Unvegetated to vegetated ratio of marsh units in eastern Long Island salt marsh complex, New York (ver. 3.0, May 2026)

Process step 1. This process step and all subsequent process steps were performed by the same person, Robert Welk, in ArcMap (ver. 10.7.1) using tools from ArcToolbox, unless otherwise stated. For complex operations, names of specific tools used are given in CAPITAL letters (any critical parameters used are given in parentheses, separated by a semicolon, immediately after the tool name). The input and output file names are provided in [square brackets] when necessary. Units for length and area calculations are meters (m) and square meters (m2) unless otherwise stated.
a) Set the data frame coordinate system and projection to NAD 1983 UTM Zone 18N.
b) Prepare elevation dataset to be clipped to the boundaries polygon. MOSAIC TO NEW RASTER(Pixel type= 32 bit float; Mosaic operator=Mean; Cellsize=1 m) the entire NED raster to a new raster dataset with 1 m resolution [elev_mosaic.tif].
c) Establish marsh unit boundaries. Dissolve the vegetated and unvegetated classes in each marsh unit to have only one class for each marsh unit. DISSOLVE (Input features=[CMU_ELI.shp]; Dissolve field=FID_CMU; Statistics field=ATOT_M2 and FLG with Statistics type= First). PROJECT (Input coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Output coordinate system=NAD 1983 UTM Zone 18N) the feature dataset to obtain dissolved marsh units [mu_diss.shp].

Process step 2. Prepare mask polygon to define analysis boundaries. In order to account for the possible influence of the surrounding terrain on the analysis, a mask area larger than the salt marsh extent is first created [UVVR_mask]. At the end of the analysis the results are clipped to the boundaries of the salt marsh area [MU_mask]. Both UVVR_mask and MU_mask are edited to decide which interior polygons are removed.
a) MERGE DEC and NWI wetland polygons to obtain [NWI_DEC.shp].
b) EXPORT features from NWI dataset after SELECT("ATTRIBUTE" LIKE 'E2%EM%' OR "ATTRIBUTE" LIKE 'E2AB3%' OR "ATTRIBUTE" LIKE 'E2EM%' OR "ATTRIBUTE" LIKE 'E2SS%' OR "ATTRIBUTE" LIKE 'E2US4%') to select from estuarine intertidal areas of 1) emergent wetland, 2) scrub-shrub area, 3) rooted vascular aquatic bed, 4) Organic unconsolidated shore classes [NWI_exclusive_select.shp].
c) BUFFER(Input features=[NWI_exclusive_select.shp]; Linear unit=5 meters; Dissolve type=All) to obtain the mask polygon [buff5m.shp] and ELIMINATE POLYGON PART(Condition=Percentage; Percentage=99; Eliminate contained part only) to obtain [UVVR_mask01.shp]. Apply buffer with -5 meters to obtain [MU_mask01.shp].
d) EXPORT features from NWI dataset after SELECT("ATTRIBUTE" NOT LIKE 'E%' OR "ATTRIBUTE" LIKE '%FO')to obtain features that are not estuarine or are forested estuarine. MULTIPART TO SINGLEPART to separate individual polygons [NWI_inclusive_single.shp].
e)To exclude the voids in the NWI map during the analysis these interior polygons need to be removed from the mask. Create a rectangular polygon that covers the domain [extent.shp]. ERASE [NWI_excusive_select.shp] from [extent.shp] and MULTIPART TO SINGLEPART to get [NWI_voids_single.shp].
f) SELECT BY LOCATION from [NWI_inclusive_single.shp] that are completely within the [MU_mask01.shp], and SELECT BY LOCATION from [NWI_voids_single.shp] that are completely within the [MU_mask01.shp]. If any additional polygons need to be removed from the mask include them in a new feature layer [erase_mask_manual.shp]. Merge all three feature sets to get polygons to be excluded [erase_inside.shp] from the final masks.
g) ERASE [erase_inside.shp] from [MU_mask01.shp] and [UVVR_mask01.shp] to obtain [MU_mask.shp] and [UVVR_mask.shp], respectively.

