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NAVEDTRA 12853 Relink Eo 01-`17-97 CHAPTER 9 OPERATIONAL OCEANOGRAPHY In this chapter we will be discussing information on description of each product will be covered along a number of oceanography products and environmental with example outputs. Further discussion on factors of utmost importance to the Aerographer’s parameter derivation and user provided inputs may Mate. be found in the NODDS Products Manual, FLENUMMETOCCENINST 3147.1. Now let’s look at By being familiar with these products, parameters, some of the products available from NODDS. limitations, and request procedures the Aerographer can provide the on-scene commander with a detailed accounting of environmental conditions above, as well CONVERGENCE ZONE as below, the ocean’s surface. RANGE (CZR) We will first discuss the products available from the Navy Oceanographic Data Distribution System LEARNING OBJECTIVES Recognize (NODDS). NODDS was developed in 1982 as a characteristics of a convergence zone. means to make FLENUMETOCCEN (FNMOC) Evaluate CZR products. Identify the two environmental products available to METOCFACS and graphic outputs of the product. METOCDETS who had no direct access to this data. Through the years, the system has grown in use as product support has expanded. NODDS 3.0 was The CZR product predicts the expected ranges to distributed in December 1991, and it was unique in its the first convergence zone for a sonar. Convergence approach to environmental data communications. Once zones are regions in the deep ocean where sound rays, a user has defined the products desired for a specific refracted from the depths, are focused at or near the area, an automatic process of acquiring data is initiated. surface. Convergence zones are repeated at regular Using a commercial “off the shelf” licensed range intervals and have been observed out to 500 nmi communications software package, the system dials or more. Convergence zone ranges are those ranges FLENUMMETOCCEN and requests the data fields capable of being achieved when operating sonar in the from a security shell in a host mainframe computer. The path of a convergence zone. required data is extracted from one of the global data bases as a compacted ASCII transmission which is SOUND DISTRIBUTION generated for each field/product. By transmitting field data and limiting the area of extraction, the The distribution of sound throughout the deep ocean transmissions are small and communications are is characterized by a complex series of shadow zones efficient. Once the raw data is received by the user’s and convergence zones. The presence and extent of NODDS, the required contouring, streamlining, these zones are determined by the sound speed profile, shading, and so forth, is performed automatically until the location of the surface, bottom, and source relative all products are in a ready-to-display format. to the profile, and the existence of caustics. The NODDS User’s Manual contains explanations of system functions and step-by-step procedures for CAUSTICS using the NODDS terminal, By selecting the “Convert Data” option of the “Data Manager” file from the main A caustic is the envelope formed by the intersection menu the user can convert the NODDS geographic of adjacent rays. When a caustic intersects the sea displays to alphanumeric displays. Underway units surface or a region at or near the surface, a convergence may also access NODDS data using a VHF Stel Modem zone is created. Convergence zones are regions of high along with a STU-III Secure phone. There are sound intensity. Thus, a receiver may be expected to limitations associated with all of the NODDS acoustic pick up high sound intensity gain within a convergence products listed in this section, such as low grid zone versus outside of it, where only a single strong resolutions and graphic depiction errors. A general propagation path occurs. 9-1 CONVERGENCE ZONE REQUIREMENTS 1. A shaded convergence zone range display, which depicts areas of predicted range in nautical miles The existence of a convergence zone requires a (nmi). See figure 9-1. The amount of the shading negative sound-speed gradient at or near the surface indicates the range as follows: and a positive gradient below. In addition, there must be sufficient depth for usable convergence zone to Clear No CZs occur, that is, the water column must be deeper than Light Short range CZs the limiting depth by at least 200 fathoms. Medium Medium range CZs Heavy Long range CZs SOUND SPEED PROFILE 2. The shaded convergence zone usage product The sound speed profile of the deep ocean varies displays the areas of CZ probability based on an with latitude. In cold surface waters the depth of the analysis of depth and/or sound speed excess. See deep sound channel axis is shallow, the range to the figure 9-2. The amount of shading indicates the convergence zone is small, and the