X-SAR radiometric calibration and data quality

In April and October, 1994 the X-SAR was flown as part of the SIR-C/X-SAR space radar laboratory missions (SRL-1/2) on the Space Shuttle. Amongst other activities DLR is responsible for the calibration of all X-SAR data products and is running the German Processing and Archiving Facility (D-PAF). Calibration activities included three major parts. Before the first mission, the authors performed a detailed analysis of the overall system to localize the main error sources and developed algorithms and procedures to correct these errors. During the missions they concentrated their efforts on calibration campaigns at the Oberpfaffenhofen super test site. Post mission activities included the determination of the antenna pattern and the absolute calibration factor as well as detailed performance analyses. This paper describes the overall approach to radiometrically calibrate the X-SAR and provides information on system performance and data quality to users in the different application fields     

A radiometric antenna gain calibration method

A radiometric method is presented for measuring the power gain of a microwave antenna. It is particularly applicable to horns with gains in the range 20-45 dB, and an absolute uncertainty (3sigma) of less than 0.1 dB is achievable in favorable cases. An absorbing screen with a circular aperture is placed in the far-field of the test antenna. The diameter of the aperture is chosen to subtend an angle much smaller than the main lobe of the radiation pattern of the test antenna. Then two sheets of microwave absorber (one at ambient temperature and the other cooled to the boiling point of liquid nitrogen) are alternately placed first behind the screen aperture and then, for normalization, across the aperture of the test horn. The ratio of the antenna temperature differences measured with a sensitive microwave radiometer is proportional to the effective antenna solid angle, and thus its directivity. Corrections must be applied for near-field effects, diffraction at the screen aperture, partial resolution of the screen aperture by the main lobe of the test antenna pattern, and ohmic losses. A comparison of black disk measurements using a large conical horn at 86 GHz with theoretical calculations confirms the accuracy of this gain calibration technique.     

风云二号卫星水汽波段在轨辐射定标新方法

将月球作为热发射波段定标参考源,在无需月表发射率和温度信息条件下,通过引入UDER参数,建立了不同热发射波段观测辐亮度间定量关系,并导出了新的波段间交叉定标方法.同时,利用FY-2E卫星多波段月球观测结果,以辐射精度较高的热红外波段为基准,在无星载全光路黑体情况下,初步实现了水汽波段在轨高精度辐射定标,且在200～220 K低温区间内的定标精度平均提高约3.5 K,并显著改善了云分类等定量产品的性能.     

A new video-synchronized multichannel biomedical data acquisition system

This data acquisition system records video frames onto a video tape, and simultaneously acquires biomedical data along with video time codes onto a computer hard disk to achieve a 30-min video-synchronized data recording with a summed data rate of 2.16 Mbit/s. A time-code-bridge-file created during acquisition matches each video frame-start with the corresponding index number of the acquired data. The mean synchronization accuracy of the system is 0.22 ms.     

FY-3A中分辨率光谱成像仪红外通道辐射定标的场地评估

对比分析了基于场地观测数据模拟的和FY-3A 中分辨率光谱成像仪(MERSI)红外通道星上定标观测卫星入瞳亮温值。主要的场地观测数据来自于2008、2009年青海湖以及2010年敦煌外场同步观测和2008、2009年青海湖浮标观测。利用光学仪器的同步观测数据共有7组有效结果,两年的青海湖有效浮标数据一共18组。通过对比分析发现,MERSI观测结果基本都在夜间低于浮标同步观测结果,而白天偏高。综合与场地同步和浮标的对比结果发现,MERSI星上定标观测亮温值系统性偏高于基于场地观测数据模拟的亮温值,平均偏高1.721.18 K。MERSI星上定标观测亮温值的系统性偏高可能主要由星上黑体发射率未经过修正引起。     

利用大洋浮标数据和NCEP再分析资料对FY-2C红外分裂窗通道的绝对辐射定标

介绍利用大洋浮标数据和NCEP再分析资料对FY-2C红外分裂窗通道进行在轨绝对辐射定标的方法,并选择了2006年10个时次的卫星数据进行辐射定标试验.将利用这种方法获得的定标结果与FY-2C卫星数据产品中提供的定标查找表进行比较分析,结果表明两套不同的定标系数反演的大气层顶(TOA)亮度温度的主要差别集中在云顶、冰雪覆盖区域等低温像元;而在常温区的陆表和海表像元定标结果差别较小,反演的TOA亮温差在2K左右.提出的替代定标方法可以极大地提高定标频次,为实现FY-2C红外分裂窗通道的实时绝对辐射定标提供了重要的方法基础.     

