Unvegetated to vegetated ratio of marsh units in Chesapeake Bay salt marshes
This data release contains coastal wetland synthesis products for Chesapeake Bay. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and tidal range are calculated for smaller units delineated from a digital elevation model, providing the spatial variability of physical factors that influence wetland health. The U.S. Geological Survey has been expanding national assessment of coastal change hazards and forecast products to coastal wetlands with the intent of providing federal, state, and local managers with tools to estimate the vulnerability and ecosystem service potential of these wetlands. For this purpose, the response and resilience of coastal wetlands to physical factors need to be assessed in terms of the ensuing change to their vulnerability and ecosystem services.
Ackerman, Kate V., Defne, Zafer, and Ganju, Neil K., 20221103, Unvegetated to vegetated ratio of marsh units in Chesapeake Bay salt marshes: data release DOI:10.5066/P997EJYB, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.
Suggested citation: Ackerman, K.V., Defne, Z., and Ganju, N.K., 2022, Geospatial characterization of salt marshes in Chesapeake Bay: U.S. Geological Survey data release, https://doi.org/10.5066/P997EJYB.
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 84.
The semi-major axis of the ellipsoid used is 6378137.0.
The flattening of the ellipsoid used is 1/298.257223563.
Table containing attribute information associated with the dataset.
Internal feature number.
Sequential unique whole numbers that are automatically generated.
Coordinates defining the features.
Unique whole numbers used to identify each conceptual marsh unit.
Range of values
Total surface area of a marsh unit.
Range of values
Surface area of the vegetated part of a marsh unit.
Range of values
Ratio of unvegetated surface area to vegetated surface area. Ordinarily, UVVR ranges from zero (completely vegetated) to infinity (completely unvegetated). However, it is assigned the value of -1 when completely unvegetated.
Range of values
Marsh unit flag indicating anomalous marsh units based on absence of vegetation, elevation, surface area and tidal range extrapolation. FLG values indicate: (-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 m^2; (-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 m^2.
Range of values
In this dataset, the salt marshes of Chesapeake Bay have been delineated to conceptual salt marsh units to facilitate unit by unit evaluation of response and resiliency of the marsh system to physical and biogeochemical drivers. Each unit is also analyzed based on the vegetated and unvegetated surface area coverage, the ratio of which can be an independent measure of marsh health for salt marshes on the Atlantic and Pacific coasts of the United States. UVVR is calculated as the ratio of unvegetated area to vegetated area in a marsh unit. Decimal values in the attribute table are a result of double precision calculations while significant digits are considered in defining the attribute measurement resolutions. Therefore, the smallest unit increment for area values and UVVR is assumed to be 1 meter and 0.001, respectively.
The purpose of this shapefile is to calculate the ratio of unvegetated area to vegetated area (UVVR) in each marsh unit. Analysis of unvegetated to vegetated marsh ratio is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes. An unvegetated area to vegetated area ratio was defined as a potential indicator of the current state of a salt marsh unit. UVVR was calculated based on U.S. Department of Agriculture National Agriculture Imagery Program (NAIP) 0.6-meter and 1.0-meter resolution imagery (and Worldview-2 1.85-meter resolution imagery for the Aberdeen Proving Ground area (region CB08A)).
Danielson, J., and Tyler, D., 20160501, Topobathymetric Model for Chesapeake Bay Region - District of Columbia, States of Delaware, Maryland, Pennsylvania, and Virginia, 1859 to 2015: U.S. Geological Survey, Reston, VA.
Downloaded Digital Elevation Model to be used for a small part of region CB08A (Aberdeen Proving Ground) that is not covered by CoNED. Tiles downloaded: chesapeake_bay/ncei19_n39x50_w076x25_2019v1.tif, chesapeake_bay/ncei19_n39x50_w076x50_2019v1.tif. Projection was NAD 1983 UTM Zone 18N with the North American Vertical Datum of 1988 (NAVD 88). Download date was 08/20/2021.
Type_of_Source_Media:Digital Source_Contribution:Elevation dataset for Aberdeen Proving Ground
NAIP (source 4 of 9)
U.S. Department of Agriculture, 2018, NAIP Digital Ortho Photo Image: USDA-FSA-APFO Aerial Photography Field Office, Salt Lake City, Utah.
