INTRODUCTION TO SONAR 



Item 12 — Clouds 



1. Type: Code the significant type of clouds 

 (WMO code 0500). 



Cirrus. 



1 Cirrocumulus. 



2 Cirrostratus. 



3 Altocumulus. 



4 Altostratus. 



5 Nimbostratus. 



6 Stratocumulus. 



7 Stratus. 



8 Cumulus. 



9 Cumulonimbus. 



X Cloud not visible because of darkness, 

 fog, duststorm, sandstorm, or other 

 phenomena. 



2. Amount: Record the fraction of the celestial 

 dome covered by clouds (in eighths) (WMO code 

 2700). 



Zero. 



1 One okta (eighth or less, but not zero). 



2 Two oktas. 



3 Three oktas. 



4 Four oktas. 



5 Five oktas. 



6 Six oktas, 



7 Seven oktas. 



8 Eight oktas. 



9 Sky obscured, 

 be estimated. 



or cloud amount cannot 



Item 13 — Waves 



Enter the mean height of the predominant 

 waves. Check the appropriate box to indicate 

 feet or meters. Record the period of the waves 

 in seconds. 



Item 14 — Sea Surface Reference Temperature 



Use the appropriate code from the accom- 

 panying list to indicate the instrument used to 

 obtain the sea surface temperature, and in 

 which system it was measured. Record tem- 

 perature to the nearest tenth of a degree. 



XX °F Bucket thermometer. 



99 °F Injection thermometer. 



89 °F Injection thermistor (NSRT). 



YY °C Bucket thermometer. 



98 °C Injection thermometer. 



88 °C Injection thermistor (NSRT). 



TRACE READOUT 



Interpretation of the BT trace is necessary 

 to obtain the required values for making up the 

 sonar message and for radio transmission of 

 BT information. The observer must insert the 

 BT grid and slide in the viewer and read off the 

 points for encoding where the BT trace changes 

 direction. This procedure is in addition to read- 

 ing surface and bottom values. 



No adjustment is made for discrepancy be- 

 tween reference temperature and BT temperature. 

 Any bias in depth (trace beginning above or below 

 zero line) must, however, be adjusted visually 

 before reading at any depth. Otherwise, the trace 

 will be in error. 



A sample BT trace readout is shown in 

 figure 5-20 with the readout figures to the right. 

 The arrows indicate points that should be re- 

 ported. Do not routinely read points at 50 or 

 100 feet unless the trace changes direction at 

 these points. When the trace is in a straight line, 

 only two readings are necessary — a surface 

 reading and a reading at the deepest depth of the 

 BT trace. 



RADIO MESSAGE INFORMATION 



The radio, or BATHY, message should contain 

 sufficient points so that the trace plotted by the 

 addressee is identical to the original trace, 

 except for minor wiggles. Provision is made on 

 the BT log for entering the readings in the proper 

 order for radio transmission. The observer 

 should not interpret the number of spaces pro- 

 vided for this information to be a restriction 

 on the number of points to be recorded. Use as 

 many lines on the BT logsheet as required to 

 describe the BT trace accurately. 



The radio message portion of the BT log- 

 sheet shown in figure 5-19 is completed as 

 described in the following itemization. 



Item 1 — Prefix 



All BT messages are prefixed by the word 

 BATHY, which is preprinted on the logsheets. 



Item 2 — Day 



Enter the code number for the day of the 

 week, starting with number 1 for Sunday. 



Item 3 — Time 



Record the GMT hour and minute at which 

 the BT entered the water. 



82 



