other particulate matter in the atmosphere. In general,
the contribution of absorption to propagation loss is
small.
l LOSS accounts for ducting in evaporation
ducts, surface-based ducts, and low-elevated ducts,
provided the transmitter of the radar antenna is
within the duct.
The program does not properly
account for the over-the-horizon region for
low-elevated ducts when the bottom of the duct is above
the transmitter or radar antenna height. The calculated
path-loss values for the LOSS display will generally be
greater than the corresponding actual values. The errors
become less the higher the elevated duct is above the
transmitter or radar antenna height and should be
insignificant when the separation exceeds a few
thousand feet.
l The LOSS display can be used for the following
applications:
— Long-range air-search radars, surface-based
or airborne.
— Surface-search radars when employed
against low-flying air targets and
surface-based combatants that are large in
comparison to the sea state.
— To determine the intercept range of radar,
sonobuoy, or communications systems by an
ESM receiver. The ESM receiver used in
this application is chosen during preparation
of the ESM system for LOSS.
— Airborne surface-search radars when the
surface radar target is large in comparison to
the sea clutter. The target should also beat
a considerable distance from the radar.
LOSS considers targets as point sources.
Close in-range targets are seen by the radar
as distributed targets.
— Surface-to-air or air-to-air communications
systems.
. The LOSS display
following applications:
— Most types of
radar.
should not be used for the
gun or missile fire-control
— Small surface targets, for example,
periscopes.
. Prior to running this program, a primary
refractivity data set must be selected.
l Output from this program is classified and should
be labeled corresponding to the classification of the EM
system used to produce the display.
. Effects of wave splash, wave shadowing,
bobbing, and rolling are not taken into account for
sonobuoy output.
FUNCTIONAL DESCRIPTION
LOSS produces an EM path loss with respect to
range display, and it plots the path-loss thresholds
(computed using the user-specified free-space ranges if
not entered) as horizontal lines on the display. The
program is structured so that two processing paths exist,
and the path taken depends upon the type of system used
(surface-based or airborne).
Figure 7-3 shows an example of the LOSS display.
The LOSS display is a graph of energy loss (dB) plotted
along range (nmi or km). There can be up to four
horizontal dotted lines present on the graph. These lines
correspond to the computed or entered free-space ranges
for the EM system. The intersections of the plotted line
and the horizontal lines indicate the path-loss threshold
values along the vertical axis and the range at which they
occur on the horizontal axis. The path-loss threshold is
the minimum amount of energy necessary for the EM
system to detect, communicate, or be detected. The
plotted line may crisscross the horizontal lines due to
interference effects.
ELECTRONIC SUPPORT MEASURE
(ESM) PROGRAM
LEARNING OBJECTIVES: Describe the
necessary data for the ESM program and
interpret the output. Identify limitations and
assumptions. Interpret the ESM range tables.
The ESM program is used to calculate and display
the maximum intercept ranges of U.S. and Russian
surface emitters by user-specified ESM receivers. Input
to the program consists of receiver and emitter
characteristics from the data base file and a refractivity
data set from the environmental data files (EDFs). The
refractivity data set consists of a modified refractive
index (M-unit) profile with respect to height, the height
of the evaporation duct, and the surface wind speed.
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