The restrictions as well as the principles taken for granted in using the LOSS program are as follows:

. LOSS assumes horizontal homogeneity (horizontal changes in the refractivity structure of the atmosphere are not accounted for).

. LOSS is valid only for EM systems with frequencies between 100 MHz and 20 GHz.

. LOSS does not include any effects produced by sea or land clutter in the calculation of detection or communication ranges. This shortcoming may be important to air-search radars in the detection of targets flying above surface-based ducts or strong evaporation ducts, but it is not expected to significantly affect the predicted enhanced detection ranges within a duct. Specifically, for surface-based ducts, the actual detection capability at some ranges maybe reduced for air targets flying above the duct.

. The model that calculates the LOSS display for surface-based systems is valid only for antenna heights between 1 and 200 m inclusive, and the program will not accept heights outside these bounds, except in the case of sonobuoys where the height is nominally 0.5 m.

. The airborne-loss display model does not include sea-reflected interference effects, which could cause both reduced and enhanced path loss for low-flying radar or radar targets. The surface-loss display model does not account for sea-reflected interference effects. Only the minimum path loss within each lobe of the interference region is plotted when the spacing between lobes becomes very close.

. There is no account made for absorption of EM energy from oxygen, water vapor, fog, rain, snow, or other particulate matter in the atmosphere. In general, the contribution of absorption to propagation loss is small.

. 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.

. 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.

. 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.

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.

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