A Review of Protocols for Fiducial Reference Measurements of Water-Leaving Radiance for Validation of Satellite Remote-Sensing Data over Water

Abstract

This paper reviews the state of the art of protocols for measurement of waterleaving radiance in the context of fiducial reference measurements (FRM) of water reflectance for satellite validation. Measurement of water reflectance requires the measurement of waterleaving radiance and downwelling irradiance just above water. For the former there are four generic families of method, based on: 1) underwater radiometry at fixed depths; or 2) underwater radiometry with vertical profiling; or 3) abovewater radiometry with skyglint correction; or 4) onwater radiometry with skylight blocked. Each method is described generically in the FRM context with reference to the measurement equation, documented implementations and the intramethod diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice and guidelines for estimating the measurement uncertainty are provided for each protocolrelated component of the measurement uncertainty budget. The state of the art for measurement of waterleaving radiance is summarized, future perspectives are outlined, and the question of which method is best adapted to various circumstances (water type, wavelength) is discussed. This review is based on practice and papers of the aquatic optics community for the validation of water reflectance estimated from satellite data but can be relevant also for other applications such as the development or validation of algorithms for remote-sensing estimation of water constituents including chlorophyll a concentration, inherent optical properties and related products.

Fiducial Reference Measurements for Satellite Ocean Colour (FRM4SOC)

“…One of the key achievements of the FRM4SOC project has been to review the state of the art of protocols for the measurement of downwelling irradiance [27] and water-leaving radiance [28]. This builds on heritage from the NASA Ocean Optics protocols series [29], recently updated in [30], but: (a) broadens the scope from oceanic waters [31] to all waters where satellite data products are used, including coastal and inland waters [32]; (b) takes account of the many protocol refinements since 2004, including input from the MERIS optical measurement protocols [33]; (c) focuses particularly on the estimation of uncertainties from the data acquisition and processing steps, as required in the FRM context.…”

“…Analyse carefully their present measurement protocol and construct an uncertainty budget including minimally the elements listed in the corresponding sections of the FRM4SOC protocols [27,28] [16] and the FRM4SOC protocols [27,28] and provide comments for their improvement.…”

“…The FRM4SOC protocols review papers for downwelling irradiance [27] and for water-leaving radiance [28] discuss in detail the different measurement approaches and the sources of uncertainty that need to be considered and provide guidelines on best practice for making these measurements. The FRM4SOC protocols review papers for downwelling irradiance [27] and for water-leaving radiance [28] discuss in detail the different measurement approaches and the sources of uncertainty that need to be considered and provide guidelines on best practice for making these measurements.…”

“…The FRM4SOC protocols review papers for downwelling irradiance [27] and for water-leaving radiance [28] discuss in detail the different measurement approaches and the sources of uncertainty that need to be considered and provide guidelines on best practice for making these measurements. The FRM4SOC protocols review papers for downwelling irradiance [27] and for water-leaving radiance [28] discuss in detail the different measurement approaches and the sources of uncertainty that need to be considered and provide guidelines on best practice for making these measurements. The FRM4SOC protocols review papers for downwelling irradiance [27] and for water-leaving radiance [28] discuss in detail the different measurement approaches and the sources of uncertainty that need to be considered and provide guidelines on best practice for making these measurements.…”

“…Summary of sources of uncertainty for the four generic families of method for measurement of water-leaving radiance. Reproduced with permission from[28].…”