Environmental Information for Naval Warfare (2003) / Chapter Skim
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3. Nature of the Problem: Sources and Limitations of Metoc Knowledge
3. Nature of the Problem: Sources and Limitations of Metoc Knowledge
Pages 53-69
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From page 53... ...
These parameters affect, among other things, visibility, ocean acoustics, and the propagation of electromagnetic waves. If some determination of required environmental parameters can be made for any particular mission, the next question is "Can the values of the required parameters be determined at the particular time and place of the mission and to the requisite accuracy?
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From page 54... ...
However, as the spatial and temporal scales of processes become smaller, the influence of nonlinearities in each environmental system becomes larger, resulting in greater uncertainty in the ability to predict the state of the environmental system. At the smallest time- and space scales, nonlinearities result in environmental processes that are dominated by stochastic processes such that
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From page 55... ...
A significant component of naval research into these areas would be beneficial because not only would it help establish additional constraints on understanding environmental information but it would also help shape assessment of the need for sensors and sensor arrays. The range of physical processes in the ocean and atmosphere and the interactions between them are fundamental in determining the physical structure that is encountered at any time and location.
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From page 56... ...
Third, the urgent need for initial and boundary condition information provides a strong rationale for developing data assimilative modeling efforts and acquiring data for input to these models. Without such efforts it is unrealistic to expect oceanic and atmospheric circulation models to have good predictive skill over a wide range of time- and space scales.
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From page 57... ...
Intercomparisons of the models used for ENS O predictions show that the forecasts are considerably better than those obtained by simply using persistence of features to determine future conditions (Latif et al., 1998~. Although the ENSO models have proven predictive skill, they still need improvement and development, especially in regard to specification of forcing fields, model initialization, and data assimilation capability (Stockdale et al., 1998~.
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From page 58... ...
The use of satellite data in data assimilation models has brought significant improvement to ocean weather forecasts, particularly in the tropics and southern hemisphere where conventional meteorological data are sparse. These global models typically provide reliable information on the scale of 100 km and greater.
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From page 59... ...
Sea breezes, which depend critically on relatively small-scale thermal gradients and near-shore terrain, are another phenomenon that can be predicted by models in a broad sense but can have significant errors in locally predicted values. In many cases, experienced forecasters who are familiar with the performance of the typical forecasting models can correct these model errors based on their own knowledge.
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From page 60... ...
Thus, it is unlikely that we will ever be able to predict the exact nature of boundary layer structure and cloud formation on small time- and space scales. DATA ACQUISITION Environmental data used by the Navy for various purposes can come from many sources.
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From page 61... ...
. The undersea warfare for surface ships, typically cruisers and destroyers, concerns self-defense, ASW, and CVBG escort.
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From page 62... ...
The MODAS effort fuses archival databases, satellite altimetric data, circulation models, and in situ data for these predictions. The needed scales for accurate predictions are fundamental and still very much of a research issue.
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From page 63... ...
Understanding how ocean and seafloor conditions affect acoustic properties can provide important tactical advantages to U.S. Navy submarines engaged in protecting surface vessels or other assets threatened by enemy submarines (Photo courtesy of the U.S.
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From page 64... ...
The components of the sonar equation provide a useful guide to the way environmental information is used in undersea warfare. For passive systems: SE=SL-TL-NL+AG+SPg-RD where SE is the signal excess, SL the source level, TL the transmission loss, NL the ambient noise level, AG the spatial array gain, SPg the signal processing gain, and RD the recognition differential.
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From page 65... ...
Stratigraphic models are based on reflection/refraction profiles. Genetic algorithms are then used to tune the layer parameters of a geoacoustic model such that there is less than +2 dB frequency averaged difference between the parabolic equation and 1/3 octaves of the broadband data.
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From page 66... ...
Insertion] systems are based on noise cancellation algorithms whose performance strongly depends on the distribution of the discrete components of the ambient noise field to improve the array gain term in the sonar equation.
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From page 67... ...
conducts a tight navigational drill. Frigates fulfill a "Protection of Shipping" mission as anti-submarine warfare combatants for amphibious expeditionary forces, underway replenishment groups, and merchant convoys (Photo courtesy of the U.S.
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From page 68... ...
All these issues place a premium on accurate predictions of transmission loss and the uncertainty associated with them. It should be noted that the shorter ranges imply less reliance on long-range refracted-reflected and refracted-surface reflected paths and more on bottominteracting paths.
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From page 69... ...
SUMMARY The spatial and temporal scales of various environmental processes may have a profound effect on efforts to predict future states. Areas where inadequate predictive skill is of concern require greater numbers and more recent observations, to either support data assimilation or supplant predictions altogether.
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