Adapting laptops to data acquisition

It is explained how portable computers, which lack expansion slots, can instead be made to accept medium-speed data through their parallel ports. The advantages of portables are recalled, and methods for attaching data acquisition instruments to personal computers are reviewed. The ability of the parallel port to serve as a data acquisition interface capable of performance substantially above that of the RS-232 serial interface is discussed. The issue of building versus buying a parallel port adapter is considered     

A search strategy for ultra-wideband signal acquisition

The ultra-wideband (UWB) channel is characterized by the presence of dense multipath and robustness to multipath fading. By taking system performance subsequent to acquisition into account, it was shown recently that there are multiple phases (called the hit set) where a receiver lock can be considered as successful acquisition. In this case, the serial search may no longer be the optimal choice for the sequential search strategy in the acquisition system. In this letter, we consider the problem of finding better search strategies in the set of all search strategies which are permutations of the search space. The large size of the search space and the absence of any exploitable structure make the problem of finding the permutation search strategy which minimizes the mean detection time prohibitively complex. However, if we take the first-order approximation that the probabilities of detection of all the hit-set phases are equal, then there exists a permutation search strategy which minimizes the mean detection time. Since the actual probabilities of detection are not equal, this search strategy, although not optimal, serves as a useful heuristic solution to an otherwise intractable problem. Furthermore, we see that this search strategy has a simple Jump-by-H structure, and improves the mean detection time by a significant amount compared with the serial search.     

A test and calibration strategy for adjustable RF circuits

A test and calibration strategy suitable for adjustable RF circuits is presented in this paper. Certain performance-affecting circuit elements are designed to be digitally controllable, providing the capability to adjust the performance characteristics of a circuit’s instance around their post-fabrication values, throughout a set of discrete states of operation. The alternate test methodology is adopted for test and calibration and a set of optimally selected test observables is used to develop regression models for the prediction of the circuit’s performance characteristics in every state of operation. In the test phase, measurements of the test observables are obtained from a subset of the circuit’s states. The processing of these observables provides accurate prediction of the RF circuit’s performance characteristics in all available states and enables the discrimination of defect-free from defective circuits. The latter is further accomplished by the exploitation of an extended superset of the test observables, the use of which intends to maximize fault coverage. Moreover, the predicted performance characteristics are also used to examine compliance with the specifications and to allow calibration of the RF circuit by identifying the appropriate state of operation at which all specifications are met and, consequently, by forcing the circuit to operate in this specific state. The efficiency of the proposed technique has been validated by its application to a typical differential RF Mixer designed in a 0.18 μm CMOS technology. Simulation results have been obtained and assessed.     

一种多磁盘毁损恢复数据策略

当发生诸如爆炸、火灾等灾难时,或者遭到恶意病毒侵害时,或者磁盘寿命终止时,布置了大量磁盘的数据系统很可能发生多个磁盘同时毁损的事件,以至于数据无法被恢复。在众多的数据备份方案中,以基于RAID6的冗余技术为基础,设计了磁盘数据恢复方案,可以对多个磁盘在确保其读写概率相同的情况下实现数据恢复。     

A statistical approach for determining radiometric precisions andaccuracies in the calibration of synthetic aperture radar imagery

A model that estimates a relative error bound for the radiometric calibration of synthetic aperture radar (SAR) imagery is presented. This model is based on a statistical `Coefficient of Variation of Error Model', which produces a relative error bound by propagating the measured or estimated uncertainties in the radar system parameters utilized to correct digitally processed SAR image intensity values. Using this model, algorithms are generated for absolute and relative radiometric calibration of SAR imagery. These algorithms are parametrically exercised using radar system parameters from an existing airborne SAR system to determine their impact on the relative error bound     

一种新的深度传感器内部参数标定方法研究

针对双镜头深度传感器(以Kinect为例)出厂标 定参数精度不高的问题,提出一种新的标定方法。 对于Kinect 2.0深度镜头,利用空间线定长约束,通过间接平差方法求解待求参数;根据求 解参数,将深度图 像坐标转转换值Kinect坐标并将其与对应的彩色影像坐标点进行关联,基于中心投影方程标 定彩色镜头。实 验结果表明,本方法将深度影像点转换到Kinect坐标时精度优于2.5 mm,深度影像坐标转换至彩色影像坐标 时精度优于1pixel,高于Kinect微软开发包内置参数的计算精度,对一些需要较高参 数精度的应用,本文算法解算的参数更优。     

Use of a new high-speed digital data acquisition system in airborneice-sounding

A high-speed digital data acquisition and signal averaging system for borehole, surface, and airborne radio-frequency geophysical measurements was designed and built by the US Geological Survey. The system permits signal averaging at rates high enough to achieve significant signal-to-noise- enhancement in profiling, even in airborne applications. The first field use of the system took place in Greenland in 1987 for recording data on a 150 by 150-km grid centered on the summit of the Greenland ice sheet. About 6000-line km were flown and recorded using the new system. The data can be used to site a proposed scientific corehole through the ice sheet     

