Title:EAARL Topography-Dry Tortugas National Park Abstract:
Lidar is a remote sensing technique that uses laser light to detect, range, or identify remote objects based on light reflected by the object or emitted through it subsequent fluorescence. Airborne ranging lidar is now being applied in coastal environments to produce accurate, cost-efficient elevation datasets with high data density. The USGS in cooperation with NASA and NPS is using airborne lidar to measure the submerged topography of the Dry Tortugas reef tract and Subaerail topography of land features; secondarily, the data will be assessed for its potential in terms of benthic characterization. Elevation measurements were collected over Dry Tortugas National Park using the NASA Experimental Advanced Airborne Research Lidar (EAARL), a pulsed laser ranging system mounted onboard an aircraft to measure subaerial and submarine coastal topography. With the NASA EAARL lidar system, submarine data is generally acquired to a maximum of approximately 1.5 secchi depths (a measure of water clarity). The system uses a high frequency laser beam directed at the earth's surface through an opening in the bottom of the aircraft's fuselage. The laser system records the time difference between emission of the laser beam and the reception of the reflected laser signal in the aircraft. The Experimental Advanced Airborne Research Lidar, developed by the National Aeronautics and Space Administration (NASA) Wallops Flight Facility (WFF) in Virginia, measures ground elevation with a vertical resolution of roughly 15 centimeters. A sampling rate of up to 3 kHz results in an extremely dense spatial elevation data set.
For more information on Lidar science and the Experimental Advanced Airborne Research Lidar (EAARL) system and surveys, see http://ngom.usgs.gov/dsp/overview/index.php and http://ngom.usgs.gov/dsp/tech/eaarl/index.php .
Raw lidar data is not in a format that is generally usable by Park Service resource managers and scientists for scientific analysis. Converting dense lidar elevation data into a readily usable format without loss of essential information requires specialized processing. The USGS converts raw lidar data into a GIS-compatible map product to be provided to National Park Service GIS specialists, managers, and scientists. The primary tool used in the conversion process is Airborne Lidar Processing System (ALPS), a multi-tiered processing system developed by a USGS/NASA collaborative project for the use of subaerial and submarine lidar in coastal change assessment. Specialized processing algorithms are used to convert raw waveform lidar data acquired by the EAARL to georeferenced spot (x,y,z) returns for submarine topography. These data are then converted to the NAD83 horizontal and NAVD88 vertical datum (using the Geoid 99 model). The final products are 2x2-km map tiles written out in a standard geotiff format with associated metadata information. These tiles are created for visual interpretation and regional quantitative analysis. Metadata files include the standard FGDC format.
The USGS, in cooperation with the National Park Service (NPS) and the National Aeronautics and Space Administration (NASA), provide the coastal management community with digital elevation products. The USGS processes aircraft lidar data provided by NASA, develops software tools and algorithms to use and analyze the data, and makes products available to the coastal management community.
Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 1.000000
Ordinates (y-coordinates) are specified to the nearest 1.000000
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257222.
Altitude_Datum_Name:North American Vertical Datum of 1988 Altitude_Resolution:.01 Altitude_Distance_Units:meters Altitude_Encoding_Method:
Explicit elevation coordinate included with horizontal coordinates
Depth_Datum_Name:North American Vertical Datum of 1988 Depth_Resolution:.01 Depth_Distance_Units:meters Depth_Encoding_Method:Explicit depth coordinate included with horizontal coordinates
This Digital Elevation Model is an Geotiff derived from point data. It is raster data consisting of cells. Each cell has an elevation value associated with it. Cell size is 1 meter by 1 meter.
This Digital Elevation Model is an Geotiff derived from point data referenced to WGS84, NAD83 UTM eastings and northings (m). The variables measured by EAARL are: distance between aircraft and GPS satellites (m), attitude information (roll, pitch, heading in degrees), scan angle (degrees), second of the epoch (sec), and 1-ns time-resolved return intensity waveform (digital counts). It is raster data consisting of cells. Each cell has an elevation value associated with it. Cell size is 1 meter by 1 meter.
The USGS Center for Coastal and Watershed Studies would like to acknowledge NASA Goddard Space Flight Center for their cooperation and assistance in the development of the data. The USGS would also like to acknowledge Park Management and personnel at Dry Tortugas National Park. The National Park Service also contributed by editing the lidar tiles to remove processing artifacts.
