Survey Standard

Qinsy supports several different standards for hydrographics surveys:

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For every one of these standards, Qinsy is able to filter datapoints whose Total Horizontal Uncertainty (THU) or Total Vertical Uncertainty (TVU) exceeds the maximum limits set out by that standard. The THU and TVU are the horizontal and vertical components, respectively, of the Total Propagated Uncertainty (TPU).

Each standard defines a set of subtypes (or Orders) that correspond to different areas, each with their own requirements for safety and accuracy (including maximum THU and TVU).

For some orders, the characterisation of the type of area to which the order applies includes strict depth limits. If the user has selected to use an order that has such limits, Qinsy will determine for each sounding whether it falls within these limits. If not, it will select the closest order of the same standard for which the depth does fall within that order's limits, or for which there are no strict depth limits.

IHO S-44

The S-44 standard is puslished by the International Hydrographic Organisation (IHO). In the S-44 standard, the IHO proposes minimum standards for Positioning and for Depths.

For each given depth d, S-44 defines:

• Horizontal uncertainty limits (THU limits) as a linear function of depth: THU_max = h + g x d
• Vertical uncertainty limits (TVU limits) as the square root of a quadratic function of depth: TVU_max = √ (a² + (b x d)²)

The parameters h, g, a and b are usually different for different orders.

The IHO regularly updates the S-44 standard with a new edition. Qinsy supports the following editions of the standard:

4th Edition

The 4th Edition of S-44 dates back to 1998. Its support in Qinsy will soon be discontinued. It is recommended to switch to a newer edition.

In the Echosounder Settings, the orders of the 4th edition are identified simply as S-44 orders, without an edition specifier.

5th Edition

The 5th Edition of S-44 was published in 2008. Its orders are identified in the Echosounder Settings by the prefix S-44 5th.

For depths, this edition sub-divides the minimum standards into four different orders:

• Special Order: Areas where under-keel clearance is critical
• Order 1a: Areas shallower than 100 meters where under-keel clearance is less critical but features of concern to surface shipping may exist
• Order 1b: Areas shallower than 100 meters where under-keel clearance is not considered to be an issue for the type of surface shipping expected to transit the area
• Order 2: Areas generally deeper than 100 meters where a general description of the sea floor is adequate

The table below summarizes Table 1 of the specification of S-44, 5th Edition to show the limits for these orders:

If we ignore the depth limits, for a number of different depths, your TVU would have to be less than the following for each of the four orders:

6th Edition

Edition 6.0.0 of the S-44 standard was published in 2020. In the Echosounder Settings, its orders are identified by the prefix S-44 6th.

For depths, this edition sub-divides the minimum standards into five different orders:

• Exclusive Order: Areas where there is strict minimum underkeel clearance and manoeuvrability criteria
• Special Order: Areas where underkeel clearance is critical
• Order 1a: Areas where underkeel clearance is considered not to be critical but features of concern to surface shipping may exist
• Order 1b: Areas where underkeel clearance is not considered to be an issue for the type of surface shipping expected to transit the area
• Order 2: Areas where a general description of the sea floor is adequate

The table below summarizes Table 1 of the specification of S-44 Edition 6.0.0 to show the limits for these orders:

If we ignore the depth limits, for a number of different depths, your TVU would have to be less than the following for each of the five orders:

The International Marine Contractors Association (IMCA) has issued guidelines specifically addressing the use of multibeam echosounders for offshore surveys (S 003), which are partly based on the IHO S-44 4th Edition standard for Special Order surveys. The IMCA has published these guidelines because existing standards were all primarily directed towards charting for safe navigation. The offshore surveys described in the IMCA guidelines all have the objective to chart or image the seafloor in its entirety.

Read our Knowledge Base document named ''How-to Total Propagated Uncertainty -TPU'' to find out more about the IHO and IMCA survey standards.

Dutch Standards for Hydrographic Surveys in the Netherlands

The Netherlands Hydrographic Service and Rijkswaterstaat carry out hydrographic surveys in the Netherlands.

In order to be able to work together effectively, a common reference frame, such as the S-44-Standards of the International Hydrographic Organisation (IHO), is important. The Dutch Hydrographic Standards are built on the 5th Edition of S-44, with some additional Standards for the Dutch situation.

The Dutch Standards prescribe the minimum requirements regarding hydrographic surveys.

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