Downloaded NAIP 4-band, 0.6-meter resolution imagery from the USGS Earth Explorer. Projection was NAD 1983 UTM Zone 18N. Download date was 01/17/2020. NAIP (2018) data was use in regions CB00, CB02, CB03, CB04, CB08, CB09, CB13, CB14A, CB15, and CB16.
Downloaded NAIP 4-band, 1-meter resolution imagery from the USGS Earth Explorer. Projection was NAD 1983 UTM Zone 18N. Download date was 01/17/2020. NAIP (2017) data was used in regions CB07, CB10, and CB11.
Downloaded NAIP 4-band, 1-meter resolution imagery from the USGS Earth Explorer. Projection was NAD 1983 UTM Zone 18N. Download date was 01/17/2020. NAIP (2016) data was used in regions CB05, CB11, CB12, and CB14B.
Downloaded Worldview-2 8-band, 1.85-meter resolution imagery from Maxar. Imagery (c) 2019 Maxar. Projection was WGS 1984 UTM Zone 18N. Download date was 07/01/2021. Worldview-2 imagery is commercially acquired by Maxar and is accessible through the website, https://evwhs.digitalglobe.com/myDigitalGlobe, by those who have access accounts. Worldview-2 data was used in region CB08A.
Type_of_Source_Media:Digital Source_Contribution:Satellite imagery dataset used for Aberdeen Proving Ground
NWI (source 8 of 9)
U.S. Fish and Wildlife Service, 20191001, National Wetland Inventory: U.S. Fish and Wildlife Service, Madison, WI.
This process step and all subsequent process steps were performed by the same person, Kate Ackerman, in ArcGIS Pro (ver. 2.8.2), unless otherwise stated. For simple operations the name of the geoprocessing tool used is given in capital letters; for complex operations, the name of geoprocessing tool used is given in capital letters and 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.
The Chesapeake Bay was split into 16 regions to complete this analysis, refer to the accompanying image (CB_regions.png) to see the location of the regions. The methodology from region to region was consistent, however small changes were made across Chesapeake Bay; the changes are noted in the process steps below.
a) Set the data frame coordinate system and projection to NAD 1983 UTM Zone 18N.
b) 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_CB.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].
c) Prepare elevation dataset. For the NC DEM: RESAMPLE the raster to 1m. MOSAIC TO NEW RASTER the USGS CoNED raster and the NC DEM, with the USGS CoNED taking precedence over the NC DEM. For the small areas in region CB08A (Aberdeen Proving Ground, APG) that are not covered by USGS CoNED data, the APG DEM (resampled to 1m) was used to fill in these areas.
d) Create a polygon that covers the area of interest [extent.shp]. CLIP the mosaicked elevation dataset created in step (c) by [extent.shp] to create [elev_mosaic.tif].
Person who carried out this activity:
U.S. Geological Survey
384 Woods Hole Road
Woods Hole, MA
508-548-8700 x2331 (voice)
Data sources used in this process:
Data sources produced in this process:
Date: 2022 (process 2 of 3)
This process step creates two mask polygons to define analysis boundaries over the area of interest. 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 created [UVVR_mask.shp]. This larger mask area is clipped to the boundaries of the salt marsh area to create [MU_mask.shp]. This process step explains how [UVVR_mask.shp] and [MU_mask.shp] are created and edited to determine which interior polygons are removed.
a) Create a shapefile of the salt marshes as defined by NWI. EXPORT features (use the same coordinate system as the data frame) from NWI dataset of all wetlands for the area (referred to here as [NWI_entire.shp]) 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 to create [NWI_exclusive_select.shp]. For Colonial National Historic Park (in region CB14), palustrine emergent wetlands with freshwater tidal modifiers ('PEM1R'and 'PEM1S') were included.
b) Create the preliminary masks that will be edited in the subsequent steps to make the final masks. BUFFER salt marsh classes (Input features=[NWI_exclusive_select.shp]; Linear unit=5 meters; Dissolve type=All) to obtain the mask polygon [buff5m.shp] and ELIMINATE POLYGON PART (Input features= [buff5m.shp]; Condition=Percentage; Percentage=99; Eliminate contained part only) to remove small interior polygons to obtain [UVVR_mask01.shp]. Apply BUFFER (Input features=[UVVR_mask01.shp]; Linear unit= -5 meters; Dissolve type= All) to obtain [MU_mask01.shp].
c) 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 [NWI_inclusive_select.shp]. MULTIPART TO SINGLEPART to separate individual polygons [NWI_inclusive_single.shp].
d) To exclude the voids in the NWI map during the analysis, these interior polygons need to be removed from the mask. ERASE [NWI_exclusive_select.shp] from [extent.shp] and MULTIPART TO SINGLEPART to get [NWI_exc_voids_single.shp].
