NOAA Vessel_Offset_Survey_Specifications.pdf

VESSEL OFFSET SURVEY SPECIFICATIONS

Report Specifications

The surveyed positions and alignments shall be delivered in a consolidated, electronically readable table with correct sign. Uncertainty shall be calculated for each reported position and alignment via mis-closure analysis, variance analysis, or comparable method. Rotations shall be calculated in the Euler-angle x-y-z convention in the ship-fixed reference frame. A report documenting the survey method, instruments used, calibration certificates, and benchmark descriptions, shall be delivered along with the consolidated position and alignment table.

Benchmarks descriptions shall include compartment name, general description of location, and two photographs- one showing the benchmark in detail, one illustrating the position of the benchmark in context of its surrounding.

Definition and Realization of Reference Frame

The spatial reference frame for the ship shall be defined by a right-hand, orthogonal system with the general orientations: x-axis forward, y-axis to starboard, and the z-axis down. The origin of this system shall be at the center of the heading and athwartships lines of the master reference block (MRB). The direction of the z-axis shall be defined as perpendicular to the design waterline plane. The direction of the x-axis shall be defined by the centerline of the keel. Positive rotations shall be defined as counter‐clockwise about the axis looking towards the origin, such that positive rotations are: in yaw (z-axis) to starboard, in pitch (y-axis) bow up, and in roll (x-axis) starboard down.

The spatial reference frame of the ship shall be realized in the following manner:

1. the z-axis orientation by fitting, in a least squares sense, a plane through the draft marks closest to the design waterline (e.g. if the design waterline is 12.3’, a plane shall be fitted to the 12’ draft marks). This is the waterline plane. The z-axis shall be perpendicular to this plane.

2. the x-axis orientation by fitting, in a least squares sense, a plane perpendicular to the waterline plane through the external keel centerline bench marks. This plane is the centerline plane. The x-axis orientation shall be embedded in this plane and perpendicular to the z-axis.

3. The y-axis shall be perpendicular to both the x and y axis.

4. The origin of the reference frame shall be the center of the heading and athwartships lines of the MRB.

Monumentation of Reference Frame

A master reference block shall be provided, consisting of a granite reference block at least 12” square, permanently scribed with orthogonal heading and athwartships lines, and aligned to the ship reference frame within 6 minutes of arc in the x, y and z axes. The block shall be mounted on a sufficiently rigid foundation and supported in a steel box by swivel-leveling threaded bolts, which shall also be used to position and level the block. After installation and alignment of the reference block, the block shall be fixed in the box with poured epoxy, Chockfast Orange, or equal.

The ship's spatial reference frame shall be additionally monumented with permanent benchmarks throughout the ship. Benchmarks shall be CRES, unpainted plates, 2inch (50 mm) square with permanently scribed center marks and unique, permanently inscribed numbers. The position of these benchmarks in the spatial reference frame of the ship shall be measured to the accuracy specified in Table 184-1. Benchmarks shall be located to maximize field of view and not be located behind equipment, cabinets, or other obstructions. Bench marks shall not be located within the area required to be cut out for installation of transducers, seachests and other equipment.

Benchmarks shall be installed as follows:

a) not less than four bench marks on the keel (forward and aft)

b) not less than four benchmarks on the aft working deck and four on the deck forward (one forward near the foremast on centerline, one on the aft working deck on centerline, and one each port and one starboard on the aft working deck perpendicular to centerline)

c) one on the 01 level weather deck forward of amidships on centerline

d) one at the transducer tube location

e) one on the base of the foremast

f) one on the upper main mast antenna servicing platform

The aft working deck benchmarks shall be located to provide alignment instruments with a clear line of sight to the main mast benchmark and adjacent benchmarks. Forward deck benchmarks shall be located to provide a clear line of sight to the foremast, other forward deck benchmarks and the main mast benchmark.

A minimum of four benchmarks, referenced to the MRB, shall be installed at each of the following locations in such a manner and quantity so as to permit accuracy in resurvey and positioning of equipment:

a) in each space containing transducers

b) in the space containing the IMU

c) in each space containing gyrocompasses

d) within line of sight at each GPS antenna, scientific antenna, and navigational antenna

Draft marks shall be surveyed to the tolerances required for benchmarks.

Installation Alignment

Unless otherwise specified, GPS antennas, DGPS antennas, AHRS antennas, the IMU, navigational antennas, directional finders, radar antennas, gyrocompasses, scientific system sensors, and scientific transducers, shall accommodate the manufacturer's system installation and alignment requirements, comply with recommended optimum sensor mounting locations, and support orthogonal survey requirements.

The following components shall be physically aligned with the ship’s Reference Frame to within 1 degree of total angle.

a) top surface of the multi-beam mounting frame flange or the underside of the “flange counterpart”

b) the IMU attitude sensor mounting plate

c) the MRB

d) the gyrocompass foundation plates

The IMU and gyrocompasses shall be mounted to these plates, physically aligned in heading within 6 minutes of arc, and fixed in place.

Multi-beam transmit and receive arrays shall be co-aligned within 1 degree and each shall be aligned to the ship frame within 1 degree, or manufacturer’s recommendations, whichever is more precise.

Each transducer housing and scientific mission sea chest shall have a forward and aft lineup mark parallel to the ship’s centerline within 1 degree to be installed on the inboard side of the hull.

Each lineup mark shall consist of two triangles with a center punch mark, separated by 2 inches (50 mm).

Measurement of Component Position and Rotation

Unless otherwise specified, the position of all GPS antennas, differential global positioning system (DGPS) antennas, attitude heading reference system (AHRS) antennas, inertial measurement unit (IMU), navigational antennas, directional finders, radar antennas, gyrocompasses, scientific transducers, scientific seachests, and all bench marks shall be surveyed in the ship’s reference frame in accordance with Table 184-1, or to manufacturer’s recommendations in cases where the manufacturer’s recommendations are more precise than the value stated in Table 184-1 for a particular piece of equipment.

TABLE 184-1

SURVEY SPECIFICATIONS

MEASUREMENT TOLERANCES

SYSTEM Horizontal Vertical Heading Pitch Roll Ship's MRB (0, 0, 0)

Coordinate reference 0+/-0.025º 0+/-0.025º 0+/-0.025º

IMU +/-5 mm +/-5 mm 0+/-0.025º 0+/-0.025º 0+/-0.025º GPS, DGPS and AHRS antennas

+/-5 mm +/-5 mm -- -- --

GPS antennas (referenced to each other)

+/- 5 mm scalar distance between antennas

Radar antennas and Gyrocompasses

+/-50 mm +/-20 mm 0+/-0.1º -- --

Scientific Multi-Beam transducers

+/-5 mm +/-5 mm 0+/-0.025º 0º+/-0.025º 0º+/-0.025º

ADCP +/-50 mm +/-20 mm 0+/-0.1º 0+/-0.1º 0+/-0.1º

Benchmarks +/-5 mm +/-5 mm -- -- -- Draft Marks +/-5 mm +/-5 mm -- -- -- Scientific seachests +/-5 mm +/-5 mm -- -- --

Scientific Single Beam transducers, directional finders, and navigational antennas

+/-50 mm +/-20 mm 0+/-0.1º 0+/-0.1º 0+/-0.1º

Vessel offset survey specifications