GRANIT Metadata for Great Bay Estuary Eelgrass, 1994
GRANIT Metadata for Great Bay Estuary Eelgrass, 1994
Title:
Great Bay Estuary Eelgrass, 1994
Time Period of Content:
1994
Initial Publication Date: 1995
Originator: Dr. Frederick Short, University of New Hampshire, Durham, NH
Abstract:
Note that yearly variations in collection methods exist. Following is a
summary of methods that have been used.
The dataset shows the locations where eelgrass was observed in the Great
Bay Estuary based on low-altitude aerial surveillance. The study area
includes 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. Aerial photographs are taken
of the study area at 3000 feet at low spring tide with roughly 60% overlap
on a calm day without preceding rain events and when the sun is at a low
angle to minimize reflection (between 7 am and 10 am). Photographs are
taken in late summer, usually late August or early September, depending on
tides and weather, to reflect the maximum eelgrass annual biomass. 35 mm film
(ASA 200) or a digital camera is used to acquire the images. Typically 300 images
are needed to cover the entire Great Bay Estuary. The orientation of the
photographs is near-vertical. This is a slight deviation from the NOAA
Coastal Change Analysis Program protocol, but follows a published method
(Short and Burdick, 1986). The photographs, in the form of 35mm slides or
digital computer images, are projected on a screen and the eelgrass images
are transferred to a base map. These maps are then digitized using GIS
software. The eelgrass habitat mapped from the aerial imagery is verified
using the ground truthing data by placing the ground-truthing locations
onto the digital image using GIS software. Ground-truthing is done
from a small boat during the same season as the photographs are taken.
Ground-truth observations are made at low tide. Samples are collected with
an eelgrass sampling hook. Positions are determined using GPS. The
ground-truth surveys assess 10-20% of the eelgrass beds mapped in the
estuary. The aerial survey is completed yearly. The first survey in the
series was completed in 1986.