To remove areas that should not be included in the mask (e.g., forest areas) the following steps were implemented:
d.1) An additional step was used for regions CB04-CB09 only: To find all of the interior features that should potentially be removed, run SYMMETRICAL DIFFERENCE (Input features=[buff5m.shp], Update features=[UVVR_mask01.shp], Join attributes= All) and MULTIPART TO SINGLEPART to obtain [UVVR_mask01_buff5m_diff_single.shp]. Do a SPATIAL JOIN (Target Features=[UVVR_mask01_buff5m_diff_single.shp], Join Features= [NWI_entire.shp]; Join operation=join one to one; Keep all target features; match option= intersect) to obtain [UVVR_nwi_sjoin.shp]. Select records that have a null value for the “attribute” field and generate a shapefile of the selected records [NWI_voids_single.shp].
Depending on the region, the e.1, e.2 or e.3 methodology was used to create the [MU_mask.shp] and [UVVR_mask.shp] (the methodology changed very slightly as work progressed through the CB): (If you are using this metadata as instructions to generate marsh units, use the e.3 methodology (region CB16), as it represents the most up-to-date methodology).
e.1) For regions CB00, CB02, CB04-CB13: SELECT BY LOCATION from [NWI_inclusive_single.shp] that are completely within the [MU_mask01.shp] and SELECT BY LOCATION from [NWI_exc_voids_single.shp] that are completely within the [MU_mask01.shp] (for regions CB04-CB09: 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 feature sets to get polygons to be excluded [erase_inside.shp] from the final masks. ERASE [erase_inside.shp] from [MU_mask01.shp] to obtain [MU_mask.shp]. To obtain [UVVR_mask.shp], BUFFER [erase_inside.shp] by -5 meters (side type= full; end type= round; method: geodesic; dissolve type: single feature) then ERASE [erase_inside.shp] from [UVVR_mask01.shp].
e.2) For regions CB03, CB14, CB15: SELECT BY LOCATION from [NWI_inclusive_single.shp] that are completely within the [MU_mask01.shp] and SELECT BY LOCATION from [NWI_exc_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 feature sets to get polygons to be excluded [erase_inside.shp] from the final masks. BUFFER [erase_inside.shp] by -5 meters, to obtain [erase_inside_buffback5m.shp] and ERASE [erase_inside_buffback5m.shp] from [UVVR_mask01.shp] to obtain [UVVR_mask.shp]. BUFFER [UVVR_mask.shp] by -5m to obtain [MU_mask.shp].
e.3) For region CB16: This methodology incorporates estuarine and marine wetland systems that are completely surrounded by salt marsh (e.g., interior ponds):
e.3a)SELECT BY LOCATION from [NWI_inclusive_single.shp] that are completely within the [MU_mask01.shp] and SELECT BY LOCATION from [NWI_exc_voids_single.shp] that are completely within the [MU_mask01.shp]. UNION all feature sets to get polygons to be excluded [erase_inside.shp] from the final masks.
e.3b) Spatially join the [NWI_entire.shp] to [erase_inside.shp] in order to assign wetland attributes to the [erase_inside.shp] polygons. SPATIAL JOIN (target features= [erase_inside.shp]; join features= [NWI_entire.shp]; output feature class= [erase_inside_NWI_info.shp]; join operation= one to one; keep all target features; match option= intersect; search radius= -1 m).
e.3c) Select the polygons that are marine or non-forested estuarine wetlands from [erase_inside_NWI_info.shp]: SELECT (ATTRIBUTE LIKE 'E1%' OR ATTRIBUTE LIKE 'E2AB%' OR ATTRIBUTE LIKE 'E2RF%' OR ATTRIBUTE LIKE 'E2SB%' OR ATTRIBUTE LIKE 'E2RS%' OR ATTRIBUTE LIKE 'E2US%' OR ATTRIBUTE LIKE 'E2EM%' OR ATTRIBUTE LIKE ‘E2SS%’ OR ATTRIBUTE LIKE ‘M1%’ OR ATTRIBUTE LIKE ‘M2%) to select all marine systems, estuarine subtidal systems, estuarine intertidal areas of aquatic bed, reef, streambed, rocky shore, unconsolidated shore, emergent or scrub-shrub [erase_inside_keepIntPonds.shp].
