A helicopter-borne eight-channel ranging scatterometer for remotesensing. I. System description

For pt.II see ibid., vol.31, no.1, p.170-9 (1993). HUTSCAT, a helicopter-borne dual-frequency FM-CW scatterometer, is described. The HUTSCAT measures the backscattering properties of a target with a range resolution of 65 cm. The real-time ranging capability is obtained by performing the fast Fourier transform (FFT) to the received time-domain signal. The measurement is made simultaneously at eight channels (VV, HH, HV, and VH modes of polarization at 5.4 GHz and 9.8 GHz). The scatterometer measures the radar return spectrum for eight channels in 16.6 ms, which corresponds to an along-track distance of 0.33 m for the helicopter speed of 20 m/s. The radar system has been designed for remote sensing of forests, sea ice, and snow     

The use of a helicopter mounted ranging scatterometer forestimation of extinction and scattering properties of forest canopies.II. Experimental results for high-density aspen

For pt.I see ibid., vol.26, no.2, p.140-3 (1988). An analytic expression is derived that describes the backscatter power from a semi-infinite plane parallel homogeneous canopy as a function of distance from an airborne radar. This model is fitted to observed data for a high-density aspen canopy by a modification of a technique developed by A.A. Tyapkin (1960). This inversion of the model provides unbiased estimates of the canopy extinction and backscattering parameters. An active radar calibrator located underneath the canopy provides an independent method of determining the volume extinction coefficient. The results reported indicate that the coefficients change throughout the year. A comparison of these coefficients with H.J. Eom and A.K. Funk's (1984) disk model, using measured canopy properties, shows that at C-band frequency, only a part of the scattering and absorption can be attributed to the canopy leaves     

A delay/Doppler-mapping receiver system for GPS-reflection remotesensing

A delay/Doppler-mapping receiver system, developed specifically for global positioning system (GPS)-reflection remote sensing, is described, and example delay/Doppler waveforms are presented. The high-quality data obtained with this system provide a more accurate and detailed examination of ground-based and aircraft GPS-reflection phenomenology than has been available to date. As an example, systematic effects in the reflected signal delay waveform, due to nonideal behavior of the C/A-code auto-correlation function, are presented for the first time. Both a single-channel open-loop recording system and a recently developed 16-channel recorder are presented. The open-loop data from either recorder are postprocessed with a software GPS receiver that performs the following functions: signal detection; phase and delay tracking; delay, Doppler, and delay/Doppler waveform mapping; dual-frequency (L1 and L2) processing; C/A-code and Y-code waveform extraction; coherent integrations as short as 125 μs; navigation message decoding; and precise observable time tagging. The software can perform these functions on all detectable satellite signals without dead time, and custom signal-processing features can easily be included into the system     

A fast two-stage classification method for high-dimensional remotesensing data

Classification for high-dimensional remotely sensed data generally requires a large set of data samples and enormous processing time, particularly for hyperspectral image data. In this paper, the authors present a fast two-stage classification method composed of a band selection (BS) algorithm with feature extraction/selection (FSE) followed by a recursive maximum likelihood classifier (MLC). The first stage is to develop a BS algorithm coupled with FSE for data dimensionality reduction. The second stage is to design a fast recursive MLC (RMLC) so as to achieve computational efficiency. The experimental results show that the proposed recursive MLC, in conjunction with BS and FSE, reduces computing time significantly by a factor ranging from 30 to 145, as compared to the conventional MLC     

A framework for analyzing and designing scale invariant remotesensing algorithms

The land surface exhibits heterogeneity across a range of spatial scales. Remote sensors provide integrated information at the pixel scale, however, there is important spatial variability at scales smaller than the scale of the sensor. On the other hand, large scale models that use remotely sensed data do not require them at the same spatial resolution at which remote sensors are required to operate. In this paper, a framework for testing aggregation-disaggregation properties of remote sensing algorithms is presented. The proposed framework provides a systematic approach for parameterizing the land surface heterogeneity effects. For the estimation of the pixel scale response, the lumped response should be modified by the variance and covariance terms. This representation of land surface heterogeneity could lead to substantial savings in remote sensing data storage and management. Using simulated land and vegetation scenarios, the authors have successfully parameterized subpixel scale heterogeneity effects for the estimation of vegetation index, by modeling the variances and covariance terms with the pixel scale values     

ERS-1 scatterometer measurements. II. An algorithm forocean-surface wind retrieval including light winds

