Eric L. Gottshall

Satellite data assimilation for improvement of Naval undersea capability

Impact of satellite data assimilation on naval undersea capability is investigated using ocean hydrographic products without and with satellite data assimilation. The former is the Navy’s Global Digital Environmental Model (GDEM), providing a monthly mean; the latter is the Modular Ocean Data Assimilation System (MODAS) providing synoptic analyses based upon satellite data. The two environmental datasets are taken as the input into the Weapon Acoustic Preset Program to determine the suggested presets for an Mk 48 torpedo. The acoustic coverage area generated by the program will be used as the metric to compare the two sets of outputs. The output presets were created for two different scenarios, an anti-surface warfare (ASUW) and an anti-submarine warfare (ASW); and three different depth bands, shallow, mid, and deep. After analyzing the output, it became clear that there was a great difference in the presets for the shallow depth band, and that as depth increased, the difference between the presets decreased. Therefore, the MODAS product, and in turn the satellite data assimilation, had greatest impact in the shallow depth band. The ASW presets also seemed to be slightly less sensitive to differences than did presets in the ASUW scenario.

Sensitivity of Satellite Altimetry Data Assimilation on a Weapon Acoustic Preset

The purpose of this research is to assess the benefit of assimilating satellite altimeter data for naval undersea warfare. To accomplish this, sensitivity of the weapon acoustic preset program (WAPP) for the Mk 48 variant torpedo to changes in the sound-speed profile (SSP) is analyzed with SSP derived from the modular ocean data assimilation system (MODAS). The MODAS fields differ in that one uses altimeter data assimilated from three satellites while the other uses no altimeter data. The metric used to compare the two sets of outputs is the relative difference in acoustic coverage area generated by WAPP. Output presets are created for five different scenarios, two anti surface warfare (ASTJW) scenarios, and three antisubmarine warfare (ASW) scenarios, in each of three regions: the East China Sea, Sea of Japan, and an area south of Japan that includes the Kuroshio currents. Analysis of the output reveals that, in some situations, WAPP output is very sensitive to the inclusion of the altimeter data because of the resulting differences in the subsurface predictions. The change in weapon presets can be so large that the effectiveness of the weapon may be affected.

Ocean nowcast/forecast systems for improvement of Naval undersea capabilities

The U.S. Navy is a major investor in ocean model development. The pay-off of such an investment is the value-added ocean nowcast/forecast systems on naval operations and warfare effectiveness. The purpose of this paper is to investigate the value added of the Navy’s nowcast/forecast system to naval antisubmarine warfare (ASW) and anti-surface warfare (ASUW). The nowcast/forecast versus observational fields were used by the Weapon Acoustic Preset Program (WAPP) to determine the suggested presets for Mk 48 variant torpedo. The metric used to compare the two sets of outputs is the relative difference in acoustic coverage area generated by WAPP. Output presets are created for five different scenarios, two ASUW scenarios and three ASW scenarios in the South China Sea. The same metrics used in the nowcast/forecast case were used to generate and compare the acoustic coverage. Analysis of the output reveals that the ocean forecast system outperformed the nowcast system in most scenarios. (MODAS) is a commonly used nowcast system, which is built on the base of the optimal interpolation (statistical model). The Navy Coastal Ocean Model (NCOM) is a Navyused ocean forecast system, which is built on the base of the Princeton Ocean Model (POM). MODAS uses climatology as an initial guess and assimilates satellite and in situ measurements such as altimetry, conductivity-temperature-depth (CTD), expendable bathythermographs (XBT), and ARGO casts. NCOM (physical model) forecasts the ocean environment using observational data such as temperature, salinity, and velocity. Representation of the Navy’s nowcast (MODAS) and forecast (POM) systems for ocean environment (SSP through T, S profiles) was verified using the CTD data collected from the South China Sea Monsoon Experiment (SCSMEX) in April – June 1998 (Chu et al., 2001, 2004b). The errors have a Gaussian-type distribution with mean temperature nearly zero and mean salinity of -0.2 ppt. However, evaluation of a value-added ocean nowcast/forecast system on the naval undersea capability has yet been conducted. At the combat level, acoustic detection of torpedoes is extremely important for undersea warfare. This is because undersea warfare has changed considerably since Admiral Farragut gave his famous battle order over a century ago. Human ingenuity and advancements in technology have taken underwater weapons from floating mines and spar torpedoes to the fast-moving, self-guided, homing torpedoes we have in the fleet today. From submarine warfare to warship design and tactics development, the modern torpedo is one of the fundamental drivers of 20th century naval warfare (cited from http://www.navy.mil/ navydata/cno/n87/usw/ i s sue_14/ torpedoes.html). In this study, the Weapon Acoustic Preset Program (WAPP) for the Mk48 torpedo is used for such an evaluation. 2. Oceanographic Observations 2.1. South China Sea The South China Sea (SCS) is a semi-enclosed tropical sea located between the Asian land mass to the north and west, the Philippine Islands to the east, Borneo to the southeast, and Indonesia to the south (Figure 1), covering a total area of 3.5× 10 km. It includes the shallow Gulf of Thailand and connections to the East China Sea (through Taiwan Strait), the Pacific Ocean (through Luzon Strait), Sulu Sea, Java Sea (through Gasper and Karimata Straits) U

