2006 NOAA Bathymetric Lidar: Puerto Rico (Southwest)

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This graphic shows the lidar coverage for the 2006 NOAA Puerto Rico bathymetric lidar.

Date that the source FGDC record was last modified.

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using 'fgdc_to_inport_xml.pl' script. Contact Tyler Christensen (NOS) for details.

Partial upload of Positional Accuracy fields only.

Partial upload to move data access links to Distribution Info.

Original full resolution dataset. | Source Geospatial Form: vector digital data | Type of Source Media: external hard drive

Data Acquisition:

For this project (OPR-I305-KRL-06), the Chief of Party was TLI's Darren Stephenson and Hydrographer was TLI's Mark Sinclair.

Data was collected between 4/7/2006 & 5/15/2006 using the LADS Mk II Airborne System. The LADS Mk II Airborne System (AS)

consists of a Dash 8-200 series aircraft, which has a transit speed of 250 knots at altitudes of up to 25,000ft and an

endurance of up to eight hours. Survey operations are conducted from heights between 1,200 and 2,200ft at ground speeds

between 140 and 175 knots. The aircraft was fitted with an Nd: YAG laser, which operates at 900 Hertz from a stabilized

platform to provide a number of different spot spacings. The survey area was sounded at 4x4m laser spot spacing

with main lines of sounding spaced at 80m, which provided the required 200% 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.

For more details on the airborne system, refer to the DAPR (Data Acquisition and Processing Report) at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/2518/supplemental/LiDAR_2006_PuertoRico_DAPR.pdf

Data Processing:

The data was processed using the LADS Mk II Ground System. It consists of a portable Compaq Alpha ES40 Series 3

processor server with 1 GB EEC RAM, 764 GB disk space, digital linear tape (DLT) drives and magazines, digital audio

tape (DAT) drive, CD ROM drive and is networked to up to 12 Compaq 1.5 GHz PCs and a HP 800ps Design Jet Plotter,

printers and QC workstations. The GS supports survey planning, data processing, quality control and data

export. The GS component also includes a KGPS base station, which provides independent post-processed position and height

data. The LADS ground system includes a reflectivity algorithm in which reflectivity is calculated for each sounding

as the ratio of returned energy to transmitted energy, normalized for losses. A comprehensive description of the GS

is provided in the Data Acquisition and Processing Report (DAPR) available at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/2518/supplemental/LiDAR_2006_PuertoRico_DAPR.pdf

Corrections to Soundings:

The optics and electronics for laser transmission and reflected waveform collection for all soundings is done by

equipment mounted on a stabilized platform within the aircraft. This platform is stabilized by an Attitude and Heading

Reference System (AHRS) that minimizes the motion effect (roll and pitch) of the aircraft and all residuals from the local

horizontal are logged by the Airborne System for correctional processing by the Ground System. Sounding depths and

positions are determined in the Ground System from the raw waveform, aircraft height and platform attitude parameters

as logged by the Airborne System. The Ground System automatically corrects soundings for aircraft height and heading,

offsets between sensors, latency, mirror and platform angles, sea surface model errors, refraction of the laser beam at

the sea surface, the effects of scattering of the beam in the water column and reduction for tide. Correct operation

of the system is verified by static and dynamic position checks, benchmark lines and analysis of overlaps, redundancy

from the 200% coverage of the seabed and cross line comparison results.

Reflectance Data:

The reflectance XYZ data was imported into CARIS HIPS and SIPS as single beam data. The reflectance data was treated

much the same as ordinary XYZ data (XY horizontal position and Z as reflectance value). The procedure used is as follows:

- Modified XYZ file to add timestamp by using the CARIS XYZ File Manipulator utility

- Created an import script using the CARIS Generic Data Parser

- Imported modified XYZ file into CARIS HIPS and SIPS

- Computed Total Propagated Error (TPE) using zero values

- Applied tide corrections using a zero value file

- Merged TPE and tide correction with data

- Created field sheet to compute BASE surface of reflectance data

The XYZ had to be modified to add timestamp to each data point. The XYZ file was divided into smaller files containing

a maximum of 1,000,000 points per file. Each modified XYZ file was imported using the CARIS Generic Data Parser, creating

an import script to recognize each field attribute. Two scripts were created to import timestamps 1000000 to 9999999 and

the other 10000000 to 138000000. Once each XYZ file was imported into CARIS a generic zero tide value was applied to each

modified XYZ file followed by a zero TPE value computation. The TPE and tide calculations were then merged with the

reflectance data. A single field sheet was then created to incorporate six 'mean' BASE surfaces, gridded at a 5m resolution,

which covered the entire survey area. Using CARIS BASE Editor, these six BASE surfaces were combined into one surface to

produce a final 'mean' reflectance BASE surface. The necessity to divide the area into six initially was purely due to

processing limitations. Also, the grid resolution does not change relative to depth, as the laser pulse footprint stays

relatively constant regardless of depth and the laser spot spacing is consistent irrespective of aircraft altitude.

