Coastal Features Extracted from Landsat Satellite Imagery, Northern Chandeleur Islands, Louisiana, 1984-2019

Frequently anticipated questions:

• What does this data set describe?
  1. How might this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  3. What similar or related data should the user be aware of?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How might this data set be cited?
   Bernier, Julie C., 20210921, Coastal Features Extracted from Landsat Satellite Imagery, Northern Chandeleur Islands, Louisiana, 1984-2019:.

   This is part of the following larger work.
   Bernier, Julie C., 20210921, Coastal Land-Cover and Feature Datasets Derived from Landsat Satellite Imagery, Northern Chandeleur Islands, Louisiana: U.S. Geological Survey data release doi:10.5066/P9HY3HOR, U.S. Geological Survey - St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida.

   Online Links:

   • https://doi.org/10.5066/P9HY3HOR

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -88.916003
   East_Bounding_Coordinate: -88.808818
   North_Bounding_Coordinate: 30.054845
   South_Bounding_Coordinate: 29.717502
   

3. What does it look like?
4. Does the data set describe conditions during a particular time period?

   Calendar_Date: 25-Mar-1984

   Currentness_Reference:

   Ground condition

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: Vector and tabular digital data
   

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?
      This is a Vector data set.
   2. What coordinate system is used to represent geographic features?
      

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:

      UTM_Zone_Number: 16
      Transverse_Mercator:

      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -87.0
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.0
      False_Northing: 0.0
      

      Planar coordinates are encoded using Coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.6096
      Ordinates (y-coordinates) are specified to the nearest 0.6096
      Planar coordinates are specified in Meters
      The horizontal datum used is D WGS 1984.
      The ellipsoid used is WGS 1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
      
7. How does the data set describe geographic features?

   nchan_features.zip

   Zip archive containing vector shoreline (nchan_shrln.shp), sand (nchan_sandext.shp), and vegetated (nchan_vegext.shp) feature extents from each of 75 Landsat image-acquisition dates in Esri shapefile (.shp) format. (Source: USGS)

   FID

   Internal feature number (Source: Esri) Sequential unique whole numbers that are automatically generated

   Shape

   Feature geometry (Source: Esri) Coordinates defining the features

   CONTOUR

   Contour value used to delineate features based on automatic thresholding of mNDWI (shoreline), NBLI (sand), and NDVI (vegetated) indices. (Source: Esri) Spectral index values range from -1 to 1 but were converted to signed integers ranging from -10000 to 10000 during processing. The units are dimensionless.

   IMG_DATE

   Image acquisition date (Source: USGS) Source image acquisition date written as DD-MON-YYYY (2-digit day, 3-letter month, 4-digit year)

   DATE_TIME

   Image acquisition date and time (Source: USGS) Source image acquisition date and time written as MM/DD/YYYY 00:00:00 PM

   ambur_perp_transects_300m.shp

   Cross-shore transect locations in Esri shapefile (.shp) format (Source: USGS)

   FID

   Internal feature number (Source: Esri) Sequential unique whole numbers that are automatically generated

   Shape

   Feature geometry (Source: Esri) Coordinates defining the features

   ID

   Baseline identifier (Source: AMBUR) AMBUR-generated baseline identifier

   Transect

   Transect number (Source: AMBUR)

   Range of values
   Minimum:	1
   Maximum:	132
   Units:	Dimensionless
   Resolution:	1

   TranSpace

   Transect spacing, in meters (Source: AMBUR)

   Range of values
   Minimum:	300
   Maximum:	300
   Units:	Meters
   Resolution:	1

   TranDist

   Transect length, in meters (Source: AMBUR)

   Range of values
   Minimum:	3500
   Maximum:	4500
   Units:	Meters
   Resolution:	1

   Location

   Location identifier (optional) (Source: AMBUR) AMBUR-generated identifier

   MaxBNum

   Maximum number of baselines (if applicable) (Source: AMBUR) Used to assign the order which transects are drawn if multiple baselines are present

   BaseOrder

   Baseline order (if applicable) (Source: AMBUR) Used if more than one baseline is present

   OFFshore

   Indicates baseline position (offshore or onshore) (Source: AMBUR)

   Value	Definition
   1	Baseline is located offshore of vector shorelines

   CastDir

   Indicates direction (left or right) transects are cast from baseline (Source: AMBUR)

