Research On In-situ Fluorescence Spectroscopy Techniques For Oceanic Chromophoric Dissolved Organic Matter

The research on chromophoric dissolved organic matter (CDOM) is very important for ocean color, global carbon cycle, oceanic ecology, oceanic dynamical environments, and pollution monitoring in ocean. CDOM measurements with fluorescence techniques have high sensitivity and selectivity, and can operate simply without water sample filter and pretreatment. Fluorescence spectroscopy has been used in CDOM research and measurements widely in recent years. While most fluorescence research at the present time needs to collect water sample and measure spectra with fluorospectrophotometer in lab. So the development of in-situ fluorescence devices and techniques has great utility value and necessity. This thesis focuses on the CDOM in-situ fluorescence techniques and devices. The main contents are as follows:1. A compact underwater CDOM in-situ fluorescence prototype has been successfully developed based on ROV platform. This prototype can get CDOM spectra curves in real time with a355nm UV laser and a small optical fiber spectrometer. The main feature of this prototype is the integration configuration design between ROV platform and in-situ fluorescence device chamber. Series performance tests such as laboratory waterproof tests, swimming pool tests, and oceanic field deployments have demonstrated the utility of the prototype as an integrated tool for research and observations. The fluorescence intensity ratio has good correlation with absorption coefficient measured with UV-VIS spectrophotometry.2. A novel multi-wavelength fluorescence measurement method was proposed and verification experiment proved its fesibility. This method provides fluorescence spectra for assessment of CDOM, chlorophyll a, and pigments with combined dual-wavelength (266nm and532nm) laser and375nm LED as excitation source.3. Time resolved fluorescence spectroscopy has been used for CDOM research with ICCD and pulsed laser excited at355nm or266nm. When excited at266nm, three main components with different fluorescence lifetime have been differentiated successfully. Furthermore, a compact ocean lidar verification device was performed with ICCD and a micro-pulsed laser.4. Fluorescence and absorption spectroscopy joint analysis has been performed with a liquid core optical fiber used as absorption sample cell. The absorption measurement with a liquid core optical fiber can improve sensitivity by increasing optical path, and can also calibrate fluorescence data in field deployments. The results show good correlation(R=0.98)between fluorescence intensity ratio and absorption in laboratory experiments.5、Fluorescence and Raman spectroscopy joint research has been performed for CDOM composition analysis. Three combination modes has been studied including deep UV fluorescence and VIS Raman joint, deep UV fluorescence and UV resonance Raman joint, deep UV fluorescence and surface enhanced resonance Raman joint. Between the three combination modes, deep UV fluorescence and surface enhanced resonance Raman joint analysis is the most satisfactory. Fluorescence and surface enhanced resonance Raman spectra were obtained simultaneously with the same device.