As a molecular fingerprint technique, Raman spectroscopy has been widely used in the qualitative identification and quantitative analysis for the targets, and it has also been gradually applied to the in situ detection of deep-sea extreme environment in past decades. The development of the laser Raman spectroscopy for deep ocean in situ detection is reviewed. The kinds of deep ocean Raman spectrometers developed by now are introduced, and the applications of the spectrometers for in situ detection of the seepage fluids, the sediment pore water, the carbonate minerals, and the hydrate are also presented. Finally, the factors that limit the broader application of the Raman spectroscopy in the deep ocean are summarized and discussed, which provides a reference for the future development of Raman spectroscopy.

Laser induced breakdown spectroscopy(LIBS) has been widely used in different fields as an effective analysis technique. Its application in underwater research is a new hot spot recently and a lot of works have been reported continuously. An overview of the recent research progress for LIBS in underwater detection is given in this work, including the simulation experiments in laboratory, the field experiments in sea trial, the fundamental research, and the technique development. As an example, the deep sea in situ LIBS system (LIBSea) is shown in detail, giving the typical results in ocean detection. Finally, the application of LIBS in ocean detection in the near future is prospected.

The measurement of optical properties of ocean water body is the basis of the development of the theory of marine optics, and the improvement of the measurement technology of optical properties has greatly promoted the development of other optical technologies and their applications. Looking back on the history, photoelectric technology and spectral technology are the main driving force of water optical measurement technology, and the development of radiate transfer theory and water color remote sensing are the main traction force of optical measurement technology. The measurement principle, method and typical products of optical properties of water body are introduced systematically, including the measurement methods of spectral radiance and spectral irradiance, spectral absorption and spectral scattering properties. Finally, the future development direction of optical property measurement is given, which can provide reference for the development of water optical instruments, related ocean optical technology and their users.

The blue-green spectrum in the range of 450～550 nm is the only low loss optical window of seawater. Due to the absorption and scattering of water, the underwater propagation of the laser beam will have time-space expansion and waveform distortion. Based on Monte Carlo simulation, the propagation characteristics of blue-green laser in seawater have been analyzed, especially the influence of laser emission parameters on the distribution of receiving light field. By adjusting the beam parameters of the transmitter and focusing the laser beam in advance, the influence of beam diffusion caused by underwater transmission can be eliminated to some extent. The analysis and simulation results show that when the pre-focusing angle is equal to the small angle scattering eigenvalue of water, a flat transmission area with slow spread of laser beam can be formed in Jerlov type IB water before the designed focus distance. When the pre-focusing angle is greater than twice the scattering angle of water, the convergence effect can be formed near the designed focus distance, and the focus effect is proportional to the pre-focusing angle. When the water quality becomes worse, the corresponding effective focus distance becomes shorter. The research results provide a new way to improve the transmission characteristics of blue-green laser signal in seawater.

The combined analysis of the discrimination performance of the atmospheric and oceanic high-spectral-resolution lidar (HSRL) can help the joint atmospheric and oceanic observation research. An atmospheric and oceanic HSRL system based on the field-widened Michelson interferometer (FWMI) discriminator is proposed in this work, which can be used to retrieve the 180-degree volume scattering function of oceanic and atmospheric particles. The core of the system is the combined-molecular dual channel, in which the molecular channel uses FWMI discriminator to filter the particle signal but transmit the molecular signal. It is shown that the retrieval error will increase proportionally with the particulate scattering ratio (the ratio of the total 180-degree volume scattering function to that of molecular), while the enhancing of the spectral discrimination ratio (the ratio of the molecular transmittance to the particulate transmittance) can significantly suppress the growth trend of the retrieval error. Because molecular scattering and particulate scattering are separated in the spectrum of oceanic HSRL, FWMI has a better discriminating characteristics in the oceanic HSRL than in the atmospheric HSRL. The proposed HSRL system based on FWMI can work in water and atmosphere, which is of great significance to the performance improvement of atmospheric and oceanic lidar.

The study of algae is significant for monitoring marine environment and exploring biological resources. Confocal Raman spectroscopy has been widely used in biology as a label-free and rapid detection technique. Currently, the commercial micro-Raman is dominated in this field, while it is not applicable to field measurements for the instrumental size and the operation condition. Hence, a fiber optic spectrometer is introduced to develop a low-cost compact confocal-raman system for algae detection at “single-cell” level. The developed system is all-in-one designed for the compactness, and is well functioned with the capacities of Raman detection, microscopic imaging and optical tweezers capture. Four typical kinds of single-cells (Skeletonema costatum, N.oceanica IMET-1, Prorocentrum donghaiense Lu and Chlorella) were used to evaluate the system detectability, and the components such as proteins, lipids, glycogen and nucleic acids were recognized. Based on that, the algae cells were successfully classified into 4 species after using principal component analysis (PCA) method, which indicates that it is feasible to apply the fiber optic spectrometer for single cell analysis of marine microbes. It is expected that the developed system will be deployed as field instrument for the deck measurements in sea trials in the future.

The community structure of phytoplankton is one of the important indicators to evaluate the marine ecological environment. At present, the research of this field is mainly based on the on-site sampling followed by laboratory analysis, lacking of rapid on-line automatic, in-situ profile and remote sensing ground verification technology. In order to meet the needs of rapid acquisition of phytoplankton community structure and ground verification of remote sensing data, a fast field measurement method of marine algae community structure based on discrete three-dimensional fluorescence spectrum was studied. Then an in-situ online measurement instrument of marine algae community structure was developed, and at last application demonstration and comparative verification were carried out. The results show that the measurement technology of marine algal community structure based on the discrete three-dimensional fluorescence spectrometry can obtain the algal community structure and chlorophyll content quickly and accurately. Compared with the existing technology, it has the advantages of fast, accurate, stable and reliable measurement, and provides advanced technical means for the acquisition of marine ecological environment monitoring data and ground verification of remote sensing data.

Adding proper amount of flocculants and coagulants into water can settle algal flocculation and remove algal bloom. Water body in scene is much complex and there are many factors affecting the flocculation effects. It is beneficial to improve the treatment effect to monitor the algae flocculation process in situ. Microcysts aeruginosa was used as a sample in this work to form flocculant suspension by adding different concentrations of polyaluminium chloride and kaolin, and then the polarization parameters of the different flocs suspension were measured by polarized light scattering technique. The results show that the polarization parameters can be used to characterize the flocculation processes affected by the dosage of flocculants and coagulants, which shows the potential of the proposed polarized light scattering technique to describe the algal flocculation process. It is indicated that the method provides an in-situ non-contact, unmarked and rapid monitoring tool for algal flocculation process research, algal blooms governance and monitoring, contaminated water treatment, pharmaceutical development, etc.