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.
The purpose was to survey the entire perimeter of Puerto Rico, Culebra and Vieques collecting data either to depths of 30m or 2000m offshore.
ground condition
These data are not to be used for navigational purposes. Acknowledgement of the U.S. Army Engineer Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBCTX) would be appreciated in products derived from these data.
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SHOALS has demonstrated capabilities that meet US Army Corps of Engineers Hydrographic Survey accuracy requirements for Class 1 surveys (1:50,000 horizontal point closure standard) and the International Hydrographic Organization nautical charting standards for Order 1.
No additional checks for topological consistency were performed on the data
The data used to create this image only included (negative) depth values from the SHOALS lidar survey. Additional data exists for this area but was not included in the process steps to generate the GeoTIFF image.
The horizontal point closure is determined by dividing the linear distance misclosure of the survey into the overall circuit length of a traverse, loop, or network line/circuit. When independent directions or angles are observed, as on a conventional survey (i.e., traverse, trilateration, or triangulation), these angular misclosures may optionally be distributed before assessing positional misclosure. In cases where GPS vectors are measured in geocentric coordinates, then the three-dimensional positional misclosure is assessed.
1 sigma or 95% confidence interval
The vertical accuracy of a survey is determined by the elevation misclosure within a level section or level loop. For conventional differential or trigonometric leveling, section or loop misclosures (in feet) shall not exceed the Class 1 limit of 0.025 times the square root of distance M (0.025*sqrtM), where the line or circuit length (M) is measured in miles.
1 sigma or 95% confidence interval
SHOALS - Puerto Rico Shoreline Survey
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 are: 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.
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Final positions and soundings were converted from an Excel formatted file to a space delimited text file and imported into Fledermaus (Avggrid).
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The soundings were gridded using a weighted moving average interpolation routine with a weight diameter of 3 and a cell size of 5 meters.
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The resulting grid was exported as a GeoTiff in geographic coordinates using Imageviewer.
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Internal feature number.
ESRI
Pixel value for red histogram.
U.S. Geological Survey
Count number for red histogram.
U.S. Geological Survey
Internal feature number.
ESRI
Pixel value for green histogram.
U.S. Geological Survey
Count value for green histogram.
U.S. Geological Survey
Internal feature number.
ESRI
Pixel value for blue histogram
U.S. Geological Survey
Count value for blue histogram.
U.S. Geological Survey
Internal feature number.
ESRI
Pixel value for hillshade histogram.
U.S. Geological Survey
Count value for hillshade histogram
U.S. Geological Survey
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Although this data set has been used by the U.S. Geological Survey (USGS) and the U.S. Army Corps of Engineers (USACE), no warranty, expressed or implied, is made by the USGS or the USACE as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS or the USACE in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
GeoTIFF
GeoTIFF format image with world file and associated metadata
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