Great Bay Estuary Eelgrass, 2024

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. 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 1.7 to 3.4 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 August 23rd, 20024. The Sentinel satellite imagery was acquired for the date of August 8th, 2024 with a nominal 10 meter spatial resolution. Environmental conditions included a low-sun angle, low tides, low cloud cover, calm winds, no preceding rain events, 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.Database file attributes for the 2024 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 2024, 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.