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| Radiative Transfer Models > Hydrolight |
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The HYDROLIGHT radiative transfer numerical model computes radiance
distributions and related quantities (irradiances, reflectances,
diffuse attenuation functions, etc.) in the ocean. Users can specify
the water absorption and scattering properties, the sky conditions, and
the bottom boundary conditions in various ways: by selection of
built-in defaults, by reading in user-supplied data (such as WETLabs®
ac-9 data), or by writing their own Fortran subroutines to define their
input. HYDROLIGHT then computes the in-water light field and other
quantities of interest to optical oceanographers, such as the
water-leaving radiance and remote-sensing reflectance. Output is
presented as ASCII printout, as Excel® spreadsheets, or as digital
files designed for plotting and analysis using IDL®. HYDROLIGHT is used
in various ways:
As a predictive tool
What will the oceanic light field be at some time in the future?
Given a prediction of water absorption and scattering properties,
HYDROLIGHT can use that information to predict the corresponding light
field. HYDROLIGHT can even become the optics component of a coupled
biological-physical-optical ecosystem model.
As a data analysis tool
What was the ambient light field when the data were taken?
For example, when imaging an underwater object in the daytime, the
ambient daylight may contribute noise (in this case, path radiance) to
the signal of interest (the light propagating from the target to the
sensor). HYDROLIGHT can compute the ambient daylight field so that it
can be subtracted from the total signal received at the sensor to
improve the signal-to-noise ratio of the detected signal.
As a system design tool
How would a proposed system perform under different environmental conditions?
HYDROLIGHT can serve as a controlled environment to predict what the
light field received by a sensor would be under a wide range of
conditions. Such control of the environment and of simulated noise
cannot be obtained in the field, which is best used for final testing
and evaluation of sensors that were first designed using numerical
simulations.
As a teaching tool
How
can someone new to the field of optical oceanography most quickly build
up "intuition" or a "working knowledge" about the marine optical
environment? The best way to gain such knowledge is of course to spend
20 years working as an optical oceanographer. The next best way is to
use HYDROLIGHT to study how oceanic light fields depend on various
environmental parameters.
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