Search

As a new alternative energy source, gas hydrate has attracted wide attention all over the world. Since gas hydrate is always associated with free gas, the evaluation of the gas hydrate and free gas system is an important aspect of hydrate reservoir exploration and development. In this study, based on identifying gas hydrate and free gas by well logging, the seismic reflection characteristics of gas hydrate and free gas are determined by an accurate well-to-seismic calibration method. On account of seismic reflection characteristics, AVO attributes are used to identify gas hydrate and free gas qualitatively. Using prestack and poststack inversion to get the ratio ofP-wave impedance andP-wave-to-S-wave velocities, we determine the three-dimensional space distribution of gas hydrate and free gas, predict their effective porosity and saturation, and eventually achieve the meticulous depiction of gas hydrate and free gas in the body, which is necessary in subsequent estimation of gas hydrate and free gas resources. Results show that according to logging interpretation, gas hydrate of the B-well is located in the depth range of 1460–1510 mbsl and free gas is in 1510–1542 mbsl. Moreover, gas hydrate of the A-well is located in the depth range of 1425–1512 mbsl, and no obvious free gas is identified. Gas hydrate is located above free gas and distributed continuously. In plane form, gas hydrate and free gas both present subelliptical distribution in the NW-SE direction. Gas hydrate has an effective porosity of 0.30–0.40, an average saturation of 0.33–0.40, and an effective thickness of 3.0–10.5 m, whereas free gas possesses an effective porosity of 0.35–0.40, a saturation of 0.24–0.32, and an effective thickness of 2.0–5.0 m.

A spatial frequency domain imaging system (SFDI) was developed to estimate the optical properties of biological samples. The system was calibrated by using a series of self-made solid phantoms which covering a wide range of absorption (µ a ) and reduced scattering coefficients ( $${\mu ^{\prime}_s}$$ ). The relative errors between the reference and calibrated values were regarded as the evaluation parameters for validation effectiveness of the system, the results showed that the maximum relative errors of µ a and $${\mu ^{\prime}_s}$$ are 3.92 and 2.39% respectively. Quantitative absorption and scattering maps at the wavelength of 527 nm were obtained for four kinds of pear samples (normal and bruised with three levels of bruised severity with impact energy of 0.025, 0.075 and 0.125 J). The normal pears could be distinguished from the bruised pears by comparing values of coefficient of variation (CV) of $${\mu ^{\prime}_s}$$ maps, and the correct rates of the discriminant analysis were 100% for non-bruised pears,and 98.33% for bruised pears. Bruises induced using 0.025 J (class 1) were distinguishable from those induced using 0.075 and 0.125 J (class 2) by comparing ratio between mean values of bruised region and normal region of $${\mu ^{\prime}_s}$$ maps, the results turned out that the class 1 had the correct rate of 90%, and class 2 had the correct rate of 87.5%. The research showed that SFDI has the potential to be used in the detection of bruises on ‘Crown’ pears and the proposed calibration method lay the foundation for future studies. Future work will be conducted with an emphasis on the acquisition of more spectral information, surface profile correction and the acceleration of detection speed.

Da Qaidam Salt Lake, northern Qaidam Basin, is known for its liquid and solid boron resource. More than that, pinnoite-bearing sediments, occurring in this lake, are rare in the world. However, little attention has been paid to the hydro-climate change and brine evolution correlation with the formation of pinnoite deposit. According to the multi-proxy records, as well as AMS 14C dating, the sediment profiles DCD02 and DCD03 from Da Qaidam Salt Lake were studied. The results revealed that the ore-forming age of three pinnoite deposits are 7.83–8.62 cal ka BP, 6.74–7.07 cal ka BP and 4.66–5.41 cal ka BP. The sedimentary evolution of Da Qaidam Salt Lake along with the pinnoite formation during the past 13,000 years can be divided into four stages, i.e., (1) relatively fresh and deep paleo-lake with low salinity during 12.98–9.00 cal ka BP; (2) seasonal variations between fresh and brackish paleo-lake during 9.00–8.62 cal ka BP; (3) salt lake stage with relatively high salinity and alkalinity during 8.62–4.66 cal ka BP, and (4) relatively shallow lake with high salinity since 4.66 cal ka BP. Under favorable sedimentologic and hydrogeochemical conditions, a series of boron deposits including pinnoite ore formed in different zones of Da Qaidam Salt Lake due to the different ore-forming mechanisms. Finally, under the differential effect of climate warming condition between the high mountain catchments and arid basin, the boron ore-forming model was established as a higher mountain–lower basin–shallower water model.

Spatial frequency domain imaging has great potential in agricultural produce quality control due to its advantage of wide-field mapping of absorption (μa) and reduced scattering (μs′) parameters. However, it is not widely adopted in real applications due to the large time cost during image acquisition and inversion calculation processes. In this study, a single snapshot technique was used to obtain ac and dc components (Rd_ac, Rd_dc) of diffuse reflectance of turbid media (phantoms and pears). The validation results for the snapshot method indicate that at the spatial frequency of 1000/3 m−1, it achieved the optimal demodulation, by comparison with the results obtained by the commonly used time-domain amplitude demodulation method. Diffusion approximation, artificial neural network, least-squares support vector machine regression (LSSVR), and LSSVR combined with a genetic algorithm (LSSVR+GA) were then used to predict μa and μs′ from the obtained Rd_ac, Rd_dc at the fx of 1000/3 m−1. Validation results indicated that the LSSVR method took the least time to calculate μa and μs′ with high performance. The proposed imaging system and algorithm were implemented for the inspection of a pear bruise. Results indicated that the bruise, which is not obviously distinguishable in original gray maps, can show obvious contrast in calculated μa and μs′ maps, especially in μa maps. Further, the contrast becomes more obvious with the passage of time. In summary, this study developed a low-cost spatial frequency imaging system and matching software that could realize fast detection of optical properties for a pear with the proposed snapshot and LSSVR algorithms.

The error in the estimation of the ground interferometric phase will reduce the accuracy of the inversion of the vegetation height in three-stage vegetation inversion method. Aiming at this problem, the new vegetation height inversion method based on the BP neural network is proposed. The new method directly fits the nonlinear mapping relationship between the complex correction coefficients and the vegetation height, so it reduces the height inversion error caused by the error in the estimated ground interferometric phase. The new method has better performance than the three-stage vegetation height inversion method, and the experiment results validate the superiority of the new method.