1International Hydrographic Organization (IHO)
provides different hydrographic survey orders according to the intended use of the survey, water depth, vessel traffic, under-keel clearance, and potential hazards on the seafloor.
2Special Order
intended to approach engineering standards.
3Special Order
It is restricted to specific critical areas where there is minimum under-keel clearance and where bottom characteristics are potentially hazardous to vessels.
4Special Order
• All error sources must be minimized.
• Closely spaced lines are required.
• 100% bottom search is required.
• Cubic features greater than 1 m must be detectable.
5Order 1
intended for harbors, inland navigation channels, and coastal areas with high commercial traffic density.
6Order 1
• Water depths of less than 100 m.
• Full bottom search in selected areas.
• Cubic features greater than 2 m must be detectable in water depths up to 40 m.
• In areas deeper than 40 m, features greater than 10% of the depth must be detectable.
7Order 2
intended for areas with depths of less than 200 m that are not covered by Special Order or Order 1.
8Order 2
It applies where the bathymetry is sufficient to ensure that there are no seafloor obstructions that would endanger the type of vessel expected to transit or work in the area.
9Order 3
intended for all areas not covered by Special Order, Order 1, or Order 2.
10Order 3
Applies to water depths in excess of 200 m.
11• Horizontal accuracy at the 95% confidence level
• Depth accuracy parameters for reduced depths
The minimum standards include:
122 m, a = 0.25 m, b = 0.0075
Special Order Horizontal and Depth Accuracy
135 m + 5% of depth, a = 0.5 m, b = 0.013
Order 1 Horizontal and Depth Accuracy
1420 m + 5% of depth, a = 1.0 m, b = 0.023
Order 2 Horizontal and Depth Accuracy
15150 m + 5% of depth, a = 1.0 m, b = 0.023
Order 3 Horizontal and Depth Accuracy
16Depth accuracy = ± square root of [a² + (b × d)²]
Where:
• a — constant depth error, representing the sum of all constant errors.
• b — factor of depth-dependent error.
• d — depth.
Depth Accuracy Formula