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Investigations On Chlorophyll Fluorescence Remote Sensing

Posted on:2009-05-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:X G XingFull Text:PDF
GTID:1100360245488183Subject:Physical oceanography
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This study makes some investigations on chlorophyll fluorescence remote sensing. Firstly, the principle, measurement and remote sensing algorithms of chlorophyll fluorescence remote sensing are introduced in detail. Then the results of reseaches concerning fluorescence line height algorithm and fluorescence quantum yield have been presented.Utilizing Hydrolight 4.2, the famous radiative transfer numerical calculating software, this study first analyses the influences of yellow substance and suspended matter on the fluorescence line height (FLH) in natural waters. The calculations show that the relative errors of FLH resulted from yellow substance reach 10% around, generally. However, the effect of suspended matter on FLH error is more remarkable. The scattering signal of suspended matter covers the chlorophyll fluorescence region, and raises the whole red and infrared spectra of remote sensing reflectance, even may entirely submerge the fluorescence signal to invalidate fluorescence algorithm when the concentration of suspended matter reaches 20~30 mg/L. Even in waters with 5 mg/L suspended matter, the influence on FLH markedly exceeds 30%.Secondly, an experiential relationship between FLH and total chlorophyll concentration is obtained, based on regression analyses using the in-situ measured data including water-leaving radiance spectra, chlorophyll concentration and absorption coefficient. The result shows a strong positive correlation between FLH and chlorophyll concentration in four regression models, such as linear, binomial, exponential and Gower's models. Especially, in the linear regression equation of FLH=0.36729+0.01788*[Chla], and the correlation coefficient, R2, reaches 0.89. The comparions among different bands on three sensors , including MODIS, MERIS and GLI, demonstrate that the correlation for MODIS bands appears higher, resulting from the right baseline band close to fluorescence peak on MERIS and GLI.Sun-induced chlorophyll-a fluorescence signals have been measured in Bohai Sea using an underwater hyperspectral spectroradiometer. This study combines these signals with other apparent and inherent optical properties to derive the in vivo fluorescence quantum yield (FQY), and came to the conclusion that the maximum was around 0.06, the average value reached 0.017, with most values ranging from 0.001 to 0.02, which are consistent with the results obtained in other sea areas. Besides, an obvious negative correlation between FQY and instantaneous photosynthetically available radiance (IPAR) was found among some adjacent stations. Some empirical relationships based on in-situ measurements are established and validated in this study, and compared with the former results. It is shown that the correlation between inherent optical properties and chlorophyll-a concentration is highly different from other sea areas; however, the relationship between diffuse attenuation coefficients is comparatively stable.On the basis of analyses of phytoplankton physiology and bio-optics, this study proposes that the CFE (chlorophyll fluorescence efficiency) algorithm is not a precision approach to estimate FQY by using moderate resolution imaging spectrometer (MODIS) data, and then presents a new MODIS algorithm for more accurate estimation of FQY. The FQY computation was done with the MODIS TERRA data obtained in Bohai and North Yellow Sea on February 23, 2006, and the comparison between the two methods was made. The results show that CFE appeared negative in many areas and distinct overestimate in some points, the new productφest was likely more effective, the maximum was about 0.05, and most values ranged from 0.001 to 0.02, which were consistent with the results obtained in situ. Through a simple error analysis ofφest, the paper holds that, for improving the accuracy, a band-ratio method for directly retrieving optical properties needs to be explored to replace these empirical relationships used in the algorithm.With the development of satellite sensors, the maturity of fluorescence remote-sensing algorithm, the accumulation and analysis of field and satellite data, chlorophyll fluorescence remote sensing will play an important role in optical oceanography, marine bionomics, phytoplankton physiology, ocean color remote sensing and HABs (harmful algal blooms) monitoring.
Keywords/Search Tags:chlorophyll fluorescence remote sensing, chlorophyll-a concentration, fluorescence line height (FLH), fluorescence quantum yeild, MODIS
PDF Full Text Request
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