   Value	Definition
   -1	Transects are cast left of baseline position

   BASE_LOC

   Location identifier (optional) (Source: AMBUR) AMBUR-generated identifier

   StartX

   UTM coordinates of transect starting x position (Source: AMBUR)

   Range of values
   Minimum:	319282.942095
   Maximum:	325039.250404
   Units:	Meters
   Resolution:	0.000001

   StartY

   UTM coordinates of transect starting y position (Source: AMBUR)

   Range of values
   Minimum:	3289009.250058
   Maximum:	3326250.763767
   Units:	Meters
   Resolution:	0.000001

   EndX

   UTM coordinates of transect ending x position (Source: AMBUR)

   Range of values
   Minimum:	316175.515168
   Maximum:	321539.969229
   Units:	Meters
   Resolution:	0.000001

   EndY

   UTM coordinates of transect ending y position (Source: AMBUR)

   Range of values
   Minimum:	3290619.808313
   Maximum:	3323927.400654
   Units:	Meters
   Resolution:	0.000001

   Azimuth

   Azimuth of transect cast (Source: AMBUR)

   Range of values
   Minimum:	48.408288
   Maximum:	117.397400
   Units:	Meters
   Resolution:	0.000001

   Creator

   AMBUR-generated descriptor (Source: AMBUR) AMBUR-generated descriptor

   nchan_featmetrics.csv

   Comma-separated values file detailing derived feature metrics for each of 75 Landsat image-acquisition dates (Source: USGS)

   IMG_DATE

   Image acquisition date (Source: USGS) Source image acquisition date written as DD-MON-YYYY

   Transect

   Transect number (Source: AMBUR)

   Range of values
   Minimum:	1
   Maximum:	132
   Units:	Dimensionless
   Resolution:	1

   SHRLN_min

   Distance in meters along transect from baseline to first intersection with shoreline vector. (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.

   Range of values
   Minimum:	308.653
   Maximum:	4134.120
   Units:	Meters
   Resolution:	0.001

   SAND_min

   Distance in meters along transect from baseline to first intersection with sand extent vector. (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	328.031
   Maximum:	4158.547
   Units:	Meters
   Resolution:	0.0010

   SAND_max

   Distance in meters along transect from baseline to last intersection with sand extent vector. (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	378.954
   Maximum:	4276.354
   Units:	Meters
   Resolution:	0.001

   VEG_min

   Distance in meters along transect from baseline to first intersection with vegetated extent vector. (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	348.025
   Maximum:	3584.820
   Units:	Meters
   Resolution:	0.001

   VEG_max

   Distance in meters along transect from baseline to last intersection with vegetated extent vector. (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	579.304
   Maximum:	3675.872
   Units:	Meters
   Resolution:	0.001

   SHRLN_max

   Distance in meters along transect from baseline to last intersection with shoreline vector. (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	597.792
   Maximum:	4337.832
   Units:	Meters
   Resolution:	0.001

   ISLP

   Width in meters of barrier-island platform (sea shoreline to back-barrier shoreline). (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	17.947
   Maximum:	1782.744
   Units:	Meters
   Resolution:	0.001

   BEACH

   Width in meters of barrier-island beach (sand extent). (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	17.566
   Maximum:	628.044
   Units:	Meters
   Resolution:	0.001

   VEG

   Width in meters of barrier-island vegetation (vegetated extent). (Source: USGS)

   Value	Definition
   NoData	Feature is not present along the transect.
   Excl	Feature was excluded from dataset (see process step description for additional details).

   Range of values
   Minimum:	17.960
   Maximum:	1499.363
   Units:	Meters
   Resolution:	0.001

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • Julie C. Bernier
2. Who also contributed to the data set?
   U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, St. Petersburg Coastal and Marine Science Center
3. To whom should users address questions about the data?
   U.S. Geological Survey

   Attn: Julie C. Bernier

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   727-502-8000 (voice)

   jbernier@usgs.gov

Why was the data set created?

How was the data set created?

