title: Use of a Spectralon panel to measure the downwelling irradiance signal: case studies and recommendations.
abstract: 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 Ed(0+) is commonly made with a reference plaque of a known reflectance. The radiance reflected by the plaque (L(dspec)) can be used to determine Ed(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 L(dspec) and Ed(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 Ed(0+). An appropriate measurement configuration was defined, which enabled Ed(0+) to be determined with an accuracy of better than +/- 15% regardless of the sky conditions.
authors.affiliation: School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, UK. david.doxaran@plymouth.ac.uk
authors.forename: David
authors.initials: D
authors.lastname: Doxaran
authors.forename: Nagur C
authors.initials: NC
authors.lastname: Cherukuru
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Lavender
authors.forename: Gerald F
authors.initials: GF
authors.lastname: Moore