Cloud height determination using satellite stereoscopy from Along Track Scanning Radiometer onboard ERS-1 satellite: A simulation study

The first ERS-1 satellite launched in May 1991 promises to make a substantial contribution towards the cloud stereoscopy. One of its payload, Along Track Scanning Radiometer (hereafter ATSR) has IR split window channels and scans the earth conically leading to earth views at two view angles (0° and 55°) in two curved swaths registered with respect to each other in image frame. This enables us to construct stereoscopic image of a cloud thereby determining its height geometrically. The present paper describes the utility of ATSR onboard ERS-1 in retrieving cloud height by synthetic stereo imaging over NOAA-AVHRR visible and thermal band observations.     

Gravity field determination from satellite gradiometry

An orbiting gradiometer measures simultaneously several gravity quantities, ideally all six second-order derivatives of the gravitational potential. These contain information on the orbit, on the structure of the gravity field, and on the attitude of the space-craft. Due to the availability of several components simultaneously it is possible to separate orbit determination from attitude or gravity field recovery. This facilitates the analysis of the gradiometer measurements and allows the use of the principles of fast spherical harmonic analysis. The separation of gravity field recovery and orbit determination is tested numerically with a simplified gravity field (with a purely zonal spherical harmonic expansion) up to degree 300. For both the potential coefficients and for the orbit an almost exact recovery is attained after two iteration steps.     

PARASOL/POLDER3卫星数据的海洋上空云检测

在卫星海洋遥感中,云作为海气耦合系统最重要的调节器之一,其检测结果对海洋上空云微物理特性的反演精度有较大影响。因此,快速而准确识别海洋上空的云像元是卫星遥感数据处理过程中首要解决的关键问题。以PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar)卫星搭载的POLDER3载荷遥感数据为研究对象,提出一种改进的海洋上空云检测方法。首先剔除海洋耀光;接着利用有云与晴空区近红外反射率差异检验识别有云像元,并利用偏振反射率检验进一步识别低反射率的云像元;然后利用近红外与可见光反射率比值检验识别晴空像元;最后建立多角度云检测结果空间融合规则,重新标记有云、晴空和未定像元。以印度洋海区为例进行实验分析,将云检测结果与Buriez方法进行对比,发现检测精度基本相当,而有云像元的识别速度却平均提高约3倍。结果表明:该方法能有效的检测出海洋上空的云像元,满足业务化数据处理的高精度及时效性要求,为后续云微物理特性反演提供可靠的数据源。     

Regularization of geopotential determination from satellite data by variance components

 Different types of present or future satellite data have to be combined by applying appropriate weighting for the determination of the gravity field of the Earth, for instance GPS observations for CHAMP with satellite to satellite tracking for the coming mission GRACE as well as gradiometer measurements for GOCE. In addition, the estimate of the geopotential has to be smoothed or regularized because of the inversion problem. It is proposed to solve these two tasks by Bayesian inference on variance components. The estimates of the variance components are computed by a stochastic estimator of the traces of matrices connected with the inverse of the matrix of normal equations, thus leading to a new method for determining variance components for large linear systems. The posterior density function for the variance components, weighting factors and regularization parameters are given in order to compute the confidence intervals for these quantities. Test computations with simulated gradiometer observations for GOCE and satellite to satellite tracking for GRACE show the validity of the approach. Received: 5 June 2001 / Accepted: 28 November 2001     

Energy integral method for gravity field determination from satellite orbit coordinates

A fast iterative method for gravity field determination from low Earth satellite orbit coordinates has been developed and implemented successfully. The method is based on energy conservation and avoids problems related to orbit dynamics and initial state. In addition, the particular geometry of a repeat orbit is exploited by using a very efficient iterative estimation scheme, in which a set of normal equations is approximated by a sparse block-diagonal equivalent. Recovery experiments for spherical harmonic gravity field models up to degree and order 80 and 120 were conducted based on a 29-day simulated data set of orbit coordinates. The method was found to be very flexible and could be easily adapted to include observations of non-conservative accelerations, such as (to be) provided by satellites like CHAMP, GRACE, and GOCE. A serious drawback of the method is its large sensitivity to satellite velocity errors. Existing orbit determination strategies need to be altered or augmented to include algorithms that focus on optimizing the accuracy of estimated velocities.     

利用CryoSat-2卫星测高资料确定北极海冰干舷高

卫星测高技术的发展使得大空间尺度探测海冰成为可能,海冰干舷高是反演海冰厚度的关键参量,获取精确的海冰干舷高对海冰探测及了解全球气候变化均具有重要的作用。本文基于近3年获取的CryoSat-2卫星SAR模式测高资料,在60°N—88°N纬度带内的北极海域通过设定阈值筛选可用的观测数据,并在此基础上计算2015—2017年间月平均海冰干舷高,最后通过IceBridge航飞数据的时空匹配验证了本文获取的干舷高计算结果是可靠的。     