One objective of this research is the creation of techniques for the surveying of coral reefs for the purposes of habitat mapping, ecological monitoring, change detection, and event assessment (e.g., bleaching, hurricanes, disease outbreaks, etc.). As part of this project, data from an innovative instrument developed at NASA Wallops Flight Facility, the NASA Experimental Airborne Advanced Research Lidar (EAARL), was used. This sensor has the potential to make significant contributions in this realm for measuring water depth and conducting cross-environment surveys. High spectral resolution, water-column correction, and low costs were found to be key factors in providing accurate and affordable imagery to managers of coastal tropical habitats.
The data are collected using a Cessna 310 aircraft. The NASA Experimental Advanced Airborne Research Lidar (EAARL) laser scanner collects the data using a green (532nm) raster scanning laser, while a digital camera acquires a visual record of the flight. The data are stored on hard drives and archived at the USGS office in St. Petersburg and the NASA office at Wallops Flight Facility. The navigational data are processed at Wallops Flight Facility. The navigational and raw data are then downloaded into the Airborne Lidar Processing System (ALPS). Data are converted from units of time to x,y,z points for elevation. The derived surface data can then be converted into raster data (geotiffs).
Person who carried out this activity:
United States Geological Survey Center for Coastal and Watershed Studies
Attn: Amar Nayegandhi
600 4th Street South
St. Petersburg, Florida
Hours_of_Service:8:00am to 5:00pm Monday thru Friday, EST Contact_Instructions:Call Survey for Details
Date: 01-Mar-2006 (process 2 of 4)
The raster dataset was opened in ERDAS IMAGINE for editing. An Area of Interest (AOI) polygon was drawn around regions of poor data quality. Poor data quality was determined visually by locating gaps in the data as well as artifacts of the lidar processing. Pixels within the AOI polygons were given a raster value of -100 to correspond with other areas of No Data.
Person who carried out this activity:
National Park Service South Florida / Caribbean Network Inventory and Monitoring Program
Attn: Judd Patterson
18001 Old Cutler Road
(305) 252-0347 (voice)
(305) 253-0463 (FAX)
Date: 24-Jan-2017 (process 3 of 4)
Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.
Person who carried out this activity:
U.S. Geological Survey
Attn: Alan O. Allwardt
Contractor -- Information Specialist
2885 Mission Street
Santa Cruz, CA
Date: 13-Oct-2020 (process 4 of 4)
Added keywords section with USGS persistent identifier as theme keyword.
Person who carried out this activity:
Brock, J.C.; Wright, C.W.; Sallenger, A.H; Krabill, W.B., and Swift, R.N, 2003, Basis and Methods of NASA Ariborne Topographic Mapper Lidar Surveys for Coastal Studies: Journal of Coastal Research, West Palm Beach, FL.
Wright, C.W. and J. Brock, 2002, EAARL: A lidar for mapping shallow coral reefs and other coastal environments: Proceedings of the Seventh International Conterence on Remote Sensing for Marine and Coastal Environments, Miami.
John Brock and Asbury Sallenger, US Geological Survey, 2001, Airborne Topographic Lidar Mapping for Coastal Science and Resource Management: US Geological Survey, St. Petersburg, FL.
How well have the observations been checked?
The expected accuracy of the measured variables are as follows: attitude within 0.07 degree, 3-cm nominal ranging accuracy, and vertical elevation accuracy of +/-20 cm for the "first return" surface. Quality checks are built into the data-processing software.
How accurate are the geographic locations?
Raw elevation measurements have been determined to be within 1 meter horizontal accuracy. Processing steps (grid interpolation) may introduce additional error which has not been tested at the time of this publication.
Where are the gaps in the data? What is missing?
Several regions of the dataset are labeled as "No Data", which corresponds to a cell value of -100 m in the GeoTiff file. These "No Data" areas are a result of the survey not covering a particular region, optical water depth of greater than 1.5 Secchi disc depths, or the manual removal of lidar processing artifacts.
How consistent are the relationships among the observations, including topology?
Each file contains data located in a 2-km by 2-km tile, where the upper-left bound can be assessed quickly through the file name. The first 3 numbers in the file name represent the left-most UTM easting coordinate (e###000) in meters, the next 4 numbers represent the top-most UTM northing coordinate (n####000) in meters, and the last 2 numbers (##) represent the UTM zone in which the tile is located (for example, ba_e123_n4567_20).
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