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LIMITATIONS AND ASSUMPTIONS - 14010_157
LIMITATIONS AND ASSUMPTIONS - 14010_159

Aerographers Mate 1 & C
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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. SHIP ICE ACCRETION (SHIP ICE) LEARNING OBJECTIVES: Interpret SHIP ICE  program  tabular  displays.  Identify limitations and assumptions. Explain how ice accretion rates are determined by the SHIP ICE program. The SHIP ICE program provides estimates of ship ice accretion rates vs. time given the wind speed and the air and sea-surface temperatures at various forecast times. Ice accretion from sea spray upon the ship’s superstructure can impair the operational capability and safety of the ship. APPLICATION This program can be used to predict the ice accretion on a ship’s superstructure due to sea spray. It can assist in planning by considering the icing effects along an Figure 7-4.-Example output of the EM coverage diagram. 7-12







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