The temperature and salinity of seawater are essential physical parameters for marine science. The measurement of conductivity is an important means of salinity measurement. In this article, seven electrodes are used to design a temperature and salinity sensor. The sensor detects voltage signal and current signal in strong marine noise environments using lock-in amplifier technology to improve the measurement accuracy of seawater conductivity. A seven-electrode temperature and salinity sensor and a Seabird SBE37-SI temperature and salinity sensor are used for laboratory comparison, the temperature measurement error and the conductivity measurement error are within ±0.005°C and ±0.0003s/m. The temperature and salinity sensor is installed on an ocean buoy, and offshore testing is carried out. The test data shows that the sensor's measurement data is accurate and reliable, and can be used to measure the temperature, conductivity, and salinity of seawater.
In the observation of CO2 flux, high-speed and high-precision measurement of CO2 concentration is an urgent problem to be solved, and the collection frequency of CO2 concentration must be greater than 10Hz. The Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology is widely used in various gas monitoring fields with high requirements for sensitivity, response time, and no background gas interference. In this paper, interband cascade laser at 4.26 micron is used as the system light source, and the second harmonic peak-peak value and the Root Mean Square (RMS) of sinusoidal are used to measure the CO2 concentration. When the laser CO2 analyzer was developed, comparative experiments were conducted using LI-7500DS and self-developed equipment. The CO2 concentration values measured by the laser gas analyzer and the LI-7500DS gas analyzer are synchronously collected using a sampling frequency of 10 Hz. The experimental results show that the trend of CO2 concentration measured by the two devices is consistent, and deviation of CO2 concentration is within ±2%, which can meet the needs of carbon dioxide flux measurement.
Seawater salinity is one of the basic elements of marine hydrological observation, and seawater conductivity measurement is an important means of salinity measurement. In order to improve the measurement accuracy of seawater conductivity sensor, a seven-electrode conductivity sensor is developed by using lock-in amplifier technology, which can measure the seawater conductivity by detecting the voltage and current signals in the strong noise environment. The comparison experiment was carried out by using seven-electrode conductivity sensor and seabird CTD sensor SBE 37-SI, the indication error of conductivity measurement is within ±0.0003s/m, which can meet the needs of high-precision measurement of seawater conductivity.
The off-line sampling destructive test is often used in the seal integrity test of vials, which has the disadvantages of long time consuming, low accuracy and high missing rate. In order to solve the above problems, the tunable diode laser absorption spectroscopy technology and wavelength modulation spectroscopy technology are used to measure the oxygen concentration in the vials. The ratio method of second harmonic and first harmonic is used to eliminate the influence of the rapid change of light intensity. The experimental results show that the system can complete the seal integrity detection of 300 vials per minute. This method belongs to the non-destructive online detection mode, which can realize the fast detection of vials without interference.
Visibility is one of the important parameters of meteorological observation. Based on the principle of infrared forward scattering and phase-locked amplification, a self-stable visibility meter is designed. The transmitter unit of visibility meter generates 875 nm light pulse at 2.3 kHz. Narrow pulse modulation technology is used to solve the problem of total power and instantaneous power of infrared LED when working, as well as the problem of natural heat dissipation, so as to reduce the aging speed of LED. The photodiode of the backscattering receiver monitors the transmitted light intensity, and adjusts the automatic feedback and the amplitude of the light pulse to keep the light intensity of the LED as the preset value. The visibility meter is compared with Visala PWD20 in the visibility measurement and verification laboratory. The experimental results show that the measurement deviations of one minute and ten minutes are within ±10% and ±4% in the range of 10~20000m. The forward scattering visibility meter is stable and has small measurement error, which can meet the requirements of visibility detection of meteorological stations.
The sinusoidal root mean square (RMS) normalization method is proposed to measure humidity, and the ratio of the second harmonic peak-peak value and the sinusoidal RMS value is used as the system output, which can effectively eliminate the influence such as windows pollution and optical intensity fluctuation. The laser humidity sensor is developed, and reflective open gas cell is used. The structure of the optical system is simple, which is easy to be adjusted. Humidity calibration tests are carried out in the north china sea standard and metrology center of state oceanic administration, and the humidity measurement deviation is less than ±0.6% in the range of 30%RH ~ 80%RH. The comparison experiment was completed between the laser humidity sensor and the traditional humidity sensor in the national meteorological basic station. Experimental results show that the consistency of the humidity data is good, which proves the validity of sinusoidal RMS normalization method for measuring environmental humidity.
