机载 LiDAR 点云更新1∶1万 DEM 关键技术探讨

结合 TerraSolid 对机载激光雷达数据进行后处理的生产流程,重点分析利用 LiDAR 数据提取 DEM 的几个关键技术：滤波技术、航带拼接技术、特征线＼特征点参与 DEM 构建技术以及点云人工编辑分类后航带间高差超限的补救性处理方法。     

基于滴谱分布的机载雷达波束匹配情况研究

基于机载双频测雨雷达外场校飞试验中获取的有效降水测量数据,利用Ku波段的雨衰系数和等效雷达反射率因子的比值估算了雨滴谱分布参数.在此基础上,通过米散射模拟计算了Ka波段在该滴谱分布下的等效雷达反射率因子,并和机载Ka波段衰减订正后的等效雷达反射率因子进行了比对.结果表明:两者的廓线基本重合,相关系数超过0.95,两部雷达探测的目标物一致,测量的雷达反射率因子的差异主要是由雷达频率的不同所引起的后向散射以及衰减的不同所造成的,波束匹配精度较高.此外,单频滴谱参数的估计依赖于单频衰减订正的精度.机载雷达外场试验中探测的都是弱降水,Ku波段衰减订正不会存在太大的误差,估计的滴谱较为可靠.必须指出的是,精确的参数估计仍然要借助双频雷达的反演方法.     

Quantifying individual tree growth and tree competition using bi-temporal airborne laser scanning data: a case study in the Sierra Nevada Mountains,California

Improved monitoring and understanding of tree growth and its responses to controlling factors are important for tree growth modeling. Airborne Laser Scanning (ALS) can be used to enhance the efficiency and accuracy of large-scale forest surveys in delineating three-dimensional forest structures and under-canopy terrains. This study proposed an ALS-based framework to quantify tree growth and competition. Bi-temporal ALS data were used to quantify tree growth in height (ΔH), crown area (ΔA), crown volume (ΔV), and tree competition for 114,000 individual trees in two conifer-dominant Sierra Nevada forests. We analyzed the correlations between tree growth attributes and controlling factors (i.e. tree sizes, competition, forest structure, and topographic parameters) at multiple levels. At the individual tree level, ΔH had no consistent correlations with controlling factors, ΔA and ΔV were positively related to original tree sizes (R?>?0.3) and negatively related to competition indices (R?R|?>?0.7), ΔV was positively related to original tree sizes (|R|?>?0.8). Multivariate regression models were simulated at individual tree level for ΔH, ΔA, and ΔV with the R² ranged from 0.1 to 0.43. The ALS-based tree height estimation and growth analysis results were consistent with field measurements.     

Simulated Airborne Flux Measurements in a LES generated Convective Boundary Layer

One aim of past boundary-layer experiments with aircraft was the determination of areally averaged heat fluxes. In spite ofsophisticated instrumentation the measured fluxes extrapolated to the ground differed significantly from fluxes measured directly at ground stations. This studypresents simulated sensible heat flux measurements with aircraft flightsthrough a synthetic convective boundary layer created by a401 × 401 × 42 cubic-grid large eddy simulation (LES) with agrid spacing of 50 m. After some considerations with respect to necessary measurement lengths using results ofLenschow and Stankov (1986 – J. Atmos. Sci. 43, 1198–1209), simulated measurementcampaigns were carried out in three modelruns. During each model run five sets ofmeasurement runs were carried out successively.During each set of runs 10 aircraftflew at 10 altitudes with a ground speedof 100 m s^-1 simultaneously throughtime and space. In total, 150 legs were carried out, 15 at each flight level. The resulting`measured' heat fluxes were compared withthose of the `true' flux profiles obtaineddirectly from the ensemble-averagedLES-generated data. No significant systematic error between `measured' and `true' profiles was observed. Furthermore, the comparison of the resulting relative error with the theory ofLenschow and Stankov showed a good agreement at allmeasurement levels.     

Soil moisture retrieval from airborne L-band passive microwave using high resolution multispectral data

For the soil moisture retrieval from passive microwave sensors, such as ESA’s Soil Moisture and Ocean Salinity (SMOS) and the NASA Soil Moisture Active and Passive (SMAP) mission, a good knowledge about the vegetation characteristics is indispensable. Vegetation cover is a principal factor in the attenuation, scattering and absorption of the microwave emissions from the soil; and has a direct impact on the brightness temperature by way of its canopy emissions. Here, brightness temperatures were measured at three altitudes across the TERENO (Terrestrial Environmental Observatories) Rur catchment site in Germany to achieve a range of spatial resolutions using the airborne Polarimetric L-band Multibeam Radiometer 2 (PLMR2). The L-band Microwave Emission of the Biosphere (L-MEB) model which simulates microwave emissions from the soil–vegetation layer at L-band was used to retrieve surface soil moisture for all resolutions. A Monte Carlo approach was developed to simultaneously estimate soil moisture and the vegetation parameter b’ describing the relationship between the optical thickness τ and the Leaf Area Index (LAI). LAI was retrieved from multispectral RapidEye imagery and the plant specific vegetation parameter b′ was estimated from the lowest flight altitude data for crop, grass, coniferous forest, and deciduous forest. Mean values of b’ were found to be 0.18, 0.07, 0.26 and 0.23, respectively. By assigning the estimated b′ to higher flight altitude data sets, a high accuracy soil moisture retrieval was achieved with a Root Mean Square Difference (RMSD) of 0.035 m³ m⁻³ when compared to ground-based measurements.     

