We investigate the key techniques in ammonia (NH3) measurement based on midinfrared quantum cascade laser absorption spectroscopy technology. As the detection object, the system chose two absorption peaks splitting near 1122.16 cm − 1 at 0.3 atm. It was also combined with wavelength modulation spectroscopy technology and a high-temperature environment to reduce NH3 absorption in dynamic measurement. Allan variance was used to analyze the stability of the system. The optimal time to measure the average was 195 s, and the minimum detection limit was 121.58 ppb.
A theoretical description of pressure-calibration method based on wavelength modulation absorption spectrometry (WMAS) with second harmonic detection for precise measurements of trace gas concentration will be present in this paper. The method can obtain the consistent relation between gas concentration and second harmonic signal in pressure changes. The signal is monotonic function when gas concentration as metrics and it becomes a complete linear function when density of particles number as metrics. It not only allows complying with traditional WMAS technique without any calibration methods, but also applying to various environment of pressure variations. Typical applications like environmental monitoring and remote sensing can be used this method to calibrated measurement results. In addition, the method is not restricted to situations with typical applications. Furthermore, it can also easily be adapted to various gas concentration detection under pressure changes. The pressure-calibration method can be useful for gas concentration measurements so that assist to ensure the accuracy of data in research.
Integrated cavity output spectroscopy (ICOS) is a very sensitive method of trace gas measurement. It is widely known as its extremely long optical path and characteristics of direct absorption. Wavelength Modulation Spectroscopy (WMS) is another sensitive measurement method that suppresses noise. We combine the ICOS technique and WMS technique to research the trace gas measurement using a narrow band tunable diode laser. By this method we get several absorption peaks of carbon dioxide in atmosphere. To combine ICOS and WMS the sensitivity of trace gas measurement has a significantly increase.
The objective of this work was to attain essential parameters by using a Gompertz model that employed a new approach of wavelength modulation spectroscopy (WMS) to describe the microorganism growth. The measurement method of WMS introduces noninvasive technique instead of complicated invasive microorganism operation analysis and quickly obtains the accurate real-time measurement results. By using the WMS measurement, the specific growth curve of microorganism growth clearly displayed every three minute, which has characteristics of high sensitivity, high spectral resolution, fast time response and overcomes the randomness and error operation of traditional analysis methods. The measurement value of BF and AF in the range of 1.008 to 1.043 and the lower MSE showed that Gompertz model can fit the data well and be capable of describing bacteria growth rate and lag time. The results of experiment data suggested that the specific growth rate of microorganism depends on the temperature. With the increase of temperature ranging from 25 °C to 42 °C , the lag time of bacteria growth has been shortened. And the suitable temperature of bacteria growth is about 37 °C . Judging from the growth rate of microorganisms, we can identify the microbial species, not only to improve the precision and efficiency, but also to provides a rapidly sensitive way for microbial detection. The lag time of microorganism growth also provides a great application prospect for shelf life of the food safety.
In recent years, there has been a rapid rise in the use of pulse cavity ring-down spectroscopy to determine the optical properties of atmospheric aerosols. In the present work ,we describes the design and performance of a CRDS system for measuring extinction coefficients of atmospheric aerosols. CRDS based methods can achieve impressive sensitivity owing to the long effective path lengths involved. More importantly, the method is not affected by laser intensity fluctuations since the rate of attenuation of light is the measured variable rather than absolute irradiance. The extinction coefficient is a function of the cavity ring-down time. Determining an accurate decay time is critical to precise measurements of the extinction coefficients. The average and standard deviation of the decay time (τ0 is measured 6 hours ,cavity filled only with dry nitrogen) is about 42.21μs and 0.16μs, respectively. Moreover, a minimum detectable aerosol extinction coefficient of 0.41Mm-1 is achieved. Allan deviation plots for the value of τ0 measurements, close to a flicker noise. The minima(~5.8x10-4μs) in the Allan plots indicate the optimum average time(~60s) for optimum detection performance. To test the performance of the CRDS system, we monitored the optical properties of ambient aerosols on the campus of the Zhejiang Normal University from January 3rd to January 7th, 2014. During this period, the average value of the extinction coefficient is 816.8Mm-1, a maximum value more than 1800 Mm-1, and a minimum aerosol extinction coefficient of 119.27 Mm-1 is detected.
High-resolution absorption measurements of H2O using direct absorption spectroscopy technology
were made to acquire the spectroscopic parameters of High Resolution Transmission Molecular
Absorption Database (HITRAN database). The most important spectral parameters frequently used in
the researchers and study, was calculated from the integrated absorbance area of H2O at the different
temperature from 296K to 923K of the spectrum near 1397nm based on the distributed feedback laser.
From the result of experiment, the calculated spectral parameters was compared with the literature
values from HITRAN database. The method and results of the measurement obtained from this paper
are expected to be helpful in the supply of the sufficient accuracy spectral parameters in the practical
measurement.
Unmanned aerial vehicle remote sensing (UAVRS) is lower in cost, flexible on task arrangement and automatic and
intelligent in application, it has been used widely for mapping, surveillance, reconnaissance and city planning. Airborne
remote sensing missions require sensors with both high resolution and large fields of view, large format CCD digital
airborne imaging systems are now a reality. A refractive system was designed to meet the requirements with the help of
code V software, It has a focal length of 150mm, F number of 5.6, waveband of 0.45~0.7um, and field of view reaches
20°. It is shown that the value of modulation transfer function is higher than 0.5 at 55lp/mm, distortion is less than
0.1%, image quality reaches the diffraction limit. The system with large format CCD and wide field can satisfy the
demand of the wide ground overlay area and high resolution. The optical system with simpler structure, smaller size and
lighter weight, can be used in airborne remote sensing.
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