The Low-Energy Telescope (LET) and SEP Central Electronics for the STEREO Mission

The Low-Energy Telescope (LET) is one of four sensors that make up the Solar Energetic Particle (SEP) instrument of the IMPACT investigation for NASA’s STEREO mission. The LET is designed to measure the elemental composition, energy spectra, angular distributions, and arrival times of H to Ni ions over the energy range from ～3 to ～30 MeV/nucleon. It will also identify the rare isotope ³He and trans-iron nuclei with 30≤Z≤83. The SEP measurements from the two STEREO spacecraft will be combined with data from ACE and other 1-AU spacecraft to provide multipoint investigations of the energetic particles that result from interplanetary shocks driven by coronal mass ejections (CMEs) and from solar flare events. The multipoint in situ observations of SEPs and solar-wind plasma will complement STEREO images of CMEs in order to investigate their role in space weather. Each LET instrument includes a sensor system made up of an array of 14 solid-state detectors composed of 54 segments that are individually analyzed by custom Pulse Height Analysis System Integrated Circuits (PHASICs). The signals from four PHASIC chips in each LET are used by a Minimal Instruction Set Computer (MISC) to provide onboard particle identification of a dozen species in ～12 energy intervals at event rates of ～1,000 events/sec. An additional control unit, called SEP Central, gathers data from the four SEP sensors, controls the SEP bias supply, and manages the interfaces to the sensors and the SEP interface to the Instrument Data Processing Unit (IDPU). This article outlines the scientific objectives that LET will address, describes the design and operation of LET and the SEP Central electronics, and discusses the data products that will result.     

Evaluating sensor technology for UAS collision avoidance

The problem of "sense-and-avoid" for Unmanned Aircraft Systems (UAS) is genuinely multi-dimensional: there is a wide range of UAS sizes, speeds, and maneuverability, as well as missions for which these UAS will be used. There are also a variety of sensors that might be used for sense-and-avoid, which have widely varying capabilities to measure distance or angle to an obstacle, as well as closing rate, and time to collision. Most sensors are not able to provide all required information about the geometry of an encounter; therefore, using a combination of sensors offers one possible solution. We are investigating the concept that there may be a variety of possible sensor solutions for each distinct UAS capability or mission. By studying the breadth of UAS types and missions, and selectively testing certain sensors in the field, we are evaluating the limits to the capabilities of sensors and sensor combinations. This report is on the progress of this multi-dimensional evaluation. We have scoped the dimensions for evaluating UAS capabilities and the capabilities of sensors. We are experimentally evaluating sensor parameters on a variety of aircraft to validate the specified capabilities. This reports on our methodology for field evaluation of sensor technology and the lessons learned on evaluation platforms and capabilities.     

A Numerical Model of the SEIS Leveling System Transfer Matrix and Resonances: Application to SEIS Rotational Seismology and Dynamic Ground Interaction

Both sensors of the SEIS instrument (VBBs and SPs) are mounted on the mechanical leveling system (LVL), which has to ensure a level placement on the Martian ground under currently unknown local conditions, and provide the mechanical coupling of the seismometers to the ground. We developed a simplified analytical model of the LVL structure in order to reproduce its mechanical behavior by predicting its resonances and transfer function. This model is implemented numerically and allows to estimate the effects of the LVL on the data recorded by the VBBs and SPs on Mars. The model is validated through comparison with the horizontal resonances (between 35 and 50 Hz) observed in laboratory measurements. These modes prove to be highly dependent of the ground horizontal stiffness and torque. For this reason, an inversion study is performed and the results are compared with some experimental measurements of the LVL feet’s penetration in a martian regolith analog. This comparison shows that the analytical model can be used to estimate the elastic ground properties of the InSight landing site. Another application consists in modeling the 6 sensors on the LVL at their real positions, also considering their sensitivity axes, to study the performances of the global SEIS instrument in translation and rotation. It is found that the high frequency ground rotation can be measured by SEIS and, when compared to the ground acceleration, can provide ways to estimate the phase velocity of the seismic surface waves at shallow depths. Finally, synthetic data from the active seismic experiment made during the HP³ penetration and SEIS rotation noise are compared and used for an inversion of the Rayleigh phase velocity. This confirms the perspectives for rotational seismology with SEIS which will be developed with the SEIS data acquired during the commissioning phase after landing.     

