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T2025_eelgrass_Locations5_w_zones_Eel_and_Widg_Submitted
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GCS_North_American_1983
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NAD_1983_StatePlane_New_Hampshire_FIPS_2800_Feet
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ItemDescription
Esri ArcGIS 13.6.0.59527
Great Bay Estuary Eelgrass, 2025
The dataset was developed to monitor the distribution of eelgrass within the Great Bay Estuary over time. With the exception of 2018 and 2020, surveys have been completed yearly since 1986 to track trends over time.
<DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>The dataset shows the locations where eelgrass was observed within the following waterbodies: Great Bay, the mouth of the Squamscott River, the tidal portion of the Lamprey River, the tidal portion of the Oyster River, the tidal portion of the Bellamy River, the Piscataqua River and Portsmouth Harbor and its associated creeks, and the coastal shore of Odiorne Point. Image processing and photointerpretation was completed on orthophotography collected via UAV, as well as Go-Pro imagery from fixed wing aircraft and Sentinel satellite imagery. Vertical UAV imagery was collected as five spectral bands inclusive of RGB, Red-Edge ,and Near Infrared bands. Imagery was collected with varying 2.0 to 6.0 cm spatial resolutions based on 100 to 400 ft flight altitudes specific to FAA maximum flight restrictions around the Pease International Tradeport. Areal Go-Pro RGB vertical aerial imagery was collected on October 9th, 2025. The Sentinel satellite imagery was acquired for the date of July 29th, 2025 with a nominal 10 meter spatial resolution. Environmental conditions, included a low-sun angle, low tides, low cloud cover, and low turbidity in the water column were maintained throughout the course of the survey. The eelgrass habitat mapped from the aerial imagery was verified using the ground truthing data from preselected locations and ad hoc locations chosen during the course of the field work. Ground truthing was done from a small boat during the same season as the photographs were taken. Ground truth observations were made on all tides using a drop camera with video recording capabilities and at low tide when visual observations were recorded. Positions were determined using a high accuracy GPS unit.</SPAN></P><P><SPAN>Database file attributes for the 2025 survey are as follows: “id,” a unique consecutive number; “Hectares,” the area of the polygon in hectares; “Acres,” the area of the polygon in acres; “Year,” equal to 2025, the year of the imagery used, “Label” for the assessment zone, and “type” to distinguish between polygons mapped as at least 10% eelgrass (type = 1), at least 10% widgeon grass (type = 3), or at least 10% eelgrass and at least 10% widgeon grass (type = 2), “Confidence,” a measure of cartographer confidence (H = Higher, M = Medium, L = Lower) of the existence and/or cover type of vegetation per polygon. “Notes,” a text field listing the types of imagery used and/or mapping limitations per polygon as observed by the cartographer. Note that sparse eelgrass areas with < 10% cover (type =0) are also recorded within the "Type" field (attribute), but do not meet the >= 10% cover threshold to be counted towards eelgrass totals within the study.</SPAN></P><P><SPAN /></P></DIV></DIV></DIV>
Eliot
Kittery
Newington
Piscataqua River
Newfields
Rye
New Hampshire
Portsmouth Harbor
New England
Estuarine
Portsmouth
Durham
Great Bay
Greenland
Bellamy River
oceans
Stratham
Squamscott River
biota
Oyster River
Little Harbor
Northeast
Eelgrass
Newmarket
Estuary
Maine
Madbury
Lamprey River
Dover
New Castle
Odiorne Point (Rye)
<DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>User is required to read metadata completely before using the data. The information provided in this coverage was developed by an independent contractor and used by the NH Department of Environmental Services (NHDES). Development of these databases is an ongoing project; they may not contain all existing and potential sites, stations, or threats. The NHDES is not responsible for the use or interpretation of this information, or for any inaccuracies in the site names or locations. All information is subject to verification. Distribution is discouraged.</SPAN></P></DIV></DIV></DIV>
File Geodatabase Feature Class
0.000
dataset
EPSG
6.12(9.3.0.0)
0
Simple
FALSE
0
TRUE
FALSE
T2025_eelgrass_Locations5_w_zones_Eel_and_Widg_Submitted
Feature Class
0
Shape
Shape
Geometry
0
0
0
Feature geometry.
Esri
Coordinates defining the features.
Hectares
Hectares
Double
8
0
0
Acres
Acres
Double
8
0
0
Year
Year
String
4
0
0
Name
Name
String
25
0
0
Confidence
Confidence
String
10
0
0
Notes
Notes
String
254
0
0
Type
Type
SmallInteger
2
0
0
LABEL
LABEL
String
50
0
0
OBJECTID
OBJECTID
OID
4
0
0
Internal feature number.
Esri
Sequential unique whole numbers that are automatically generated.
ID
ID
Integer
4
0
0
Shape_Length
Shape_Length
Double
8
0
0
Length of feature in internal units.
Esri
Positive real numbers that are automatically generated.
Shape_Area
Shape_Area
Double
8
0
0
Area of feature in internal units squared.
Esri
Positive real numbers that are automatically generated.
20260512