Change Detection of Marine Environments Using Machine Learning

NPS NRP Project PosterChange Detection of Marine Environments Using Machine LearningHQMC Intelligence Department (I)This research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.

Change Detection of Marine Environments Using Machine Learning

NPS NRP Technical ReportChange Detection of Marine Environments Using Machine LearningHQMC Intelligence Department (I)This research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.

Change Detection of Marine Environments Using Machine Learning

NPS NRP Executive SummaryChange Detection of Marine Environments Using Machine LearningHQMC Intelligence Department (I)This research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.

Exhaust of Underexpanded Jets from Finite Reservoirs

The response of an underexpanded jet to a depleting finite reservoir is examined with experiments and simulations. An open-ended shock-tube facility with a variable reservoir length is used to obtain images of nitrogen- and helium-jet structures at successive instances during the blowdown from initial pressure ratios of up to 250. The reservoir and ambient pressures are simultaneously measured to obtain the instantaneous pressure ratio. We estimate the time scales for jet formation and reservoir depletion as a function of the specific heat ratio of the gas and the initial pressure ratio. The jet structure formation time scale is found to become approximately independent of the pressure ratio for ratios greater than 50. In the present work, no evidence of time dependence in the Mach disk shock location is observed for rates of pressure decrease associated with isentropic blowdown of a finite reservoir while the pressure ratio is greater than 15. The shock location in the finite-reservoir jet can be calculated from an existing empirical fit to infinite-reservoir jet data evaluated at the instantaneous reservoir pressure. For pressure ratios below 15, however, the present data deviate from a compilation of data for infinite-reservoir jets. A new fit is obtained to data in the lower-pressure regime. The self-similarity of the jet structure is quantified, and departure from similarity is noted to begin at pressure ratios lower than about 15, approximately the same ratio that limits existing empirical fits

Unsteady high-pressure flow experiments with applications to explosive volcanic eruptions

Motivated by the hypothesis that volcanic blasts can have supersonic regions, we investigate the role of unsteady flow in jets from a high-pressure finite reservoir. We examine the processes for formation of far-field features, such as Mach disk shocks, by using a shock tube facility and numerical experiments to investigate phenomena to previously unobtained pressure ratios of 250:1. The Mach disk shock initially forms at the edges of the vent and moves toward the centerline. The shock is established within a few vent diameters and propagates downstream toward the equilibrium location as the jet develops. The start-up process is characterized by two different timescales: the duration of supersonic flow at the nozzle exit and the formation time of the Mach disk shock. The termination process also is characterized by two different timescales: the travel time required for the Mach disk shock to reach its equilibrium position and the time at which the Mach disk shock begins significantly to collapse away from its equilibrium position. The critical comparisons for the formation of steady state supersonic regions are between the two start-up timescales and the termination timescales. We conclude that for typical vulcanian eruptions and the Mount St. Helens directed blast, the Mach disk shock could have formed near the vent, and that there was time for it to propagate a distance comparable to its equilibrium location. These experiments provide a framework for analysis of short-lived volcanic eruptions and data for benchmarking simulations of jet structures in explosive volcanic blasts

Morphological response of variable river discharge and wave forcing at a bar-built estuary

17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.1016/j.ecss.2021.107438Observations of morphological evolution at Carmel River State Beach, Carmel, CA, USA, were made during two winter periods where the estuary underwent transitions from closed to open states episodically during each observation period. However, each winter was climatologically distinct: the first (Dec 2016–May 2017) was a high river discharge year (several events >200 m³ /s) with westerly offshore waves and the second (Dec 2017–May 2018) was a low river discharge year with northwesterly offshore waves. The morphological response of the beach was measured using Structure-from-Motion from both aircraft and unmanned aerial vehicles (UAVs) and shows two distinct seasonal trends. The first (in 2016–2017) indicates rapid (hours) and frequent (days-weeks) migration of the river breach channel across the span of the beach. The second (in 2017–2018) indicates no migration of the initial breach channel, despite multiple breach events. Analysis of the offshore wave energy using the Coastal Data Information Program (CDIP) hindcast model results indicate a stronger longshore wave radiation stress during the migratory breach year. In addition, discharge rates during this year were more than three times stronger than the non-migratory year, indicating a stronger offshore jet from the breach site. These observations support the hypothesis that migration requires both a strong river discharge and a longshore wave radiation stress component.Naval Postgraduate School Naval Research ProgramOffice of Naval Research-CRUSER Progra

Trident Room Podcast Episode 3: Prof. Mara Orescanin, Oceanography and the Navy [audio]

The Trident Room Podcast officially started broadcasting in the summer of 2020. It was created by an HSI/OR student who wanted to capture conversations he was having with the impressive array of faculty, students, and staff roaming the halls of NPS. Podcasting provides a direct and unfettered connection with listeners, and he wanted to bring that same kind of informative, yet intimate exchange to the Naval Postgraduate School community.Professor Mara Orescanin discusses her drone research and her passion of engaging students in critical thinking.The Trident Room Podcast was developed with support provided by the Naval Postgraduate School Alumni Association and Foundation (NPSAAF)