The Modelling of Background Noise in Astronomical Gamma Ray Telescopes

Gamma ray photons interact with matter through a wide variety of complex physical mechanisms, which can be readily imitated by other particle processes. Unfortunately since γ-ray telescopes are obliged to function in a hostile radiation environment above the earth's atmosphere the net result is low signal to noise observations and a corresponding loss in sensitivity. Consequently, understanding the generation of the systematic background noise is crucial if the full performance of a γ-ray instrument is to be realised. In the past it was not possible to reliably estimate the background levels in a fully quantitative manner; semi-empirical methods were employed. Although the basic underlying sources of the background noise were reasonably well understood, and the spectral intensities of the associated particles were reasonably well known, it was not possible to associate resultant noise components with the input source of that noise with any real degree of accuracy. The advent of sophisticated and accurate computer programmes capable of dependably representing the requisite particle physics processes and interactions coupled with the advances made in the context of high power/low cost computers has revolutionised the situation. The so-called ‘mass modelling’ technique is a truly physics-based approach, which takes the input particle spectra of the local radiation environment together with a computer representation of the mechanical structure and chemical composition of the instrumentation and associated spacecraft to trace the trajectories and interactions of all the incident particles throughout the system. All energy deposits from the various interactions and likewise those from the prompt and delayed secondary products are also accurately recorded. Subsequent energy discriminators and time coincidences can be applied to the event arrays with additional software to simulate on-board electronics systems. Internal spectral counting rates may be readily derived and analysed in terms of a wide variety of desired purposes. The impact of an accurate physics-based mass modelling technique has been to expand application of the procedure to effectively all the main aspects of a space γ-ray astronomy mission: instrument design; internal counting rates and spectral sensitivity estimates; optimisation of the design of the on-board processing electronics; operational planning and mission optimisation; estimation of radiation damage and its limitation; calibration planning and interpretation; the production of accurate instrumental response matrices; data analysis software; normalisation of astronomical results across instrument and instrumental degradation boundaries; and data archiving. This revised version was published online in June 2006 with corrections to the Cover Date.     

The development of a digital video motion detection test set

This paper describes the current effort to develop a standardized data set, or suite of digital video sequences, that can be used for test and evaluation of digital video motion detectors (VMDs) for exterior applications. We have drawn from an extensive video database of typical application scenarios to assemble a comprehensive data set. These data, some existing for many years on analog videotape, have been converted to a reproducible digital format and edited to generate test sequences several minutes long for many scenarios. Sequences include non-alarm video, intrusions and nuisance alarm sources, taken with a variety of imaging sensors including monochrome CCD cameras and infrared (thermal) imaging cameras, under a variety of daytime and nighttime conditions. The paper presents an analysis of the variables and estimates the complexity of a thorough data set. Some of this video data test has been digitized for CD-ROM storage and playback. We are considering developing a DVD disk for possible use in screening and testing VMDs prior to government testing and deployment. In addition, this digital video data may be used by VMD developers for further refinement or customization of their product to meet specific requirements. These application scenarios may also be used to define the testing parameters for future procurement qualification. A personal computer may be used to play back either the CD-ROM or the DVD video data. A consumer electronics-style DVD player may be used to replay the DVD disk. This paper also discusses various aspects of digital video storage including formats, resolution, CD-ROM and DVD storage capacity, formats, editing and playback     

Multisensor multitarget bias estimation for general asynchronous sensors

A novel solution is provided for the bias estimation problem in multiple asynchronous sensors using common targets of opportunity. The decoupling between the target state estimation and the sensor bias estimation is achieved without ignoring or approximating the crosscovariance between the state estimate and the bias estimate. The target data reported by the sensors are usually not time-coincident or synchronous due to the different data rates. Since the bias estimation requires time-coincident target data from different sensors, a novel scheme is used to transform the measurements from the different times of the sensors into pseudomeasurements of the sensor biases with additive noises that are zero-mean, white, and with easily calculated covariances. These results allow bias estimation as well as the evaluation of the Cramer-Rao lower bound (CRLB) on the covariance of the bias estimate, i.e., the quantification of the available information about the biases in any scenario. Monte Carlo simulation results show that the new method is statistically efficient, i.e., it meets the CRLB. The use of this technique for scale and sensor location biases in addition to the usual additive biases is also presented.     

飞机着陆时的容错导航

研究了飞机在微波着陆环境中的传感器容错系统。该系统的主要目的是检测辅助导航设备和机载传感器的故障,并在这些传感器可能发生故障时提供可靠的飞机状态估计值。自动导航和控制系统利用这些状态估计控制和引导飞机按预定路线降落。     

A hardware signal processing platform for sensor systems

A field programmable gate array-based computing platform for high-speed sensors such as short-range radars is presented. The circuit performs necessary A/D conversions, raw data stream compression and target detection, and constructs a message structure suitable for external displays. In the prototype, USB is the connecting path to a laptop computer. An elementary pulse radar is utilized as an application example. An application interest would be in collision avoidance systems. Observed data transfer rates with real radar input signals were 36 Mbytes/s when typical target detection algorithms were applied.     

