Obviously, not all methods may be used at all times, and some methods work better than others in different situations.  When  a  cloud  layer  height  value  falls halfway between two reportable valves, round down to the nearest reportable increment given in table 1-3. Table 1-3.—Reportable Values for Cloud Layer Height and Ceiling Height HEIGHT IN FEET REPORTABLE VALUE £ 50 0 5,000 or less Nearest 100 feet 5,001  to  10,000 Nearest 500  feet Above 10,000 Nearest   1,000 feet NAVMETOCCOMINST 3141.2 and NAVMET- OCCOMINST 3144.1 discuss in detail the various methods  and  procedures  used  to  determine  cloud  height and ceiling height. Q24. Q25. Q26. Q27. Q28. Q29. Q30. REVIEW  QUESTIONS How is the amount of cloud layer coverage and total sky coverage measured? Define cloud layer. Define cloud ceiling. Define  total  obscuration. Define summation sky coverage. Given: Layer No.1 is 1/8 fog (SFC) Layer No.2 is 2/8 cumulus 3,000 ft Layer No.3 is 2/8 altocumulus 12,000 ft Layer No.4 is 5/8 cirrus 20,000 ft What is the ceiling height? A cloud height of 7,550 feet would be reported as what height? VISIBILITY LEARNING   OBJECTIVES:   Describe prevailing  visibility,  sector  visibility,  and differing level visibility. Define runway visual range. Visibility,  as  well  as  ceiling  height,  aids  in decisions involving air traffic control. For this reason, the observation of visibility must be timely, accurate, and representative. There are four types of visibility that you must observe: (1) prevailing visibility, (2) sector visibility, (3) differing level visibility, and (4) runway visual  range.  Both  NAVMETOCCOMINST  3141.2 and NAVMETOCCOMINST 3144.1 provide thorough and  detailed  guidance  on  visibility  observations. Ashore, visibility is observed in statute miles. Aboard ship, visibility is observed in nautical miles. Observing stations  located  outside  the  United  States  report visibility  in  meters. When  observing  visibility,  you  should  note  the distance as follows: To the nearest 1/16 mile when visibility is less than  3/8  mile To the nearest 1/8 mile when it is between 3/8 and 2 miles To the nearest 1/4 mile, between 2 and 3 miles To the nearest mile, from 3 to 15 miles In 5-mile increments, above 15 miles When the visibility falls between two values, the lower value  is  always  used. For  example,  a  measured visibility  of  3  3/4  miles  is  called  "3  miles."  See Appendix II of this module for a visibility conversion table. PREVAILING  VISIBILITY Prevailing  visibility  is  the  greatest  distance  that known objects can be seen and identified throughout half or more of the horizon circle. The most reliable method for determining prevailing visibility is by the eye of a trained observer. The sensors provided with automatic  observing  systems  provide  only  an approximation  of  prevailing  visibility  based  on  the sampling  of  obstructions-to-vision  present  in  only  a small  area  around  the  sensor.     To  aid  in  the determination of prevailing visibility, observation stations are required to maintain a visibility chart. The visibility chart identifies each daytime and nighttime visibility marker with direction and distance to the marker.  Daytime  markers  are  generally  dark,  prominent objects that stand out when viewed against the lighter sky. Nighttime markers are usually unfocused lights of moderate intensity, such as radio tower lights or channel marker lights. At sea, since the ship is usually moving, fixed visibility  markers  are  not  available.  The  Combat Information  Center  (CIC),  however,  maintains  tracks 1-28