The Millimeter Wave Atmospheric Sounder (MAS): a shuttle-basedremote sensing experiment

The Millimeter Wave Atmospheric Sounder (MAS) will be launched in the spring of 1992 as part of the ATLAS 1 (Atmospheric Laboratory for Application and Science) mission. Using passive limb-scanning millimeter-wave radiometry, it will sense the thermal emission produced by ozone at 184 GHz, water vapor at 183 GHz, chlorine monoxide at 204 GHz, and oxygen (for retrieval of temperature and pressure) at 60 GHz. From these observations, concentration profiles of these gases throughout the middle atmosphere will be made. The fundamentals of the measurements, the design of the radiometers, and the approaches used for the data analysis are described     

Prelaunch and in-flight radiometric calibration of the Atmospheric Infrared Sounder (AIRS)

With 2378 infrared spectral channels ranging in wavelength from 3.7-15.4 /spl mu/m, the Atmospheric Infrared Sounder (AIRS) represents a quantum leap in spaceborne sounding instruments. Each channel of the AIRS instrument has a well-defined spectral bandshape and must be radiometrically calibrated to standards developed by the National Institute of Standards and Technology. This paper defines the algorithms, methods, and test results of the prelaunch radiometric calibration of the AIRS infrared channels and the in-flight calibration approach. Derivation of the radiometric transfer equations is presented with prelaunch measurements of the radiometric accuracy achieved on measurements of independent datasets.     

Formulation and validation of simulated data for the Atmospheric Infrared Sounder (AIRS)

Models for synthesizing radiance measurements by the Atmospheric Infrared Sounder (AIRS) are described. Synthetic radiances have been generated for developing and testing data processing algorithms. The radiances are calculated from geophysical states derived from weather forecasts and climatology using the AIRS rapid transmission algorithm. The data contain horizontal variability at the spatial resolution of AIRS from the surface and cloud fields. This is needed to test retrieval algorithms under partially cloudy conditions. The surface variability is added using vegetation and International Geosphere Biosphere Programme surface type maps, while cloud variability is added randomly. The radiances are spectrally averaged to create High Resolution Infrared Sounder (HIRS) data, and this is compared with actual HIRS2 data on the NOAA 14 satellite. The simulated data under-represent high-altitude equatorial cirrus clouds and have too much local variability. They agree in the mean to within 1-4 K, and global standard deviation agrees to better than 2 K. Simulated data have been a valuable tool for developing retrieval algorithms and studying error characteristics and will continue to be so after launch.     

Sub-Terahertz Channel Sounder: Review and Future Challenges

Due to the large amount of unused and unexplored spectrum resources, the so-called subTerahertz(sub-THz) frequency bands from 100 to 300 GHz are seen as promising bands for the next generation of wireless communication systems. Channel modeling at sub-THz bands is essential for the design and deployment of future wireless communication systems. Channel measurement is a widely adopted method to obtain channel characteristics and establish mathematical channel models. Channel measurements depend o...     

风云三号(D)气象卫星微波湿温度计系统建模和仿真

针对风云三号卫星微波湿温度计,该文建立了全功率式微波辐射计系统的仿真模型,重点对热辐射噪声源、混频器、低噪放、滤波器与检波器等关键性器件进行了参数化建模。从信号处理的角度对全功率式微波辐射计的工作过程进行了模拟,并对仿真系统的输出功率、灵敏度和线性度进行评估与分析。通过与实际仪器的测试结果对比,验证了所提仿真模型的正确性。

     

Multiorder Etalon Sounder (MOES): a new technique for passive highresolution atmospheric temperature and moisture sounding from satellite

A technique based on the Fabry-Perot interferometer for measuring atmospheric temperature, moisture, and other trace species with high spectral resolution from satellite is described. The key technologies incorporated into the remote sensing technique and instrument design include high spectral resolution through the use of a Fabry-Perot interferometer (FPI), high sensitivity through multiplexing of orders, the use of an innovative FPI focal plane detection technique called the Circle to Line Interferometer Optical system, and the simultaneous sampling of all spectral bands and channels. Studies show that the Multiorder Etalon Sounder is feasible and can greatly improve the sounding capability of present infrared atmospheric sounders     

Time-domain optimized near-field estimator for ultrasound imaging: initial development and results