Sensor systems signal processing platform

A field programmable gate array-based computing platform for high-speed sensors such as short-range radars is presented. The circuit performs necessary A/D conversions, raw data stream compression and target detection, and constructs a message structure suitable for external displays. In the prototype, USB is the connecting path to a laptop computer. An elementary pulse radar is utilized as an application example. An application interest would be in collision avoidance systems. Observed data transfer rates with real radar input signals were 36 Mbytes/s when typical target detection algorithms were applied.     

Instrument Failure Detection in Partially Observable Systems

Instrument failure detection using the dedicated observer scheme (DOS) depends on partial state observability through each instrument which is monitored. For instrument fault detection by the DOS technique, a quantitative measure of partial state observability is established for each instrument and used to determine a necessary condition on the output structure of the system. This measure, called the internal redundancy of the instrument, indicates the complexity of the logic required for failure detection, and it also indicates where some hardware redundancy can be introduced into the system to improve the fault detection capability of the DOS. The principles developed are applied to a simulation of the pitch axis autopilot of the A7 jet aircraft.     

PEACE: A PLASMA ELECTRON AND CURRENT EXPERIMENT

An electron analyser to measure the three-dimensional velocity distribution of electrons in the energy range from 0.59 eV to 26.4 keV on the four spacecraft of the Cluster mission is described. The instrument consists of two sensors with hemispherical electrostatic energy analysers with a position-sensitive microchannel plate detectors placed to view radially on opposite sides of the spacecraft. The intrinsic energy resolutions of the two sensors are 12.7% and 16.5% full width at half maximum. Their angular resolutions are 2.8° and 5.3° respectively in an azimuthal direction and 15° in a polar direction. The two sensors will normally measure in different overlapping energy ranges and will scan the distribution in half a spacecraft rotation or 2 s in the overlapped range. While this is the fastest time resolution for complete distributions, partial distributions can be recorded in as little as 62.5 ms and angular distributions at a fixed energy in 7.8 ms. The dynamic range of the instrument is sufficient to provide accurate measurements of the main known populations from the tail lobe to the plasmasheet and the solar wind. While the basic structure of the instrument is conventional, special attention has been paid in the design to improving the precision of the instrument so that a relative accuracy of the order of 1% could be attained in flight in order to measure the gradients between the four spacecraft accurately; to decreasing the minimum energy covered by this technique from 10 eV down to 1 eV; and to providing good three dimensional distributions.     

The Galileo Probe Atmosphere Structure instrument

The Galileo Probe Atmosphere Structure Instrument will make in-situ measurements of the temperature and pressure profiles of the atmosphere of Jupiter, starting at about 10^-10 bar level, when the Probe enters the upper atmosphere at a velocity of 48 km s^-1, and continuing through its parachute descent to the 16 bar level. The data should make possible a number of inferences relative to atmospheric and cloud physical processes, cloud location and internal state, and dynamics of the atmosphere. For example, atmospheric stability should be defined, from which the convective or stratified nature of the atmosphere at levels surveyed should be determined and characterized, as well as the presence of turbulence and/or gravity waves. Because this is a rare opportunity, sensors have been selected and evaluated with great care, making use of prior experience at Mars and Venus, but with an eye to special problems which could arise in the Jupiter environment. The temperature sensors are similar to those used on Pioneer Venus; pressure sensors are similar to those used in the Atmosphere Structure Experiment during descent of the Viking Landers (and by the Meteorology Experiment after landing on the surface); the accelerometers are a miniaturized version of the Viking accelerometers. The microprocessor controlled experiment electronics serve multiple functions, including the sequencing of experiment operation in three modes and performing some on-board data processing and data compression.     

ICP加速度传感器恒定电流对其灵敏度的影响

在振动与冲击测试中,ICP加速度传感器应用较为广泛,而传感器灵敏度是其最基本的指标之一。实际使用时,ICP加速度传感器通常都会配有信号调节仪,该调节仪为ICP加速度传感器提供恒定电流,不同的信号调节仪所提供的恒定电流也会有所不同。在不同恒定电流情况下,传感器灵敏度是否随之变化,如何变化？针对这一问题我们展开讨论。     

The Polar plasma wave instrument

The Plasma Wave Instrument on the Polar spacecraft is designed to provide measurements of plasma waves in the Earth's polar regions over the frequency range from 0.1 Hz to 800 kHz. Three orthogonal electric dipole antennas are used to detect electric fields, two in the spin plane and one aligned along the spacecraft spin axis. A magnetic loop antenna and a triaxial magnetic search coil antenna are used to detect magnetic fields. Signals from these antennas are processed by five receiver systems: a wideband receiver, a high-frequency waveform receiver, a low-frequency waveform receiver, two multichannel analyzers; and a pair of sweep frequency receivers. Compared to previous plasma wave instruments, the Polar plasma wave instrument has several new capabilities. These include (1) an expanded frequency range to improve coverage of both low- and high-frequency wave phenomena, (2) the ability to simultaneously capture signals from six orthogonal electric and magnetic field sensors, and (3) a digital wideband receiver with up to 8-bit resolution and sample rates as high as 249k samples s^–1.     

