Upland boundary lines, points, and transects with rates for the Point Aux Chenes and Grand Bay Estuaries in Mississippi and Alabama from 1848 to 2022

Topographic sheets (t-sheets) for 1848 (T00243 and T00273) and 1957/1958 (T10744, T10745, and T10752) were added to ArcMap and projected into the North American Datum of 1983 Universal Transverse Mercator Zone 16N (NAD83 UTM 16N). Data was checked by the creating user as well as a second ArcGIS user on the project to ensure positional accuracy with other published data sources. During this check, it was discovered T00273 was slightly shifted from T00243 due to an error within the published NOAA data. Using the ArcGIS Pro georeferencing toolbar, the T00273 t-sheet was georectified using the T00243 t-sheet as a reference. Each t-sheet contained lines representing the upland boundary that were heads up digitized within ArcMap using the Editor toolbar at a scale of 1:1500.

WorldView 2 imagery from 20191116 (YYYYMMDD) and 20220511 were downloaded from Maxar’s G-EGD. The images were radiometrically and atmospherically corrected and then pansharpened using ERDAS IMAGINE 2020 (version 16.6.0) to obtain measures of ground reflectance. The output image was reprojected into the common projection system of Universal Transverse Mercator World Geodetic System of 1984 datum (UTM zone 16N, WGS 1984). The image was then co-registered to high-resolution aerial imagery (NAIP) using the AutoSync-workstation in ERDAS Image pixels. First, an NAIP image mosaic was created for an extent larger than the WV image coverage. Ground control points coincident on both images were used to adjust the WV image to the corresponding location on the NAIP. Control points with an error value greater than 1 meter were removed. A methodology similar to that described by Maglione and others (2014) was used to generate vector lines from WorldView (WV) images. Normalized difference vegetation index (NDVI) was calculated using WV band 5 in the visible red spectrum (RED) and band 7 in the near-infrared spectrum (NIR1) using the following formula: NDVI=(NIR1−RED)/(NIR1+RED). High values (above 0.65) were classified as upland, low values (less than 0.21) as water, and in between values (0.21 to 0.65) as marsh. Using ArcGIS Pro expand-and shrink tools, isolated pixels were removed from the wetland-upland raster. In ArcGIS Pro, the classification boundaries were smoothed to remove any extraneous cells missed in the expand and shrink steps. The raster was then converted into polygons and the polygons were converted into polylines. To smooth the ridged cell edges the Polynomial Approximation with Exponential Kernel (PAEK) algorithm and a 2-meter smoothing filter was used. During a quality review, it was discovered that there were several single cells that were classified as upland but were not visibly upland on the WorldView imagery. Collections of these cells with a circumference less than 100 meters was removed as they often were misclassified cells and not upland. Lines were then projected into NAD83 UTM 16N.

The vectorized upland lines produced in the previous process steps were compiled and edited in ArcGIS Pro. Once all lines were edited and checked, all dated lines were merged into a single shapefile for inclusion in this data release as Upland_lines_1848_1957_2022.shp. Attributes were edited to include information regarding the date and source of the original data. Compiled upland lines were processed using the Analyzing Moving Boundaries Using R (AMBUR) statistical package for R to add required missing attributes and calculate upland change rates. AMBUR performs a boundary change analysis on vector digital lines using a transect based method (Jackson, 2010). All necessary attribute fields must be present in order to run various AMBUR functions; the following fields are required for boundaries: "Id", "Date_", "Accuracy", "SHORE_LOC", "CLASS_1", "CLASS_2", "CLASS_3", and "GROUP". To determine if all the required fields were present in the merged boundary datasets, an AMBUR sub-routine (ambur.check) was used to check all upland shapefiles for missing attribute fields. During the change analysis, AMBUR also creates shorepoints. A shorepoint was created at each transect and upland line intersect point, referred to as upland boundary points in this metadata. Several transects intersected upland lines that doubled back or intersected both sides of a creek. In these instances, multiple shorepoints were created for the same date on the same transect. To remove the duplicate points, the shorepoint file was run through an R code to remove all shorepoints after the first intersection for each date. For more information about the AMBUR file requirements see the AMBUR user manual (Jackson, 2010). Some fields created by AMBUR ("SHORE_LOC", "CLASS_1", "CLASS_2", "CLASS_3", and "GROUP") are required and have null values as placeholders. Null fields were left in the final published file as they are required by AMBUR and are necessary to replicate this study.

Transects were generated by buffering the upland datasets produced in the previous step to create inner (landward of the upland lines) and outer (seaward of the upland lines) baselines. The baselines form the start and end point for upland line-perpendicular transects. Baselines were input into the AMBUR statistical package for R. AMBUR has several tools, which utilize parallel baselines to generate transects that are generally perpendicular to the upland lines. Transects were constructed at a sampling distance of 50 meters. Once transects were created, the "Filter Transects" tool was used to adjust and even out the spread of transects. Where upland lines experience sharp bends transects may fall at a non-perpendicular angle. Areas with non-perpendicular transects were manually edited in ArcGIS Pro to ensure transects were perpendicular to the upland. Transects were manually edited to reduce errors in the analyses. Transects and upland lines were run through AMBUR to generate shorepoints (upland boundary points) and transects with change rates. The following analysis parameters were used: first intersection (if transect intersects the same upland line more than once, then by default it selected the first intersection), confidence level 95 (confidence level for the linear regression statistics), unit label m (the units of measure for the map is for Universal Transverse Mercator and in meters), analysis type is advanced (advanced includes additional statistics for a robust linear regression), and time unit for rates is yr (utilizes years for calculating rates of change). For more information on the AMBUR program, refer to Jackson (2010).