Assessment of ocean prediction model for naval operations using acoustic preset

The outcome of a battlefield engagement is often determined by the advantages and disadvantages held by each adversary. On the modern battlefield, the possessor of the best technology often has the upper hand, but only if that advanced technology is used properly and efficiently. In order to exploit this advantage and optimize the effectiveness of high technology sensor and weapon systems, it is essential to understand the impact on them by the environment. In the arena of anti-submarine warfare (ASW), the ocean environment determines the performance of the acoustic sensors employed and the success of any associated weapon systems. Since acoustic sensors detect underwater sound waves, understanding how those waves propagate is crucial to knowing how the sensors will perform and being able to optimize their performance in a given situation. To gain this understanding, an accurate depiction of the ocean environment is necessary. How acoustic waves propagate from one location to another under water is determined by many factors, some of which are described by the sound speed profile (SSP). If the environmental properties of temperature and salinity are known over the entire depth range, the SSP can be compiled by using them in an empirical formula to calculate the expected sound speed in a vertical column of water. One way to determine these environmental properties is to measure them in situ, such as by conductivity-temperature-depth or expendable bathythermograph (XBT) casts. This method is not always tactically feasible and only gives the vertical profile at one location producing a very limited picture of the regional ocean structure. Another method is to estimate the ocean conditions using numerical models. The valued-aided ocean prediction models to ASW are assessed in this study. Such quantitative analyses offer a means to optimize the ASW requirements and technical capabilities of new weapon systems. We use observed and modeled 3D fields of temperature, salinity, and sound speed. Compare model profiles to observed profiles. Do ocean models predict the vertical features of the observational data? We run representative modeled and observed SSP profiles through Navys acoustic models to see if there is an acoustic difference in propagation and weapon preset

Satellite data assimilation for naval undersea capability improvement

Impact of the satellite data assimilation on the naval undersea capability is investigated using the ocean hydrographic data without and with satellite data assimilation. The former is the Navys Global Digital Environmental Model (GDEM) providing the monthly mean; and the latter is the Modular Ocean Data Assimilation System (MODAS) proving the synoptic data. The two environmental datasets are taken as the input into the Weapon Acoustic Preset Program to determine the suggested presets for a Mk 48 torpedo. The acoustic coverage area generated by the program will be used as the metric to compare the two sets of outputs. The output presets were created for two different scenarios, an ASUW and an ASW, and three different depth bands, shallow, mid, and deep. After analyzing the output, it became clear that there was a great difference in the presets for the shallow depth band, and that as depth increased, the difference between the presets decreased. Therefore, the MODAS data (in turn the satellite data assimilation) was optimized in the shallow depth band. The ASW presets also seemed to be slightly more resistant to differences in the presets than was the ASUW scenario.