基于二次多项式拟合的超短基线声线修正方法

超短基线定位解算中的距离观测值是指换能器与水下应答器之间的直线距离,而海水声速的不均匀分布导致声波在海水中的实际传播路径为连续弯曲的曲线,需要结合实测声速剖面进行声线修正。根据声速在分层介质中的传播特性,本文提出了一种基于二次多项式拟合的声线跟踪算法,采用线性插值方法对声速剖面数据进行合理加密并按等深度进行分层,设定每层声速梯度是不断变化的,用二次多项式拟合声速,基于运动学原理建立了完整的数学解算模型。仿真结果表明,该方法修正后的水下目标分布具有明显的收敛性,且优于等梯度声线跟踪算法和等效声速剖面法,显著提高了超短基线水声定位系统的定位精度。     

基于长基线系统深海采矿ROV精确定位

对于深海采矿集矿机ROV的定位,采用传统的长基线水声定位系统通常存在较大误差。对此提出了一种新的算法模型,首先通过比较集矿机测量位置与前一次修正位置的几何关系,对当前集矿机的位置进行修正,然后利用新的集矿机位置修正声速的数值,并得出重新修正后的集矿机测量位置。这样反复的多重迭代使得在某一时刻集矿机ROV的测量位置逐步趋近其理想位置,实现长基线系统的水声精确的三维立体定位。通过数值仿真分析,结果显示与传统的长基线水声定位方法相比,通过该方法获得的集矿机行驶轨迹能更好地趋近其理想行驶曲线,表明该算法的有效性。     

Methanol masers and their environment at high resolution

We have used the Australia Telescope Compact Array (ATCA) to make high-resolution images of the 6.7-GHz 5₁ → 6₀A⁺ maser transition of methanol towards 33 sources in the Galactic plane. Including the results from 12 methanol sources in the literature, we find that 17 out of 45 sources have curved or linear morphology. Most of the 17 have a velocity gradient along the line, which is consistent with masers lying in an edge-on circumstellar disc surrounding a massive star. We also made simultaneous continuum observations of the sources at 8.6 GHz, in order to image any associated H  ii region. 25 of the sources are associated with an ultracompact H  ii region, with a detection limit of ∼0.5 mJy beam⁻¹. We argue that the methanol sources without an associated H  ii region represent less massive embedded stars, not an earlier stage in the lifetime of the star, as previously suggested.     

GPS在遥感信息对地定位应用中的试验研究

1990年7—11月由中国科学院遥感应用研究所,北京航空航天大学,清华大学,航空航天部三院,北京工业大学组成的GPS联合试验组在北京地区进行了机载GPS定位试验,取得了满意的结果。 本文从分析遥感信息对地定位的现状和存在问题入手,确定本试验研究的目标,介绍三次机载GPS飞行试验情况和取得的结果,最后展望了GPS技术在遥感中应用的前景。     

The Planck Surveyor mission and gravitational lenses

An extremely sensitive all-sky survey will be carried out in the millimetre/submillimetre waveband by the forthcoming ESA mission Planck Surveyor . The main scientific goal of the mission is to make very accurate measurements of the spatial power spectrum of primordial anisotropies in the cosmic microwave background radiation; however, hundreds of thousands of distant dusty galaxies and quasars will also be detected. These sources are much more likely to be gravitationally lensed by intervening galaxies compared with sources discovered in surveys in other wavebands. Here the number of lenses expected in the survey is estimated, and techniques for discriminating between lensed and unlensed sources are discussed. A practical strategy for this discrimination is presented, based on exploiting the remarkable sensitivity and resolving power of large ground-based millimetre/submillimetre-wave interferometer arrays. More than a thousand gravitational lenses could be detected: a sample that would be an extremely valuable resource in observational cosmology.     

长三角区域对流层延迟简易模型的建立

在对流层经验模型Saastamoinen模型和EGNOS模型的基础上,通过对长三角地区近40年气象规律的研究,总结了温度、气压、相对湿度相对于年积日的函数关系,建立了适用于长三角区域的对流层天顶延迟的简易模型。通过实验验证了该模型的有效性,该模型输入参数是年积日,不仅方便快捷,还提高了经验模型的精度,为更精确的区域模型研究提供了参考。     

Centimeter-Level Positioning of Seafloor Acoustic Transponders from a Deeply-Towed Interrogator

An array of three seafloor transponders was acoustically surveyed to centimeter precision with a deeply-towed interrogator. Measurements of two-way acoustic travel time and hydrostatic pressure made as the interrogator was towed above the array were combined in a least-squares adjustment to estimate the interrogator and transponder positions in two surveys spanning two years. No transponder displacements were expected at this site in the interior of the Juan de Fuca Plate (48^?11′ N, 127^?12′ W) due to the lack of active faults. This was confirmed to a precision of ±2 cm by least-squares adjustment. Marginally detectable blunders in the observations were shown to affect the transponder position estimates by no more than 3 mm, demonstrating the geometric strength of the data set. The accumulation of many hundreds of observations resulted in a significant computational burden on the least-squares inversion procedure. The sparseness of the normal matrix was exploited to reduce by a factor of 1000 the number of calculations. The acoustic survey results suggested that the near-bottom sound speed fields during the two surveys were in better agreement than inferred from yearly single-profile conductivity, temperature, and pressure (CTD) measurements.