Dim prospects for radar detection of Europa's ocean

The thickness of a porous regolith on Europa is estimated to be ∼1 km. Provided that this regolith contains as little as 1% by volume of cavities with sizes comparable to the radar wavelength, its presence poses an insurmountable obstacle in the search for Europa's ocean by means of a sounding radar.     

Abrupt alteration of Asteroid 2004 MN4's spin state during its 2029 Earth flyby

We predict that when Asteroid 2004 MN4 passes 5.6±1.4 Earth radii from Earth's center on April 13, 2029, terrestrial torques during the flyby will alter its spin state in a dramatic manner that will be observable using groundbased telescopes. Although the asteroid will most likely not undergo catastrophic disruption, it may be subject to localized failure across its surface and interior, providing a unique opportunity to measure otherwise inaccessible mechanical properties of an asteroid.     

Investigating the correlation between radar backscatter and in situ soil property measurements

Utilizing remote sensing techniques to extract soil properties can facilitate several engineering applications for large-scale monitoring and modeling purposes such as earthen levees monitoring, landslide mapping, and off-road mobility modeling. This study presents results of statistical analyses to investigate potential correlations between multiple polarization radar backscatter and various physical soil properties. The study was conducted on an approximately 3 km long section of earthen levees along the lower Mississippi river as part of the development of remote levee monitoring methods. Polarimetric synthetic aperture radar imagery from UAVSAR was used along with an extensive set of in situ soil properties. The following properties were analyzed from the top 30–50 cm of soil: texture (sand and clay fraction), penetration resistance (sleeve friction and cone tip resistance), saturated hydraulic conductivity, field capacity, permanent wilting point, and porosity. The results showed some correlation between the cross-polarized (HV) radar backscatter coefficients and most of these properties. A few soil properties, like clay fraction, showed similar but weaker correlations with the co-polarized channels (HH and VV). The correlations between the soil properties and radar backscatter were analyzed separately for the river side and land side of the levee. It was found that the magnitude and direction of the correlation for most of the soil properties noticeably differed between the river and the land sides. The findings of this study can be a good starting point for scattering modelers in a pursuit of better models for radar scattering at cross polarizations which would include more diverse set of soil parameters.     

合成孔径雷达对地观测应用中目标感兴趣区域的自动获取

在简要评述国内外对地观测应用中,利用SAR图像进行目标ROI的自动获取方面的研究成果及存在问题的基础上,提出了一种SAR图像目标ROI自动获取新方案,包括SAR图像自动目标检测方案和SAR图像自动目标鉴别方案并解决其中的关键技术。实测数据的实验结果证明了新方案具有稳健性强、适用性广、自动化程度高、计算量小、工程实现易等特点,说明了该方案对于空间对地观测具有广泛的应用前景。     

华中区域LRUC系统的构建与试验

如何将区域观测资料在中尺度模式中快速有效同化是提高区域精细化数值预报准确率和时效性的关键所在。本文简单介绍了基于LAPS和WRF建立的快速循环同化预报系统LRUC,以一次影响长江中游的典型梅雨锋暴雨过程为例,设计几种试验方案,结合实况降水分布,对比分析华中区域多普勒雷达资料循环同化对改善暴雨预报的作用;根据个例试验结果,设计批量后报试验方案,对比分析雷达资料同化对华中区域2007年主汛期(6—8月)多个时效降水预报评分。暴雨个例试验结果表明,华中区域多普勒雷达资料在LAPS中的同化,能为WRF提供更优初值场;同化华中区域地面资料和雷达资料后,比仅同化地面资料更能改进模式初值,改善模式降水预报,且降雨量级越大,24 h降水预报TS评分越高。批量后报试验结果表明,建立的快速循环同化预报系统LRUC,能对区域多源观测资料进行多时次循环同化分析,为模式初值增加观测资料的时间演变信息,提高模式对暴雨量级降水的预报水平;系统具有稳定性和一定的评分水平。     

基于雷达四维变分分析系统的强对流高分辨率模拟个例分析和批量检验

利用以雷达资料快速更新四维变分同化(RR4DVar)技术和三维数值云模式为核心的模拟分析系统,通过同化京津冀区域6部新一代天气雷达逐6 min的径向速度和反射率因子资料,并融合区域自动站逐5 min观测和中尺度数值模式结果,对发生在京津冀地区的18个对流风暴"事件"进行了高分辨率数值模拟,开展了个例分析和全部模拟结果的检验评估。个例分析结果表明,模拟的低层三维动力、热动力和水汽特征可以明确解释复杂地形条件下对流风暴的局地新生、组织化和线状中尺度对流系统(MCS)的形成。高分辨率模拟结果也明确指示了线状中尺度对流系统中对流风暴单体不断新生(再生)和"后向传播"的机制,以及地形强迫在风暴形成和演变中的重要作用。基于一部风廓线雷达、两部地基微波辐射计、一个秒级探空和一个边界层观测塔等局地高频非常规观测数据对18个对流风暴"事件"模拟结果的检验表明,0-3 km的风速、风向和温度的模拟误差(包括偏差和均方根误差)总体较小。其中,最低模式层(187.5 m)风速偏差和均方根误差分别在-0.5和0.9 m/s以内,最高检验层(2.8125 km)风速偏差和均方根误差分别在-0.9和1.6 m/s以内,风速误差随高度逐渐增大;风向偏差在14°-22°,风向均方根误差小于38°;温度偏差和均方根误差分别在-1和1.8℃以内。系统模拟的低层风速、风向和温度的偏差和均方根误差在对流风暴内部稍大于外部。上述研究表明,该系统模拟结果对对流风暴生消、发展及生命史特征的临近预报和预警具有重要指示意义。     