由星载GPS相位数据确定地球重力场模型若干问题研究

人造地球卫星在地球引力场中运动,可以探测地球重力场的长波信息。随着GPS技术的发展,星载GPS技术日趋成熟,因此由星载GPS相位数据确定地球重力场模型是当前国际地学研究的热点之一。本文给出了确定地球重力场模型中的星载GPS星地相位双差观测量,阐述了Cowell II数值轨道积分公式,导出了参数估计中星地双差观测量的偏导数,利用分块Bayes最小二乘参数估计地球引力场位系数等有关参数。     

Error analysis of satellite attitude determination using a vision-based approach

Improvements in communication and processing technologies have opened the doors to exploit on-board cameras to compute objects’ spatial attitude using only the visual information from sequences of remote sensed images. The strategies and the algorithmic approach used to extract such information affect the estimation accuracy of the three-axis orientation of the object.This work presents a method for analyzing the most relevant error sources, including numerical ones, possible drift effects and their influence on the overall accuracy, referring to vision-based approaches. The method in particular focuses on the analysis of the image registration algorithm, carried out through on-purpose simulations. The overall accuracy has been assessed on a challenging case study, for which accuracy represents the fundamental requirement. In particular, attitude determination has been analyzed for small satellites, by comparing theoretical findings to metric results from simulations on realistic ground-truth data. Significant laboratory experiments, using a numerical control unit, have further confirmed the outcome.We believe that our analysis approach, as well as our findings in terms of error characterization, can be useful at proof-of-concept design and planning levels, since they emphasize the main sources of error for visual based approaches employed for satellite attitude estimation. Nevertheless, the approach we present is also of general interest for all the affine applicative domains which require an accurate estimation of three-dimensional orientation parameters (i.e., robotics, airborne stabilization).     

High precision orbit determination of CHAMP satellite

IntroductionCHAMP satellite was launched on July 15 ,2000 to study the earth gravity field, magneticfield, and at mosphere/ionosphere . CHAMPmission is managed by GeoForshungsZentrum(GFZ) Potsdam withinternational partners .In-cluding accelerometer ,star …     

The cloud phase discrimination from a satellite

A new technique to identify mixed-phase clouds but also clouds with supercooled water droplets using satellite measurements is proposed. The technique is based on measurements of the backscattered solar light at wavelengths 1.55 and 1.67 /spl mu/m in combination with cloud brightness temperature measurements at 12 /spl mu/m. For the first time, the concept of the phase index-temperature correlation plot (the P-T diagram) is introduced in the cloud remote sensing. Retrievals of cloud temperature and cloud phase index are performed using data from the Advanced Along Track Scanning Radiometer (AATSR) and Scaning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) both onboard the Envisat platform.     

资源三号卫星激光测距定轨精度分析

基于卫星激光测距定轨是目前遥感卫星在轨位置测量的重要手段之一,其测量精度关系到遥感卫星的应用水平。为了分析我国首颗民用立体测绘卫星——资源三号携带的国产激光角反射器在轨运行情况,该文利用全球激光联测期间卫星激光测距数据与GPS事后联合定轨结果,从遥感影像几何定位和轨道预报两个方面定量分析和评价卫星激光测距参与的定轨精度。试验表明,基于卫星激光测距与GPS定轨结果,影像几何定位无控精度较实时定轨精度提升1~2m,有效提升了卫星影像几何处理精度;轨道预报1d星下点位置较实际过境轨迹偏差优于250m,2d优于500m,1d预报侧摆精度达到0.035°,满足检校外业和成像计划精度需求。     

GOCE实测数据反演高阶重力场模型的Torus方法

不同于当前广泛使用的空域法、时域法、直接解法,本文尝试采用Torus方法处理GOCE实测数据,利用71 d的GOCE卫星引力梯度数据反演了200阶次GOCE地球重力场模型,实现了对参考模型的精化。首先,采用Butterworth零相移滤波方法加移去—恢复技术,处理引力梯度观测值中的有色噪声,并利用泰勒级数展开和Kriging方法对GOCE卫星引力梯度数据进行归算和格网化,计算得到了名义轨道上格网点处的引力梯度数据。然后,利用2D-FFT技术和块对角最小二乘方法处理名义轨道上数据,获得了200阶次的GOCE地球重力场模型GOCE_Torus。利用中国和美国的GPS/水准数据进行外部检核结果说明,GOCE_Torus与ESA发布的同期模型的精度相当;GOCE_Torus模型与200阶次的EGM2008模型相比,在美国区域精度相当,但在中国区域精度提高了4.6 cm,这充分体现了GOCE卫星观测数据对地面重力稀疏区的贡献。Torus方法拥有快速高精度反演卫星重力场模型的优势,可以在重力梯度卫星的设计、误差分析及在轨快速评估等方面得到充分应用。     

由卫星云图获取云层分布等值线图

大气中云的分布状况是气象预报的重要依据。本文探讨了利用卫星云图对云的分布作定量分析的可能性。并提出了一种通过红外云图获取云顶高度等值线的快速算法,最后给出了一些实验结果。     

Comparison of methods for marine gravity determination from satellite altimetry data in the Labrador Sea

One-year average satellite altimetry data from the Exact Repeat Missions (ERM) of GEOSAT have been used to determine marine gravity disturbances in the Labrador Sea region using the inverse Hotine approach with FFT techniques. The derived satellite gravity information has been compared to shipboard gravity as well as gravity information derived by least-squares collocation (LSC), GEMT3 and OSU91A geopotential models in the Orphan Knoll area. The RMS and mean differences between satellite and shipboard gravity disturbances are about 8.0 and 2.8 mGal, respectively. There is no significantly difference between the results obtained using FFT and LSC.     

