Data Management Plan (Deprecated)

These data were collected by the SHOALS (Scanning Hydrographic Operational Airborne Lidar Survey) system which consists of an airborne laser transmitter/receiver

capable of measuring 400 soundings per second. The system operates from a deHavilland DHC-6 Twin Otter flying at altitudes between 200 and 400 meters with a

ground speed of about 100 knots. The SHOALS system also includes a ground-based data processing system for calculating accurate horizontal position and water depth.

Lidar is an acronym for LIght Detection And Ranging. The system operates by emitting a pulse of light that travels from an airborne platform to the water surface where a small

portion of the laser energy is backscattered to the airborne receiver. The remaining energy at the water's surface propagates through the water column and reflects off the

sea bottom and back to the airborne detector. The time difference between the surface return and the bottom return corresponds to water depth. The maximum depth

the system is able to sense is related to the complex interaction of radiance of bottom material, incident sun angle and intensity, and the type and quantity of organics

or sediments in the water column. As a rule-of-thumb, the SHOALS system should be capable of sensing bottom to depths equal to two or three times the Secchi depth.

Original contact information:

Contact Org: U.S. Army Corps of Engineers JALBTCX

Phone: 251-690-3467

Process Steps:

• 1999-12-01 00:00:00 - The SHOALS airborne system acquires a tremendous volume of raw data during a single mission. The lidar data are unique and require a specialized Data Processing System (DPS) for post-processing. The DPS main functions 1) import airborne data stored on high density data tape; 2) perform quality control checks on initial depths and horizontal positions; 3) provide display and edit capabilities; 4) calculate depth and position (XYZ) values for each sounding; and 5) output final positions and depths for each sounding. DPS possesses a fully automated capability to post-process the data to obtain corrected depth and horizontal positions within the specified system accuracies. This is accomplished by accurately identifying the surface and bottom returns from the airborne data. Depths are determined by computing the time difference between the arrival of the surface and bottom returns. Corrections are computed and applied for depth biases associated with light propagation, water level fluctuations, and various inherent system characteristics. Surface waves are modeled and removed so that depths can be referenced to a common mean water surface. Applying tidal corrections then produces a depth reference to a known water level datum. A manual processing capability also allows evaluation of anomalous data by providing display and edit functions of sounding data and system parameters. Video imagery of the survey area permits visual scrutiny of the area to aid the hydrographer in deciding whether to exclude suspect data from further processing. Output from the DPS is a digital data set of XYZ (positions/depths) for each laser sounding that is compatible with most most GIS and other contouring and mapping systems.
• 2012-01-01 00:00:00 - The NOAA Office for Coastal Management (OCM) received topographic files in ASCII format. The files contained bathymetric depth measurements. Some sections of the data were received in NAD27 Hawaii State Plane (various zones), other sections were received in NAD27 UTM Zones 4 and 5. The data were vertically referenced to MLLW (feet or meters). OCM performed the following processing for data storage and Digital Coast provisioning purposes: 1. The topographic las files were converted from Projected coordinates (State Plane or UTM) to Geographic coordinates. 2. If the vertical units were feet they were converted to meters. 3. The data were converted from ASCII to LAS V1.2 4. All points were classified to Class 11 (Bathymetry).

This data can be obtained on-line at the following URL:

https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=1457

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