The 5m grid provides the largest amount of detail that can be supported by the LiDAR data density.

Quality Control & Product Creation:

CARIS HIPS and SIPS 6.1, Terramodel, Generic Mapping Tool, Visualization Tool Kit and Olex were used for data visualization,

quality control and final product creation. Validation proceeds through the following steps:

1. Examining the Depth Profile for the correct processing of each expected Survey Run.

2. Examining the Position Confidence (C3) profile to verify that adequate position accuracy is maintained during the

Survey Run. Note: Other profiles of supporting data such as EHE, number of satellites, and latency may also be examined

as run profiles.

3. Examining the Coverage Confidence (C6) profile to verify that no coverage gaps exist in the Survey Run.

Resolving anomalous soundings by examining data points in the Survey Run by checking:

a. The Primary Depth Display

b. The Waterfall Display

c. The Waveform Display

d. The Local Area Display

Editing operations include selection of the alternate depth, assignment of NBA or deletion of the sounding as appropriate.

Based on assessments made in the above steps the operator segments the line classifying each segment as:

a. Accepted

b. Anomalous (data not to be used) or

c. Rejected (for refly)

All operator interactions during the validation phase are logged so that complete traceability is maintained.

Data Visualization - All validated and checked data is exported from the GS in a defined ASCII format for spatial

presentation and checking. The position, depth, run and other relevant information are extracted from the line-based

data for use in the generation of Triangulated Irregular Networks (TINs) and gridded data sets. Both of these are used

to produce contour plots, sun-illuminated color banded images and coverage check plots. Anomalies found in these plots are

reported back to the checkers for remedial action in the GS.

Data Gaps -The survey area was sounded at 4x4m laser spot spacing with main lines of sounding spaced at 80m, which provided

the required 200% coverage. It should be noted that at 4x4m laser spot spacing, there is a gap of 1 to 1.5m between the

illuminated areas of adjacent soundings at the sea surface. There is a possibility that small objects in shallow water

along the coastline may fall between consecutive 4x4m soundings and not be detected. There are also some gaps in the data

due to turbidity and very shallow water, as well as an intermittent laser problem on the last survey sortie. This has resulted

in some along track and cross track anomalies and at the time this satisfied the requirement of the survey.

Position Checks - Two independent positioning systems were used during the survey. Real-time positions were aided by WADGPS

(Wide Area Differential Global Positioning System). A post-processed KGPS position was also determined relative to a local GPS

base station that was established on the rooftop of the Courtyard Marriott Hotel in San Juan. The post-processed KGPS position

solutions were applied to each sounding during post-processing and the height used in the datum filter.

Horizontal Control - Data collection and processing were conducted on the Airborne and Ground Systems in World Geodetic

System (WGS84) on Universal Transverse Mercator (Northern Hemisphere) projection UTM (N) in Zone 19, Central Meridian 69 W.

All units are in meters. This data was post-processed and all soundings are relative to the North American Datum 1983 (NAD83).

For more details, please see the Vertical and Horizontal Control Report.

Water Clarity - The water clarity in the survey area was ideal for laser bathymetry as the water was very clear. Coverage

was obtained for the majority of the survey area. The only area where coverage was not achieved was due to turbidity or very

shallow water. Water depths to 50m were achieved at the extent of the predominant reef structure in SW Puerto Rico. The majority

of the survey area is less than 20m deep. There are a number of areas throughout the survey area where no depths were achieved

due to turbidity or very shallow water. The water clarity in some areas did vary on a daily basis, which required careful

management. Additional survey lines were planned and flown to minimize the data gaps due to turbidity.

The final images were re-projected from Transverse Mercator to NAD 1983 UTM Zone 19N using ArcGIS. Holidays (i.e., missing data

values) were filled using a nearest neighbor interpolation technique.

The NOAA Office for Coastal Management received the bathymetric lidar and reflectance data in two 5X5 m grids, in geotiff format.

The data were in UTM Zone 19N, meters, NAD83 coordinates and were vertically referenced to MLLW. The vertical units

of the data were meters. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The data (both bathymetry and reflectance) were converted from geotiff format to xyz text format.

2. The bathymetric data file was split up into 12 smaller files, using the linux command, split.

3. The 12 bathymetric files (xyz) and the reflectance file (xyr) were combined into 12 xyzr files using the NOAA OCM script, brundle.

4. The 12 xyzr files were processed through VDatum to convert from UTM coordinates to geographic coordinates and to convert

from MLLW depths to NAVD88 heights.

5. The 12 xyzr files were converted to las format and the point classifications set to 11 (NOAA OCM bathymetry) using the lastools

tool, txt2las

6. The data were converted from NAVD88 heights to ellipsoid heights using Geoid 12a and the geotiff keys were assigned.

7. Data were zipped to laz format