Invited column “Ocean optics”
2018, 47(9): 903001.
doi: 10.3788/IRLA201847.0903001
Underwater 3D triangular range-intensity correlation imaging(RICI) is a novel scannerless 3D imaging technique beyond underwater visibility range, and can fill the current gap between short-range high-resolution conventional video cameras without 3D information and long-range low-resolution sonar systems. The development of 3D RICI was reviewed, and the introduction of 3D triangular RICI in the Institute of Semiconductors, CAS was focused. A 3D triangular RICI with multi-pulse time delay integration method was proposed, and the typical time parameters in the method were given. The prototype 3D range-gated imaging systems of Lvtong, Fengyan, Longjing were established, and can realize 3D imaging with 1 360 pixel1 024 pixel beyond the visibility range of 4.8 AL. The systems have been used in fishnet detection, marine in situ detection, underwater target detection and recognition.
2018, 47(9): 903002.
doi: 10.3788/IRLA201847.0903002
The encapsulation of ultrafine DFB fiber laser hydrophone probe was studied. A theoretical model of encapsulation structure was built by finite element method. The factors affecting the frequency response and sensitivity fluctuation of ultrafine fiber laser hydrophone were discussed. A balance was found upon sensitivity, frequency response consistency and other indexes. Finally, a fiber laser hydrophone was made. Its diameter was 6 mm, length was 55 mm, sensitivity was -130 dB and sensitivity response fluctuation between 100 Hz -2 kHz was 4 dB. The conformity of theoretical analysis and simulation was verified by experimental test.
2018, 47(9): 903003.
doi: 10.3788/IRLA201847.0903003
China is in the critical period of implementing the strategic deployment of the 21st Century Ocean Silk Road. The development of ocean optical technology is an important direction to support the country's medium and long-term development strategy. Ocean laser remote sensing technology is one of the important research fields in ocean optics. As a new active remote sensing technology developing rapidly in recent years, lidar has been widely used in the field of ocean laser remote sensing because of its high precision and high spatial-temporal resolution. In this paper, based on Brillouin scattering lidar and ocean imaging lidar, the research progress of ocean laser remote sensing technology and its application in water parameter measurement, underwater target detection and laser remote sensing of ocean topography in China were introduced.
2018, 47(9): 903004.
doi: 10.3788/IRLA201847.0903004
The colored fraction of dissolved organic matter, CDOM, directly influences water optical properties and spectral quality, playing an important role in aquatic ecosystems, optical remote sensing and carbon circulation in the sea. Measuring in situ CDOM absorption coefficient, however, is difficult because it requires prefiltration of water samples. An analytical laboratory and field instrument for fast diagnosis of chromophoric dissolved organic matter(CDOM) in water was developed. The laser fluorometer was integrated with spectral fluorescent signature(SFS) analysis of the laser stimulated emission excited at 405 nm and hyper spectra for surveillance of CDOM. CDOM and water Raman scattering components were derived from the laser stimulated emission spectra measured in the laboratory and field conditions with SFS technology, which added to analytical Lidar sensing the capability of detecting and identifying trace substances in a variety of targets in the presence of other background matters responding to optical excitation with overlapping signals. The influence of temperature change on CDOM fluorescence data in water was investigated in laboratory, and a temperature calibration method was employed for calibrating fluorometer data. Laboratory and in-situ studies with the laser fluorometer in the East China Sea (ECS) in April 2013 were carried out. Significant and positive correlation in the ECS was observed between CDOM absorption measurements and CDOM fluorescence (R2=0.83). The result demonstrated the possibilities of CDOM monitoring in real time based upon the laser fluorometer.
2018, 47(9): 903005.
doi: 10.3788/IRLA201847.0903005
A diversified array optical receiving antenna was designed for the problem of alignment difficulty in underwater wireless laser communication systems. The optical structures of the composite optical receiving antenna and diversity array optical receiving antenna were designed by the optical design software Zemax, and the field of view angle, the light gathering efficiency and the light source moving range of the two kinds of antenna were analyzed. Besides, the light gathering efficiency as a function of the light source moving range and the incident angle of the light source of the two kinds of optical receiving antennas was given by experiments and Matlab simulations. The results show that when the light source size is 10 mm, the light gathering efficiency of the composite optical receiving antenna is 0.06%, the receiving field angle is 6, the moving range of the light source is 6 mm. And the light gathering efficiency of the diversity array optical receiving antenna is 0.06%, the receiving field angle is 16, the moving range of the light source is 22 mm. Therefore, the diversity array optical receiving antenna was more suitable for underwater laser communication systems.
2018, 47(9): 903006.
doi: 10.3788/IRLA201847.0903006
An optical passive imaging interference system (OPⅡS) was proposed for the real-time and long-term detection of hydrothermal methane's concentration, temperature and pressure. Firstly, the forward model that consisted of deep ocean gas emission model, seawater transmission model and instrument responding model was built by interface description language (IDL), and its forward interference fringers were simulated. The SNRs of the forward interference fringes were in the range of (50-70) in general. And the detection sensitivity of concentration measurement is was at least 0.1 mmol/L, the temperature was at least 2 K, and the pressure was at least 0.1 MPa. Then, OPⅡS's data were processed accurately and rapidly by combining imaging interference technology and partial least squares (PLS) algorithm. The multi-dependent variable PLS regression model of methane was established by using 25 modeling samples, and this PLS regression model was cross-validated by using 25 prediction samples. And the max error for concentration prediction of this regression model was 1.9%, for temperature prediction was 0.38%, and 1.0% for pressure prediction.
