9.0 Physical Seabed Samples
For NOAA ISD surveys, if Field Units have been tasked with collecting physical seabed samples, the character of the bottom must be determined, particularly in harbors, designated anchorages, and other areas where vessels may anchor.
In general, sampling the surface sediment layer is usually adequate to define the bottom characteristics for charting. Clamshell bottom snappers or similar physical seabed samplers should be used to obtain as large a sample as possible. For NOAA ISD surveys, if a more detailed study of the ocean floor is required, the Hydrographic Survey Project Instructions will specify the type of sampler to use.
For NOAA ISD surveys, if a Field Unit is assigned to conduct seabed samples, the Field Unit should review the sampling plan provided within the Project Instructions to the survey data acquired. The Field Unit should contact their OCS Project Manager to discuss modifying the sampling plan if the data suggest more appropriate locations for the seabed samples (e.g., depth at specified sampling location is > 80 m, backscatter data indicate homogeneous bottom type, etc.). The survey data will often better differentiate varying bottom characteristics within the survey area when compared to the sample plan provided. This may increase or decrease the sample density but should closely maintain the same number of samples per survey as originally assigned.
For NOAA ISD surveys, in areas where seabed samples are not required but where the general trend of the newly surveyed depths significantly differs from charted depths, the Field Unit must contact their OCS Project Manager as appropriate to determine if seabed samples are necessary and to define the sample density.
The hydrographer must record the position of each sample obtained. In addition, each sample must be described and attributed in the Feature File. Refer to the Feature Attribute Encoding Guide for more details on physical seabed sample encoding.