Data Management Plan

These data were collected by the SHOALS-1000T(Scanning Hydrographic Operational Airborne Lidar Survey)system which consists of an airborne laser transmitter/receiver with a 1kHz. bathymetric laser and a10 kHz topographic laser. The system was operated from a Beechcraft King Air 90aircraft. Data were collected with the bathymetric laser while flying at altitudes of about 400 meters and a groundspeed of about 124 knots. The topographic laser data was collected at altitudes of about 700 m and a groundspeed of 150 kts. One KGPS base stations was used during processing of the dataset. The SHOALS system includes a ground-based data processing system for calculating accurate horizontal position and water depth / elevation. 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\x92s 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 sunangle and intensity, and the type and quantity of organics or sediments in the water column. As a rule-of-thumb, the SHOALS 1000 system is capable of sensing bottom to depths equal to two or three times the Secchi depth. Topographic elevations are gridded in this dataset.

Process Steps:

• 2005-05-20 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 Ground Control System (GCS) for survey planning and post-processing. The GCS main functions1) import airborne data stored on removable hard drives;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; and5) output final positions and depths for each sounding. The GCS possesses an 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 and/or KGPS corrections then produces a depth referenced to a known datum. A manual processing capability also allows evaluation of anomalous data by providing display and edit functions of sounding data and system parameters. Digital photos collected once per second (and easily viewed during editing) permit visual scrutiny of the area to aid the hydrographer in deciding whether to exclude suspect data from further processing. Output from the GCS is a digital data set of XYZ(positions/depths) for each laser sounding that is compatible with most GIS and other contouring and mapping systems.
• 2006-04-01 00:00:00 - Both positional information and project control for the LIDAR survey were supplied by the KGPS in the ellipsoidal datum of NAD83.For ease of merging the data set with existing multibeam sounding data, survey instructions required the data to be projected during post-processing and delivered in the UTM Zone 10 projection. The Geoid99 height model was used to convert the vertical datum from the ellipsoidal 3-D datum of NAD83 to the orthometric vertical datum NAVD88. But to accurately merge the LIDAR data with existing multibeam sounding data, the data sets must obviously be in the same vertical reference frame (Milbert 2002).Since the multibeam sounding data were referenced to an averaged tidally-derived vertical datum (MLLW) and the LIDAR data were referenced to an orthometric vertical datum (NAVD88) based on Mean Sea Level (MSL), a VDatum model (Spargo et. al 2006)was used to vertically transform the LIDAR data to MLLW for compatibility and comparison with the multibeam sounding data. The VDatum model relates the NAVD88 to MLLW by using a grid, or zone, of tide model comparisons with known leveled tide benchmark stations to better account for the spatial variability of tidal dynamics over a given area (Milbert 2002;Spargo et. al 2006). The VDatum model that was used is available for download athttp://chartmaker.ncd.noaa.gov/csdl/vdatum_projectsWA.htm.