5. Conclusions
The Water Colour Simulator WASI is a user-friendly program for forward and
inverse modeling of optical in situ measurements in aquatic environments. It supports
all common types of spectral data obtained from shipborne instruments deployed above
and below the water surface. Computationally, the program uses analytic models which
are suited for all water types: deep and shallow, inland, coastal, and oceanic. Regionspecific optical properties can be accounted for by exchanging the relevant input data.
The main application for WASI is data analysis. WASI is designed to automatically invert large series of spectra in a reasonable time, i.e. on the order of seconds
per spectrum. In addition, it is well-suited to analyze errors from different sources by
means of simulations. Since a consistent set of models is implemented and the same
input data are used for the different spectrum types, data from different instruments can
be compared easily (optical closure studies). Vice versa, optical properties of water
constituents can be derived indirectly from non-specialized instruments, such as
absorption of water constituents from reflectance measurements. Further applications of
WASI are visualization of spectral changes upon parameter variation, data simulation,
and student training.
WASI does have some restrictions. The implemented models are analytic
approximations and do not account for all physical effects, such as fluorescence and
Raman scattering or for certain water constituents such as detritus and bubbles. Vertical
profiles cannot be calculated, nor can images be processed. Data from instruments on
satellite and aircraft cannot be analyzed directly, since no atmospheric model is
included. However, the latter can be done indirectly by coupling WASI with such a
program.
6. Acknowledgements
We are grateful to Nicole Pinnel (Technical University Munich) for providing
unpublished measurements of bottom albedo, and to Laurie Richardson (Florida
International University) for improving the English of our manuscript.
This work was supported by the German Federal Ministry for Education and
Research, Project ID 07 UFE 16/1. It is part of the Special Collaborative Program SFB
454 “Lake Constance” littoral funded by the German Research Foundation DFG.
7. References
Ahn, Y.H., A. Bricaud and A. Morel. 1992. Light backscattering efficiency and related properties of some
phytoplankton. Deep-Sea Research, 39:1835-1855.
Albert, A., and C. D. Mobley. 2003. An analytical model for subsurface irradiance and remote sensing
reflectance in deep and shallow case-2 waters. Optics Express 11, 2873-2890. http://www
opticsexpress.org/abstract.cfm?URI=OPEX-11-22-2873.
Albert, A. 2004. Inversion technique for optical remote sensing in shallow water. Ph.D. thesis, University of
Hamburg. http://www.sub.uni-hamburg.de/opus/volltexte/2005/2325/
Albert, A. and P. Gege. 2005. Inversion of irradiance and remote sensing reflectance in shallow water
between 400 and 800 nm for calculations of water and bottom properties. Applied Optics (submitted).
Babin, M., and D. Stramski. 2002. Light absorption by aquatic particles in the near-infrared spectral region.
Limnology and Oceanography, 47(3), 911-915.
Bricaud, A., A. Morel and L. Prieur. 1981. Absorption by dissolved organic matter of the sea (yellow
substance) in the UV and visible domains. Limnology and Oceanography, 26:43-53.
Buiteveld, H., J. H. M. Hakvoort and M. Donze. 1994. The optical properties of pure water. Ocean Optics XII,
SPIE, Vol. 2258:174-183.
107
Inverse Modeling of Spectral Measurements
The Water Colour Simulator WASI is a user-friendly program for forward and
inverse modeling of optical in situ measurements in aquatic environments. It supports
all common types of spectral data obtained from shipborne instruments deployed above
and below the water surface. Computationally, the program uses analytic models which
are suited for all water types: deep and shallow, inland, coastal, and oceanic. Regionspecific optical properties can be accounted for by exchanging the relevant input data.
The main application for WASI is data analysis. WASI is designed to automatically invert large series of spectra in a reasonable time, i.e. on the order of seconds
per spectrum. In addition, it is well-suited to analyze errors from different sources by
means of simulations. Since a consistent set of models is implemented and the same
input data are used for the different spectrum types, data from different instruments can
be compared easily (optical closure studies). Vice versa, optical properties of water
constituents can be derived indirectly from non-specialized instruments, such as
absorption of water constituents from reflectance measurements. Further applications of
WASI are visualization of spectral changes upon parameter variation, data simulation,
and student training.
WASI does have some restrictions. The implemented models are analytic
approximations and do not account for all physical effects, such as fluorescence and
Raman scattering or for certain water constituents such as detritus and bubbles. Vertical
profiles cannot be calculated, nor can images be processed. Data from instruments on
satellite and aircraft cannot be analyzed directly, since no atmospheric model is
included. However, the latter can be done indirectly by coupling WASI with such a
program.
6. Acknowledgements
We are grateful to Nicole Pinnel (Technical University Munich) for providing
unpublished measurements of bottom albedo, and to Laurie Richardson (Florida
International University) for improving the English of our manuscript.
This work was supported by the German Federal Ministry for Education and
Research, Project ID 07 UFE 16/1. It is part of the Special Collaborative Program SFB
454 “Lake Constance” littoral funded by the German Research Foundation DFG.
7. References
Ahn, Y.H., A. Bricaud and A. Morel. 1992. Light backscattering efficiency and related properties of some
phytoplankton. Deep-Sea Research, 39:1835-1855.
Albert, A., and C. D. Mobley. 2003. An analytical model for subsurface irradiance and remote sensing
reflectance in deep and shallow case-2 waters. Optics Express 11, 2873-2890. http://www
opticsexpress.org/abstract.cfm?URI=OPEX-11-22-2873.
Albert, A. 2004. Inversion technique for optical remote sensing in shallow water. Ph.D. thesis, University of
Hamburg. http://www.sub.uni-hamburg.de/opus/volltexte/2005/2325/
Albert, A. and P. Gege. 2005. Inversion of irradiance and remote sensing reflectance in shallow water
between 400 and 800 nm for calculations of water and bottom properties. Applied Optics (submitted).
Babin, M., and D. Stramski. 2002. Light absorption by aquatic particles in the near-infrared spectral region.
Limnology and Oceanography, 47(3), 911-915.
Bricaud, A., A. Morel and L. Prieur. 1981. Absorption by dissolved organic matter of the sea (yellow
substance) in the UV and visible domains. Limnology and Oceanography, 26:43-53.
Buiteveld, H., J. H. M. Hakvoort and M. Donze. 1994. The optical properties of pure water. Ocean Optics XII,
SPIE, Vol. 2258:174-183.
107
Inverse Modeling of Spectral Measurements