The restrictions as well as the principles taken for granted in using the COVER program areas follows:

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

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

. COVER 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 y, for surface-based ducts, the actual detection capability at some ranges may be reduced for air targets flying above the duct.

. The model that calculates the coverage display for surface-based systems is valid only for antenna heights between 1 and 100 m, and the program will not accept heights outside these bounds. The antenna heights for airborne systems are limited to the maximum height of the selected coverage system in the EM system data file.

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

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

. COVER accounts for ducting in evaporation ducts, surface-based ducts, and low-elevated ducts, provided the transmitter or radar antenna is within the elevated 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 ranges for the coverage display will generally be less than the corresponding actual ranges. The errors become less the higher the elevated duct is above the transmitter of radar antenna height and should be insignificant when the separation exceeds a few thousand feet.

. The coverage 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

Surface-to-air or air-to-air communication systems

Sonobuoys (only with the proper antenna height and frequency)

The coverage display should not be used for the following applications:

Airborne or surface-based surface-search radars employed against surface targets

Most types of gun- or missile-fire control radar

. It is not the intent of the coverage display model to calculate the maximum radar range for a given radar and target, but rather to show the relative performance of a radar (or communications) system at different altitudes as affected by the environment. It is up to the user to use free-space ranges that are appropriate for the application at hand.

. 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.

COVER diagrams are contours of constant electric field strength information in the vertical plane that indicates areas where radar targets might be detected. The contours chosen for display represent radar receiver thresholds against a particular size (radar cross section) target. COVER diagrams are also used to assess very high frequency (VHF) or ultra high frequency (UHF) communications coverage.

The method used to construct the COVER diagram depends on whether the EM system is surface-based or airborne. Both methods employ raytracing, but for surface-based systems, coherent interference between direct and sea-reflected paths, sea-surface roughness, and diffraction effects are considered.

Figure 7-4 shows an example output of a surface-system COVER diagram. A surface-system COVER diagram is composed of up to four coverage lobes. A COVER diagram for an airborne system has one lobe, drawn by straight lines, emanating from the antenna height.

A lobe describes the vertical and horizontal limits of the radar coverage. The shape and size of the lobes are dependent on the antenna type and the computed or entered free-space ranges or path-loss thresholds. Each lobe is where the particular radar device would detect a certain size target at a specified probability of detecting that target. Also involved is whether the target is steady or fluctuating and the probability of receiving a false alarm on the radar screen.

This information is now available on CD in Adobe PDF Printable Format

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing