layer transports induced by eddy driving from below seem to be 

 of the right magnitude and direction. 



MODE-I provided conclusive evidence for the existence of 

 midocean eddies and a four-dimensional densely sampled data 

 case history for analysis. As a direct result, successor and prede- 

 cessor experiments will be interpreted with confidence in the 

 context of a mesoscale eddy field. 



SOFAR Floats for POLYMODE 



One of the most successful instruments used in the MODE-I 

 experiment was the SOFAR float. SOFAR floats are neutrally 

 buoyant and can be adjusted to depths from 700 m to 2,000 m. 

 They are carried along by ocean currents and emit regular 

 acoustic signals. The acoustic signals are "trapped" in the 

 SOFAR channel and propagate over ranges greater than 1,000 

 km. The time of arrival of the acoustic signal is detected at 

 shore-based listening stations and is used to fix the position of 

 the float. The MODE-I float tracks (see IDOE Progress Report 

 Volume 3, fig. 12, page 13), referred to as the "spaghetti 

 diagram" by MODE scientists, qualitatively explain a great deal 



about the nature of oceanic flows — a seemingly disorganized 

 westward meandering with intermittent high-velocity bursts. 



Some major modifications were made to the MODE-I floats 

 for the POLYMODE experiment. To track more floats at 

 greater ranges, the signaling system was changed to a chirped, 

 frequency-modulated signal: every 8 hours the float transmits 

 an 80-second signal in which the frequency is swept upward 

 about 1.5 Hz. Floats are identified by different frequencies and 

 their time of signaling. Ten frequency channels are used, be- 

 tween 230 and 270 Hz, with about 4.7 Hz between channels. 

 In a given frequency band, each float is assigned a time window 

 of 10 minutes width for signal transmission. 



POLYMODE floats have been designed to stay at a constant 

 pressure (the MODE-I floats sank slowly, about 0.5 m per day, 

 owing to inelastic creep in the aluminum float housing) and to 

 telemeter temperature and pressure data. Data telemetry is by 

 pulse delay modulation. Once every 24 hours, 2 to 10 minutes 

 after the regular signal, an auxiliary signal is transmitted. The 

 period between the two signals is a function of the data being 

 telemetered. For a float at 2,000 dB, the pressure range is 

 ±200 dB, the resolution, ±0.4 dB; and the temperature range 

 is 3.2° to 4.2°C, the resolution, ±0.002°C. Two-day averages 



80°W 75° 70° 65° 60° 55° 50° 45° 40° 35° 30° 25° 20° 15° 10° 5°W 



R7 



SYNOPTIC/ INT 



\ 

 USSR 



NSIV 



50°N 



BIO ARRAY 



CLUSTER A 

 (ARRAY III) 



CLUSTER C 

 (ARRAYI II) 



Figure 14. — Geographical distribution of field work in POLYMODE. 



22 



