共查询到20条相似文献,搜索用时 31 毫秒
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L波段微波辐射计是探测土壤湿度和海水盐度的有效遥感器。但是,全球定位系统(GPS)信号、雷达信号以及一些商用电子产品的电磁辐射造成的频谱污染都可以对微波辐射计的探测造成干扰,使得被动微波遥感对地观测结果具有一定的偏差,降低了地表参数的反演精度。该文通过实验模拟脉冲式噪声干扰,观测其在L波段(全功率接收型式)微波辐射计系统中的传输特性,分析输出信号特性与辐射计参数(积分时间、灵敏度)的相关性,获取其数字特征参数,结合脉冲检测法(APB),提出一种新的自相关检测(ACD)算法,能够有效用于周期性的脉冲式辐射干扰的检测,在微波辐射计系统积分时间1 ms的情况下,能够检测1.5 K的噪声干扰,满足卫星遥感探测反演地表参数精度的需求。 相似文献
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《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1967,55(9):1577-1582
A digital measurement method for narrowband noise power is described and analyzed in the case of flat spectrum Gaussian noise. Noise power is measured by counting the number of times the noise voltage crosses upwards a fixed voltage level. The method should be useful in noise-figure measurements, and by applying it a digital radiometer can be constructed. This digital radiometer has the same theoretical (about 9 percent worse than the best possible radiometer) as conventional radiometers now in use but offers several advantages in comparison with them. A switched digital radiometer is somewhat more sensitive to large gain variations than a normal switched radiometer. 相似文献
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Stokes参数是描述极化波的强度量纲,在电磁测量、合成孔径雷达、辐射计中均有广泛应用.文中提出了求解Stokes参数的数字化方法,具有带宽高、稳定性高等特点.针对将模拟信号采样量化后求解Stokes参数的方法,本文分别就自相关和互相关两种计算过程,详细分析并给出了数字量化对最终亮温的误差贡献.文中证明了高于3bit量化引入的亮温误差小于1*10-5K,进一步给出了量化后的系统灵敏度,分析了由数字量化产生的亮温灵敏度偏差.当量化位数为3bit时,数字相关系统灵敏度可以达到理想模拟相关系统的95%.本文为不同应用条件下,满足不同精度时,如何选择特定量化位数与量程提供了依据. 相似文献
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为实现微波辐射计大带宽数字化探测的需求,解决现场可编程门阵列(Feild Programmable Gate Array,FPGA)内部处理速度限制输入数据速率的问题,提出了一种基于多相滤波器组和高级快速傅里叶变换(Fast Fourier Transform,FFT)结构的高速数字谱仪设计方案,介绍了多相滤波器组和高级FFT理论基础并给出了具体的硬件设计和硬件实现,完成了硬件的功能仿真,将MATLAB仿真和硬件功能仿真的结果进行对比,验证了该设计方案的可行性.在低时间成本和低经济成本条件下,该方案可实现微波辐射计后端的灵活配置和共享多个微波辐射计前端的功能. 相似文献
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Guo Wei Zhang Zuyin Lu Yin 《Journal of Infrared, Millimeter and Terahertz Waves》1994,15(8):1407-1412
The total power radiometer has simple structure and high theoretical sensitivity. But its actual sensitivity can not be so high as the application demands because of the effect of the gain fluctuation and other factors. This paper provides a 8mm total power radiometer system with periodic calibration which can be used on the ground and the aeroplane, it decreases the effect of the gain fluctuations effectively and increases the radiometer sensitivity. Experiments has also been made to analyse the effect of the calibration parameters upon the radiometer sensitivity. The results is given in the paper. Besides, the paper gives the way to do absolute calibration. 相似文献
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《Geoscience and Remote Sensing, IEEE Transactions on》1995,33(5):1222-1229
A numerical simulator is developed to assess various design implications of a digital correlator used by a synthetic aperture interferometric radiometer (SAIR). The simulator permits control of the type of digitization, the digitization thresholds with respect to noise power, and the degree of correlation between the two antenna signals which are being cross correlated. Digitization schemes are considered which use 2, 3, 4, and 8 levels. Estimates are made of the increase in inherent radiometer noise (ΔT) due to the digitization. The increase in ΔT is found to depend strongly on the degree of correlation, with higher correlations suffering less increase. In most cases, 3 level digitization is recommended based on this sensitivity consideration. Two levels perform significantly noisier and four levels only slightly cleaner. Several case studies are also considered regarding the need to control the signal level relative to the digitizer thresholds. Automatic gain control circuitry prior to digitization is found not to be necessary, provided the thresholds are preset within a fairly broad region of minimum sensitivity to variations in signal power, and provided the system noise temperature of the radiometer is monitored with reasonable accuracy. It is also found that, under conditions of very high correlation between the two signals, digital correlators have better SNR performance than analog. Reasons for this behavior are discussed 相似文献
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介绍了微波辐射计接收机两点定标法,并进行了误差分析.对自行研制的23.8GHz数字增益自动补偿微波辐射计进行了定标,计算定标误差范围.对接收机两点定标法得到的定标方程进行了验证实验,结果表明采用两点定标法对辐射计接收机进行定标有良好的准确性. 相似文献