e.3d) Remove the polygons from [erase_inside_NWI_info.shp] that should be retained (these are the interior ponds): ERASE (input feature= [erase_inside_NWI_info.shp]; erase feature= [erase_inside_keepIntPonds.shp]; output feature= [erase_inside_final.shp]).
e.3e) If any additional polygons need to be removed from the mask, include them in a new feature layer [erase_mask_manual.shp] and MERGE with [erase_inside_final.shp].
e.3f) Remove any unwanted polygons from the original [MU_mask01.shp] to make the final [MU_Mask.shp]: ERASE (input feature= [MU_mask01.shp]; erase feature= [erase_inside_final.shp]; output feature= [MU_mask.shp]).
e.3g) BUFFER [MU_mask.shp] by 5m (side type= full; end type= round; method: geodesic; dissolve type: single feature) to obtain [UVVR_mask.shp].
Data sources used in this process:
Data sources produced in this process:
Date: 2022 (process 3 of 3)
Compute vegetated and unvegetated areas by image processing.
a) MOSAIC TO NEW RASTER the NAIP tiles (for region CB08A, Worldview-2 tiles).
b) EXTRACT BY MASK from the elevation raster [elev_mosaic.tif] and the NAIP (and Worldview-2) imagery raster using [UVVR_mask.shp] polygon and append “UVVR_mask” to the file name. Rescale the elevation raster values to the same range with 8-bit NAIP imagery (0 to 255) using min-max scaling in RASTER CALCULATOR (map algebra expression: (("elev_mosaic_UVVR_mask.tif"-(min value of the input raster))*(255-0)/(max value of the input raster)-( min value of the input raster)))+0). Perform ISO CLUSTER UNSUPERVISED CLASSIFICATION with 5 input bands: the 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. (For region CB08A, the ISO CLUSTER UNSUPERVISED CLASSIFICATION was performed with the Worldview-2 8 bands and the rescaled elevation raster.) RECLASSIFY the classified raster by visually comparing the NAIP imagery to obtain the unvegetated-vegetated raster [UVVc.tif]. In some regions, a couple of the 32 classes are classified as vegetated in one area but unvegetated in another area. For these classes, the area can be split into separate sections to allow one section to be classified as vegetated and the other as unvegetated.
c) 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 GROUP(Number of neighbors=4; Zone grouping method=Within; Add Link field to output) to get the [UVV_region.tif], and TEST("Count" < 9) to set a threshold value of 9 raster cells [lt9.tif]. Use RASTER CALCULATOR to toggle the value of the Link field in the region raster [Map algebra expression=Con("%lt9.tif%", ~Lookup("%UVVc_region.tif%","LINK"),Lookup("%UVVc_region.tif%","LINK"))], where the test raster indicates regions with areas smaller than the threshold.
d) RASTER TO POLYGON(Simplify polygons=False) and CLIP with the final marsh complex outline [mu_diss.shp] to obtain [UVVc_filt_clip.shp].
e) REPAIR GEOMETRY, ADD GEOMETRY ATTRIBUTES(Geometry properties=Area_geodesic; Area unit=Square_meters), CALCULATE FIELD(Python_9.3 expression; Field name=gridcode, Expression=filt(!gridcode!, !AREA_GEO!), Code Block= def filt(gridcode, AREA_GEO):/if gridcode== 0 and AREA_GEO < 9:/return 1/else:/return gridcode) and DISSOLVE(Create multipart features=False) to get filtered, clipped and dissolved unvegetated-vegetated polygons [UVVc_filt_clip_diss.shp].
f) INTERSECT the final conceptual marsh units [mu_diss.shp] with unvegetated-vegetated polygons [UVVc_filt_clip_diss.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) and REPAIR GEOMETRY to get [UVV_poly_diss.shp]. Add fields "TYP", "APGN_M2", and "ATOT_M2" for type of polygon indicating vegetated or unvegetated, surface area of the polygon, and total surface area of the marsh unit, respectively, and calculate "APGN_M2" and "ATOT_M2" areas. Visually inspect and manually remove marsh units that are fully forested due to polygon artifacts that are a result of buffering.
g) 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.
