ENCODING BATHYTHERMOGRAPH SOUNDINGS

temperature with depth. Figure 2-9 depicts the three types of temperature gradients as they would appear on a bathythermograph trace. Selection of Significant Data Points Certain criteria have been established for selecting data points from a bathythermograph trace. Remember that the objective of selecting these points is to provide a fairly accurate representation of the temperature profile of the water column. The following points on a bathythermograph trace are always considered significant and must be reported: The surface (or the first readable temperature in the upper 10 meters or 30 feet). The Mixed Layer Depth (MLD). Tops and bases of isothermal layers. Inflection points in the trace; that is, significant points on the trace where the temperature changes from positive to negative or vice versa. The deepest point of the trace. If the BT strikes the bottom, be sure to encode the value using the 00000 indicator group. Following these procedures, there should never be a need to report more than 20 points in the upper 500 meters (1,640 feet) of the trace. Once the significant levels are selected, the sounding may be entered into onboard computer systems for processing, and then encoded in the bathythermograph log. Figure 2-10 shows an unusual bathythermograph trace from an AN/SSQ-56 recorder. Significant levels have been selected. Some airborne expendable bathythermograph (AXBT) systems produce digital printouts of depth/temperature data vice actual depth/temperature traces. Although these can be difficult to work with, the same criteria is applied when selecting significant data points. Q15. Q16. Q17. Q18. Q19. REVIEW QUESTIONS What might cause the stylus on an AN/BQH-7A to make erratic excursions to the right on the recording chart? Other than equipment or probe malfunction, what might be the cause of anomalous features on a XBT recording trace? What term describes an increase in temperature with depth? What significant points on a BT trace must be evaluated and encoded? What is the maximum number of points that should be encoded in a BT observation report in the upper 500 meters (1640 feet) of the trace? ENCODING BATHYTHERMOGRAPH SOUNDINGS LEARNING OBJECTIVES: Describe how elements observed during a bathythermograph sounding are properly encoded in the BATHY code. Identify the meaning of each element in the BATHY code. The CNMOC 3167/2 Bathythermograph Log contains a foldout cover sheet with complete instructions for completing the log and encoding the observation in the proper International Code, which is WMO Code FM 63-X BATHY. The Bathythermo- Figure 2-9.—Types of temperature gradients. 2-12