This process step and all subsequent process steps were performed by the same person, Kate Ackerman, 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 (m^2) unless otherwise stated.
a) Set the data frame coordinate system and projection to NAD 1983 UTM Zone 18N.
b) Dissolve the vegetated and unvegetated classes in each marsh unit to have only one class for each marsh unit. DISSOLVE(Input features=[CMU_BW.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; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain dissolved marsh units [mu_diss.shp].
c) Create a rectangular polygon that covers the domain [extent.shp]. CLIP the CoNED elevation dataset by the boundaries polygon [elev_mosaic.tif].
d) Remove pixels from elevation raster that are hydro-flattened. Use FOCAL STATISTICS(Input raster=[elev_mosaic.tif], Output raster=[FocalStats_3x3_range.tif], Neighborhood settings=3x3 cell, Statistics type=range) and RASTER CALCULATOR to identify [Map algebra expression: Con("%FocalStats_3x3_range.tif%" == 0,-1,1); Output raster=[elev_mosaic_One_NegOne.tif]] and remove [Map algebra expression: SetNull("%elev_mosaic_One_NegOne.tif%", "%elev_mosaic.tif%", "value = -1"); Output raster=[elev_mosaic_noHF.tif]] all hydro-flattened areas from [elev_mosaic.tif] to create [elev_mosaic_noHF.tif].
e) Calculate the mean elevation for each marsh unit with ZONAL STATISTICS AS TABLE(Feature zone data=[mu_diss.shp], Zone field=FID_CMU; Input value raster=[elev_mosaic_noHF.tif]; Statistics type=Mean; Output table=[mu]; Ignore Nodata=True). ADD JOIN (Layer name=[mu_diss.shp]; Input join field=FID_CMU; Join Table=[mu]; Output join field=FID_CMU) to marsh units layer based on the "FID_CMU" field.
f) Export dataset as a shapefile [mu_elev.shp] and keep the 'mu_MEAN" and "mu_ATOT_M2" fields from the join operation.
g) In [mu_elev.shp], add field (MU_HFAR) to calculate the percent of the marsh unit that has hydro-flattened area. If the percent hydro-flattened area is greater than 25 percent, the marsh unit elevation is set to -9999.
h) Calculate elevation of the vegetated areas only. SELECT BY ATTRIBUTES FROM [CMU_BW.shp] where "TYP"= 'vegetated.' Follow steps (e) to (g) using the selected features to export [veg_elev.shp].
i) JOIN FIELD(Input table=[mu_elev.shp]; Input join field=mu_FID_CMU; Join table=[veg_elev.shp]; Output join field=vg_FID_CMU; Join fields=vg_AVEG_M2, vg_ATOT_M2, vg_MEAN). Change the field names to "VG_ELEV" and "MU_ELEV" for the fields with the mean elevation for the vegetated area only and mean elevation for the entire marsh unit, respectively. Name fields "AVEG_M2" and "ATOT_M2" for vegetated and total area, respectively; and "MU_HFAR" and "VG_HFAR" for the percent (in decimal form) of the marsh unit, and of the vegetated portion, that has hydro-flattened area, respectively. Set MU_ELEV to -9999 if MU_HFAR is greater than 0.25; set VG_ELEV to -9999 if there is no vegetated area in the marsh unit or if VG_HFAR is greater than 0.25. Export to a new shapefile [mu_elev_BW.shp].
j) Run Python script (marsv5.py) in ArcPro (used 2.4.1 for this data release) to calculate metrics that quantify the distribution of marsh unit elevation values. Skewness ("SKWNSS") is the measure of asymmetry of the elevation distribution in the vegetated part of a marsh unit. Positive skewness values, i.e. right-skewed distributions, indicate clustering of elevation distributions towards lower elevations. Negative skewness values indicate a left-skewed distribution and clustering towards higher elevations. Lower third ("LOW3RD") is the percent of elevation values that fall within the lowest third of the elevation range within the vegetated part of a marsh unit. SKWNSS and LOW3RD parameters are calculated by applying the formulation of Raposa et al. (2016) to the elevation raster within the vegetated part of each marsh unit. If SKWNESS and LOW3RD values= 0 and VG_ELEV= -9999, set SKWNESS and LOW3RD values to -9999.
k) SELECT BY ATTRIBUTES from [CMU_BW.shp] where "TYP"= 'vegetated,’ and join field "APGN_M2" from [CMU_BW.shp] to the feature dataset [mu_elev_BW.shp] and rename this field "AVEG_M2."
l) Add field "FLG" to flag anomalous marsh units based on absence of vegetation, elevation and surface area. 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 0.2 percentile; (-200) greater than 25 percent of the marsh unit elevation is hydro-flattened; (-1000) marsh unit surface area less than 900 m^2; 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 m^2.
m) 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 elevation dataset [mu_elev_BW.shp].
Reference:
Raposa, K. B., Wasson, K., Smith, E., Crooks, J. A., Delgado, P., Fernald, S. H., et al. (2016). Assessing tidal marsh resilience to sea-level rise at broad geographic scales with multi-metric indices. Biological Conservation, 204, 263–275.
https://doi.org/10.1016/J.BIOCON.2016.10.015.
