Standards for Hydrographic Surveys

2 Position

2.1 Introduction

If the accuracy of a position is affected by different parameters, the contributions of all parameters to the total position error must be accounted for.

A statistical method, combining different error sources, for determining positioning accuracy must be adopted. The position error, at 95% confidence level, must be recorded together with the survey data (see § 8 Data Attribution).

Positions must be referenced to the World Geodetic System 84 (WGS 84) or the North American Datum 83 (NAD 83, CSRS). It is important to understand and document which coordinate system was used to account for the fact that these two systems are no longer considered equivalent.

Whenever positions are determined by terrestrial systems, redundant lines of position shall be observed. Standard quality assurance checks techniques shall be completed prior to, during and after the acquisition of data. Satellite systems shall be capable of tracking at least five satellites simultaneously, and integrity monitoring for Exclusive Order, Special Order and Order 1a surveys is recommended.

2.2 Horizontal Control

Primary shore control points shall be established by ground survey methods to a relative accuracy of 1 part in 100,000. When geodetic satellite positioning methods are used to establish such points, the error shall not exceed 10cm at 95% confidence level with respect to WGS84 or NAD83 (CSRS).

Secondary stations for local positioning which will not be used for extending the control shall be located such that the error does not exceed 1 part in 10,000 for ground survey techniques or 50cm at 95% confidence level using geodetic satellite positioning.

For more information on GPS positioning, refer to the appropriate national and/or provincial geodetic agencies.

2.3 Soundings

The position of soundings, dangers, and all other significant submerged features shall be determined such that the horizontal accuracy is as specified in Table 1.

The accuracy of the position of a sounding is the accuracy at the position of the sounding on the bottom located within a geodetic reference frame.

2.4 Navigation Aids and other Features

The horizontal positions and/or elevations of navigation aids and other conspicuous features shall be determined to the accuracy stated in Table 2, at 95% confidence level.

The order to use for the positioning of navigation aids and other features such as bridge piers, wall, clearances, etc. should be determined in accordance with the importance for the safety of navigation in the surveyed area. As an example, bridge piers located along a critical channel have a higher significance than those located in an intertidal area and should therefore be positioned with higher accuracy. The examples of typical areas stated in Table 1 can be used as a guideline.

Table 2: Standards for Positioning of Navigation Aids and Important Features