Inherent optical properties (IOPs), e.g., absorption, back scattering coefficients, and volume scattering function, are
important parameters for radiance transfer simulation. Commercially available instruments (e.g., Wetlabs ACS, BB9, etc,
and HOBILabs a-sphere, HS6, etc) basically only measure absorption and back scattering coefficients. In this paper, we
used the same IOPs of International Ocean-Colour Coordinating Group (IOCCG) report 5 and Hydrolight to simulate the
radiance distribution, however, different phase functions, say, a new phase function derived from the measured data by
multispectral volume scattering meter (MVSM) in coastal waters, the widely used Petzold average phase function, and
the Fournier-Forand (FF) phase function, were employed in the simulations. The simulation results were used to develop
the retrieval algorithm with angular effects correction based on the quasi-analytical algorithm(QAA) developed by Lee et
al.. Results showed that not only the back scattering probability, but also the angular shape of phase function are
important for ocean color retrieval algorithm. Considering the importance of phase function in ocean color remote
sensing, methods to validate the phase function data should be developed.
Coastal areas of the China Seas are typical the so called case II waters or turbid waters, the retrieval and validation of the
ocean color satellites' data in the China Seas have become one of the most difficult field in the ocean color remote
sensing community. In this study, the semi-analytical (SA) algorithm for optically shallow water developed by Lee et al.
is tuned for the China Seas using numerical simulation technique of the radiative transfer equation based on the field
investigation data (China Joint Global Ocean Flux Study, JGOFS and some unpublished data) and literature of the China
Seas. It is found that the tuned SA algorithm for the China Seas is better than that of Gordon et al. and Lee et al., the
applicability of the tuned SA algorithm is improved in the China Sea. The percentage error between the retrieved
chlorophyll concentration by the tuned SA algorithm for the China Seas and the in-situ data is about 28% using the field
campaign data in the East China Sea in 1998.
During recent years, more and more efforts have been focused on developing new models based on ocean optics theory
to retrieve water's bio-geo-chemical parameters or inherent optical properties (IOPs) from either ocean color imagery or
in situ measurements. Basically, these models are sophisticated, and hard to invert directly, look up table (LUT)
technique or optimization methods are employed to retrieve the unknown parameters, e.g., chlorophyll concentration,
CDOM absorption, etc. Many researches prefer to use time-consuming global optimization methods, e.g., genetic or
evolutionary algorithm, etc. In this study, different optimization methods, smooth nonlinear optimization (NLP), global
optimization (GO), nonsmooth optimization (NSP), are compared based on the sophisticated hyper-spectral semianalytical
(SA) algorithm developed by Lee et al., retrieval accuracy and performance are evaluated. It is found that
retrieval accuracy don't have much difference, the performance difference, however, is much larger, NLP works very
well for the SA model. For a given model, it is better to analyze the model is linear, nonlinear or nonsmooth category
problem, sometimes, convex also need to be determined, or linearize some nonsmooth problem caused by if decision,
then select the corresponding category optimization methods. Initial values selection is a big issue for optimization, the
simple statistical models (e.g., OC2 or OC4) are used to retrieve the unknowns as initial values.
The purpose of this research is to study the effect of nonuniform vertical profiles of chlorophyll concentration on
apparent optical properties with Radiative transfer model Hydrolight. The vertical profiles of chlorophyll concentration
were approximated according to a Gaussian function(Lewis et al, 1983).The simulated AOPs for nonuniform chlorophyll
profiles were compared with those for homogenous ocean whose chlorophyll concentration was identical to the
background chlorophyll concentration of inhomogenous cases. The results reveal that the subsurface maximal
chlorophyll concentration increase remote sensing reflectance in the blue wavelength and decrease it in the green
wavelength, and nonuniform vertical profiles of chlorophyll concentration change the diffuse attenuation coefficient
profiles and the angular structure of the light field in the seawater.
