Analysis of factors affecting vent system for underground gas storage

The operating conditions of vent system for underground gas storage was introduced. The numerical simulation of the diffusion process of natural gas was conducted using process hazard analysis software tool （PHAST） with gas release velocity greater than 40 000 m^3/h. The effects of release velocity, atmospheric stability and wind speed on the diffusion area, flash fire, explosion and spray fire of natural gas were analyzed. The results show that the higher release velocity is, the bigger explosive area is; the stabler atmosphere is, the less natural gas diffuses; the lower wind speed is, the less natural gas diffuses, and the lower diffusion speed is, the bigger dangerous area is. Moreover, wind speed also has an effect on flash fire and heat radiation. In order to ensure safety of vent process of natural gas storage, the release velocity should be controlled and atmospheric conditions should be considered at the same time.

Orbital Milling Hole of Aerospace Al-Alloy with Big Pitch

To improve the processing efficiency and the quality of orbital milling hole of aerospace Al-alloy, the big-pitch influence on cutting force and hole quality was studied experimentally. First, a program based on horizontal lathe was proposed based on kinematics analysis of orbital milling. Then, the cutting force at different stages and the hole quality with different pitches were measured. Results show that the axial force and radial force increase with the pitch amplification during orbital milling. However, the axial force in the orbital milling hole is about 8—10 times smaller than that in the conventional drilling. The diameter error of milling hole is 48—93 μm, and the surface roughness of milling hole is 1.2—1.7 μm. Finally, an orbital milling device with big pitch was designed.

Assessment of wind products obtained from multiple microwave scatterometers over the China Seas

Sea surface winds （SSWs） are vital to many meteorological and oceanographic applications, especially for regional study of short-range forecasting and Numerical Weather Prediction （NWP） assimilation. Spaceborne seatterometers can provide global ocean surface vector wind products at high spatial resolution. However, given the limited spatial coverage and revisit time for an individual sensor, it is valuable to study improvements of multiple microwave scatterometer observations, including the advanced scatterometer onboard parallel satellites MetOp-A （ASCAT-A） and MetOp-B （ASCAT-B） and microwave scatterometers aboard Oceansat-2 （OSCAT） and HY-2A （HY2-SCAT）. These four scatterometer-derived wind products over the China Seas （0°-40°N, 105°-135°E） were evaluated in terms of spatial coverage, revisit time, bias of wind speed and direction, after comparison with ERA-Interim forecast winds from the European Centre for Medium-Range Weather Forecasts （ECMWF） and spectral analysis of wind components along the satellite track. The results show that spatial coverage of wind data observed by combination of the four sensors over the China Seas is about 92.8% for a 12-h interval at 12：00 and 90.7% at 24：00, respectively. The analysis of revisit time shows that two periods, from 5：30-8：30 UTC and 17：00-21：00 UTC each day, had no observations in the study area. Wind data observed by the four sensors along satellite orbits in one month were compared with ERA-Interim data, indicating that bias of both wind speed and direction varies with wind speed, especially for speeds less than 7 m/s. The bias depends on characteristics of each satellite sensor and its retrieval algorithm for wind vector data. All these results will be important as guidance in choosing the most suitable wind product for applications and for constructing blended SSW products.

Contribution of Ground-Based Cloud Observation to Satellite-Based Cloud Discrimination

One of the biggest factors to deteriorate the satellite product quality is cloud coverage. Therefore, cloud masking process is important to improve the quality of various satellite products. However, satellite-based cloud discrimination algorithm has been developing and efficient ground-based cloud observations are necessary to validate satellite-based cloud discrimination. The purpose of this study is to develop the efficient ground-based cloud observation methodology using whole sky camera. This paper deals with methods how to discriminate cloud portions on whole sky image, how to apply the ground-based cloud observation to the validations for satellite products. For the cloud discrimination on whole sky image, we propose SI （sky index） and BI （brightness index） calculated from RGB （red, green and blue） channels. SI shows the extent of the blueness and gray scale and BI indicates the extent of the brightness. Sun, cloud and blue sky portions are divided by SI and BI threshold. As an application of ground-based cloud observation for the validation of satellite products, clouds portions discriminated from whole sky image are projected onto ground surface with map coordinate. We also examine to compare with cloud portions on whole sky images and MODIS （MODerate resolution Imaging Spectroradiometer） image as one of experiments. The proposed ground-based cloud observation method and its extension to satellite-based cloud discrimination should be connected to improve the quality of satellite products.