For nearly four decades, adaptive beamforming (ABF) algorithms have been applied in RADAR and SONAR signal processing. These algorithms reduce the contribution of undesired off-axis signals while maintaining a desired response along a specific look direction. Typically, higher resolution and contrast is attainable using adaptive beamforming at the price of an increased computational load. In this paper, we describe a novel ABF designed for medical ultrasound, named the Time-domain Optimized Near-field Estimator (TONE). We performed a series of simulations using synthetic ultrasound data to test the performance of this algorithm and compared it to conventional, data independent, delay and sum beamforming (CBF) method. We also performed experiments using a Philips SONOS 5500 phased array imaging system. CBF was applied using the default parameters of the Philips scanner, whereas TONE was applied on per channel, unfocused data using an unfocused transmit beam. TONE images were reconstructed at a sampling of 67 microm laterally and 19 microm axially. The results obtained for a series of five 20-microm wires in a water tank show a significant improvement in spatial resolution when compared to CBF. We also analyzed the performance of TONE as a function of speed of sound errors and array sparsity, finding it robust to both.     

NPOESS aircraft sounder testbed-microwave: observations of clouds and precipitation at 54, 118, 183, and 425 GHz

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Aircraft Sounder Testbed-Microwave (NAST-M) includes spectrometers operating near the oxygen lines at 50-57, 118.75, and 424.76 GHz, and a spectrometer centered on the water vapor absorption line at 183.31 GHz. All four of the spectrometers' antenna horns are collocated, have 3-dB (full-width at half-maximum) beamwidths of 7.5/spl deg/, and are directed at a single mirror that scans cross-track beneath the aircraft with a swath up to 100-km wide. The first part of the paper describes the instrumentation and calibration for the newly installed spectrometers at 183.31 and 424.76 GHz. The second part demonstrates the potential performance of NAST-M, by presenting radiance images and precipitation rate and cell-top retrievals obtained during overflights of isolated convective storm cells, and by comparing these results with coincident visible images. NAST-M radiances are also compared with visible, infrared, and radar images. The nonlinear retrieval method was trained with a simple precipitation model. The data were obtained during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE 2002) and the Pacific THORpex (THe Observing-system Research and predictability experiment) Observing System Test (PTOST 2003).     

武汉VHF相干散射雷达及初始观测结果

武汉VHF雷达坐落于武汉大学(30.5°N,114.4°E),工作频率为48.2 MHz,是我国首部用于观测中纬度电离层场向不均匀体实时演变特征的相干散射雷达。首先详细介绍该雷达系统设计,主要包括天线阵系统、功放系统、接收系统、波束控制系统以及数据处理系统;然后利用噪声基底拟合方式去除射频干扰,增强RTI图的可读性和雷达有效回波结构的清晰度。武汉VHF雷达E层不均匀体的观测结果表明,中纬E层准周期回波的发生是风剪切激发K-H不稳定性所致。     

Detection algorithm and initial laboratory results using V-BLASTspace-time communication architecture

The signal detection algorithm of the vertical BLAST (Bell Laboratories Layered Space-Time) wireless communications architecture is briefly described. Using this joint space-time approach, spectral efficiencies ranging from 20-40 bit/s/Hz have been demonstrated in the laboratory under flat fading conditions at indoor fading rates. Early results are presented     

The results of WARC-HFBC (87): technical implications

The planning principles and technical parameters that were decided at the 1987 second session of the World Administrative Radio Conference (WARC) for the planning of the HF bands allocated to the broadcasting service (HFBC) are described. These planning principles and parameters are intended for use in developing test plans to satisfy the world's high-frequency broadcast requirements. Those parameters that were modified at the second session of the conference are discussed toward obtaining a workable and universally acceptable planning system for shortwave broadcasting. With reference to the results of the planning exercises that were used as the basis of decisions at the second session, the likely impact of these decisions on the HF broadcast planning process is described. Some issues that are likely to concern the US broadcasters in preparation for the third session of WARC are summarized in conclusion     

Ground and flight test results for standard VOR and double parasitic loop counterpoise antennas

Results of ground and flight tests carried out at 109 MHz to study the vertical plane radiation patterns of standard VOR and double parasitic loop counterpoise antennas above ground are discussed. The ground tests consist of the measurement of the fields produced in the quasi-radiation zone of the test antenna The flight tests consist of measuring the far field with the help of an aircraft flying at a constant altitude along chosen radial paths to and from the test antenna. The reduced test results are compared with available theoretical values.     