Process step 3. Compute vegetated and unvegetated boundaries by image processing.
a) EXTRACT BY MASK from elevation raster [elev_mosaic.tif] using [UVVR_mask.shp] polygon. Rescale the elevation raster values to the same range with 8-bit NAIP imagery (0 to 255) using min-max scaling. Perform ISO CLUSTER UNSUPERVISED CLASSIFICATION with 4-bands (near infrared, blue, green, and red from the NAIP imagery and the rescaled elevation raster with 32 classes and a minimum class size of 5000 cells. RECLASSIFY the classified raster by visually comparing the NAIP imagery to obtain the unvegetated-vegetated raster [UVVc.tif]. For marsh units with invalid elevation data, the classification was processed with imagery bands only and later merged with the rest of the dataset.
b) Dissolve unvegetated regions smaller than a threshold value to the surrounding vegetated regions and vice versa to clean the UVV raster. For this purpose use the REGION(Number of neighbors=4; Zone grouping method=Within; Add Link field to output) to get the [UVV_region.tif], and TEST("Count" less than 9) to set a threshold value of 9 raster cells [UVV_test.tif]. Use RASTER CALCULATOR to toggle the value of the Link field in the region raster, where the test raster indicates regions with areas smaller than the threshold.
c) In the version 3 revision, this step was re-run (using ArcGIS Pro 3.4.3). RASTER TO POLYGON(Simplify polygons=False) and CLIP with the final marsh complex outline [mu_diss.shp] to obtain [UVVc_filt_clip.shp].
d) In the version 3 revision, this step was re-run (using ArcGIS Pro 3.4.3). REPAIR GEOMETRY and DISSOLVE(Create multipart features=False) to get filtered, clipped and dissolved unvegetated-vegetated polygons [UVVc_filt_clip_diss.shp].
e) In the version 3 revision, this step was re-run (using ArcGIS Pro 3.4.3). INTERSECT the dissolved conceptual marsh units [mu_diss.shp] with unvegetated-vegetated polygons [UVVc_filt_clip.shp], REPAIR GEOMETRY, and calculate the area of unvegetated and vegetated polygons in each marsh unit. To do this ADD GEOMETRY ATTRIBUTES(Geometry properties=Area_geodesic; Area unit=Square_meters) to get [UVV_poly.shp], and DISSOLVE(Input features=UVV_poly.shp; Dissolve fields=FID_CMU, gridcode; Statistics field=gridcode.MEAN, Area_geo.SUM) and REPAIR GEOMETRY to get [UVV_poly_diss.shp]. Edit the fields to have "TYP", "APGN_M2", and "ATOT_M2" fields for type of polygon indicating vegetated or unvegetated, surface area of the polygon, and total surface area of the marsh unit, respectively.
f) In the version 3 revision, this step was re-run (using ArcGIS Pro 3.4.3). Add field "UVVR" and calculate unvegetated to vegetated ratio based on "TYP", "APGN_M2" and "ATOT_M2" fields. If the vegetated area is zero for a marsh unit set the value of UVVR to -1.
g) In the version 3 revision, this step was re-run (using ArcGIS Pro 3.4.3). DISSOLVE(Input features=UVV_poly_diss.shp; Dissolve fields=FID_CMU, gridcode; Statistics field=UVVR, ATOT_M2 and FLG with Statistics type= First for all) to obtain mu_UVVR_FIIS.shp]. FLG flags anomalous marsh units based on absence of vegetation, elevation, surface area, and tidal range extrapolation. The flags are calculated in their respective shapefile (i.e., elevation flags are calculated in the elevation shapefile). Set FLG to: (-1) no vegetated area in the marsh unit; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than the 0.2 percentile; (-200) greater than 25 percent of the marsh unit elevation is hydro-flattened; (-1000) marsh unit surface area less than 900 square meters; (-10000) mean tidal range of marsh unit is extrapolated; and (0) no flag. Combination of negative values indicates a combination of flags; for example, -1001 indicates no vegetated area and area less than 900 square meters.
h) In the version 3 revision, this step was re-run (using ArcGIS Pro 3.4.3). SELECT BY ATTRIBUTES FROM [CMU_ELI] where "TYP"= 'vegetated', and JOIN FIELD "APGN_M2" from [CMU_ELI.shp] to [mu_UVVR_ELI.shp] and rename this field "AVEG_M2."
i) In the version 3 revision, this step was re-run (using ArcGIS Pro 3.4.3). Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Input coordinate system=NAD 1983 UTM Zone 18N; Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain the final conceptual marsh units [mu_UVVR_ELI.shp].

Process step 4. Added keywords section with USGS persistent identifier as theme keyword.

Process Step 5. Version 2 updates. Updates were performed in ArcGIS Pro 2.8.8. Duplicate marsh units were manually identified and compared to make sure the most appropriate duplicate marsh unit was deleted. Seventy-six duplicate marsh units were identified (out of 2828) in Mecox Bay, Sagaponack Pond and Georgica Pond and have been removed. After the duplicate marsh units were deleted, the elevation, hydroflattened percentage and elevation flag values were recalculated. Authorship was updated to include Kate Ackerman.

Process Step 6. Version 3 Updates. All updates were completed in ArcGIS Pro 3.4.3, using the version 2 of the dataset as the starting dataset. In the original dataset, each marsh plain was not subdivided into smaller parcels ("marsh units") because two processing steps were not completed. For Version 3, these processing steps were completed, resulting in each marsh plain being properly subdivided into these smaller marsh units. Using the new marsh units, UVVR and elevation values were recalculated. Tide range values were carried over from the original (larger) marsh plain polygons and applied to the new, smaller marsh units.
In this dataset (mu_UVVR_ELI), the calculations found in process step 3 had to be re-run once the marsh units were created.
However, exposure potential (SCoRR) values and shoreline change values could not be recalculated at the marsh unit scale. They remain unchanged and still represent the larger marsh plain polygons. In the SCoRR and shoreline change datasets, the field FID_CMU has been renamed to MP to indicate that those polygons correspond to marsh plains, not the newly created marsh units. In the title of the data release for exposure potential and shoreline change, the words "marsh units" were changed to "marsh plains." Throughout the exposure potential and shoreline change metadata, the term 'marsh unit' is still used, but readers should understand that it actually refers to the marsh plain. Previous versions of the data can be obtained by contacting whsc_data_contact@usgs.gov.

Process Step 7. Removed the web services distribution formats in preparation for ScienceBase moving platforms and those services no longer being available.