Transmit Antenna Selection in MIMO-OFDM System Based on CO-SFBC Schemes

A transmit antenna selection(TAS)multi-input multi-output orthogonal frequency-division multiplexing(MIMO-OFDM)system based on channel-orthogonalized space-frequency block coding(CO-SFBC)schemes was proposed for better performance.Firstly,the principles and criterions for designing CO-STBC/SFBC schemes with angle feedback were proposed,and then the effect of quantization for the feedback angle information within such schemes was discussed.Meanwhile,the TAS scheme was applied to the system to further improve the overall performance.Simulation results show that the combination of the proposed CO-STBC and TAS schemes can significantly improve the system performance,which is much larger than only applying them to systems individually.

环境因素对公路隧道洞外亮度L_(20)(S)值的影响研究

洞外亮度L_(20)(S)作为公路隧道入口段照明的基本参数,影响着过渡段的照明设计,其值受到多种因素的共同作用。洞外亮度测量影响因素较多,文章从洞外天空率、洞门型式以及洞外路面面层颜色等3种因素进行分析,开展各因素对洞外亮度L_(20)(S)值的影响研究。调研重庆主城范围内的相应公路隧道,并选择符合要求的隧道为研究对象,结合理论分析与现场测试验证,得出各个指标参数对隧道洞外亮度L_(20)(S)的影响规律,提出基于现场亮度测试方法的公路隧道洞外亮度指标。研究结果表明:(1)秋冬季节的洞外亮度L_(20)(S)推荐值至少为实际测试亮度值的1倍及以上;(2)路面亮度值与RGB值所呈现规律一致;(3)端墙式洞门的洞外亮度小于削竹式洞门。

A unified model of bidirectional reflectance distribution function for the vegetation canopy

An accurate and operational bidirectional reflectance distribution function （BDRF） canopy model is the basis of quantitative vegetation remote sensing. The canopy reflectance should be approximated as the sum of the single scattering reflectance arising from the sun, pl, and the multiple scattering reflectance arising from the canopy, fin, as their directional characteristics are dramatically different. Based on the existing BRDF model, we obtain a new analytical expression of ρ1 and ρm in this paper, which is suitable for different illumination conditions and different vegetation canopies. According to the geometrical optic model at the leaf scale, the anisotropy of ρ1 can be ascribed to the geometry of the object, sun and the sensor, multiple scale clumping, and the fraction of direct solar radiation and diffuse sky radiation. Then, we parameterize the area ratios of four components： the sunlit foliage, sunlit ground, shadow foliage and shadow ground based on a Poisson distribution, and develop a new approximate analytical single scattering reflectance model. Assuming G=0.5, a recollision probability theory based scattering model is developed which considers the effects of diffuse sky radiation, scattering inside the canopy and rebounds between the canopy and soil. Validation using ground measurements of maize and black spruce forest proves the reliability of the model.

An algorithm for terrain-aided inertial navigation based on nonlinear optimal filtering

When the initial position error or the altimeter measurement noise is large,the BUAA Inertial Terrain-Aided Navigation (BITAN) algorithm based on extended Kalman filtering can not be located accurately.To solve this problem,we propose a modified BITAN algorithm based on nonlinear optimal filtering.The posterior probability density correction is obtained by using the prior probability density of the system's state transition model and the most recent observations.Hence,the local unobservable system caused by the measurement equation through terrain linearization is avoided.This algorithm is tested by using the digital elevation model and flight data,and is compared with BITAN.Results show that the accuracy of the proposed algorithm is higher than BITAN,and the robustness of the system is improved.

Verification of SPE probability forecasts at the Space Environment Prediction Center(SEPC)

In space weather forecasting, forecast verification is necessary so that the forecast quality can be assessed. This paper provides an example of how to choose and devise verification methods and techniques according to different space weather forecast products. Solar proton events(SPEs) are hazardous space weather events, and forecasting them is one of the major tasks of the Space Environment Prediction Center(SEPC) at the National Space Science Center of the Chinese Academy of Sciences. Through analyzing SPE occurrence characteristics, SPE forecast properties, and verification requirements at SEPC, verification methods for SPE probability forecasts are identified, and verification results obtained. Overall, SPE probability forecasts at SEPC exhibit good accuracy, reliability, and discrimination. Compared with climatology and persistence forecasts, the SPE forecasts are more accurate. However, the forecasts for SPE onset days are substantially underestimated and need to be considerably improved.