3-16
SECTION 3:
SETUP AND ACTIVATION
3100-P PORTABLE SUB-BOTTOM
0004802_REV_F
1
2 𝑥𝑥 20 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑥𝑥 10 𝑘𝑘𝑘𝑘𝑘𝑘
15 𝑘𝑘𝑘𝑘𝑘𝑘
= 6.6 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑
Equation 1
The same criteria apply to vehicle roll, which is how much in degrees it is listing to port or starboard.
Sensors can be installed on the tow vehicle to measure its pitch and roll under various towing
conditions.
3.9.2
Conducting Sediment Classification Surveys When Towing
To conduct sediment classification surveys, the reflection coefficient should be measured with better than
10% accuracy. The normal component of the sea floor reflection must arrive within the angle
corresponding to one half of the -1 dB beam width of the acoustic axis of the vehicle at the center
frequency of the pulse, the frequency where most of the acoustic energy is concentrated and where the
reflection coefficient is measured. As a rule of thumb, for a 0.5-meter long hydrophone array, the -1 dB
beam width at 10 kHz is 4 degrees.
For example, if the sea floor is expected to have slopes of up to 5 degrees during the survey, and a vehicle
with a 0.5-meter hydrophone array and a 2 to 10 kHz FM pulse is selected, the -1 dB beam width should
be at least 10 degrees at 6 kHz. For this pulse and receiving array, the -1 dB beam width at 6 kHz is about
7 degrees, or
4 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑥𝑥 10 𝑘𝑘𝑘𝑘𝑘𝑘
6 𝑘𝑘𝑘𝑘𝑘𝑘
= 6.6 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑
Equation 2
Therefore, only reflection coefficient measurements made when the sea floor slope is within 3.5 degrees
of horizontal will be accurate within 10% (1 dB).
The attitude of the tow vehicle with respect to the horizontal plane must meet the -1 dB criteria described
above for sediment classification surveys. Rough sea conditions tend to move the vehicle up and down
vertically, causing oscillations in the images. DISCOVER 3100-P SB has a swell filter that will help reduce
the heave effect on the record. Refer to the “DISCOVER 3100-P SB Sub-Bottom Software User’s Manual”
for details. For sediment classification, the tow fish pulses must be calibrated by the end user. This
calibration procedure is described in the software manual.
Summary of Contents for Model 3100P Sub-bottom Sonar System
Page 24: ......
Page 29: ...2 5 Figure 2 4 Tiger Board Set SIBU aka Sonar Interface Board 0011637...
Page 33: ...2 9 Figure 2 6 SB 424 Towfish Outline Drawing...
Page 60: ...SECTION 5 TROUBLESHOOTING 5 4 Figure 5 1 35M Tow Cable Diagram 0002899...
Page 61: ...5 5 Figure 5 2 3100 P Topside Interconnect 0004674...
Page 62: ...SECTION 5 TROUBLESHOOTING 5 6 Figure 5 3 Wiring Diagram Spider Box SB 424 Tow Vehicle...
Page 63: ...5 7 Figure 5 4 Wiring Diagram SB 424 Tow Vehicle...
Page 64: ...SECTION 5 TROUBLESHOOTING 5 8 Figure 5 5 Wiring Diagram Spider Box SB 216S Tow Vehicle...
Page 65: ...5 9 Figure 5 6 Wiring Diagram SB 216S Tow Vehicle...
