CHAPTER 2 BATHYTHERMOGRAPH OBSERVATIONS

CHAPTER 2 BATHYTHERMOGRAPH OBSERVATIONS INTRODUCTION In this chapter, we briefly review the basic properties that affect sound in seawater. We then discuss the various uses of bathythermograph data and the equipment used to obtain this data, particularly the AN/SSQ-61(A) bathythermograph set and the AN/BQH-7(A) oceanographic data system. Next, we discuss the evaluation of the bathythermograph trace. W e e x p l a i n h o w t o u s e t h e i n t e r n a t i o n a l bathythermograph observation reporting code and also cover the disposition of observation records. We then complete the chapter by explaining how to decode messages received from drifting environmental buoys, another valuable source of oceanographic data. SEAWATER TRAITS AND DEFINITIONS LEARNING OBJECTIVE: Identify the three basic properties of ocean water on which sound-path predictions are based. Undersea Warfare (USW), which involves the detection and prosecution of hostile submarines, is one of the largest and most important missions of the U.S. Navy. One of the key factors that enable U.S. Navy submarines, surface ships, and aircraft to detect hostile submarines is our ability to predict the propagation path of sound in the ocean waters. This same knowledge also helps our submarines avoid detection by hostile ships and aircraft. Sound-path predictions are based on measurements of salinity, temperature, and depth in the ocean waters. SALINITY Salinity changes in deep ocean areas occur so slowly that we may, in most cases, consider salinity a constant. Salinity measurements in each ocean have been determined by oceanographic research ships and are available in many data bases. Salinity measurements are not routinely needed or made by operational ships. TEMPERATURE Temperature is by far the most important factor in determining sound propagation paths in the upper layers of the ocean. Surface and intermediate ocean- depth temperatures change more rapidly than in deep water, with the faster changes occurring at the surface. Hourly satellite observations allow all significant changes in sea surface temperature to be routinely monitored. However, significant changes in water temperature near the surface and at intermediate depths require ships and aircraft to routinely measure these temperatures at depths of up to 6,000 feet. Deep ocean waters change temperature so slowly that routine measurements are not required. Accurate data is available from oceanographic data bases that are updated by research ships and other sources. OCEAN DEPTH Ocean depth is also important to USW operations since the pressure of seawater is the dominant factor affecting sound velocity in the deep layers of the ocean. Ocean depth also affects sound propagation paths, such as bottom bounce and convergence zone. REVIEW QUESTIONS Q1. What property affecting sound propagation in seawater is normally considered a constant? Q2. What is the most important factor affecting sound propagation in the upper layers of the ocean? Q3. What is the dominant factor affecting sound speed in deep ocean layers? USE OF BATHYTHERMOGRAPH OBSERVATIONS LEARNING OBJECTIVES: Identify the main uses of bathythermograph data. Identify when bathythermograph observations are conducted. 2-1