Data Management Plan

This image represents a LiDAR (Light Detection & Ranging) 3x3 meter resolution relative seafloor reflectivity surface for an area including and surrounding Buck Island Reef National Monument (BUIS), St. Croix in the U.S. Virgin Islands (USVI). The image's horizontal coordinate system is NAD83 UTM 20 North. Fugro LADS, in collaboration with NOAA's NOS/NCCOS/CCMA Biogeography Branch, the University of New Hampshire and the National Park Service, acquired bathymetry, relative seafloor reflectivity and hyperspectral imagery in St. Croix from 2/21 to 2/22/2011. Hyperspectral data were acquired using a Hyspex VNIR-1600 sensor. Bathymetry and reflectivity data were acquired using a LADS (Laser Airborne Depth Sounder) Mark II Airborne System from altitudes between 1,200 and 2,200ft at ground speeds between 140 and 175 knots. The 900 Hertz Nd: YAG (neodymium-doped yttrium aluminum garnet) laser (1064 nm) acquired 3x3 meter spot spacing and 200% seabed coverage. In total, 32.2 square kilometers of LiDAR relectivity were collected between 0 m and 49 m in depth. Environmental factors such as wind strength and direction, cloud cover, water clarity and depth influenced the area of data acquisition on a daily basis. The data was processed using the LADS Mark II Ground System and data visualization, quality control and final products were created using CARIS HIPS and SIPS and CARIS BASE Editor. All users should individually evaluate the suitability of this data according to their own needs and standards.

Process Steps:

• 2011-01-01 00:00:00 - James Guilford and Scott Ramsay from Fugro LADS lead this mapping effort. Hyperspectral data were acquired using a Hyspex VNIR-1600 sensor. Bathymetry and reflectivity data were acquired using a LADS (Laser Airborne Depth Sounder) Mark II Airborne System from altitudes between 1,200 and 2,200ft at ground speeds between 140 and 175 knots. The 900 Hertz Nd: YAG (neodymium-doped yttrium aluminum garnet) laser (1064 nm) acquired 3x3 meter spot spacing and 200% seabed coverage. Green laser pulses are scanned beneath the aircraft in a rectilinear pattern. The pulses are reflected from the land, sea surface, within the water column, and from the seabed. The height of the aircraft is determined by the infrared laser return, which is supplemented by the inertial height from the Attitude and Heading Reference System and GPS height. Real-time positioning is obtained by an Ashtech GG24 GPS receiver combined with Wide Area DGPS (Differential Global Positioning System) provided by the Fugro Omnistar to provide a differentially corrected position. Ashtech Z12 GPS receivers are also provided as part of the Airborne System and Ground Systems to log KGPS (Kinetic Global Positioning System) data on the aircraft and at a locally established GPS (Global Positioning System) base station. | Source Produced: Raw Lidar Data (Citation: Raw Lidar Data)
• 2011-01-01 00:00:00 - The reflectivity of an LADS pulse is a measure of the amount of energy reflected from the seabed for each individual laser pulse at the wavelength of the laser, 532nm (green/blue). The basic difference between processing an ALB waveform for depth and for reflectivity is that depth processing focuses on the leading edge of the return waveform, whereas reflectivity requires integration of the entire return pulse. Each sounding is assessed for suitability. Dry soundings and soundings in very shallow water are not processed for reflectivity. Each sounding is normalized for the electronic gain applied to the photo multiplier tube to which the received laser energy is optically routed. The gain-normalized return waveform is then analyzed to determine energy returning from the seabed. Integration of the waveform from the seabed will produce a numerical value of reflectivity. To ensure that this value accurately and meaningfully describes variation in seabed reflectivity several parameters must be taken into consideration. Energy is lost from the pulses transmitted from the aircraft. These losses include the air/water interface and those through the water column, and any system specific losses such as optical filtering and receiver field of view. Reflectivity value, calculated for each pulse, is the ratio between the received energy normalized for the losses described and the transmitted energy. Once a relative reflectivity value has been calculated, further statistical cleaning to remove outliers is completed. Because the dataset is of relative reflectivity rather than an absolute value for each point, the entire dataset is scaled to ensure the full dynamic range is used over the dataset. This scaling is applied over an entire survey area to ensure dataset consistency (Collins et al. 2007). Collins et al. 2007 is available online here: http://www.fugrolads.com/datasheets/Hydro_Intl_LiDAR_Seabed_Classification.pdf | Source Produced: Processed Lidar Data (Citation: Raw Lidar Data)