Guidelines Followed During Acquisition of Aerial Imagery
1. Tidal Stage - Imagery was acquired at low tide, +/- 0-1.5
feet, as predicted by the National Ocean Survey tables.
2. Plant Growth - Imagery was acquired when growth stages ensured
maximum delineation of SAV, and when phenologic stage overlap was greatest.
3. Sun Angle - Imagery 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.
4. Turbidity - Imagery 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.
5. Wind - Imagery was acquired during periods of no or low wind.
Offshore winds were preferred to onshore winds when wind conditions could
not be avoided.
6. Atmospherics - Imagery 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.
7. Sensor Operation - 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).
8. Land Features - Each flight line included sufficient identifiable
land area to assure accurate plotting of grass beds.