海洋激光雷达反演水体光学参数

研制了一套船载海洋激光雷达,用于探测海水光学参数垂直廓线。2017年8月,该系统在黄海海域进行了实验测量。在准单次散射模型中引入原位测量的光学参数,实现了理想激光雷达回波信号的模拟,并将该理想信号与系统响应函数卷积后精确复现了实验的激光雷达信号。采用Fernald后向迭代积分法(简称Fernald法),比较了不同水体悬浮物激光雷达比下反演的激光雷达衰减系数α与原位漫射衰减系数Kd的差别。基于停航时标定的水体悬浮物激光雷达比,采用Fernald法获得了走航时的激光雷达衰减系数。进一步地,提出一种基于米散射激光雷达数据和原位测量的后向散射数据的融合算法,模拟了高光谱分辨率激光雷达(HSRL)反演α的过程,并将其与Fernald法进行了比较。实验结果表明,自研的海洋激光雷达能够有效探测海水光学参数,基于合适的水体悬浮物激光雷达比的Fernald法可以有效应用于米散射激光雷达的反演,未来无需假设的HSRL在海水光学参数探测领域具有更大的优势。     

GNSS反射信号海面溢油回波DDM仿真研究

海上溢油已成为影响海洋生态环境的重要污染物之一,我国近40年发生约3200起海上溢油事故。当今用于监测海上溢油的遥感主要是光学和雷达卫星,卫星遥感往往重访周期长,而海上溢油事件时常发生,给海洋带来严重的环境污染,需要快速、准确的监测其状况。GNSS R技术具有全天候监测海洋的特点,因此更适合用于海面溢油检测。为了验证GNSS R技术在检测海面溢油的可行性,利用2013年中国青岛海洋溢油事故的遥感图像的溢油结果,作为仿真实验检测目标,进行岸基的GNSS R海面溢油检测仿真研究。利用Z V散射模型和海水／溢油的均方坡度(MSS)模型结合,建立了能反映海面状况GNSS散射信号特征的时延 多普勒图(DDM)。仿真得到DDM中检测到海面溢油区域,验证了利用GNSS反射信号进行海面溢油检测的可行性。      

偏振激光雷达探测大气—水体光学参数廓线

激光雷达在上层水体垂直廓线的遥感中展现出巨大优势。本文研制了一套高垂直分辨率的实时探测偏振激光雷达,提出了一种基于偏振激光雷达回波信号的反演算法,采用Fernald理论和多次散射原理反演非均匀大气—水体的衰减和退偏光学产品,以高效稳定地处理偏振激光雷达实验数据。展示了一个中国内陆水体激光雷达探测实例,观测到了两次气溶胶积聚现象和一次水体浑浊现象。对实验数据的分析表明,退偏比主要由前向多次散射和后向单次散射产生的退偏两部分组成。当多次散射强度较大时,退偏比的变化主要取决于多次前向散射退偏;反之,则主要依赖于单次后向散射退偏。     

大气遥感双视场米散射激光雷达信号拼接

介绍了一种双视场米散射激光雷达信号拼接方法。主要思想是寻找近场和远场信号都具有高信噪比的最佳拼接区域,求解该区域两种信号之间的函数关系,自动实现激光雷达近场信号与远场信号的有效拼接和反演。拼接结果兼具近场信号探测盲区低和远场信号探测高度高的优点。反演结果表明,该方法能够准确有效地实现双视场信号拼接,并能反演得到高精度的气溶胶光学特性。     

