If a towed sensor such as a side scan sonar is used on a survey, HIPS and SIPS can compute the sensor’s position relative to the ship's position by calculating the horizontal layback and the direction to the sensor using the information in the Tow Point component.
The Tow Point component has the following attributes in its Attributes window:
• Date: The year and Julian day of the current towed sensor time stamp (see Component Time Stamps).
• Time: The hour and minute of the current towed sensor time stamp (see Component Time Stamps).
• Time Correction: The time correction value.
• Delta X: Offset of the tow point from the vessel’s reference point (RP).
• Delta Y: Offset of the tow point from the vessel’s RP.
• Delta Z: Height of the tow point (negative upwards) in relation to the datum that is referenced to the sensor depth (in most cases, this is the waterline height).
• Layback Error: The error in the computed or recorded horizontal layback.
This value is subtracted from the computed horizontal layback. As an example, it can be used to compensate the recorded layback data or tow cable length for the distance between the origin of the measurements and the defined tow point location in the tow cable length.
• Manufacturer: The maker of the towed sensor.
• Model: The make of the towed sensor.
• Serial Number: The serial number of the towed sensor.
• Comments: A text field for your use.