"Submerged Aquatic Vegetation" (SAV) refers to plants which grow underneath the water's surface in the sounds and intracoastal
waterways of North Carolina. The aerial imagery and mapping products are generated by the Photogrammetry Unit at the request
of the North Carolina Department of Environmental Quality (DEQ) and Albennarle-Pamlico National Estuary Partnership (APNEP).
APN EP uses the aerial imagery and mapping products to measure the overall health of North Carolina's coastal water
ecosystems as documented in a 2020 APNEP blog article on seagrass mapping.
The NCDOT SAV mapping program was initially setup with the help of Dr. Randy Ferguson, formerly of the National Oceanic
and Atmospheric Administration (NOAA), a noted expert in the field of SAV delineation. Current Guidance on Benthic Habitat
Mapping is located as part of NOAAs Office for Coastal Management.
The advance in technology away from film cameras to megapixel digital cameras equipped with highly accurate position
and orientation systems and the capability to image and produce both color and color infrared mapping products has
enabled large areas of SAV to be accurately mapped. When areas to be mapped are imaged, several factors such as
clouds, sun angle, tide, water quality, wind speed and direction, and fetch (distance over water wind travels unobstructed)
need to align for a successful mission. These conditions are continuously monitored by both NCDOT Photogrammetry Unit
and APNEP staff in the office, but also checked by ground crews on site whenever possible.
North Carolina has 2 types of SAV which differ in salinity. These are a lower salinity, fresh water type and a higher salinity,
estuarine water type. Both SAV types are important as a nursery for many species of fish and various other creatures. SAV
growth acts as a relative guide to the health of the waterway. North Carolina is unique in that 3 species of estuarine
SAV can be found here: Eelgrass, Shoalgrass, and Widgeongrass.
Photogrammetry Unit staff have found through experience that viewing aerial color infrared (CIR) imagery in stereo with 3-D
monitors and 3-D glasses is better for SAV delineation as opposed to color imagery even though the light penetration of
color imagery is better. The bed edges appear better defined using the CIR imagery making delineation easier. The minimum
mapping unit defines what detail the SAV beds are delineated, and these delineations are generally based on percentage of
area covered by grass.