激光雷达回波模型辅助的坡地森林冠层高度反演

大光斑激光雷达数据已广泛应用于森林冠层高度提取,但通常仅限于地形坡度小于20°的平缓地区。在地形坡度大于20°的陡峭山区,地形引起的波形展宽使得地面回波和植被回波信息混合在一起,给森林冠层高度提取带来巨大挑战。本文利用激光雷达回波模型和地形信息,提出了一种模型辅助的坡地森林冠层高度反演算法。该方法以激光雷达回波信号截止点为参考,定义了波形高度指数H50和H75,使用激光雷达回波模型与已知地形信息模拟裸地的激光雷达回波,将裸地回波信号截止点与森林激光雷达回波信号截止点对齐,利用裸地回波计算常用的波形相对高度指数RH50和RH75,对森林冠层高度进行反演。并与高斯波形分解法和波形参数法的反演结果进行了比较。研究结果表明:(1)利用所提取的波形指数RH50和RH75对胸高断面积加权平均高(Lorey’s height)进行了估算,在坡度小于20°时,高斯波形分解法、波形参数法和模型辅助法的估算结果与实测值线性拟合的相关系数(R2)分别为0.70,0.78和0.98,对应的均方根误差(RMSE)分别为2.90 m,2.48 m和0.60 m,模型辅助法略优于其他两种方法;(2)在坡度大于20°时,高斯波形分解法、波形参数法和模型辅助法的R2分别为0.14,0.28和0.97,相应的RMSE分别为4.93 m,4.53 m和0.81 m,模型辅助法明显优于其他两种方法;(3)在0°—40°时,模型辅助法对Lorey’s height估算结果与实测值的R2为0.97,RMSE为0.80 m。本研究提出的模型辅助法具有更好的地形适应性,在0°—40°的坡度范围内具备对坡地森林冠层高度反演的潜力。     

SAR海洋内波表层流反演方法探讨

基于海洋内波SAR成像机理与M4S海面微波散射成像模型,提出SAR海洋内波表层流反演新方法。首先从SAR图像上获得内波剖面的海面后向散射强度,利用AH理论的线性近似关系得到猜测表层流,通过海面微波散射成像模型仿真海洋内波的SAR海面后向散射强度,利用二分法不断地修改风速和流速梯度等参数,使仿真信号最大程度的逼近实际SAR图像上的海面后向散射强度,输出最终海表层流。以中国南海海区3景海洋内波SAR图像为例,对该方法进行了探讨。结果表明,仿真的海洋内波SAR海面后向散射强度剖面和实际SAR图像上的信号剖面吻合,两者的相关系数达90%以上,说明该反演方法是收敛与可行的。     

利用卫星测高数据反演海洋重力异常研究

全面研究了利用卫得测高数据反演海洋重力异常3种主要方法（即Stokes数据解析反解以及逆Vening-Meinesz公式）的技术特点，建立了3种算法的数学模型及其谱计算式，在以1440阶次位模型定义的标准场中完成了3种算法的数值比较和内部检核，通过仿真试验实现了3种算法的可靠性和稳定性检验，最后，本文利用卫得测高实测对南中国海地区的海洋重力异常进行了实际反演，并将反演结果同船测数据进行了比较。     

北斗海上无源定位解析求解新方法

提出一种北斗无源定位解析求解新方法.该方法具有很高的计算效率,并在一定程度上减弱了几何观测图形欠佳对定位精度的影响.仿真计算结果表明,新方法比"三星 高程"法和双曲线解析求解法具有更高的计算效率和定位精度.     

改进的半参数模型法在GNSS时间序列季节性信号提取中的应用

GNSS基准站坐标时间序列具有明显的季节性变化。基于谐波函数模型的最小二乘拟合方法只能得到固定振幅的季节性信号,而真实的季节性信号其振幅是变化的。采用半参数模型进行季节性信号提取时又存在最优平滑因子确定困难、迭代速度慢的问题。提出一种赋相对权比的半参数模型,采用迭代更快速的黄金分割法与改进效率法相结合的策略确定最优平滑因子。通过模拟数据实验,验证了改进模型的可用性。实验表明:改进方法的计算效率明显提高,对于10 a长度的模拟数据,相较GCV函数法搜索速度提高68.1%,相较L-曲线法速度提高25.8%;计算精度较最小二乘法和半参数模型法均有提高,所得残差中没有明显的季节性信号。     

海洋重力异常数据的EGM2008模型插补方法

针对加权平均模型中反映信号区域性变化特征的权系数不易确定的问题,提出了利用EGM2008模型计算的重力异常数据表示重力场的趋势性变化以改进传统的加权平均法。基本步骤是利用实测海洋重力异常数据,借助EGM2008全球重力位模型,在移去-恢复技术框架下内插出残差重力异常数据,进而得到内插点的海洋空间重力异常。海区实测数据分析结果表明,本文所述方法计算的内插值,无论是分布情况还是与实测值差值的大小,都明显优于传统的加权平均法。     

