基于MODIS与GPS的D-InSAR大气延迟改正量提取

受GPS站点密度的限制,利用GPS数据改正D-InSAR中大气延迟误差往往达不到很好的效果。为此,研究了GPS与MODIS联合实现大气延迟改正量提取方法,利用两期GPS观测数据及相应时间的MODIS数据分析GPS-PWV与MODIS-PWV的关系,进一步得到MODIS水汽的校正模型。经过GPS+MODIS算法改正后,大气延迟改正精度为3.618mm,满足形变测量的要求。实验结果表明:在大气状态变化缓慢时,利用GPS结合MODIS数据对D-InSAR大气延迟改正有一定的效果。     

基于RPC模型的高分辨率卫星影像精确定位

介绍高分辨率卫星影像RPC模型的定义及其解算方法,推导RPC模型立体定位的基本方程,在此基础上对RPC模型的区域网平差进行深入研究。IKONOS卫星数据的实验结果表明,RPC模型误差呈现较强的系统性,但通过物方或像方的补偿立体定位可达到优于1.3 M的定位精度,区域网平差是最优的定位方法,精度可达1.1 M。     

RIEMS2.0模式提高分辨率对中国气温模拟能力的影响

利用区域环境集成系统模式(RIEMS2.0)在60 km和30 km两种分辨率下进行中国区域的长期模拟试验(1991~2000年),开展不同分辨率下中国气温平均气候态和年际变率的模拟能力分析研究。结果表明:(1)RIEMS2.0能较好模拟出多数分区多年平均气温的空间分布,与观测空间分布较接近。随着水平分辨率的提高,模式模拟的气温空间分布模拟更精细,使得平均气温的模拟冷偏差减小,模拟结果更趋于实测。对年均温和冬季气温来说,中国及多数分区模拟与观测的偏差减少,且通过显著性检验(P0.01);对夏季气温来说,中国及多数分区的偏差增加,气温的模拟能力没有明显提高。(2)对年际变率来说,随着水平分辨率的提高,大部分区域模拟能力有一定程度的提高。特别是年均温和冬季气温的年际变率,多数地区模拟改进效果较好;而夏季气温年际变率的模拟在中国大部分地区没有明显改善。     

基于CCD提高射电望远镜极轴校准精度及修正

射电望远镜极轴的安装定位是否准确直接影响其指向精度和成像质量,通过运用光学CCD原理精确测量射电望远镜极轴偏差角度,用以安装校准极轴,达到提高射电望远镜指向精度和成像质量的效果,并且结合计算机可实现多极轴同时校准,提高工作效率。同时,基于CCD技术可以及时发现天线极轴出现的偏差并进行修正,提高了数据的质量。     

A numerical comparison of time and frequency‐domain marine electromagnetic methods for hydrocarbon exploration in shallow water

In shallow water the frequency domain controlled source electromagnetic method is subject to airwave saturation that strongly limits the sensitivity to resistive hydrocarbon targets at depth. It has been suggested that time‐domain CSEM may offer an improved sensitivity and resolution of these deep targets in the presence of the airwave. In order to examine and test these claims, this work presents a side‐by‐side investigation of both methods with a main focus on practical considerations, and how these effect the resolution of a hydrocarbon reservoir. Synthetic noisy data for both time‐domain and frequency domain methods are simulated using a realistic frequency dependent noise model and frequency dependent scaling for representative source waveforms. The synthetic data studied here include the frequency domain response from a compact broadband waveform, the time‐domain step‐response from a low‐frequency square wave and the time‐domain impulse response obtained from pseudo‐random binary sequences. These data are used in a systematic resolution study of each method as a function of water‐depth, relative noise and stacking length. The results indicate that the broadband frequency domain data have the best resolution for a given stacking time, whereas the time‐domain data require prohibitively longer stacking times to achieve similar resolution.     

