sound

This article traces the development of acoustic navigation media, or “sonar,” in the first half of the twentieth century, focusing on the relationships forged between underwater sound, electric media, and new techniques of listening. The central argument is that sonar shaped, and was shaped by, the expansion of warfare and capital underwater, and that this expansion came to be conceptualized by nautical organizations as dependent upon the control of underwater sound. Through analysis of key episodes in the conquest of subsea space, the author explores scientific, military, and commercial efforts to sense underwater objects and demonstrates how these efforts helped reconceptualize oceanic water as a component of undersea acoustic media and led to the material reorganization of the ocean’s acoustic field. Cet article retrace le développement de médias acoustiques de navigation ou <> dans la première moitié du vingtième siècle en mettant l’accent sur les rapports créés entre les sons sous-marins, les médias électriques et les nouvelles techniques d’écoute. L’argument central de l’article est qu’il y a eu une influence réciproque entre le sonar et l’expansion sous-marine de la guerre et du capital, et que les organisations nautiques ont commencé à concevoir cette expansion comme nécessitant le contrôle des sons sous-marins. Au moyen d’une analyse d’épisodes clés dans la conquête de l’espace sous-marin, l’auteur explore les efforts scientifiques, militaires et commerciaux pour repérer les objets sous l’eau et démontre comment ces efforts ont aidé à réaliser une nouvelle conception de l’eau océanique comme composante des médias acoustiques sous-marins, menant à une réorganisation matérielle du champ acoustique de l’océan.

Internal multiple elimination: Can we trust an acoustic approximation?

Correct handling of strong elastic, internal, multiples remains a challenge for seismic imaging. Methods aimed at eliminating them are currently limited by monotonicity violations, a lack of a-priori knowledge about mode conversions, or unavailability of multi-component sources and receivers for not only particle velocities but also the traction vector. Most of these challenges vanish in acoustic media such that Marchenko-equation-based methods are able in theory to remove multiples exactly (within a certain wavenumber-frequency band). In practice, however, when applied to (elastic) field data, mode conversions are unaccounted for. Aiming to support a recently published marine field data study, we build a representative synthetic model. For this setting, we demonstrate that mode conversions can have a substantial impact on the recovered multiple-free reflection response. Nevertheless, the images are significantly improved by acoustic multiple elimination. Moreover, after migration the imprint of elastic effects is considerably weaker and unlikely to alter the seismic interpretation.

Sparsity-promoting multi-parameter pseudoinverse Born inversion in acoustic media

Least-squares reverse-time migration has become the method of choice for quantitative seismic imaging. The main drawback of such scheme is that it requires many migration/modeling cycles. The convergence of least-squares reverse-time migration can be accelerated by using a suitable preconditioner. In the context of extended domain in a variable density acoustic media, the pseudoinverse Born operator is the recommended preconditioner, providing quantitative results within a single iteration. This method consists of two steps: application of the pseudoinverse Born operator, and inversion of two parameters using an efficient weighted least-squares approach based on the Radon transform. As expected, cross-talk artifacts are generated in the second step due to limited acquisition. We present a variable density pseudoinverse Born operator constrained with the ℓ1-norm for each model parameter to suppress the artifacts. The fast iterative shrinkage-thresholding algorithm is used to carry out the optimization problem. In classical iterative least-squares migration, the ℓ1-norm constraints would affect the whole imaging process. As the imaging method is split into two steps, only the Radon transform part is modified, where no wave-based operators are involved. Through numerical experiments, we verify the robustness of the proposed method against different migration artifacts including the parameter cross-talk, interfaces with abrupt truncations, sparse shot acquisition geometry, noisy data and high contrast complex structures.

Iterative solution of the Lippmann-Schwinger equation in strongly scattering acoustic media by randomized construction of preconditioners

Summary In this work the Lippmann-Schwinger equation is used to model seismic waves in strongly scattering acoustic media. We consider the Helmholtz equation, which is the scalar wave equation in the frequency domain with constant density and variable velocity, and transform it to an integral equation of the Lippmann-Schwinger type. To directly solve the discretized problem with matrix inversion is time-consuming, therefore we use iterative methods. The Born series is a well-known scattering series which gives the solution with relatively small cost, but it has limited use as it only converges for small scattering potentials. There exist other scattering series with preconditioners that have been shown to converge for any contrast, but the methods might require many iterations for models with high contrast. Here we develop new preconditioners based on randomized matrix approximations and hierarchical matrices which can make the scattering series converge for any contrast with a low number of iterations. We describe two different preconditioners; one is best for lower frequencies and the other for higher frequencies. We use the fast Fourier transform (FFT) both in the construction of the preconditioners and in the iterative solution, and this makes the methods efficient. The performance of the methods are illustrated by numerical experiments on two 2D models.