海潮对高精度GPS网的影响初探

本文叙述了海洋负荷潮改正的基本原理，结合算例分析了海潮对GPS网的影响，结果显示：对于近海地区较短时段的GPS观测，考虑海潮负荷改正可以明显地提高解算精度，特别对改善高程方向的精度贡献明显。影响可达数厘米，这种影响的量级对水平方向不明显；对于远离海洋地区，海潮负荷改正的影响已不明显，可以不与考虑。     

Assessing the influence of return density on estimation of lidar-based aboveground biomass in tropical peat swamp forests of Kalimantan,Indonesia

The airborne lidar system (ALS) provides a means to efficiently monitor the status of remote tropical forests and continues to be the subject of intense evaluation. However, the cost of ALS acquisition can vary significantly depending on the acquisition parameters, particularly the return density (i.e., spatial resolution) of the lidar point cloud. This study assessed the effect of lidar return density on the accuracy of lidar metrics and regression models for estimating aboveground biomass (AGB) and basal area (BA) in tropical peat swamp forests (PSF) in Kalimantan, Indonesia. A large dataset of ALS covering an area of 123,000 ha was used in this study. This study found that cumulative return proportion (CRP) variables represent a better accumulation of AGB over tree heights than height-related variables. The CRP variables in power models explained 80.9% and 90.9% of the BA and AGB variations, respectively. Further, it was found that low-density (and low-cost) lidar should be considered as a feasible option for assessing AGB and BA in vast areas of flat, lowland PSF. The performance of the models generated using reduced return densities as low as 1/9 returns per m² also yielded strong agreement with the original high-density data. The use model-based statistical inferences enabled relatively precise estimates of the mean AGB at the landscape scale to be obtained with a fairly low-density of 1/4 returns per m², with less than 10% standard error (SE). Further, even when very low-density lidar data was used (i.e., 1/49 returns per m²) the bias of the mean AGB estimates were still less than 10% with a SE of approximately 15%. This study also investigated the influence of different DTM resolutions for normalizing the elevation during the generation of forest-related lidar metrics using various return densities point cloud. We found that the high-resolution digital terrain model (DTM) had little effect on the accuracy of lidar metrics calculation in PSF. The accuracy of low-density lidar metrics in PSF was more influenced by the density of aboveground returns, rather than the last return. This is due to the flat topography of the study area. The results of this study will be valuable for future economical and feasible assessments of forest metrics over large areas of tropical peat swamp ecosystems.     

利用水位修正模型精化潮位数值模拟

利用海洋动力模式FVCOM（finite volume coast and ocean model）模式建立了高分辨率的海州湾及其外海域潮汐数值模型,提取了整个场内各个网格点上天文潮位值的时间序列。利用该区域内分布的5个验潮站资料提取水位修正模型,对场内的网格点进行水位修正,得到高精度的格点水位时间序列,然后对修正前后的水位值进行比较。结果表明,基于水位修正后的潮位数值模拟结果水位精度提高了10 cm左右。     

面向森林植被的星载大光斑激光雷达回波仿真

利用星载激光雷达的大光斑全波形数据估测植被结构参数、监测森林生态已受到广泛关注。为了更准确地理解森林植被的结构参数和光学特性对激光雷达回波波形的影响,利用实测森林植被数据提取植被空间分布的统计规律,考虑地形坡度变化和植被冠层反射特性的影响,生成参数化的森林植被空间轮廓反射模型,结合星载激光雷达的回波理论,建立了面向植被的星载激光雷达波形仿真器。由大兴安岭地区的实测植被数据提取的统计规律生成的森林目标仿真波形与地球科学激光测高仪系统（Geoscience Laser Altimeter System,GLAS）真实回波波形具有较好的一致性,平均相关系数R2达到0.91。通过波形仿真分析发现,光斑尺寸减小有利于大坡度地形的森林信息反演,研究成果对中国未来研制星载激光雷达载荷的系统参数设计具有参考意义。     

Chronology and backtracking of oil slick trajectory to source in offshore environments using ultraspectral to multispectral remotely sensed data

