Acquisition of Through-water Aerial Survey Images: Surface Effects and the Prediction of Sun Glitter and Subsurface Illumination

The behavior of light at the air/water interface has substantial effects on the quality of vertical, or nadir-looking imagery used to interpret subsurface features for purposes such as marine habitat mapping. Reflection of the direct solar beam into the sensor by waves on the surface of the water creates bright glints, which obscure bottom features of interest. Sun angle, refraction, and reflection of the direct solar beam affect the amount of subsurface illumination and shadowing of bottom features. Simple interpretations of these sea surface effects are made with sufficient accuracy to improve planning for airborne, vertical image capture, particularly aerial photography or video imagery. The time available for image capture over shallow water is typically limited to a short period in the morning. The start time is controlled by subsurface illumination levels, which are determined by sun angle and locally variable factors, such as light attenuation by the water column, rather than surface reflection or subsurface shadowing. The end time is determined by sun glitter effects, which in this case study, are predictable from sun angle, camera field of view, and wind speed with an R 2 value of 0.9554. © 2005 American Society for Photogrammetry and Remote Sensing.