Onboard absolute radiometric calibration and validation of the satellite calibration spectrometer on HY-1C.

As the reference radiometric calibration standard of sensors on the Haiyang-1C (HY-1C) satellite platform, the satellite calibration spectrometer (SCS) is equipped with an onboard calibration system composed of double solar diffusers and an erbium-doped diffuser to monitor the postlaunch radiometric response change. Herein, through onboard calibration data analysis, the calibration diffuser performance remains stable without degradation, and the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra is adopted as a reference to repeatedly verify onboard radiometric calibration results by selecting different dates and reflectance scenes. The SCS equivalent reflectance is obtained by combining the mean digital number (DN) of the SCS crossing area image with the radiometric calibration coefficient. The spectral reflectance is obtained via interpolation and iteration, which is adopted as the actual MODIS incident pupil spectral reflectance because the small imaging time interval can be ignored and almost vertically observed, and it is convoluted with the MODIS spectral response function to obtain the predicted equivalent reflectance. Validation is completed by comparing the predicted MODIS equivalent reflectance to the measured value based on the onboard calibration coefficient. The results show that (1) the difference between the measured and predicted MODIS band equivalent reflectance is between -0.00466 and 0.0039, and (2) the percentage difference between the measured and predicted MODIS band equivalent reflectance ranges from 4.17% and 1.24%, indicating that the calibration system carried on HY-1C can perform high-precision SCS radiometric calibration, meeting the cross-calibration accuracy requirements of other loads on the same platform.

[New Algorithms to Separate the Contribution of Petroleum Substances and Suspended Particulate Matter on the Scattering Coefficient Spectrum from Mixed Water].

In the water with petroleum pollution, the petroleum will be adsorbed on the surface of suspended particulate matter and form a double-layer structure, which impacts on the spectrum characteristics to the scattering coefficient. It is a key to improve the accuracy of the scattering theory model that the contribution of petroleum substances and suspended particulate matter on the scattering spectrum coefficient is be separated. A backward scattering coefficient spectrum measurement system was being built from linkage observation of three kinds of instruments, including DAWN HELEOS Ⅱ18 angle scattering measuring instrument (Wyatt company, American), LISST-100-xB size instrument(SEQUOIA SCIENTIFIC, INC, American), HydroScat-6 Sprctral Backscattering Sensor (HS6) ( Hobilabs company, American). Many parameters were measured such as voltage value of the scattering intensity, the particle size distribution, particle concentration and backward scattering coefficient in different water samples. Using the Mie scattering theory, a new algorithm to separate the scattering coefficient spectrum and new way of thinking to calculate volume scattering function ß(λ, θ) of the unknown refractive index material were proposed. The matching experiments were done by selecting quartz sand as particles whose refractive index (m) is known and petroleum sewage collected from different oilfield area. On the basis of matching experiments different water samples with different properties were obtained and related data were determinated. Firstly, according to Mie scattering theory the water volume scattering function ß(λ, θ) for each sample is calculated. Secondly, the equation was set up which can convert the scattering intensity corresponding to the voltage value V(θ) measured by DAWN HELEOS Ⅱ 18 Angle laser scattering instrument into volume scattering function ß(λ, θ). Thirdly, according to the method of optimum the equivalent refractive index (mos) of the oil sands mixed and the refractive index (mo) of petroleum sewage were estimated; Finally, using ß(λ, θ) and estimation of mos values and mo values to calculate the backscatter coefficient bb(λ) of all kinds samples, and new algorithms were set up which seperated quartz sand bb, s(λ) and petroleum sewage bb, o(λ) from mixed water with petroleum and sands respectively. The establishment of these separation algorithms improves the accuracy of the scattering theory model of the water petroleum pollution, on the other hand expands the Mie scattering theory in the application of ocean color remote sensing.

[Analysis of fluorescence spectrum of petroleum-polluted water].