Experimental simulations of the May 18, 1980 directed blast at Mount St. Helens, WA

The 1980 directed blast at Mount St. Helens erupted from a high-pressure magma chamber into atmospheric conditions at a pressure ratio of ~150:1, producing a high-velocity dusty gas flow. Decompression from even modestly high pressure ratios (>2:1) produces supersonic flow and thus, this event was modeled as a supersonic underexpanded jet by Kieffer (1981). Steady-state underexpanded jets have a complex geometrical structure in which there is an abrupt, stationary, normal shock wave, called the Mach disk shock. For steady flow, a log-linear relationship between pressure ratio and Mach disk standoff distance, known as the Ashkenas-Sherman relation, is valid for pressure ratios above 15:1 given by x/D=0.67(Rp)^(0.5) where Rp is the pressure ratio, and x/D is the standoff distance normalized to vent diameter. The effects of unsteady discharge from a finite reservoir and application to Mount St. Helens have not been previously investigated. In order to simulate the blast, we use laboratory and numerical experiments of unsteady flow from a finite reservoir to examine jet structure. The reservoir and test section correspond to the magma chamber and ambient atmospheric conditions at Mount St. Helens respectively. We completed a series of laboratory experiments in which we varied the initial pressure ratio, reservoir length and reservoir gas (nitrogen, helium). The numerical simulations show that the Mach disk initially forms close to the vent and then travels downstream to its equilibrium position. The experiments show that as the reservoir pressure continuously decreases during the venting, or “blowdown”, the Mach disk shock continuously moves back toward the reservoir after its formation at the equilibrium position. Results of these experiments indicate that above a pressure ratio of 15:1, the Mach disk standoff distance for unsteady flow falls on the empirical Ashkenas-Sherman curve for steady flow. We present a new relation for the location of the Mach disk shock for pressure ratios below 15:1 given by x/D=0.41(Rp)^(0.66). The results indicate no dependence of the normalized Mach disk location on the finiteness of the reservoir. These results may be of interest not only for high pressure eruptions such as Mount St. Helens, but to low pressure steam eruptions as well because helium is a good analog to steam

Effects of a shallow flood shoal and friction on hydrodynamics of a multiple-inlet system

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 6055–6065, doi:10.1002/2016JC012502.Prior studies have shown that frictional changes owing to evolving geometry of an inlet in a multiple inlet-bay system can affect tidally driven circulation. Here, a step between a relatively deep inlet and a shallow bay also is shown to affect tidal sea-level fluctuations in a bay connected to multiple inlets. To examine the relative importance of friction and a step, a lumped element (parameter) model is used that includes tidal reflection from the step. The model is applied to the two-inlet system of Katama Inlet (which connects Katama Bay on Martha's Vineyard, MA to the Atlantic Ocean) and Edgartown Channel (which connects the bay to Vineyard Sound). Consistent with observations and previous numerical simulations, the lumped element model suggests that the presence of a shallow flood shoal limits the influence of an inlet. In addition, the model suggests an increasing importance of friction relative to the importance of the step as an inlet shallows, narrows, and lengthens, as observed at Katama Inlet from 2011 to 2014.ASD(R&E); NOAA Sea Grant; NSF; ONR2018-01-2

Federated Bayesian Deep Learning: The Application of Statistical Aggregation Methods to Bayesian Models

Federated learning (FL) is an approach to training machine learning models that takes advantage of multiple distributed datasets while maintaining data privacy and reducing communication costs associated with sharing local datasets. Aggregation strategies have been developed to pool or fuse the weights and biases of distributed deterministic models; however, modern deterministic deep learning (DL) models are often poorly calibrated and lack the ability to communicate a measure of epistemic uncertainty in prediction, which is desirable for remote sensing platforms and safety-critical applications. Conversely, Bayesian DL models are often well calibrated and capable of quantifying and communicating a measure of epistemic uncertainty along with a competitive prediction accuracy. Unfortunately, because the weights and biases in Bayesian DL models are defined by a probability distribution, simple application of the aggregation methods associated with FL schemes for deterministic models is either impossible or results in sub-optimal performance. In this work, we use independent and identically distributed (IID) and non-IID partitions of the CIFAR-10 dataset and a fully variational ResNet-20 architecture to analyze six different aggregation strategies for Bayesian DL models. Additionally, we analyze the traditional federated averaging approach applied to an approximate Bayesian Monte Carlo dropout model as a lightweight alternative to more complex variational inference methods in FL. We show that aggregation strategy is a key hyperparameter in the design of a Bayesian FL system with downstream effects on accuracy, calibration, uncertainty quantification, training stability, and client compute requirements.Comment: 22 pages, 9 figure