贵州威宁边界层风廓线雷达与L波段探空雷达的风向风速一致性初探

利用2019年6月至12月威宁县边界层风廓线雷达数据和威宁探空数据,预设二者风速偏差<=3m/s、风向偏差<=20°为有效数据样本,研究两者在不同风速、风向范围和不同高度、时次、降水条件下风向、风速数据对比及相关性分析。结果表明：（1）风廓线雷达和探空的风速、风向均具有较好的正向相关性;（2）在不同高度下,且无论有无降水或任意时次,风速有效样本比率大体上高于风向有效样本比率,500米左右高度以下有效样本比率总是最小（不足50%）,而中高层较大;（3）不同时次对风速、风向数据有效性影响不大;（4）有降水时风速、风向有效样本比率比无降水时偏小且变化剧烈;（5）除东北（20°-40°）和西南（200°-260°）风向外,其他方位风向数据一致性较差;（6）除大于24m/s的风速外其他大小风速均具有较好的一致性。     

Radar absorption due to a corotating interaction region encounter with Mars detected by MARSIS

Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) is a subsurface and topside ionosphere radar sounder aboard the European Space Agency spacecraft Mars Express, in orbit at Mars since 25 December 2003, and in operation since 17 June 2005. The ionospheric sounding mode of MARSIS is capable of detecting the reflection of the sounding wave from the martian surface. This ability has been used in previous work to show that the surface reflection is absorbed and disappears during periods when high fluxes of energetic particles are incident on the ionosphere of Mars. These absorption events are believed to be the result of increased collisional damping of the sounding wave, caused by increased electron density below the spacecraft, in turn caused by impact ionization from the impinging particles. In this work we identify two absorption events that were isolated during periods when the surface reflection is consistently visible and when Mars is nearly at opposition. The visibility of the surface reflection is viewed in conjunction with particle and photon measurements taken at both Mars and Earth. Both absorption events are found to coincide with Earth passing through solar wind speed and ion flux signatures indicative of a corotating interaction region (CIR). The two events are separated by an interval of approximately 27 days, corresponding to one solar rotation. The first of the two events coincides with abruptly enhanced particle fluxes seen in situ at Mars. Simultaneous with the particle enhancement there are an abrupt decrease in the intensity of electron oscillations, typically seen by the Mars Express particle instrument ASPERA-3 between the magnetic pileup boundary and the martian bow shock, and a sharp drop in the solar wind pressure, seen in the proxy quantity based on MGS magnetometer observations. The decrease in oscillation intensity is therefore the probable effect of a relaxation of the martian bow shock. The second absorption event does not show a particle enhancement and complete ASPERA-3 data during that time are unavailable. Other absorption events are the apparent result of solar X-ray and XUV enhancements. We conclude that surface reflection absorption events are sometimes caused by enhanced ionospheric ionization from high energy particles accelerated by the shocks associated with a CIR. A full statistical analysis of CIRs in relation to observed absorption events in conjunction with a quantitative analysis of the deposition of ionization during space weather events is needed for a complete understanding of this phenomenon. If such analyses can be carried out, radar sensing of the martian ionosphere might be useful as a space weather probe.     

Radarclinometry of the sand seas of Africa’s Namibia and Saturn’s moon Titan

Radarclinometry is a powerful technique for estimating heights of landforms in synthetic aperture radar (SAR) images of planetary surfaces. In particular, it has been used to estimate heights of dunes in the sand seas of Saturn’s moon Titan (Lorenz, R.D., and 39 colleagues [2006]. Science 312, 724-727). In this work, we verify the technique by comparing dune heights derived from radarclinometry to known topography of dune fields in the Namib sand sea of western Africa. We compared results from three different image grid spacings, and found that 350 m/pixel (the same spacing at which the Cassini RADAR data was processed) is sufficient to determine dune height for dunes of similar morphometry to those of the Namib sand sea. At this grid spacing, height estimates derived from radarclinometry are largely representative of, though may underestimate by as much as 30%, or overestimate by as much as 40%, true dune height. Applying the technique to three regions on Titan, we estimate dune heights of 45-180 m, and dune spacings of 2.3-3.3 km. Obtaining accurate heights of Titan’s dunes will help to constrain the total organic inventory on Titan.     

Spatial conservation planning framework for assessing conservation opportunities in the Atlantic Forest of Brazil

Historic rates of habitat change and growing exploitation of natural resources threaten avian biodiversity in the Brazilian Atlantic Forest, a global biodiversity hotspot. We implemented a twostage framework for conservation planning in the Atlantic Forest. First, we used ecological niche modeling to predict the distributions of 23 endemic bird species using 19 climatic metrics and 12 spectral and radar remote sensing metrics. Second, we utilized the principle of complementarity to prioritize new sites to augment the Atlantic Forest's existing reserves. The best predictors of bird distributions were precipitation metrics (the seasonality of rainfall) and radar remote sensing metrics (QSCAT). The existing protected areas do not include 10% of the habitat of each of the 23 endemic species. We propose a more economical set of protected areas by reducing the extent to which new sites duplicate the biodiversity content of existing protected areas. There is a high concordance between the proposed conservation areas that we designed using computerized algorithms and Important Bird Areas prioritized by BirdLife International. Insofar as deforestation in the Atlantic Forest is similar to land conversion in other biodiversity hotspots, our methodology is applicable to conservation efforts elsewhere in the world.