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Water insight spectrometer with three radiometers

Water insight spectrometer with three radiometers

The water insight spectrometer with three radiometers (WISP-3) is a hand-held radiometer which automatically operates measurements with 3 radiometers simultaneously (Lsky, Lu, Ed) for water quality monitoring.

WISP-3 directly derives values of water quality parameters (Chl, SPM, phycocyanin and Transparency) by the use of standard algorithms:

  • Chl-a: Chlorophyll-a (0–120 µg l−1).
  • SPM: suspended particulate matter (0–100 mg l−1).
  • Phycocyanin concentration (0–1200 mg m−3).
  • Transparency (kd m−1).

The absorption by colored dissolved organic matter (aCDOM) water quality parameter is also indirectly derived by WISP-3. In this case, more advanced algorithms are used which need the use of computers.

Technical description

The WISP-3 device is composed by three Ocean Optics, Inc. JAZ radiometers, a portable computer and a battery. One of the radiometers is connected through optical fibers to a cosine corrector to measure the downwelling irradiance [Ed (λ)]. The other two radiometers are connected to two Gershun tubes in order to measure the downwelling radiance from the sky [ Lsky (λ, θ)] in which θ=42 deg from the zenith and the total upwelling radiance [Lu (λ,θ)] at 42 deg from the nadir (θ=138 deg). The three radiometers and the mentioned angles are chosen conforming to Mobley's guidance.

Function

Optical close range devices and satellites measure the light that is reflected from the water bodies. In order to derive water quality parameters ( Chl-a, SPM, aCDOM and Secchi depth) from these measurements, algorithms are used. The WISP-3 spectro-radiometer measures three optical signals that allow deriving reflectance values from the water surface. Using adapted band ratio algorithms determined by the water type where the measurements are taken, real time concentration of Chl-a, phycocyanin, SPM and Transparency are computed.

Contribution

When monitoring small water bodies, the land might influence the accuracy of the satellite data. The spatial resolution of these measurements might result in too rough data. WISP-3 is a hand-held, autonomous and close range optical device which allows in situ water quality monitoring and assessment, allowing more precise data measurement. At the same time, these measurements can be used for satellite data validation and to obtain reflection spectra of water bodies for remote sensing objectives.

For instance, WISP-3 spectro-radiometer has been used for validation of atmospheric corrected HICO images, in the project called "Using HICO data for the preparation of the incoming Italian satellite hyper-spectral mission PRISMA". It also has been used for monitoring activities of Blue-green algae in the IJsselmeer, in the Netherlands.

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