NAVIGATION PROCESSING

The tow fish was positioned by the merging and filtering of a) ship's POS1 data , b) HPR Acoustic positioning data on the tow-fish depressor (range, depth from POS1, bearing from ship's heading), and c) cable length, tow-fish depth and azimuth as measured and recorded by the TOBI data loggers. To do so we developed a model of the cable. The attitude data data were used applied in the following sequence:

1.

analyze the catenary problem and develop the cable model (2nd order aproximation of the catenary equation)

2.

merge the nav data (ship and tow-fish) into a single file

3.

smooth the tow-fish nav data (5 min moving average) (wire out, depth and heading)

4.

smooth the ship's heading (5 min moving average)

5.

median filter the HPR data (bearing and depth) based on the discrepency between observed value and the model's predicted value

6.

resample at 1 min rate

7.

smooth the HPR's range, bearing (11 min window)

8.

calculate the best tow-fish position using ship position, filtered HPR range and bearing (in case of lack of HPR data the model prediction is used)