Broadband passive acoustic technique for target motion parameterestimation

A nonlinear least-squares method is formulated to estimate the motion parameters of a target whose broadband acoustic energy emissions are received by a ground-based array of sensors. This passive technique is applied to real acoustic sensor data recorded during the passage of a variety of ground vehicles past a planar cross array and its effectiveness verified by comparing the results with the actual values of the target motion parameters. The technique cam also be applied to airborne targets     

多输入多输出电磁矢量阵列雷达的DOD和DOA联合估计

研究一种基于电磁矢量传感器阵列的多输入多输出(MIMO)雷达目标波离角(DOD)和波达角(DOA)的联合估计算法.提出了一种新型MIMO雷达系统,发射阵列采用常规阵元,而接收阵列采用电磁矢量传感器,在此基础上,算法首先利用矢量传感器的内在结构特点结合子空间旋转不变性质获得目标DOA预估计,随后采用最佳加权子空间拟合算法...     

Detecting Instrument Malfunctions in Control Systems

A scheme for automatically detecting incipient failures in the feedback sensors (or instruments) of control systems is described. The feasibility of the scheme is investigated by applying it to a simplified version (fourth order) of the flight control system for a hydrofoil boat. A single set of inertial instruments is used to provide the feedback signals; the redundancy which is normally obtained by multiple instrument sets is obtained here, artificially, by a subsystem of multiple Luenberger observers and logic circuits. Tests indicate that scale factor errors, errors due to threshold effects, and bias errors in the instruments are detected as they occur. The tests also indicate further analytical work which should be done to explore the limitations of the basic scheme.     

The THEMIS ESA Plasma Instrument and In-flight Calibration

The THEMIS plasma instrument is designed to measure the ion and electron distribution functions over the energy range from a few eV up to 30 keV for electrons and 25 keV for ions. The instrument consists of a pair of “top hat” electrostatic analyzers with common 180°×6° fields-of-view that sweep out 4π steradians each 3 s spin period. Particles are detected by microchannel plate detectors and binned into six distributions whose energy, angle, and time resolution depend upon instrument mode. On-board moments are calculated, and processing includes corrections for spacecraft potential. This paper focuses on the ground and in-flight calibrations of the 10 sensors on five spacecraft. Cross-calibrations were facilitated by having all the plasma measurements available with the same resolution and format, along with spacecraft potential and magnetic field measurements in the same data set. Lessons learned from this effort should be useful for future multi-satellite missions.     

基于FBG 传感器的复合材料固化监测

温度和内应力是影响复合材料固化过程和结构性能的重要因素,将双光栅的FBG传感器埋入到玻璃纤维/环氧树脂预浸层合板结构中,监测热压固化过程中温度、黏度和内应力变化,并简要分析了固化后的残余应变。实验证明FBG传感器可有效监测复合材料结构固化过程的温度、黏度和内应力,能够作为智能固化控制依据,且固化结束之后,相同的传感器可以被用于提供结构使用过程中产生的温度/机械变化的信息。     

The ACE Magnetic Fields Experiment

The magnetic field experiment on ACE provides continuous measurements of the local magnetic field in the interplanetary medium. These measurements are essential in the interpretation of simultaneous ACE observations of energetic and thermal particles distributions. The experiment consists of a pair of twin, boom- mounted, triaxial fluxgate sensors which are located 165 inches (=4.19 m) from the center of the spacecraft on opposing solar panels. The electronics and digital processing unit (DPU) is mounted on the top deck of the spacecraft. The two triaxial sensors provide a balanced, fully redundant vector instrument and permit some enhanced assessment of the spacecraft's magnetic field. The instrument provides data for Browse and high-level products with between 3 and 6 vector s−1 resolution for continuous coverage of the interplanetary magnetic field. Two high-resolution snapshot buffers each hold 297 s of 24 vector s−1 data while on- board Fast Fourier Transforms extend the continuous data to 12 Hz resolution. Real-time observations with 1-s resolution are provided continuously to the Space Environmental Center (SEC) of the National Oceanographic and Atmospheric Association (NOAA) for near- instantaneous, world-wide dissemination in service to space weather studies. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the interplanetary medium in support of the fundamental goals of the ACE mission and cooperative studies with other ACE investigators using the combined ACE dataset as well as other ISTP spacecraft involved in the general program of Sun-Earth Connections. This revised version was published online in June 2006 with corrections to the Cover Date.