For pt.I see ibid., vol.36, no.2, p.603-22 (1998). An algorithm for retrieving European Remote Sensing Satellite (ERS-1) scatterometer winds, denoted the Rufenach-Bates-Tosini (RBT) algorithm, is developed and used to retrieve winds collocated within ±25 km of buoy measurements in two oceanic regions, equatorial and midlatitude. An improvement in the retrieved RBT winds over the European Space Agency (ESA) winds is due mainly to a geophysical model employing the full available wind-speed range, including the lightest winds. This model, denoted BMOD5, is tuned by using the scatterometer and buoy measurements, resulting in two different models for the midlatitude and equatorial regions. The RBT retrieved winds exhibit (1) a larger number of solutions (wind vectors) and (2) smaller biases in wind speed than the ESA wind product. The increase in the number of retrieved winds is primarily due to lighter winds employed, 0.2 m/s to 18 m/s; whereas, the ESA winds are truncated near 3 m/s. The ESA winds underestimate the highest winds significantly, by about 20%, and overestimate the lightest winds. The RBT wind bias is less than a few percent at the highest winds and a few tenths of a m/s at the lowest winds. Both algorithms retrieve 180° ambiguous directions almost as often as the true direction. Regression fits to the winds using the RBT algorithm produce standard deviations of 1 m/s and 25° near the equator for winds varying from 0.2-10 m/s and 1.2 m/s and 250 at midlatitudes for winds varying from 0.2-18 m/s, provided that the ambiguities are removed     

The use of a helicopter mounted ranging scatterometer forestimation of extinction and backscattering properties of forestcanopies. I. Experimental approach and calibration

A helicopter-borne C-band scatterometer with the capability of collecting the backscattered power as a function of range is described. This instrument was repeatedly flown from May to September 1984 to study the microwave properties of forest canopies of aspen and black spruce in the Superior National Forest in Minnesota. The characteristics of the instrument, its calibration, the data collection, and reprocessing, are described     

A C-band scatterometer for remote sensing the air-sea interface

An airborne C-band scatterometer system (C-Scat) has been developed to remotely sense ocean surface winds and improve upon the present understanding of the relationship between normalized radar cross section (NRCS) and ocean surface roughness influences such as wind speed and direction, wave height and slope, and the air-sea temperature difference. The scatterometer utilizes a unique frequency-steered microstrip array antenna that is installed beneath the fuselage of an airplane. The antenna is electronically scanned in elevation, from 20° to 50° off-nadir, and mechanically spins in azimuth. The system is capable of measuring ocean surface NRCS from altitudes as high as 25000 ft. The system is divided into four subsystems: the transmitter and receiver, the spinning antenna, the computer control and data acquisition subsystem, and the digital and analog interface electronics     

A new proposal for eight-channel optical demultiplexer based on photonic crystal resonant cavities

In this paper, we used the novel defective resonant cavities to design an eight-channel photonic crystal demultiplexer. We showed that by choosing appropriate values for the width of the resonant cavity, the desired wavelengths can be separated. The proposed platform has a square lattice of dielectric rods immersed in air. The value of transmission efficiency for channels was obtained in 94\(-\)99 % range. In addition, the maximum value of crosstalk and average quality factor for channels were calculated –11.2 dB and 2200, respectively.     

A spaceborne LFM scatterometer for ocean surface wind vectormeasurement-a time domain approach

The limitations of the currently used continuous-wave-pulse (CW-pulse) spaceborne scatterometers for wind-vector retrieval are reviewed. The disadvantages due to purely time-domain or frequency-domain (Doppler filtering) approaches are described. To overcome the limitations of these methods, a modified scheme is proposed wherein the pulse transmitted is linearly frequency modulated (LFM) and the processing is carried out in the time domain. This method is described and compared with other techniques to highlight the improved results obtainable with this LFM technique     

一种对高速运动目标的单光子测距方法

作为一种前沿的激光探测技术,单光子激光测距技术已成功应用于月球测距、卫星测距和地面测高等领域。然而,单光子测距在机载空对空、地对空平台上对高速运动目标进行跟踪测距时,回波光子落在不同的时间窗,导致直接计数无法有效提取信号的问题仍需解决。针对空对空条件下单光子激光测距的应用需求,基于时间相关光子计数技术设计一种适用于全天时、宽时域、多噪声条件下对高速运动目标的单光子测距方法。该方法采用阵列单光子探测器和相邻时间窗相关统计多帧处理算法提取激光回波光子信号,并在Matlab平台上对算法进行仿真实验,使用多元阵列单光子探测器实现最大测程百公里以上、背景噪声计数率约为5 MHz、单脉冲回波光子计数平均值为1条件下的回波光子信号提取。该方法能够克服传统单光子探测只能对准静态目标测距,只能在小接收视场和小波门范围等弱背景噪声及目标轨迹可预测条件下应用的限制,将单光子探测由只能固定平台夜晚对准静态目标测距推广至通用平台全天时对高速运动目标测距。     

