1999 USACE Bathymetric LiDAR: Hawaiian Islands
This kmz file shows the extent of coverage for the 1999 USACE Hawaiian Isalnds bathymetric
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 acurate 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 propogates 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.
Cite this dataset when used as a source.
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| Point of Contact
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|Data Presentation Form:
|| Digital image
|Dataset Progress Status
|Data Update Frequency:
|| As needed
||The purpose of the survey was to investigate the near-shore bathymetry and coral reefs
near the west shore of Oahu, the south shore of Moloka'i and all the shores of Maui.
||1999-03-01 to 1999-04-01
|Spatial Reference System:
|Spatial Bounding Box Coordinates:
|Spatial Coverage Map:
- lidar survey
- Hydrographic Survey
| Use Constraints
|| No constraint information available
|| Fee information not available.
|| Lineage statement not available.
| Processing Steps
- 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 funcions 1) import airborne data stored on
high density datatape; 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 propogation, 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
scutiny 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.
- The NOAA Coastal Services Center (CSC) 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).
CSC 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). 5. The data were converted to LAZ format.
- The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp
transfer from the NOAA Coastal Services Center. The data are currently
being served via NOAA CSC Digital Coast at http://www.csc.noaa.gov/digitalcoast/.
The data can be used to re-populate the system. The data are archived in LAS or LAZ
The LAS format is an industry standard for LiDAR data developed by the American Society
of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless compressed version
LAS developed by Martin Isenburg (http://www.laszip.org/). The data are exclusively
in geographic coordinates (either NAD83 or ITRF94). The data are referenced vertically
the ellipsoid (either GRS80 or ITRF94), allowing for the ability to apply the most
up to date geoid model when transforming to orthometric heights.
Metadata Last Modified: 2013-03-28
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