Application of SWAT Model to Non-point Source Pollution in Xincai River Basin

[Objective]The study aimed to simulate the production and transportation process of surface runoff,sediment and non-point source pollution in Xincai River basin based on SWAT model.[Method]On the basis of analyzing the principles of SWAT model,the correlative parameters of runoff,sediment and water quality were calibrated,then the spatial and temporal distribution of runoff,sediment and non-point source pollutants in Xincai River basin were studied by using SWAT model.[Result]The results of calibration and validation showed that SWAT model was reasonable and available,and it can be used to simulate the non-point source pollution of Xincai River basin.The simulation results revealed that the load of sediment and various pollutants was the highest in the rainy year,followed by the normal year,while it was the minimum in the dry year,indicating that the production of sediment and non-point source pollutants was closely related to annual runoff.[Conclusion]The research could provide scientific references for the prevention of non-point source pollution in a basin.

Implementation and uniformity calibration of LED array for photodynamic therapy

Irradiance uniformity is an important parameter for a Photodynamic Therapy(PDT)device.The calibration and verification of a LED array light source based on computer vision technology were implemented and carried out.First,the correlation coe±cients between the pulse width modulate value and the irradiance were calibrated.Then,the correction of the actual light center and divergence angle were solved by image processing to reduce errors from each LED lens.Finally,uniformity was optimized according to the irradiance formula of the Lambertian source.The lowest coe±cients of variation of irradiance were 4.87%in a 5 cm×12 cm area and 3.55%in a 3 cm×10 cm area within the depth range of 8–12 cm when the expected irradiance was 100 mW/cm^(2).This finding indicated that the light source can achieve a more uniform illumination and provide a better therapeutic effect for the PDT of port-wine stains.

A novel radiant source for infrared calibration by using a grooved surface

A radiant source with a large aperture at 5--95℃ in the wavelength bands of 8--12μm for calibrating infrared imaging systems has been designed. The effective emissivity of its flat bottom with concentric V-grooves was evaluated by the Monte-Carlo method whose correctness was tested and accuracy was discussed. The structure of the source was completed by incorporating the simulation results with the blackbody cavity effect. The source was certificated via an optical measurement system. The source can provide a consistent radiant flux with temperature uniformity of ±0.1℃ over an area of diameter of φ80 mm.

Distributed sound source localization algorithm with sound velocity calibration in windy environments

A new sound source localization method with sound speed compensation is proposed to reduce the wind influence on the performance of conventional TDOA （Time Difference of Arrival） algorithms. First, the sound speed is described as a set of functions of the unknown source location, to approximate the acoustic velocity field distribution in the wind field. Then, they are introduced into the TDOA algorithm, to construct nonlinear equations. Finally, the particle swarm optimization algorithm is used to estimate the source location. The simulation results show that the proposed algorithm can significantly improve the localization accuracy for different wind velocities, source locations and test area sizes. The experimental results show that the proposed method can reduce localization errors to about 40% of the original error in a four nodes localization system.

A performance analysis of multi-satellite joint geolocation

Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of factors, such as errors in the measurement of signal parameters, uncertainties regarding the position of satellites, and errors in the location of calibration sources, are known to degrade the accuracy of target localization in satellite geolocation systems. We systematically analyze the performance of multi-satellite joint geolocation based on time difference of arrival （TDOA） measurements. The theoretical analysis starts with Cramer Rao bound （CRB） derivations for four localization scenarios under an altitude constraint and Gaussian noise assumption. In scenario 1, only the TDOA measurement errors of the emitting source are considered and the satellite positions are assumed to be perfectly estimated. In scenario 2, both the TDOA measurement errors and satellite position uncertainties are taken into account. Scenario 3 assumes that some calibration sources with accurate position information are used to mitigate the influence of satellite position perturbations. In scenario 4, several calibration sources at inaccurate locations are used to alleviate satellite position errors in target localization. Through comparing the CRBs of the four localization scenarios, some valuable＇s insights are gained into the effects of various error sources on the estimation performance. Two kinds of location mean-square errors （MSE） expressions under the altitude constraint are derived through first-order perturbation analysis and the Lagrange method. The first location MSE provides the theoretical prediction when an estimator assumes that the satellite locations are accurate but in fact have errors. The second location MSE provides the localization accuracy if an estimator assumes that the known calibration source locations are precise while in fact erroneous. Simulation results are included to verify the theoretical analysis.