1. From what previous works were the data drawn?
2. How were the data generated, processed, and modified?

   Date: 2019 (process 1 of 5)

   For each image acquisition date, top-of-atmosphere (TOA) reflectance (reflective bands), TOA brightness temperature (BT; thermal infrared [TIR] bands), and surface reflectance-derived NDVI images were downloaded from the EROS ESPA On Demand Interface (https://espa.cr.usgs.gov/). Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Julie C. Bernier

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   727-502-8000 (voice)

   jbernier@usgs.gov

   Date: 2019 (process 2 of 5)

   All images were batch-processed using Spatial Model Editor in ERDAS IMAGINE 2016. The TOA and BT bands were stacked to create 7- (TM, ETM+) or 9- (OLI) band multispectral images and clipped to the study-area extent. From these composite images, two additional spectral indices, mNDWI and NBLI, were calculated. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Julie C. Bernier

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   727-502-8000 (voice)

   jbernier@usgs.gov

   Date: 2019 (process 3 of 5)

   Land-cover classification was performed using progressive, automatic thresholding of spectral indices. First, Otsu's method (Otsu, 1979) for automatic histogram thresholding was applied to mNDWI images to create a binary land-water raster for each image acquisition date. Second, water area was masked from NBLI and NDVI images, and Otsu's method was applied to the masked images to create binary bare earth-"unclassed" and vegetated-"unclassed" rasters, respectively. Because thresholding was applied to masked NBLI and NDVI simultaneously, some pixels along the sand-vegetation boundary were classed as both sand and vegetated in this step. We mapped these pixels as sand using the following rule: if NBLI = sand and NDVI = vegetated, then final = sand (based on visual analysis during workflow development). Next, water, bare earth (sand), and vegetated areas were masked from mNDWI images, and Otsu's method was applied to the masked mNDWI image to separate the "submerged" and "emergent" intertidal areas. Finally, the binary land-cover images were converted to thematic rasters, merged, and single-pixel "clumps" were removed using a 3x3 majority filter to create a final land-cover raster dataset. All steps were batch-processed using the Image Processing toolbox in MATLAB version R2018a (Otsu thresholding and binary image creation) or Spatial Model Editor in ERDAS IMAGINE 2016 (spectral index masking and generation of classed land-cover rasters). Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Julie C. Bernier

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   727-502-8000 (voice)

   jbernier@usgs.gov

   Date: 2020 (process 4 of 5)

   Vector shoreline (representing the boundary between intertidal and open-water areas), sand, and vegetated extents were extracted by contouring the mNDWI and masked NBLI and NDVI images using the calculated Otsu thresholds. The resulting shapefiles (one per image acquisition date) were merged into 3 shapefiles (one each for shoreline, sand, and vegetated feature extents). Contouring was batch-processed using PythonWin 2.7 with Esri ArcGIS 10.5. Vector features corresponding to a minimum mapping unit of less than 5 pixels were excluded from the final dataset. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Julie C. Bernier

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   727-502-8000 (voice)

   jbernier@usgs.gov

   Data sources produced in this process:

   • nchan_shrln.shp
   • nchan_sandext.shp
   • nchan_vegext.shp

   Date: 2020 (process 5 of 5)

   Barrier platform, beach, and vegetated widths were calculated from the intersection of the shoreline, sand, and vegetated vectors with transects spaced 300 m (10 pixels) apart alongshore. The software package AMBUR version 1.1.27 (Analyzing Moving Boundaries Using R; Jackson and others, 2012) was used to create transects perpendicular to an offshore baseline and extract feature positions along the transects. The western islands, isolated back-barrier islands that are less than 8 pixels in size, and back-barrier islands that are more than 8 pixels from the contiguous island extent were excluded from the features dataset. Feature widths were calculated in Microsoft Excel for Mac version 16.50. Feature widths were not calculated along transect 57, where the oblique nature of the back-barrier marsh island, coupled with a change in baseline orientation, caused inconsistencies in delineating feature extents. Features less than 17 m wide along-transect are considered unresolvable based on the stated 12-m RMSE for Landsat L1TP products (sqrt(12^2 + 12^2) = 16.97) and were also excluded from the final dataset. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Julie C. Bernier

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   727-502-8000 (voice)

   jbernier@usgs.gov

   Data sources produced in this process:

   • ambur_perp_transects_300m.shp
   • nchan_featmetrics.csv

3. What similar or related data should the user be aware of?
   Bernier, Julie C., Miselis, Jennifer L., and Plant, Nathaniel G., 20210921, Satellite-derived barrier response and recovery following natural and anthropogenic perturbations, northern Chandeleur Islands, Louisiana: Remote Sensing Special Issue "New Insights into Ecosystem Monitoring Using Geospatial Techniques".

   Online Links:

   • https://doi.org/10.3390/rs13183779

   Otsu, Nobuyuki, 1979, A Threshold Selection Method from Gray-Level Histograms: IEEE Transactions on Systmes, Man and Cybernetics Volume 9.