Offshore natural seepage confirms the occurrence of an active petroleum system with thermal maturation and migration, regardless its economic viability for petroleum production. Ocean dynamics, however, impose a challenge for correlation between oil seeps detected on the water surface and its source at the ocean floor. This hinders the potential use of seeps in petroleum exploration. The present study aims to estimate oil exposure time on the water surface via remote sensing in order to help locating ocean floor seepage sources. Spectral reflectance properties of a variety of fresh crude oils, oil films on water and oil–water emulsions were determined. Their spectral identity was used to estimate the duration of exposure of oil–water emulsions based on their temporal spectral responses. Laboratory models efficiently predicted oil status using ultraspectral (>2000 bands), hyperspectral (>300 bands), and multispectral (<10 bands) sensors covering near infrared and shortwave infrared wavelengths. An oil seepage recorded by the ASTER sensor on the Brazilian coast was used to test the designed predictive model. Results indicate that the model can successfully forecast the timeframe of crude oil exposure in the ocean (i.e., the relative “age” of the seepage). The limited spectral resolution of the ASTER sensor, though, implies less accurate estimates compared to higher resolution sensors. The spectral libraries and the method proposed here can be reproduced for other oceanic areas in order to approximate the duration of exposure of noticeable natural oil seepages. This type of information is optimal for seepage tracing and, therefore, for oceanic petroleum exploration and environmental monitoring.     

Assimilation of Earth rotation parameters into a global ocean model: length of day excitation

Changes in the oceanic current system and in the oceanic mass distribution alter, together with other processes, the state of the Earth’s rotation. This state is characterized by the length of day (LOD) and the tilt of the pole-to-pole axis. The aim of our study was to derive the respective governing physical mechanisms in the ocean. Therefore, Earth rotation observations were assimilated into a global circulation model of the ocean. Although assimilation is a well-established tool in climate science, the assimilation of Earth rotation observations into a global ocean model was done here for the first time. Prior to the assimilation, the Earth rotation observations were projected onto the angular momentum of the ocean. Non-oceanic contributions were removed. The result of the subsequent assimilation procedure is a time varying ocean model state that reproduces the projected Earth rotation observations well. This solution was studied to understand the oceanic generation of Earth rotation deviations and to identify governing physical mechanisms. This paper focuses on LOD anomalies although polar motion was assimilated simultaneously. Our results indicate that changes in the oceanic LOD excitation are mostly attributed to changes in total ocean mass. Changes in the spatial distribution of ocean mass turned out to have a minor contribution to the LOD deviations. The same applies to changes in the current system.     

合成孔径高度计的海面回波仿真

本文首先采用经验海浪谱仿真了三维海面,进而在此基础上根据镜面反射理论计算了海面小面元散射系数。然后根据雷达方程和合成孔径高度计的合成孔径处理计算了海面回波信号的矩阵,以便给出最终的功率回波。在目前国内外缺少相应试验数据的条件下,验证了合成孔径高度计工作方式的有效性,经验证其回波模型基本正确。同时,为了与传统高度计比较,给出了传统高度计在相同参数下的回波仿真结果。文章还通过展示合成孔径高度计在同种波高、不同涌浪和风浪方向情况下的回波,说明波浪方向也会影响合成孔径高度计回波。     

Accuracy assessment of lidar-derived digital elevation models

Despite the relatively high cost of airborne lidar-derived digital elevation models (DEMs), such products are usually presented without a satisfactory associated estimate of accuracy. For the most part, DEM accuracy estimates are typically provided by comparing lidar heights against a finite sample of check point coordinates from an independent source of higher accuracy, supposing a normal distribution of the derived height differences or errors. This paper proposes a new methodology to assess the vertical accuracy of lidar DEMs using confidence intervals constructed from a finite sample of errors computed at check points. A non-parametric approach has been tested where no particular error distribution is assumed, making the proposed methodology especially applicable to non-normal error distributions of the type usually found in DEMs derived from lidar. The performance of the proposed model was experimentally validated using Monte Carlo simulation on 18 vertical error data-sets. Fifteen of these data-sets were computed from original lidar data provided by the International Society for Photogrammetry and Remote Sensing Working Group III/3, using their respective filtered reference data as ground truth. The three remaining data-sets were provided by the Natural Environment Research Council's Airborne Research and Survey Facility lidar system, together with check points acquired using high precision kinematic GPS. The results proved promising, the proposed models reproducing the statistical behaviour of vertical errors of lidar using a favourable number of check points, even in the cases of data-sets with non-normally distributed residuals. This research can therefore be considered as a potentially important step towards improving the quality control of lidar-derived DEMs.