CHAPTER 9 OPERATIONAL OCEANOGRAPHY In this chapter we will be discussing information on a  number  of  oceanography  products  and  environmental factors  of  utmost  importance  to  the  Aerographer’s Mate. By  being  familiar  with  these  products,  parameters, limitations, and request procedures the Aerographer can provide  the  on-scene  commander  with  a  detailed accounting  of  environmental  conditions  above,  as  well as below, the ocean’s surface. We will first discuss the products available from the Navy   Oceanographic   Data   Distribution   System (NODDS).   NODDS   was   developed   in   1982   as   a means   to   make   FLENUMETOCCEN   (FNMOC) environmental  products  available  to  METOCFACS  and 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 distributed in December 1991, and it was unique in its approach  to  environmental  data  communications.  Once a user has defined the products desired for a specific area, an automatic process of acquiring data is initiated. Using   a   commercial   “off   the   shelf”   licensed communications software package, the system dials FLENUMMETOCCEN and requests the data fields from a security shell in a host mainframe computer. The required data is extracted from one of the global data bases as a compacted ASCII transmission which is generated  for  each  field/product.  By  transmitting  field data   and   limiting   the   area   of   extraction,   the transmissions  are  small  and  communications  are efficient. Once the raw data is received by the user’s NODDS,  the  required  contouring,  streamlining, shading, and so forth, is performed automatically until all  products  are  in  a  ready-to-display  format. The NODDS User’s Manual contains explanations of system functions and step-by-step procedures for using the NODDS terminal, By selecting the “Convert Data” option of the “Data Manager” file from the main menu the user can convert the NODDS geographic displays to alphanumeric displays. Underway units may also access NODDS data using a VHF Stel Modem along  with  a  STU-III  Secure  phone.  There  are limitations associated with all of the NODDS acoustic products  listed  in  this  section,  such  as  low  grid resolutions and graphic depiction errors. A general description  of  each  product  will  be  covered  along with  example  outputs.  Further  discussion  on parameter derivation and user provided inputs may be   found   in   the   NODDS   Products   Manual, FLENUMMETOCCENINST  3147.1.  Now  let’s  look  at some of the products available from NODDS. CONVERGENCE ZONE RANGE (CZR) LEARNING   OBJECTIVES   Recognize characteristics   of   a   convergence   zone. Evaluate  CZR  products.  Identify  the  two graphic  outputs  of  the  product. The  CZR  product  predicts  the  expected  ranges  to the first convergence zone for a sonar. Convergence zones are regions in the deep ocean where sound rays, refracted from the depths, are focused at or near the surface. Convergence zones are repeated at regular range intervals and have been observed out to 500 nmi or more. Convergence zone ranges are those ranges capable of being achieved when operating sonar in the path of a convergence zone. SOUND DISTRIBUTION The distribution of sound throughout the deep ocean is characterized by a complex series of shadow zones and convergence zones.    The presence and extent of these zones are determined by the sound speed profile, the location of the surface, bottom, and source relative to the profile, and the existence of caustics. CAUSTICS A caustic is the envelope formed by the intersection of adjacent rays. When a caustic intersects the sea surface or a region at or near the surface, a convergence zone is created. Convergence zones are regions of high sound intensity. Thus, a receiver may be expected to pick  up  high  sound  intensity  gain  within  a  convergence zone versus outside of it, where only a single strong propagation  path  occurs. 9-1