h) DISSOLVE(Input features=[UVV_poly_diss.shp]; Dissolve fields=FID_CMU; Statistics field=UVVR, ATOT_M2 and FLG with Statistics type= First for all) to obtain [mu_UVVR_CB.shp].
i) SELECT BY ATTRIBUTES FROM [CMU_CB.shp] where "TYP"= 'vegetated,' and join field "APGN_M2" from [CMU_CB.shp] to [mu_UVVR_CB.shp] and rename this field "AVEG_M2."
j) Add field "FLG" to flag 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 m^2; (-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 m^2.
k) Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere) the feature dataset to obtain the UVVR for each marsh unit [mu_UVVR_CB.shp].
Data sources used in this process:
How well have the observations been checked?
Marsh unit boundaries and water and land boundaries inherit their accuracy from the source data, the conceptual marsh units. Vegetated and unvegetated polygon accuracy is based on the 0.6-meter and 1.0-meter resolution National Agriculture Imagery Program (NAIP) products, and the elevation datasets (primarily: USGS CoNED, for NC: NOAA NC DEM).
Where are the gaps in the data? What is missing?
The marsh polygons are bound to the borders of the Chesapeake Bay estuarine intertidal areas that include: 1) emergent wetlands, 2) scrub-shrub areas, 3) rooted vascular aquatic beds, 4) organic unconsolidated shores, and 5) channels of open water that are narrower than 10 meters.
Sliver polygons of open salt water along the marsh edges may also be included in some instances as a result of geoprocessing (e.g., marsh unit 36608).
In a few cases, linear marsh unit features that are artifacts of the NWI dataset are retained (e.g., marsh units 17309, 17310, 20453).
Occasionally, marsh units are retained in this dataset even though the imagery displayed extreme change (e.g., partially or completely converted to water) from the NWI wetland delineation (e.g., marsh units 18150, 36504).
In some marsh units there are small sliver gaps due to coupling of artifacts of the NWI (e.g., NWI polygons for ditches that are classified as riverine) and geoprocessing when the marsh polygons were closer than 10 meters at a specific section that is followed by a wider distance (e.g., access roads, fringing forests, etc.). The effect of these sliver gaps on the calculations is negligible (e.g., south of marsh unit 19742).
In a few marsh units there are small gaps that inadvertently did not get incorporated into the marsh unit; the effect of these gaps on the calculations is negligible (e.g., marsh unit 33957).
A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries than those established through this analysis.
At Colonial National Historic Park, Virginia, palustrine emergent persistent wetlands (with freshwater tidal modifiers) were included to ensure complete coverage of the estuarine and palustrine emergent wetlands within the Park boundaries.
In region CB16 (at the VA-NC border), the methodology was changed slightly to include estuarine and marine wetland polygons that are completely surrounded by salt marsh (see process step e.3).
In region CB08A (Aberdeen Proving Ground, in northern Chesapeake Bay), Worldview-2 imagery was used due to the unavailability of NAIP imagery.
How consistent are the relationships among the observations, including topology?
Topological errors that occurred during geoprocessing were automatically removed by the topological rules used for the analysis. The polygons were checked for correct geometry and do not overlap. Small polygons (less than 9 m^2) were assumed to be marginal and were assigned the classification from the surrounding majority value. In two areas (around marsh units 4028 and 5358), there are marsh units that have straight lines for boundaries; this is due to larger areas of hydro-flattened bathymetry/elevation values that do not allow the basin analysis to identify ridge lines between basins. Most of these marsh units have a flag that shows that the hydro-flattened area of the marsh unit is greater than 25 percent of the marsh unit area.
A visual comparison between NAIP imagery was performed at randomly selected sites to verify the land and water boundaries. Marsh polygons without any vegetation were assigned a UVVR value of -1.
The unvegetated to vegetated ratio for each marsh unit is defined for scientific research purposes and should not be used as a sole source of reference for any regulations and policy making. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the source of this information.
Denver Federal Center, Building 810, Mail Stop 302
What's the catalog number I need to order this data set?mu_UVVR_CB.zip (ZIP file contains the shapefile mu_UVVR_CB.shp and the additional shapefile components), an image of the regions used to complete the analyses (CB_regions.png), a browse graphic (UVVR_CB_Browse.png) and FGDC CSDGM metadata in xml format.
Although these data have been processed successfully on a computer system at the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.