NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY
US4TD4I0 - FEDERATED STATES OF MICRONESIA - POHNPEI HARBOR

INDEX:
NOTE 1
NOTE 2
CELL ACCURACY
LIDAR SURVEYS
CAUTION 1
CAUTION 2
CAUTION 3
TIDAL INFORMATION
SUPPLEMENTAL INFORMATION

NOTE 1:
The original soundings were in fathoms.

NOTE 2:
The positions of some aids to navigation have been upgraded through the use of Commercial Satellite Imagery.  However, positions of many aids to navigation could not be verified.

CELL ACCURACY:
Owing to the age and quality of the source information, some details on this cell may not be positioned accurately. Particular caution is advised when navigating in the vicinity of dangers, even when using an electronic positioning system such as GPS.

LIDAR SURVEYS:
Much of the hydrography on this chart is based on surveys using Laser Image Detection and Ranging, or LIDAR. The ability of LIDAR to detect depths and hazards is limited by water conditions, such as water clarity, depth and the state of the sea surface. Therefore, certain LIDAR-surveyed areas are not thoroughly examined, particularly in areas with depth greater than 20 meters. In such areas, additional sources may have been used.

CAUTION 1:
Significant discrepancies have been observed between the older chart and survey data and the newer LIDAR survey. While the LIDAR data is accurate, the LIDAR survey lacks adequate coverage of the bottom, particularly in the areas marked. These areas lack adequate information to produce an accurate depiction of the seafloor. The mariner is warned to exercise caution in all areas of this chart, especially in those areas marked, as uncharted hazards may exist. Local knowledge is recommended.

CAUTION 2:
Many reefs on this chart have been updated through the use of Commercial Satellite Imagery of 2017. Such imagery cannot provide reliable detection of all hazards to navigation. Uncharted hazards may exist. Discrepancies in the location and extent of reefs have been observed between the imagery and older chart sources. Reefs have been shown to the fullest extent from any given source. Where there are large discrepancies, previously charted reefs may have been collected as dangerous areas.

CAUTION 3:
Fish Aggregating Devices (FADs), anchored or drifting, are commonly deployed within the waters of many Pacific Islands and may not be charted. Even though many of the installations are temporary in nature, FADs pose significant risk to navigation safety. Prudent mariners should exercise caution in navigating these waters.

TIDAL INFORMATION:
Refer to Admiralty Total Tides Program for the latest information.

SUPPLEMENTAL INFORMATION:
Consult National Geospatial-Intelligence Agency Pub. 126, Sailing Directions, for important supplemental information. 

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