Guidelines Followed During Acquisition of Aerial Imagery
Photography was acquired at low tide, +/- 0-1.5 feet, as predicted by the National Ocean Survey tables.
Imagery was acquired when growth stages ensured maximum delineation of SAV, and when phenologic stage overlap was greatest.
Photography was acquired when surface reflection from sun glint did not cover more than 30 percent of frame. Sun angle was generally between 20º and 40º to minimize water surface glitter. At least 60 percent line overlap and 20 percent side lap were used to minimize image degradation due to sun glint.
Photography was acquired when clarity of water ensured complete delineation of grass beds. This was visually determined from the airplane to insure that the observer could see SAV.
Photography was acquired during periods of no or low wind. Offshore winds were preferred to onshore winds when wind conditions could not be avoided.
Photography was acquired during periods of no or low haze and/or clouds below aircraft. There could be no more than scattered or thin broken clouds, or thin overcast above aircraft, to ensure maximum SAV contrast to bottom.
Photography was acquired in the vertical mode with less than 5 degrees tilt. Scale/altitude/film/focal length combination permitted resolution and identification of one square meter area of SAV (at the surface).
Each flight line included sufficient identifiable land area to assure accurate plotting of grass beds.