A neural-network approach to radiometric sensing of land-surfaceparameters

A biophysically-based land-surface process/radiobrightness (LSP/R) model is integrated with a dynamic learning neural network (DLNN) to retrieve the land-surface parameters from its radiometric signatures. Predictions from the LSP/R model are used to train the DLNN and serve as the reference for evaluation of the DLNN retrievals. Both horizontally polarized and vertically polarized brightnesses at 1.4 GHz, 19 GHz, and 37 GHz for an incidence angle of 53° make up the input nodes of the DLNN. The corresponding output nodes are composed of land-surface parameters, canopy temperature and water content, and soil temperature and moisture (uppermost 5 mm). Under no-noise conditions, the maximum of the root mean-square (RMS) errors between the retrieved parameters of interest and their corresponding reference from the LSP/R model is smaller than 28 for a four-channel case with 19 GHz and 37 GHz brightnesses as the inputs of the DLNN. The maximum RMS error is reduced to within 0.5% if additional 1.4 GHz brightnesses are used (a six-channel case). This indicates that the DLNN produces negligible errors onto its retrievals. For the realization of the problem, two different levels of noises are added to the input nodes. The noises are assumed to be Gaussian distributed with standard deviations of 1 K and 2 K. The maximum RMS errors are increased to 9.3% and 10.3% for the 1 K-noise and 2 K-noise cases, respectively, for the four-channel ease. They are reduced to 6.0% and 9.1% for the 1 K-noise and 2 K-noise cases, respectively, for the six-channel case. This is an implication that 1.4 GHz is a better frequency in probing soil parameters than 19 GHz and 37 GHz     

A look into the future of data acquisition

The basic Fabry-Perot interferometer sensor is made of a cavity formed by a gap in a fiber optic cable. The end of the fiber is minimally reflecting. Losses associated with a simple cleavage of the fiber eliminate the need for treating the remaining fiber as a cavity     

Database support to data fusion automation

Because the development of robust context-sensitive data fusion algorithms can require the evaluation of sensor-derived data with respect to large scale domain knowledge bases, database management systems can be expected to play an increasingly important role in machine-based reasoning. This paper offers a top-down view of key algorithm and database management system requirements associated with advanced data fusion applications. A database kernel design is outlined that seeks to achieve an effective compromise across a range of algorithm performance and database efficiency requirements     

基于NiosII软核的高速数据采集系统

为了达到数据采集系统中对高速的要求,提出了一种基于NiosⅡ软核的高速数据采集系统,将3个NiosⅡ微处理器集成到一个FPGA(Field Programmable Gate Array)芯片当中分工协作完成数据采集、处理.由于3个NiosⅡ软核处理器并行运行,大大提高了数据采集系统的速度.     

A 20 b dynamic-range floating-point data acquisition system

The design and engineering of a floating-point data-acquisition system are described. The system has both automatic gain and software-programmable gain adjustment features. In automatic gain adjustment mode, the gain is set automatically dependent on the input amplitude so that the full conversion resolution is maintained irrespective of the signal dynamic range. A high-speed flash ADC with an approximately 35 ns conversion time is used to convert the signal quickly into 8 b data. A programmable array logic (PAL) then transfers this 8 b digital data into 12 b information for setting the gain of the variable-gain amplifier. The amplifier gain settings are all powers of two; thus, the normalization of the digitized data requires only a bit shifting operation and no complex software division. The gain information and the 12 b sampling ADC output increase the dynamic range to 20 b. The software package includes commands needed for the system initiation, automatic gain or software programmable gain selection, sampling and conversion, and data normalization     

提高多通道数据采集系统采集精度的新方法

采集精度除了与ADC的实际转换位数相关的量化误差有关外,还会受到一些噪声和通道间信号串扰的影响。为提高多通道数据采集系统的采集精度,本文提出通过FPGA控制ADC对输入信号进行过采样,然后在FPGA内部实现抽取滤波和求平均值算法提高ADC转换分辨率。该方法用廉价的芯片实现了只有昂贵芯片才能得到的精度指标,并且易于实现。文中最后利用了直方图分析法对不同工作方式下所采集的数据进行了分析比较,结果显示该方法能够有效的减小系统的测量误差,提高了系统测量精度。     

A new calibration algorithm of wide-band polarimetric measurementsystem

The principle and experimental results of a new self-consistent calibration algorithm for a wideband polarimetric scattering measurement system are presented. The calibration targets include a flat plate, a dihedral corner reflector, and a rotated dihedral corner reflector. The rotation angle of the third calibrator can be derived in the calibration process and used to verify the calibration performance. Experimental results show that the calculated rotation angle of the third calibrator over the operation bandwidth is in good agreement with its actual angle, hence it provides a self-consistent parameter of the calibration algorithm. Based on the signal-to-noise consideration, an optimal rotation angle for a dihedral corner reflector is found to be 22.5°. This calibration technique is also useful in characterizing the frequency and polarization responses of dual-polarization antennas