Wet Labs ECO VSF, User Manual

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6 ECO VSF User’s Guide (VSF) Revision AN 14 Sept. 2011
2. Theory of Operation
The angular distribution of scattered radiation in the backward hemisphere is important in the
interpretation of remote sensing measurements, investigations of particle shape, and models of
visibility in seawater. The
ECO VSF measures the optical scattering at 100, 125, and 150 degrees,
thus providing the shape of the Volume Scattering Function (VSF) throughout its angular domain.
Motivated by the need to better understand the relationship of water-leaving radiance with the
backscattering into the same direction, the three-angle measurement allows determination of
specific angles of backscattering through interpolation. Conversely, it also can provide the total
backscattering coefficient by integration and extrapolation from 90 to 180 degrees.
Figure 3 shows the optical configuration for the VSF. The
ECO VSF consists of a potted
monolithic optical flange and a housing containing the signal processing and controller circuitry.
The optics include three LED-based transmitters that couple to a single receiver. The transmitters
and receiver are located to establish centroid light scattering angles of approximately 100, 125,
and 150 degrees respectively. For each angle the region of intersection encompasses a FWHM
bandwidth of about 18 degrees.
Figure 3. Optical configuration of ECO -VSF
The controller electronics sequence through the individual transmitters at approximately 1 Hz per
sample cycle. The individual transmitters operate synchronously with the receiver to reject
ambient light. A directly coupled reference detector indicates relative LED intensity during
operation. Signals from the receiver and reference detector are digitized and subsequently stored
or telemetered from the instrument.
The
ECO VSF can be configured for a variety of applications. In addition to providing a
continuous output, the instrument can internally record up to 65,000 samples of data.
Additionally, for long-term deployments, the instrument can come equipped with an anti-fouling
shutter to retard bio-fouling of the optical surfaces. Models with internal and external batteries are
also available. Each sensor operates at one wavelength. Presently these wavelengths are factory
configurable for 470 nm, 530 nm, and 650 nm
.