In four ratio experiments, natural waters, sampled from the mountain reservoir and the sea water around Dalian city, were mixed with the sewage from petroleum refinery and petroleum exploitation plants. The fluorescence spectra of water samples containing only chromophoric dissolved organic matters(CDOM), samples containing only petroleum, and samples containing a mixture of petroleum and CDOM were analyzed, respectively. The purpose of this analysis is to provide a basis for determining the contribution of petroleum substances and CDOM to the total absorption coefficient of the petroleum-contaminated water by using fluorescence technique. The results showed that firstly, CDOM in seawater had three main fluorescence peaks at Ex: 225-230 nm/Em: 320-330 nm, Ex: 280 nm/Em: 340 nm and Ex: 225-240 nm/Em: 430-470 nm, respectively, and these may arise from the oceanic chlorophyll. CDOM in natural reservoir water had two main fluorescence peaks at EX: 240- 260 nm/Em: 420-450 nm and Ex: 310~350 nm/Em: 420--440 nm, respectively, and these may arise from the terrestrial sources; secondly, the water samples containing only petroleum extracted with n-hexane had one to three fluorescence spectral peaksat Ex: 220-240 nm/Em: 320-340 nm, Ex: 270-290 nm/Em: 310-340 nm and Ex: 220-235 nm/Em: 280-310 nm, respectively, caused by their hydrocarbon component; finally, the water samples containing both petroleum and CDOM showed a very strong fluorescence peak at Ex: 230-250 nm/Em: 320-370 nm, caused by the combined effect of CDOM and petroleum hydrocarbons.

Spectral variability of sea surface skylight reflectance and its effect on ocean color.

In this study, sea surface skylight spectral reflectance ρ(λ) was retrieved by means of the non-linear spectral optimization method and a bio-optical model. The spectral variability of ρ(λ) was found to be mainly influenced by the uniformity of the incident skylight, and a model is proposed to predict the ρ(λ) spectral dependency based on skylight reflectance at 750 nm. It is demonstrated that using the spectrally variable ρ(λ), rather than a constant, yields an improved agreement between the above-water remote sensing reflectance R(rs)(λ) estimates and concurrent profiling ones. The findings of this study highlight the necessity to re-process the relevant historical above-water data and update ocean color retrieval algorithms accordingly.

[Study on using apparent spectrum to retrieve the inherent optical properties of ocean water].

The inherent optical properties are needed when establishing the semi-analytic model in the ocean color retrieval algorithm. Using the in-situ measurements, a retrieval model for inherent optical properties from remote sensing reflectance was established. The in-situ data measured in the 2003 spring cruise over the Yellow and East China Seas is introduced. The measurement method for remote sensing reflectance, particle backscattering and absorption coefficients are detailed. Based on the bio-optical model, the inherent optical properties were retrieved by optimization of Nelder-Mead simplex. The retrieval results of the absorption and backscattering coefficients for the material other than pure water were compared with the counterpart of the in-situ measurements. The comparison shows that the root-mean-square relative error for the absorption coefficient of materials other than water is less than 33%. The value is 30% for the particle backscattering coefficient. The analysis of the error shows that the retrieval model established in this paper can provide an efficient approach to retrieving the absorption and backscattering coefficients. The retrieval model can provide a reference for the application of remotely sensed data to the research on the bio-optical properties of Yellow and East China Seas.

[Influence of petroleum concentration in water on spectral backscattering coefficient].

The petroleum pollutants mixing proportion experiment and in-situ experiment were carried out in the estuary of Panjin, Liaoning province in May 2008 and August 2009. The optical properties and biochemical properties were measured to get the effect of petroleum concentration in water on backscattering coefficients spectrum. The results show that the power-law index of backscattering coefficient decreases as TSM concentration increases and the relationship of these variables follows logarithm mode. Specific backscattering coefficient's value of 440 to 856 nm is between 0.006 and 0.035 m2 x g(-1) and decreases as wavelength increases. The petroleum mass-specific backscattering coefficients (backscattering coefficients of unit petroleum concentration) decreases with the wavelength increasing and follows power law for petroleum concentration. Petroleum concentration has little effect on the power-law index of backscattering coefficient.