SUMMARY 



During six acoustic experiments conducted between 1971 and 1975, a total of 1987 

 XBT temperature profiles were acquired. Of this total, 26 were made with 1830-m XBT 

 systems and the balance, 1961 profiles, were made with 460-m XBT systems. Included were 

 special sets of measurements to provide data for several absolute and relative temperature- 

 accuracy studies. The measurements were made on 1 1 different 460-m and two different 

 1830-m systems from four ships - LEE, DE STEIGUER, MOANA WAVE, and CAPE - 

 and two Scripps Institution of Oceanography research platforms — ORB and FLIP. Therm- 

 istor chain profiles were made during the SUDS I experiments and surface temperatures 

 were measured during the Gulf of Alaska experiments by means of a towed thermistor, and 

 during CAPER and RAPLOC/DEEPTOW by means of a bucket thermometer. In addifion, 

 22 hydrocasts and 192 STD/SV, CTD/SV, or SVTP profiles were acquired. Many of these 

 measurements were quasisimultaneous with XBT measurements. These measurements were 

 made for the purpose of calibrating the XBT systems to a common temperature standard. 



SIPPICAN XBT CHARACTERISTICS AND OPERATIONAL PROCEDURES 



All XBT temperature profiles used in this accuracy study were obtained with 

 Sippican Corporation XBT systems. The system consists of a temperature probe, launcher, 

 and recorder. The Sippican System measures temperature with a thermistor bead sensor and 

 depth by measuring time. Time is converted to depth by knowing the rate of fall of the 

 temperature probe through the water. According to the Sippican Corporation, the range of 

 measurement and the system accuracy for the XBT system are as follows: 



Temperature: -1.7 to 35.6°C ±0.2°C 



Depth: to 230 m ±4.6 m 



>230m±2.0%. 



According to Mr R.P. Demeo, Manager, Quality Assurance and Reliability Engineering, 

 Sippican Corporation, the ±0.2°C system temperature accuracy is considered to be an 

 absolute accuracy and is not to be interpreted as equivalent to a standard deviation in the 

 statistical sense (personal communication). Tlie output of the XBT system is an analog 

 record consisting of a continuous trace of temperature as a function of depth from the 

 surface to 460 m or 1 830 m. The length of the -2.0-to-35.0°C temperature scale is 1 7.42 cm, 

 of the O-to-460-m depth scale 12.26 cm, and of the O-to-1830-m depth scale 49.17 cm. 



The recorder is controlled by an automatic program which is initiated by inserting 

 an XBT probe into the launcher. Closing the launcher breech completes a circuit between 

 the probe and the recorder and triggers the recorder into a check/run mode. The chart 

 drive operates for about 2 s and records a calibration temperature of 16.7°C ±0.1 °C. The 

 chart drive then stops in the launch mode, but starts again in the measure mode when the 

 temperature probe is released and enters the water. During 88 s (460-m probe) or 358 s 

 (1830-m probe), the temperature versus depth profile is recorded and the chart drive stops 

 in the reload mode. 



Before a series of XBT measurements, or at weekly intervals when measurements 

 are being made over a period of time, a calibration check of the complete system is required. 

 A test canister is loaded into the launcher, and the system is run through the operating 

 cycle. At the start of the cycle, the chart drive will operate for about 2 s, marking a 



15 