In this study, a simulated-annealing algorithm is combined with well known semi-analytical model for deep water's
inherent optical properties (IOPs) parameters. The IOPs is an important factor in considering and evaluating water type,
subsurface light field, turbidity and pigment concentration. A simulated annealing (SA) algorithm is a global optimum
process that could be applied for non-linear optimization problem in which multiparameter are present. In this work, four
parameters are presented: Chl, ag440, S and bbp550. We evaluate our approach with self-computed data and IOCCG
data set. The comparison between the retrieved results and the measured coefficients suggests that the differences are
close to the accuracy limitations, and the two sets of results are in nice agreement, so the inversion results can be
With the broadening and deepening of GIS applications, the GIS system is beginning to process a much larger amount of spatial data. Further analysis and processing of spatial data depend on data quality to a great extent, i.e. the accuracy, integrity and coherence of the data. Different methods have been developed for the purpose of controlling data quality. In this paper, a novel solution is proposed, which is a workflow-based system design for the online inspection of spatial
data combined with the role-task based access control model and the versioning function of ArcSDE on a database. The design is charactered by precise workflow modeling of the online inspection of spatial data. There are two significant advantages about this design: a) A more secure access control mechanism in GIS workflow; b) A more effective solution to support long transactions of GIS workflow. This workflow-based system design has been successfully used in the
active fault seismic data which have been collected from more than twenty cities in China and include different disciplines. It is charactered by stronger security and easier maintenance. Moreover, it can also be used for other kinds of online inspection of spatial data with its universal applicability.
In this study, measurements and models are used to test the closure between remote-sensing reflectance and IOPs. Measurements include those by AC9 (Wetlabs, Inc.) and HS6 (HOBI labs, Inc.), while models include both empirical models (e.g., Voss' beam attenuation coefficient model) and radiative transfer model (e.g., Hydrolight). It is found that, generally, AC9 works better than HS6 in providing scattering and backscattering coefficients. HS6 need more accurate calibration; absorption coefficients by AC9 are consistent with those by Spectrix or Spectrometer. Good linear relationship is found between AC9 measured beam attenuation coefficients (c) and the Voss model; while those measurements by HS6 needs some adjustments before feeding to HYDROLIGHT.
Ocean environment attracts more and more attention, whereas monitoring ocean environment using ocean color imagery (e.g., MODIS) has become one of the important fields in modern oceanography. After analyzing a few individual modules of the radiative transfer process, an end-to-end numerical model for ocean remote sensing is developed. This model combines MODTRAN and HYDROLIGHT, both are state-of-the-art radiative transfer models for atmosphere and water, respectively. Also, a simple but realistic cloud model is added to it. This combined model calculates the downward radiance on water surface using MODTRAN and the independent cloud model, which replaces the empirical and semi-empirical models used in RADTRAN (Gregg and Carder 1991). Especially, with information of cloud's location and brightness from by the cloud model, the combined model provides more accurate radiance on water surface. Further, the effects of cloud position (from 30 degree to 180 degree for the cloud central azimuth angle) and coverage (from about 10% to 80%) on retrieved chlorophyll concentration by standard MODIS algorithm is analyzed. It is found that the nearer the cloud to the Sun the smaller the effect on the derived chlorophyll.
The HYDROLIGHT ocean radiative transfer code is a well established standard for simulating the water leaving radiance from the visible to the near infrared. However, its efficient use is a task not easily accomplished for running thousands of different cases and processing the generated results. HydroPPT is a tool integrated with HYDROLIGHT to generate input data and Fortran files and process the digital output files in batch mode. This paper describes workflows and examples for simulating a dataset. This paper also provides some tips to port HYDROLIGHT to some other compilers (e.g., Intel visual Fortran compiler) and platforms (e.g., SGI IRIX, HP TRU64, SUN Solaris, etc) to improve the computing efficiency and effectively use the computing resources. Based on our tests, Intel visual Fortran compiler provides improved performance for HYDROLIGHT code than that by the LAHEY Fortran compiler on the Intel processor based platforms.