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G. Zibordi and K.J. Voss
it through prisms or gratings. Detectors translate the radiant flux received from
the optics into an electrical signal which is then converted into a digital number.
Optics vary with the type of measurement. In the case of radiance measurements,
the radiant flux is generally collected through field stops defining the full-angle fieldof-view of the radiometer. This typically varies in the range of 1–20 ◦ depending on
the application or detector features. In the case of irradiance measurements the input
radiant flux is collected through a diffuser called collector. This is shaped to ideally
gather the directional radiance contributions with a response varying as the cosine
of the incident angle. Detectors include single- or multiple-detectors generally coupled with spectral filters in multispectral systems, or detector-arrays coupled with
prisms and gratings in hyperspectral systems.
The elements commonly defining the performance of a radiometer are the spectral bandwidth and resolution, the responsivity (output counts per input of incident
radiant flux), the detectivity (responsivity divided by the root mean square noise of
the detector output) and the operational range (defined by the minimum radiant flux
saturating the detector’s output).
Systems for marine optical radiometry can be roughly separated into aboveand in-water systems. Above-water systems provide the capability of determining the so called water-leaving radiance which carries information on the seawater
optically significant constituents. In-water systems can provide comprehensive characterization of the in-water radiometric properties through radiance and irradiance
measurements from a variety of configurations and deployment gears (e.g., profilers,
buoys). Distinctive examples of in-water optical radiometer systems are provided by
imaging devices utilized to map the radiance distribution.
18.3.1 Above-Water Systems
Above-water radiometry, when compared to the more consolidated and widely
used in-water radiometry, had been almost unexploited up to the 1980s when specific measurement methods were proposed and applied (Morel, 1980; Carder and
Steward, 1985). Relevant contributions to the refinement of the early methods came
with the theoretical work of Mobley (1999) and Fougnie et al. (1999), followed by
the experimental activities of Toole et al. (2000), Hooker et al. (2002a), Zibordi et al.
(2002) and Deschamps et al. (2004).
Most of the published methods determine the water-leaving radiance, L w (λ),
from measurements of the total radiance from above the sea, L T (θ ,φ,λ), (which
includes water-leaving, sky-glitter and sun-glint radiance contributions) and the
diffuse radiance from the sky, L i (θ ,φ,λ) (i.e., sky radiance), applying rigorous
protocols (Deschamps et al., 2004; Hooker et al., 2004; Zibordi et al., 2004c).
This implies the adoption of rigid measurement geometries (see the example
in Fig. 18.2).
The accuracy of radiometric products determined from measurements performed
with above-water systems heavily depends on the capability of minimizing glint
perturbations in L T (θ ,φ,λ). The methods currently applied utilize filtering schemes
G. Zibordi and K.J. Voss
it through prisms or gratings. Detectors translate the radiant flux received from
the optics into an electrical signal which is then converted into a digital number.
Optics vary with the type of measurement. In the case of radiance measurements,
the radiant flux is generally collected through field stops defining the full-angle fieldof-view of the radiometer. This typically varies in the range of 1–20 ◦ depending on
the application or detector features. In the case of irradiance measurements the input
radiant flux is collected through a diffuser called collector. This is shaped to ideally
gather the directional radiance contributions with a response varying as the cosine
of the incident angle. Detectors include single- or multiple-detectors generally coupled with spectral filters in multispectral systems, or detector-arrays coupled with
prisms and gratings in hyperspectral systems.
The elements commonly defining the performance of a radiometer are the spectral bandwidth and resolution, the responsivity (output counts per input of incident
radiant flux), the detectivity (responsivity divided by the root mean square noise of
the detector output) and the operational range (defined by the minimum radiant flux
saturating the detector’s output).
Systems for marine optical radiometry can be roughly separated into aboveand in-water systems. Above-water systems provide the capability of determining the so called water-leaving radiance which carries information on the seawater
optically significant constituents. In-water systems can provide comprehensive characterization of the in-water radiometric properties through radiance and irradiance
measurements from a variety of configurations and deployment gears (e.g., profilers,
buoys). Distinctive examples of in-water optical radiometer systems are provided by
imaging devices utilized to map the radiance distribution.
18.3.1 Above-Water Systems
Above-water radiometry, when compared to the more consolidated and widely
used in-water radiometry, had been almost unexploited up to the 1980s when specific measurement methods were proposed and applied (Morel, 1980; Carder and
Steward, 1985). Relevant contributions to the refinement of the early methods came
with the theoretical work of Mobley (1999) and Fougnie et al. (1999), followed by
the experimental activities of Toole et al. (2000), Hooker et al. (2002a), Zibordi et al.
(2002) and Deschamps et al. (2004).
Most of the published methods determine the water-leaving radiance, L w (λ),
from measurements of the total radiance from above the sea, L T (θ ,φ,λ), (which
includes water-leaving, sky-glitter and sun-glint radiance contributions) and the
diffuse radiance from the sky, L i (θ ,φ,λ) (i.e., sky radiance), applying rigorous
protocols (Deschamps et al., 2004; Hooker et al., 2004; Zibordi et al., 2004c).
This implies the adoption of rigid measurement geometries (see the example
in Fig. 18.2).
The accuracy of radiometric products determined from measurements performed
with above-water systems heavily depends on the capability of minimizing glint
perturbations in L T (θ ,φ,λ). The methods currently applied utilize filtering schemes