Multipoint communication and group working for businessapplications: goals and initial results of the MIMIS project

The paper presents a brief overview of project R2025 MIMIS (Multipoint Interactive Multimedia Interpersonal System) of the European Community's RACE II programme. The project is dedicated to the development of a desktop broadband multimedia conference system. The system will be designed according to the business communication requirements of its potential users and user groups. The practical aim of the project is to develop four demonstrators: three intermediate versions and a final one, containing all conference facilities, using an ATM broadband network. It describes the project's aims, the distinction between MIMIS and commercially available systems and initial results of the study on user requirements and the system specification     

Impact ionization MOS (I-MOS)-Part II: experimental results

Part I of this paper dealt with the fundamental understanding of device physics and circuit design in a novel transistor, based on the field-effect control of impact-ionization (I-MOS). This paper focuses on experimental results obtained on various silicon-based prototypes of the I-MOS. The fabricated p-channel I-MOS devices showed extremely abrupt transitions from the OFF state to the ON state with a subthreshold slope of less than 10 mV/dec at 300 K. These first experimental prototypes of the I-MOS also showed significant hot carrier effects resulting in threshold voltage shifts and degradation of subthreshold slope with repeated measurements. Hot carrier damage was seen to be much worse in nMOS devices than in pMOS devices. Monte Carlo simulations revealed that the hot carrier damage was caused by holes (electrons) underneath the gate in pMOS (nMOS) devices and, thus, consequently explained the difference in hot carrier effects in p-channel versus n-channel I-MOS transistors. Recessed channel devices were also explored to understand the effects of surfaces on the enhancement in the breakdown voltage in I-MOS devices. In order to reduce the breakdown voltage needed for device operation, simple p-i-n devices were fabricated in germanium. These devices showed much lower values of breakdown voltage and excellent matches to MEDICI simulations.     

Airborne SAR imagery of ocean surface waves obtained during LEWEX:some initial results

The potential and the difficulties of using airborne synthetic-aperture radar (SAR) to study ocean surface waves are presented. Airborne C-band SAR imagery obtained with the real-time SAR processor on the Canada Centre for Remote Sensing (CCRS) Convair 580 during the Labrador Extreme Waves Experiment (LEWEX) shows waves propagating through the marginal ice zone as well as through open water regions. Examples are chosen to illustrate both coherent and noncoherent scene motion effects. Coherent scene motion effects include velocity bunching. acceleration defocus, and coherence time limitations. Noncoherent scene motion effects include scanning distortion and look misregistration. The slow platform velocity of airborne SAR precludes replication of spaceborne observations, largely due to coherent motion effects     

Long-Range VNA-Based Channel Sounder: Design and Measurement Validation at MmWave and Sub-THz Frequency Bands

With the increasing demand for high bandwidth wireless communication systems, and with a congested spectrum in the sub-6 GHz frequency bands, researchers have been looking into exploration of millimeter wave(mmWave) and sub-terahertz(subTHz) frequency bands. Channel modeling is essential for system design and performance evaluation of new wireless communication systems. Accurate channel modeling relies on reliable measured channel data,which is collected by high-fidelity channel sounders.Further...     

Through-wall imaging (TWI) by radar: 2-D tomographic results and analyses

A two-dimensional nonlinear inverse scattering technique is developed for imaging objects in a multilayered medium that simulates the effects of building walls in the context of through-wall imaging (TWI). The effectiveness and capacity of the inversion algorithm and the feasibility of through-wall imaging is demonstrated via a number of numerical examples. It has been shown that using multifrequency data high-quality image reconstruction can be achieved with a limited array view.     

Influence of initial microstructure and impurities on Cu room-temperature recrystallization (self-annealing)

The initial microstructure of thin electroplated Cu films was investigated for different layer thicknesses and plating conditions. The initial grain size of electroplated Cu thin films was found to be distributed homogeneously whereas the initial texture was inhomogeneous over film thickness. With increasing film thickness a transition occurs from a basis-oriented into a field-oriented texture. The knowledge about initial Cu microstructure for different plating conditions helped to clarify the factors of influence for Cu room-temperature recrystallization, called self-annealing. Furthermore, beside the microstructure also incorporated impurities were found to be of great importance for Cu self-annealing particularly in the case of a varying additive content in electrolyte.     

国外无人机发展趋势及关键技术

介绍了网络中心战(NCW)对无人机(UAV)的性能需求,归纳了当前国外无人机发展领域的热点和趋势,着重针对影响无人机关键性能的几大前沿技术的各自特点、研制现状及方向进行了分析和综述,并对其近期发展前景做出了预测,最后对国内无人机的相关研制工作提出了一些建议.