   Online Links:

   • https://doi.org/10.1109/TSMC.1979.4310076

   Other_Citation_Details: Pages 62-66
   

   Jackson, Chester W. Jr., Alexander, Clark R., and Bush, David M., 2012, Gradistat: Application of the AMBUR R package for spatio-temporal analysis of shoreline change: Jekyll Island, Georgia, USA: Computers & Geosciences Volume 41.

   Online Links:

   • https://doi.org/10.1016/j.cageo.2011.08.009
   • https://ambur.r-forge.r-project.org/

   Other_Citation_Details: Pages 199-207
   

How reliable are the data; what problems remain in the data set?

1. How well have the observations been checked?
   
2. How accurate are the geographic locations?
   Geodetic accuracy of Landsat L1TP data products depend on the accuracy of the ground control points and the resolution of the digital elevation model (DEM) used. All L1TP data products and derived Level-2 science products meet pre-defined image-to-image georegistration tolerances of <= 12-meter (m) radial root mean square error (RMSE). The positional accuracy of the satellite-derived features was not systematically evaluated in this study; however, recent analyses of satellite-derived shoreline (SDS) positions extracted using similar methods to those presented here report offsets of 1/3 to 1/2 pixel (10 to 15 m) seaward of measured in-situ shoreline positions. Compared with methods that extract shoreline position from precise elevation measurements (for example, lidar or GPS surveys), SDS positions are not based on a vertical datum (for example, mean sea level or mean high water); instead, SDS positions may include intertidal areas.
3. How accurate are the heights or depths?
   
4. Where are the gaps in the data? What is missing?
   193 Landsat TM, ETM+, and OLI images (Worldwide Reference System 2 [WRS-2] path 21 row 39) acquired between March 1984 and January 2019 were identified that were cloud free and, for Landsat 7 ETM+ images, were either pre-scan line corrector failure (SLC-off) or SLC-off gap free over the study area. To minimize the effects of water-level variations on land-cover classification, only images that were collected within 2 hours of predicted low tide or were collected on a rising tide with predicted water levels at time of acquisition less than mean sea level (National Ocean Service [NOS] Center for Operational Oceanographic Products and Services [CO-OPS] station 8760172, Chandeleur Light, LA) were analyzed. The resulting dataset consisted of 52 Landsat 5 TM, 10 Landsat 7 ETM+, and 13 Landsat 8 OLI images.
5. How consistent are the relationships among the observations, including topology?
   For each image-acquisition date, Landsat Collection 1 Level-1 Precision and Terrain (L1TP) corrected data products and Level-2 science products were downloaded from the USGS Earth Resources Observation and Science (EROS) Center Science Processing Architecture (ESPA) On Demand Interface (https://espa.cr.usgs.gov/).

How can someone get a copy of the data set?

1. Who distributes the data set? (Distributor 1 of 1)
   
   U.S. Geological Survey

   Attn: Julie C. Bernier

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   USA

   727-502-8000 (voice)

   jbernier@usgs.gov
2. What's the catalog number I need to order this data set? nchan_featmetrics.csv, ambur_perp_transects_300m.shp, nchan_sandext.shp, nchan_shrln.shp, and nchan_vegext.shp
3. What legal disclaimers am I supposed to read?
   This publication was prepared by an agency of the United States Government. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.
4. How can I download or order the data?
   • Availability in digital form:

     Data format:	This zip archive contains vector feature datasets in Esri shapefile (.shp) format, a comma-separated values (.csv) file detailing derived feature metrics, and accompanying metadata for each of 75 Landsat image-acquisition dates. in format Compressed (zip) archive
     Network links:	https://coastal.er.usgs.gov/data-release/doi-P9HY3HOR/data/nchan_features.zip

   • Cost to order the data: None, if obtained online

5. What hardware or software do I need in order to use the data set?
   These vector datasets were created using Esri ArcGIS version 10.5 and can be opened using Esri ArcGIS version 10.0 or higher; these data may also be viewed using the free Google Earth Pro GIS viewer.

Who wrote the metadata?

Dates:

Last modified: 21-Sep-2021

Metadata author:

U.S. Geological Survey

Attn: Julie C. Bernier

Geologist

600 4th Street South

St. Petersburg, FL

USA

727-502-8000 (voice)

jbernier@usgs.gov

Metadata standard:

FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)