Naval Postgraduate School

About: Naval Postgraduate School is a education organization based out in Monterey, California, United States. It is known for research contribution in the topics: Tropical cyclone & Nonlinear system. The organization has 5246 authors who have published 11614 publications receiving 298300 citations. The organization is also known as: NPS & U.S. Naval Postgraduate School.

A simple neutrally buoyant sensor for direct measurement of particle velocity and intensity in water

Abstract: Acoustic particle velocity is commonly inferred from measurement of pressure or pressure gradient; however, in water, direct measurement is simple. A moving‐coil sensor embedded in a neutrally buoyant package produces a voltage directly proportional to the particle velocity in the surrounding fluid for frequencies above the mass‐spring resonance. Leslie et al. [J. Acoust. Soc. Am. 28, 711–715 (1956)] built such a sensor by mounting a moving‐coil element inside a hollow brass sphere. The sensor described in this paper is identical in principle but is considerably easier to fabricate. Useful from tens of hertz to several kilohertz, this sensor consists of a glass‐ microballoon‐and‐epoxy composite cast around a small, commercial geophone. The sensor is inexpensive, rugged, and has good immunity to interference. In conjunction with a pressure hydrophone, acoustic intensity can be measured without the errors associated with subtraction of nearly equal signals (as in the two‐hydrophone method).

A Nyquist folding analog-to-information receiver

Abstract: Many radar and communications applications require detection and estimation of signal information across an extremely wide radio frequency (RF) bandwidth. In practice, however, direct digitization of this broadband RF environment is problematic. Physical limitations in analog-to-digital converter (ADC) technology restrict the total bandwidth that can be digitized, as well as the ability to digitize high RF signals directly. This paper describes a novel ldquoanalog-to-informationrdquo receiver, motivated by recent developments in compressed sensing (CS), which overcomes both of these challenges in certain settings. The proposed receiver performs frequency modulated pulsed sampling at sub-Nyquist/Shannon rates to compress a broadband RF environment into an analog interpolation filter. The RF sample clock modulation induces a Nyquist-zone dependent frequency modulation on the received signals, allowing separation and recovery of the signal information from a sparse broadband RF environment.

Role of the upper ocean in the energy budget of Arctic sea ice during SHEBA

Abstract: [1] As part of the 1997–1998 Surface Heat Budget of the Arctic Experiment (SHEBA), a nearly yearlong record of upper ocean observations was obtained below a drifting ice camp in the Beaufort Gyre. A combination of observational and numerical modeling techniques are used to estimate heat fluxes across the under-ice ocean boundary layer. Over the Canada Basin, the upper pycnocline contained moderate heat, but strong stratification effectively insulated it from mixed layer turbulence. Average resulting heat fluxes at the base of the mixed layer (Fpyc) and at the ocean-ice interface (F0) were small (0.3–1.2 and 0.2 W m−2, respectively). Over the Chukchi Borderlands, the presence of relatively warm and salty Pacific origin water increased upper pycnocline heat content and reduced stratification, which permitted moderate Fpyc and F0 (2.1–3.7 and 3.5 W m−2, respectively). Solar insolation was the dominant heat source during the final, summertime portion of the drift. During the heating period, Fpyc was relatively small (0.4–1.5 W m−2) while F0 was large (16.3 W m−2). The drift-averaged value of F0 was 7.6 W m−2. Energy budgets for the ice cover were constructed. The oceanic contribution to the budget during the portion of the drift over the Chukchi Borderlands, supported by entrainment of heat stored in the upper pycnocline, was responsible for a 15% reduction in ice growth. During the summer heating season, the F0 estimates were larger than the latent energy changes associated with basal melting.