Tomographic airborne ground penetrating radar imaging: Achievable spatial resolution and on-field assessment

Ground Penetrating Radar (GPR) airborne systems are gaining an increasing attention as effective monitoring tools capable of underground investigation of wide areas. With respect to this frame, the paper deals with a reconstruction approach specifically designed to image buried targets from airborne gathered scattered field data. The role of the measurement configuration is investigated in order to address the practical problem of how multi-monostatic and multi-frequency data should be gathered, in terms of synthetic aperture length and frequency range, and how the available data affect the achievable reconstruction capabilities. Such an analysis allows us to evaluate the performance of the reconstruction approach in terms of transversal and depth resolution limits. Finally, an experimental validation of the approach is performed by processing real data.     

时间域航空电磁系统瞬变全时响应正演模拟

近年来很多专家学者致力于时间域航空系统正反演的研究.本文针对一维均匀层状介质和三维模型进行正演.不仅计算垂直方向上的电磁响应,还计算了同线方向上的电磁响应,为航空电磁多分量观测提供理论依据.通过比较航空电磁系统的脉冲响应和阶跃响应特征,发现脉冲响应在早期时间存在奇异性,造成计算不稳定.然而,阶跃响应在早期时间没有奇异性,因而利用系统的阶跃响应可得到一种计算时间域航空电磁系统全时响应的稳定算法.该算法具有较高的精度,并很好地保持了磁场强度B和磁感应dB/dt关系的一致性.该算法推广到三维地质体的时间域正演模拟亦取得很好的效果.     

Blue Earth River quality monitoring using ARCHER hyperspectral data and field measurements

In past decades, remote sensing studies on water quality mapping mainly focused on lakes using medium resolution imagery. Little research utilizes hyperspectral images to assess river water quality. This study aims to assess the capability of using Airborne Real-time Cueing Hyperspectral Enhanced Reconnaissance (ARCHER) for river water quality mapping and to characterize spatial patterns of turbidity and chlorophyll in the Blue Earth River (BER) system of Minnesota. The BER was characterized by both hyperspectral imagery (HSI) and laboratory analysis of synchronously collected water quality data. The optimal bands for water quality mapping were determined using a method based on hyperspectral profiles and derivative analysis. Finally, based on the regression analysis and modelling, we mapped continuous surface water turbidity. The results revealed that the ratio of HSI band 17 to band 9 effectively determined turbidity and chlorophyll concentrations. The study also found that turbidity and chlorophyll in the river generally increases downstream.     

Hyperspectral discrimination of tree species with different classifications using single- and multiple-endmember

Discrimination of tree species with different ages is performed in three classifications using hyperspectral data. The first classification is between Broadleaves and pines; the second classification is between Broadleaves, Corsican Pines, and Scots Pines, and the third classification is between six tree species including different ages of Corsican and Scots Pines. These three classifications are performed by having single- and multiple-endmember and considering five different spectral measure techniques (SMTs) in combination with reflectance spectra (ReflS), first and second derivative spectra. The result shows that using single-endmember, derivative spectra are not useful for a more challenging classification. This is further emphasized in multiple-endmember classification, where all SMTs perform better in ReflS rather than derivative in all classifications. Furthermore, using derivative spectra, discrimination accuracy become more dependent on the type of SMTs, especially in single-endmember. By employing multiple-endmember, the within-species variation is significantly reduced, thereby, the remaining challenge in discriminating tree species with different ages is only due to the between-species similarity. Overall, discrimination accuracies around 92.4, 76.8, and 71.5% are obtained using original reflectance and multiple-endmember for the first, second, and third classification, which is around 14.3, 17, and 8.3% higher than what were obtained in single-endmember classifications, respectively. Also, amongst the five SMTs, Euclidean distance (in both single- and multiple-endmember) and Jeffreys–Matusita distance (in single-endmember and derivative spectra) provided the highest discrimination accuracies in different classifications. Furthermore, when discrimination become more challenging from the first to second and third classification, the performance difference between different SMTs is increased from 1.4 to 3.8 and 7.3%, respectively. The study shows high potential of multiple-endmember to be employed in remote sensing applications in the future for improving tree species discrimination accuracy.     

秭归沙镇溪镇千将坪滑坡航空遥感调查

2003年7月13日千将坪滑坡造成严重的人员伤亡和巨大的经济损失。采用人机交互解译135m高程临蓄水前航摄像片和现场验证相结合的方法获取了千将坪新老滑坡的各要素特征、规模及滑坡前后的地质环境,分析认为千将坪滑坡为老滑坡大部分滑体的复活,目前滑坡整体已基本稳定,但滑体上各部分的调整活动还将继续,东侧边界老滑体遭受了强大的剪切力,滑坡堆积受到严重干扰,近期会不断发生牵引和塌滑。