targets.  It  is  also  used  to  plan  the  flight  profile  of attacking aircraft against a surface target to minimize the probability of the aircraft being detected by the target. Another use is to alert surface units to holes in their  radar  coverage  against  attacking  aircraft  or missiles. This capability provides the information on which to plan the disposition of surface units and to base requirements  for  airborne  coverage. LIMITATIONS AND ASSUMPTIONS 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). l  COVER  is  valid  only  for  EM  systems  with frequencies between 100 MHz and 20 GHz. l 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. l 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. l  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) -  - l 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. l  Output from this program is classified and should be  labeled  corresponding  to  the  classification  of  the  EM system  used  to  produce  the  display. l  Effects  of  wave  splash,  wave  shadowing, bobbing, and rolling are not taken into account for sonobuoy output. FUNCTIONAL DESCRIPTION COVER diagrams are contours of constant electric field strength information in the vertical plane that indicates areas where radar targets might be detected. 7-11