In this chapter we will be discussing information on
a number of oceanography products and environmental
factors of utmost importance to the Aerographers
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 oceans 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 users
NODDS, the required contouring, streamlining,
shading, and so forth, is performed automatically until
all products are in a ready-to-display format.
The NODDS Users 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 lets look at
some of the products available from NODDS.
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.
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.
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.