强跟踪自适应SRCKF的卫星姿态确定算法

针对卫星星敏感器/陀螺姿态确定系统在空间中存在模型不确定性、状态突变和不良测量问题,该文提出了基于强跟踪自适应平方根容积卡尔曼滤波器(STSRCKF)的卫星姿态确定算法。在平方根容积卡尔曼滤波的基础上,通过引入渐消因子,解决了由于模型不确定和状态突变引起的精度下降、稳定性差和收敛慢的问题;通过增加异常检测和引入自适应因子,获得了应对不良测量的良好跟踪能力。通过仿真实验对算法进行了验证。     

Modeling GPS satellite attitude variation for precise orbit determination

High precision geodetic applications of the Global Positioning System (GPS) require highly precise ephemerides of the GPS satellites. An accurate model for the non-gravitational forces on the GPS satellites is a key to high quality GPS orbit determination, especially in long arcs. In this paper the effect of the satellite solar panel orientation error is investigated. These effects are approximated by empirical functions to model the satellite attitude variation in long arc orbit fit. Experiments show that major part of the long arc GPS orbit errors can be accommodated by introducing a periodic variation of the satellite solar panel orientation with respect to the satellite-Sun direction, the desired direction for solar panel normal vector, with an amplitude of about 1 degree and with a frequency of once per orbit revolution.     

基于随机森林的FY-2G云检测方法

根据遥感影像中云检测原理,提出了基于随机森林的遥感影像云检测方法,并将其应用于FY-2G影像。结合国家气象卫星中心（NSMC）的云检测产品数据进行了算法的精度检验,云检测个例的精度检验结果显,最高命中率（POD）为88.32%,最低误报率（FAR）为9.36%,临界成功指数（CSI）为80.14%。结果表明,该方法有效地提高了云检测精度,同时能正确标识NSMC中部分误判的情况。     

验潮站和深海压力仪用于卫星高度计性能评估的可行性分析

在传统卫星高度计定标途径之外,探索了远海孤岛验潮站和深海压力仪分别用于卫星高度计性能评估的可行性。采用Harvest石油平台验潮站、1890000号验潮站和21419号深海压力仪,计算了Jason-3测量海面高偏差以及Jason-2、Jason-3海面高之间的相对偏差。由3种设备得到的Jason-3海面高偏差序列的标准差分别为3.98、2.87、8.61 cm,Jason-2、Jason-3海面高之间的相对偏差(Jason-3—Jason-2)分别为-3.62±2.17、-2.58±1.97、-2.60±1.30 cm,与国外定标站计算结果相比较,结果表明:Jason-3海面高相比于Jason-2海面高低约3.0 cm;选用的深海压力仪适合用于Jason-2、Jason-3之间海面高相对偏差的计算,但不适用于单颗卫星的定标或性能评估;远海孤岛验潮站适用于两者。     

卫星测高与卫星重力对洋流的研究

卫星测高与卫星重力的发展为进一步研究洋流提供了前所未有的机遇。本文从EGM 96 ,GGM0 1与未来的GOCE任务获取的高精度高分辨率海洋大地水准面的角度对洋流的研究方法与可行性进行了分析     

TJS-2 geostationary satellite orbit determination using onboard GPS measurements

This study analyzes the quality of onboard data of tracking signals from GPS satellites on the far side of the earth and determines the orbit of the geostationary satellite using code and carrier phase observations with 30-h and 3-day orbit arc length. According to the analysis results, the onboard receiver can track 6–8 GPS satellites, and the minimum and maximum carrier to noise spectral densities were 24 and 45 dB-Hz, respectively. For a GPS receiver on a high-altitude platform above the navigation constellations, the blocking of the earth and a weak signal strength usually cause a piece-wise GPS signal tracking and an increase in the number of ambiguity parameters. Individual GPS satellites may be continuously tracked for as little as several minutes and as long as 3 h. Moreover, considering the negative sign of elevation angles reflects the fact that GPS satellites are tracked below the receiver in the study. GPS satellites appear mainly in the elevation angle range of ??53° to ??83°, and dilution of precision values could reach ten or one hundred and more. Also, it is observed that when a signal suffers from atmospheric refraction, other GPS signals tracked simultaneously by the receiver experience strong systematic errors in the code observations. Based on single-frequency code and carrier phase measurements, the mean 3D root mean square (RMS) value of the overlap comparisons between 30-h orbit determination arcs is 2.14 m. However, we found that there were also some biases in the carrier phase residuals, which contributed to poor orbit accuracy. To eliminate the effects of the biases, we established a correction sequence for each GPS satellite. After corrections, the mean 3D RMS was reduced to 0.99 m, representing a 53% improvement.