The linearity and the stain resistance of existing humidity sensor is poor, which exists the problems such as low resolution at low temperatures, low faded wet in high humidity environment, large measurement error and long response time. Tunable diode laser absorption spectroscopy technology is studied to measure the environmental humidity, and digital quadrature lock-in amplifiers are used to extract the first harmonic signal and the second harmonic signal, which can eliminate the influence of the phase delay angle and can improve the detection accuracy of the system. Comparative experiment between TDLAS humidity sensor and R.M.YOUNG humidity sensor was completed in the lab, experimental results show that the consistency of the humidity data is very good, which can proves the validity of the TDLAS humidity measurement technology.
Marine expendable temperature/depth profiler (XBT) is a disposable measuring instrument which can obtain temperature/depth profile data quickly in large area waters and mainly used for marine surveys, scientific research, military application. The temperature measuring device is a thermistor in the conventional XBT probe (CXBT)and the depth data is only a calculated value by speed and time depth calculation formula which is not an accurate measurement result. Firstly, an optical fiber expendable temperature/depth sensor based on the FBG-LPG cascaded structure is proposed to solve the problems of the CXBT, namely the use of LPG and FBG were used to detect the water temperature and depth, respectively. Secondly, the fiber end reflective mirror is used to simplify optical cascade structure and optimize the system performance. Finally, the optical path is designed and optimized using the reflective optical fiber end mirror. The experimental results show that the sensitivity of temperature and depth sensing based on FBG-LPG cascade structure is about 0.0030C and 0.1%F.S. respectively, which can meet the requirements of the sea water temperature/depth observation. The reflectivity of reflection mirror is in the range from 48.8% to 72.5%, the resonant peak of FBG and LPG are reasonable and the whole spectrum are suitable for demodulation. Through research on the optical fiber XBT (FXBT), the direct measurement of deep-sea temperature/depth profile data can be obtained simultaneously, quickly and accurately. The FXBT is a new all-optical seawater temperature/depth sensor, which has important academic value and broad application prospect and is expected to replace the CXBT in the future.
Humidity is an important environmental parameter, which is difficult to be measured accurately and quickly using traditional measurement methods. Under the environment of low temperature or high humidity, traditional humidity and temperature sensor has shortages in humidity measurement accuracy, corresponding time and wet fade speed. To solve these problems, this paper proposes a method to measure the environmental humidity with wavelength modulation technology and harmonic detection technology based on tunable diode laser absorption spectroscopy. H2O molecular absorption line near 1392 nm is selected as the characteristic spectra. The effects of temperature, pressure and water concentration on the absorption spectrum width, the wavelength modulation coefficient and the amplitude of the harmonic signal are analyzed. Humidity and temperature sensor is modified using temperature and pressure compensation model, and the influence of the water concentration variation is eliminated by the iterative algorithm. The new humidity and temperature sensor prototype is developed, and the structure of the optical system is simple, which is easy to be adjusted. The response frequency of the humidity detection is 40 Hz. The experiment was carried out for 3 months at Qingdao national basic weather station. Experimental results show that the consistency of the humidity and temperature data is very good, which can proves the validity of the humidity measurement technology.
The chlorophyll-a and turbidity sensor based on the principles of fluorescence induction and scattering-light detection is designed. Using fluorescence induction technology, scattering-light detection technology and weak signal detection technology, chlorophyll-a concentration measurement and turbidity measurement in seawater are integrated in a set of testing equipment to implement software and hardware reuse and improve the integration of the device, which has the features of small size and easy operation. The comparative experiments and repetitive experiments are completed with ALEC ACLW-CAR chlorophyll / turbidity sensor. Experiment results show that chlorophyll-a concentration, turbidity and the system output values have good linear relationships, and the fitting coefficients are 0.999. Repeatability standard deviations of chlorophyll-a detection and turbidity detection are better than 0.08 μg/L and 0.04 FTU, respectively, and the accuracy of the device within ± 2%. Chlorophyll-a and turbidity in-situ monitoring in seawater can be achieved using this testing equipment.
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