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数字增益和补偿微波辐射计是一种新型的微波辐射计,它能很好地实现增益补偿,有效地提高微波辐射计性能,更适合星载使用,本文对以全功率微波辐射计为基础的数字增益自动2微波辐射计进行仿真,分析了全功率微波辐射计的特点,并在此荐 ,提出了在频程跨度很大时实现系统频域仿真的有效方法,仿真结果不仅证明功率微波辐射计的特点,在此基础上,提出了在频程跨度很大时实现系统频域仿真的有效方法,仿真的结果不仅证明所采用的方 相似文献
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The advent of fast computers and digital signal processing permits many aspects of radiometer operation to be decided in real time so that precision and accuracy are maximized. Closed-form expressions for precision, optimal antenna/load dwell times, and maximum chopping period are derived for a class of radiometers that uses two loads to calibrate its measurements of antenna brightness temperature. The importance of load brightness temperature selection emphasizes the need to develop "cold" calibration loads that can operate at ambient temperature. A method of incorporating critical thermistor data into the radiometer brightness temperature calibration can be used to help stabilize measurements against drift and may permit radiometers to operate without thermal control in some low-accuracy applications. 相似文献
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周期两点定标微波辐射计原理研究 总被引:1,自引:0,他引:1
根据热辐射理论,任何温度处于绝对零度以上的物体都存在热辐射。通常用亮度温度来表征物体的辐射强度,其取决于物体本身的几何特性与介电特性。微波辐射计是用于测量物体微波辐射能量的被动遥感仪器,在军事、环境科学上都有重要的作用。阐述了微波辐射计的定标原理,介绍了周期两点定标方法,并简要描述了某毫米波成像辐射计的结构组成和工作原理。 相似文献
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Fischman M.A. England A.W. Ruf C.S. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(3):671-679
The phase coherence limitations of L-band digital correlation radiometry are investigated for receiver architectures that use low A/D converter resolution (1-3 bits). Statistical models and measurements of a 1.4 GHz digital radiometer system show that coarse quantization can cause excess fringe washing losses which degrade the spatial resolution capabilities in synthetic thinned array radiometry (STAR) implementations. For single-bit STAR, excess fringe washing is discernible immediately away from the boresight direction and, further from the center of the image, can result in as much as 2 dB loss in visibility information. To accommodate low-bit correlators in remote sensing STAR, a novel band division correlation (BDC) processor is proposed. BDC improves the time-coherence of each correlated brightness signal while it also maintains the system bandwidth and noise-equivalent sensitivity of a conventional STAR radiometer. Analytical and numerical solutions are presented for the point spread function of a 27 m L-band STAR sensor to evaluate the band-slicing technique. The results show that with 4 subband channels, BDC improves swath edge resolution from 17.0 to 10.2 km and reduces correlation loss from 2.5 to 0.2 dB 相似文献
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《Microwave Theory and Techniques》1981,29(1):32-40
The total power radiometer is an attractive choice for imaging applications due to its high sensitivity and simple configuration. However, available theoretical results are inadequate to allow an accurate radiometer performance prediction in the presence of receiver gain fluctuations and other receiver characteristics with nonuniform fluctuation power spectra. An improved analysis of the total power radiometer Delta T is presented in terms of the receiver output fluctuation power spectral density and a transfer function due to postdetection filtering and periodic calibration. Verification of this analysis is obtained by measuring the fluctuation power spectrum of a 94-GHz receiver and comparing the predicted Delta T with a direct measurement. Numerical results including application to an example radiometer system are presented. These results indicate that the total power radiometer should function well in short integration time, periodically calibrated radiometer systems. 相似文献
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本文针对目前合成孔径辐射计中存在的相关器单元过于复杂,难以星载应用的问题,提出了一种新的数字相关方法.借鉴了软件无线电中的数字接收机技术,利用大规模可编程门阵列(FPGA),用一块芯片来实现功率分配和大量复相关器的工作,实现了片上系统(SOC),解决了多天线单元合成孔径辐射计相关器系统中存在的体积、重量、功耗和硬件复杂程度过大的问题.通过仿真表明,多路高阶数字相关器系统得到的天线阵列的干涉方向图与模拟相关器系统得到的干涉方向图基本一致,证明该方案可行。 相似文献
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全极化微波辐射计是进行海面风场测量的新型被动式遥感器。数字极化辐射计通过数字相关器对两个极化通道做相关处理,完成四个Stokes矢量参数的测量,反演海面风场。文中提出辐射计核心器件宽带数字相关器的设计方法。双极化通道通过IQ变换转化为两对正交信号,四片国内自主研制的A/D转换器以2.2Ghz采样率采样四路信号,采样结果通过多路复用DEMUX芯片复用后,传输到新一代现场可编程门阵列(FPGA)-Virtex5芯片中作进一步多路复用和相关运算。文中详细介绍了系统结构,数据处理流程和测试结果。 相似文献