Odom ECHOSCAN, Manual

Page: 32 / 44

04/26/02 32
Revision 1.11
Figure 18
ECHOSCAN CALIBRATION
(Bi-Level Bar Check Method)
draft
Level 1
Level 2
DEPTH =
2
+ k + DRAFT
V x (pulse travel time)
s
As seen from the above equation, depth measurement
accuracy is primarily dependent upon the accuracy of two
external variables; Vs (sound velocity in water) and
DRAFT (the distance between the transducer and the
water surface). The bi-level bar check procedure
described below offers the most straightforward approach
to multibeam calibration in that both DRAFT and Vs
corrections are optimized. The calibration may be very
accurate, current and wind conditions permitting. Even
the system constant (k) is automatically compensated
using this method.
1. Lower the bar to a depth of 4 meters (or 10 feet) below the transducer. This will
be Level 1.
2. Pull down the
Digitizer Settings menu on the LCDU, select Range Gate , and
adjust the GATEDEPTH to Level 1 depth. Set the GATEWIDTH to 2 meters.
Allow time for the digitizer to "lock in".
3. Pull down the
Setup menu and adjust Draft as required to correct the depth value
displayed below Channel # . Normally, Channel 15 is monitored.
4. Lower the bar to Level 2 and set
GATEDEPTH to Level 2 (depth limited only by
chain length, water depth, or current and wind conditions).
5. Under
Setup , adjust the Velocity correction until the depth value displayed is
correct.
6. Return the bar and
GATEDEPTH setting to Level 1 and repeat the Draft
adjustment (step 3).