range interval probability as follows: between zones is small. In the Mediterranean Sea, the bottom water is much warmer than in the open Clear No CZs ocean and, consequently, the sound speed near the Medium Possible CZs bottom is higher. Since the limiting depth is much Heavy Reliable CZs shallower and the acoustic energy is refracted upward at a much shallower depth, ranges are much shorter than those generally found in the open ocean. BOTTOM BOUNCE RANGE (BBR) Although the acoustic characteristics and sufficient depth excess for convergence zone propagation may exist, bathymetry does play a role as LEARNING OBJECTIVES: Explain the the presence of a seamount or ridge may block the theory associated with the BBR. Evaluate convergence zone path. BBR products. Identify the two graphic outputs of the product. EXAMPLE OUTPUT The BBR product provides an estimate of the There are two graphic outputs available with the horizontal ranges expected for active sonars CZR product. operating in the bottom bounce mode. Figure 9-1.-A shaded convergence zone range display. 9-2 Figure 9-2.-A shaded contoured convergence zone probability display. In the bottom bounce mode, sound energy is signal and reduce the extent of the shadow zone. The directed towards the bottom. This path is successful major factors affecting bottom bounce transmission because the angle of the sound ray path is such that include the angle at which the sound ray strikes the the sound energy is affected to a lesser degree by bottom (grazing angle), the sound frequency, the sound speed changes than the more nearly horizontal bottom composition, and the bottom roughness. ray paths of other transmission modes (that is, surface duct, deep sound channel, convergence zone). EXAMPLE OUTPUT RANGE VERSUS DEPTH There are two graphic outputs available with the BBR product. Long-range paths can occur with water depths greater than 1,000 fathoms, depending on bottom 1. A shaded bottom bounce range display. The slope. At shallower depths high intensity loss is amount of shading indicates the range in nmi. See produced from multiple-reflected bottom bounce figure 9-3. paths that develop between the source and receiver. Since 85 percent of the ocean is deeper than 1,000 Light 1-5 nmi range fathoms and bottom slopes are generally less than or Medium 5-10 nmi range equal to 1°, relatively steep angles can be used for Heavy >10 nmi range single bottom reflection. With steeply inclined rays, transmission is relatively free from thermal effects at 2. A shaded bottom bounce probability display. This the surface, and the major part of the sound path is product provides estimates of the existence of low-loss in nearly stable water. bottom bounce paths between a sonar (source) and the target (receiver) based on the environmental and ACTIVE DETECTION geoacoustic parameters. See figure 9-4. The amount of shading indicates the probability conditions as Inactive detection, bottom bounce transmission follows: can produce extended ranges with fewer shadow zones because more than one single-reflected bottom Clear No path exists between the sonar and the target. These Medium Fair paths combine to produce an increase in the received Heavy Good 9-3 Figure 9-3.-A shaded bottom bounce range display. SONIC LAYER DEPTH (SLD) The SLD product displays the layer depth that can be used to locate areas of strong sound propagation in the near-surface layer. The sound field in a layer LEARNING OBJECTIVES Recognize depends greatly upon the layer depth. The deeper the characteristics of the SLD. Evaluate SLD product. Identify the graphic output layer, the farther the sound can travel without having products. to reflect off the surface and the greater is the amount of energy initially trapped. Figure 9-4.-A shaded bottom bounce probability display. 9-4 EXAMPLE OUTPUT In the mixed (or surface) layer the velocity of sound is susceptible to the daily and local changes of There is only one graphic output available with the heating, cooling, and wind action. Under prolonged SLD product. It is a shaded sonic layer depth display. calm and sunny conditions the mixed layer disappears The amount of shading indicates the range of depth in and is replaced by water where the temperature feet. See figure 9-5. decreases with depth. Clear <50 ft Light 50-100 ft ADVANTAGES OF THE SURFACE Medium 100– 350 ft DUCT Heavy >350 ft The potential for using these ducts in long-range SURFACE DUCT CUTOFF detection was not fully realized in early sonar FREQUENCY (SFD) operation since the equipment was generally in the supersonic frequency range (24 kHz and above) and attenuation due to leakage and absorption was great. LEARNING OBJECTIVES: Describe the As a result of the continuous trend in sonar toward two conditions under which a surface duct lower frequencies, the use of this duct is an aid for may occur. Evaluate the SFD product.
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