Field determinations of the remote sensing reflectance signal are necessary to validate ocean color satellite sensors. The measurement of the above-water downwelling irradiance signal <i>E</i><sub><i>d</i></sub>(0+) is commonly made with a reference plaque of a known reflectance. The radiance reflected by the plaque (<i>L</i><sub>dspec</sub>) can be used to determine <i>E</i><sub><i>d</i></sub>(0+) if the plaque is assumed to be near Lambertian. To test this assumption, basic experiments were conducted on a boat under changing sky conditions (clear, cloudy, covered) and with different configurations for simultaneous measurements of <i>L</i><sub>dspec</sub> and <i>E</i><sub><i>d</i></sub>(0+). For all measurement configurations, results were satisfactory under a clear sky. Under cloudy or covered skies, shadow effects on the plaque induced errors up to 100% in the determination of <i>E</i><sub><i>d</i></sub>(0+). An appropriate measurement configuration was defined, which enabled <i>E</i><sub><i>d</i></sub>(0+) to be determined with an accuracy of better than ±15% regardless of the sky conditions.
© 2004 Optical Society of America
(000.2170) General : Equipment and techniques
(010.4450) Atmospheric and oceanic optics : Oceanic optics
(120.4800) Instrumentation, measurement, and metrology : Optical standards and testing
David Doxaran, Nagur C. Cherukuru, Samantha J. Lavender, and Gerald F. Moore, "Use of a Spectralon Panel to Measure the Downwelling Irradiance Signal: Case Studies and Recommendations," Appl. Opt. 43, 5981-5986 (2004)