一种提高二次雷达测距精度的方法

测距精度决定了二次雷达系统的目标分辨能力。针对现有二次雷达测距算法测距精度低的问题，分析了二次雷达的测距原理和引入的误差，提出了改进的自适应测距方法。在不更改二次雷达信号格式和硬件设计的前提下，采用分布式处理方式，使询问机和应答机能自动周期性测试本机内部延时，并在询问应答过程中自动分别扣除本设备的内部延时，从而提高二次雷达系统的测距精度。     

A new signal processing technique for ISAR ranging: the Vernierranging method

A new technique for inversed synthetic aperture radar (ISAR) ranging, which resembles the principle of the Vernier measuring system, is presented. In this technique, the transmitted ISAR pulse comprises a train of chirp subpulses with uniformly stepped up center frequencies. The return ISAR echo is first processed, using hardware, to determine a coarse estimate of the target range. Further refinements of the range estimate are achieved through software processing, consisting of two stages of discrete Fourier transform operation. The ranging accuracy can be increased without the need for increased bandwidth, but at the expense of a slight increase in computational complexity. Numerical evaluation shows that a noiseless system is capable of achieving high-ranging accuracy, of the order of millimeters, even in the presence of dispersion and target motion. From computer simulations, the proposed system is also found to be robust against additive system noise and frequency jitter under practical conditions     

A calculus for network delay. II. Network analysis

For pt.I see ibid., vol.37, no.1, p.114-31 (1991). A method to analyze the flow of data in a network consisting of the interconnection of network elements is presented. Assuming the data that enters the network satisfies burstiness constraints, burstiness constraints are derived for traffic flowing between network elements. These derived constraints imply bounds on network delay and buffering requirements. By example, it is shown that the use of regulator elements within the network can reduce maximum network delay. It is also found that such a use of regulator elements can enlarge the throughput region where finite bounds for delay are found. Finally, it is shown how regulator elements connected in series can be used to enforce general burstiness constraints     

A ranging based scheme for detecting the wormhole attack in wireless sensor networks

Wireless sensor networks have been widely used in general and military scenarios. And this leads to a need for more security. Wireless sensor network are easy vulnerable to attack and compromise. Wormhole attack is a harmful against routing protocol which can drop data randomly or disturbing routing path. In this paper, we proposed a novel method to detect the wormhole attack based on statistical analysis. In the proposed method, a sensor can detect the fake neighbors which are caused by wormhole through the neighbor discovery process, and then a k-means clustering based method is used to detect wormhole attack according to the neighbor information. That is, by using this proposed method, we can detect the wormhole only by the neighbor information without any special requirement. We did some experiments to evaluate the performance of this method, and the experimental results show that our method can achieve satisfying results.     

Art and technology II. A call for collaboration

As decribed in Part I, the collaboration of art and engineering in the creation of new art works has become a serious preoccupation of many modern artists, who are asking for the help of engineers. A number of organizations now exist whose aim is to facilitate the contact between artists and engineers and to help support them in their collaborative projects. You need not be a Renaissance Man, it is said, to apply for a match with an artist. It won't be all fun and games, although part of it will be, and you might even end up doing something so useless from an engineering point of view, and so right from another point of view, that you could begin wondering why engineering is practiced the way it is?i.e., you might get turned on. This article tells you a bit about what it was like for some others who have already tried, and calls on you to join the action.     

A map matching approach for train positioning. II. Application andexperimentation

For pt.I see ibid., vol.49, no.2, p.467-75 (2000). In this paper, applications of the map matching algorithm proposed in part I are presented. In particular, steady-state Kalman filters are proposed and applied for filtering the yaw rate and tachometer signals. In addition, experimental results, using a quartz yaw rate sensor and axle encoders aboard a freight train, are included to show the performance of the proposed map matching algorithm     

Optimum receiver design for OFDM-based broadband transmission .II.A case study

This paper details on the design of OFDM receivers. Special attention is paid to the OFDM-specific receiver functions necessary to demodulate the received signal and deliver soft information to the outer receiver for decoding. In part I of the paper, the effects of nonideal transmission conditions have been thoroughly analyzed. To show the impact of the synchronization algorithms-which are most critical in OFDM-on system performance and complexity we consider the design of a complete receiver consisting of symbol synchronization, carrier/sampling clock synchronization and channel estimation. The performance of the algorithms is analyzed and a qualitative estimate of the resulting complexity is given. This allows one to draw conclusions concerning the achievable system performance under realistic complexity assumptions     

WTA 2007 - II.3 - A Meta-tool for Adaptive Technology support

This work aims to propose an environment generator (meta-environment) which enables the environment automatic generation for adpative application projects. This generator is based on Adaptive Technology concepts and allows the definition of rule-driven adaptive devices. When developing the present study, we considered the general architecture of an environment for the project of adaptive applications and the architecture for an environment generator of applications modeling using a specific adaptive device Based on the concepts mentioned, the implementation of some tools were done to show such concepts and some experiments were made to demonstrate the use of such tools and adaptive devices in application projects.