Comparison of ground- and aerial-based approaches for quantifying polygonal terrain network geometry on Earth and Mars via spatial point pattern analysis

Recently, a particular statistical method - spatial point pattern analysis (SPPA) - has been introduced as an effective means by which qualitative, observable variations in polygonal terrain network arrangements on Earth and Mars can be quantified. A number of ground- and aerial-based techniques are available from which to derive the required input data: the spatial (x-y) coordinates of all polygon trough intersections within the site. However, each of the data collection methods may contain some level of error. Thus, the overarching question addressed by this research is: “how are the results of SPPA affected by the method by which the input data were generated?” At two polygonal terrain sites in the Canadian High Arctic, we performed ground-based surveys using differential and non-differential Global Positioning Systems (GPS) as well as photogrammetric analysis of aerial and satellite images of varying resolution to determine the trough intersection coordinates. It was found that the most robust statistical results were produced when using data from a combination of differential GPS surveys and high-resolution (∼0.25 m/pixel) aerial images. Images of pixel size ≥1 m were found to be unsuitable for this type of analysis. With respect to the investigation of similar Martian landforms, HiRISE and MOC images of polygonal terrain sites in southwestern Utopia Planitia were analyzed. Our results show that it is strongly preferable to perform SPPA using HiRISE images, though an empirical model is outlined that could be used to correct for errors arising from the reduced resolution inherent to MOC images.     

大规模脉冲星候选体信号的无监督聚类分析研究

随着500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical radio Telescope, FAST)等大型射电望远镜的建设和使用,脉冲星巡天数据进入PB时代.为解决如此大量高速采样的标量数据挖掘问题,促进新天文现象的发现,提出一种基于无监督聚类的脉冲星候选体筛选方案.该方案采用基于密度层次、划分方法的混合聚类算法,结合MapReduce/Spark并行计算模型和基于滑动窗口的分组策略,进而提高大量候选体信号筛选的效率.通过在脉冲星数据集HTRU2 (High Time Resolution Universe)上的对比实验,结果表明该算法能取得较高的精确度和召回率,分别是0.946和0.905,并且当并行节点足够时,该算法的时间复杂度相比串行执行明显下降.可见,该方法为脉冲星观测大数据的分析挖掘提供一种可行思路.     

利用Hilbert变换计算重力归一化总梯度

针对提高重力勘探正反演解释的分辨率问题,提出利用Hilbert变换计算和研究重力归一化总梯度.文中从理论上详细地证明了方法的可行性,给出了适合计算机实现的计算方法.为探讨该方法对油气藏的分辨能力,在模型计算中,分别利用Fourier级数法、Fourier变换法和本文提出的Hilbert变换法计算模型的GH场值,发现当三度体储油球冠模型（模拟似三度贮油气藏背斜模型）油气藏部分（低密度体）厚度减小到低于球冠厚度的十分之一时,Fourier级数及变换法不能分辨出低密度体所产生的异常,而Hilbert变换法仍然可以清晰地识别,这说明用Hilbert变换法计算的GH场对异常识别的分辨率优于其他两种方法.     

A Modified Becker''s Split-Window Approach for Retrieving Land Surface Temperature from AVHRR and VIRR

In order to provide a long time-series, high spatial resolution, and high accuracy dataset of land surface temperature (LST) for climatic change research, a modified Becker and Li's split-window approach is pro- posed in this paper to retrieve LST from the measurements of Advanced Very High Resolution Radiometer (AVHRR) onboard National Oceanic and Atmospheric Administration (NOAA)-7 to -18 and the Visible and InfraRed Radiometer (VIRR) onboard FY-3A. For this purpose, the Moderate Resolution Transmittance Model (MODTRAN) 4.1 was first employed to compute the spectral radiance at the top of atmosphere (TOA) under a variety of surface and atmosphere conditions. Then, a temperature dataset consists of boundary temperature Ts (which is one of the input parameters to MODTRAN), and channels 4 and 5 brightness temperatures (T4 and T5) were constructed. Note that channels 4 and 5 brightness tempera- tures were simulated from the MODTRAN output spectral radiance by convolving them with the spectral response functions (SRFs) of channels 4 and 5 of AVHRRs and VIRR. The coefficients of modified Becker and Li's split-window approach for various AVHRRs and VIRR were subsequently regressed based on this temperature dataset using the least square method. As an example of validation, one AVHRR satellite image over Beijing acquired at 0312 UTC 27 April 2008 by AVHRR onboard NOAA-17 was selected to retrieve the LST image using the modified Becker and Li's approach. The comparison between this LST image and that from the MODIS level-2 LST product provided by the University of Tokyo in Japan indicates that the correlation coefficient is 0.88, the bias is 0.6 K, and the root mean square deviation (RMSD) is 2.1 K. Furthermore, about 70% and 37% pixels in the LST difference image, which is the result of retrieved LST image from AVHRR minus the corresponding MODIS LST image, have the values within ±2 and ±1 K, respectively.