On-orbit relative radiometric calibration of optical video satellites without uniform calibration sites

The rapid development of optical video satellite constellations provides a new data model for resource and environmental monitoring, and for commercial applications of satellite remote sensing. High-frequency on-orbit relative radiometric calibration is an indispensable means of improving the quality of raw frames. However, the conventional on-orbit calibration method relies on a uniform field (e.g. desert, snow, clouds, etc.), which renders it unable to perform high-frequency radiometric calibration. Here, a method of on-orbit relative radiometric calibration without uniform calibration sites for optical video satellites is proposed taking into consideration the high frame-rate characteristics of video satellites. The method can be applied using any multi-frame data, it does not require a uniform field, it is not affected by the type of field, and it can achieve near-real-time, high-frequency calibration of video satellites. Moreover, this approach is expected to increase the frequency of on-orbit radiometric calibrations while reducing the associated costs. Our results suggest that the proposed method can effectively calibrate the non-uniformity of each sensor detector, and the compensation effect is equivalent to the on-orbit calibration method based on uniform sites.     

An improved method to estimate reference cloud-free images for the visible band of geostationary satellites

Geostationary images have been used frequently in the past 50 years to derive geophysical information. As a complement to all-sky observations, clear-sky counterparts play an important role in the derivation of cloud properties. We investigated ways to improve estimates of top-of-atmosphere (TOA) visible clear-sky images, over the full spatial and temporal resolution of Meteosat First Generation (MFG) satellites. Estimation was based on TOA measurements in MFG’s visible channel, collected for a specific time of the day over the span of several days. In addition, a cloud climatology aided estimation.

Parameter optimization and the introduction of a spatial filter over ocean resulted in a bias of ?1.0 to ?2.0 digital counts (DC) and a root mean square error (RMSE) of 2.0–3.0 DC when averaged over the complete field of view. This excludes the Spring period which has up to ?3.5 DC bias and up to 5.5 DC RMSE. Reasons for these exceptional differences were found in rapid greenness change, affecting reflectances over vegetated surfaces, and dust storms, with an effect over tropical land and ocean surfaces. Similarly, sea ice and snow affected polar regions seasonally. Applied to 24 years of MFG imagery, we successfully used improved clear-sky estimates to stably detect clouds. Additionally, these clear-sky estimates may prove useful for characterization of instrument degradation as well as cloud feedback studies.     

环境一号B星红外多光谱相机综合辐射定标

环境一号B星红外多光谱相机(简称HJ-1B星IRS)在轨运行过程中受各种因素的影响,其探测性能不断发生衰减,绝对辐射定标可有效地改善遥感器辐射特性的测量精度,从而提高遥感数据辐射质量.文中针对HJ-1B星IRS星上定标系统特点,利用2010年8月地面同步试验数据对IRS热红外通道进行综合辐射定标,修正了原始定标系数,并进行定标系数的真实性检验.结果表明借助地面试验数据进行的综合辐射定标弥补了星上定标系统的不足,获得的定标系数准确可靠,可满足遥感数据定量化应用的需要.     

On the in-flight absolute calibration of high spatial resolution spaceborne sensors using small ground targets

The in-flight absolute calibration of spaceborne instruments working in the solar reflective region (0.4-2.5 mu m) has often been performed with large uniform ground areas, such as White Sands, U.S.A., or La Crau, France. The method presented here describes an alternative for high spatial resolution sensors employing artificial small ground targets. The required target size is seven times the size of the sensor's spatial resolution, the ground projected instantaneous field-of-view (GIFOV), if the Gaussian full width 2 sigma of the image point spread function (PSF), atmospheric blurring removed, is less or equal to 1.5 * GIFOV. For near-future multispectral instruments with a spatial resolution of 1 to 10 m the required ground reference areas with very homogeneous reflectance properties will be sized 7 m * 7 m to 70 m * 70 m, respectively. The proposed method can also be employed for panchromatic sensors.     

On-board radiometric calibration for thermal emission band of FY-3C/MERSI

On-board radiometric calibration is the most efficient method to improve the measurement accuracy of satellite-borne sensors. Chinese Medium Resolution Spectral Imager (MERSI), loaded on the Fengyun-3C (FY-3C) satellite, uses one satellite-borne fixed-temperature blackbody (BB) for its thermal emission band’s (TEB) radiometric calibration, but its optimal calibration algorithm is not determined. By using MERSI’s on-board calibration data taken on November 2013, this article investigates two algorithms of linear and semi-nonlinear calibration for MERSI TEB’s on-board radiometric calibration and finds that the linear calibration is more reasonable than semi-nonlinear calibration because linear coefficients’ variation tendency can reflect MERSI’s inherent systematic properties better. The relative difference between linear properties and inherent properties for pixel variability being 9.5%, mirror-side variability being 21.5% and scan variability being 17.8% are all smaller than those between semi-nonlinear case and inherent case. All of those suggest that the linear calibration is coincident with the inherent systematic properties. By using MERSI’s calibration data at June 2014, the performance of those two algorithms is validated by comparing the difference between inferred BB radiance L_I and standard BB radiance L_S (0.01%), and between inferred BB brightness temperature T_I and standard BB temperature T_S (0.25 K).     

IMRAN: a noise estimation method for relative radiometric calibration data

Radiometric calibration is the foundation for remote sensors to accurately record the reflected energy from targets and to also effectively display the reflectance diversity among them. As one of the calibration methods, pre-launch laboratory relative calibration is essentially a normalizing process for each detector of a sensor at different intensity levels of various radiation sources. However, interferences such as stray light, dark current, and stochastic noise will cause some deviation of the normalizing correction factor. In this article, we propose an integral noise (a combination of the aforementioned three noises) estimation method based on the correlation between the elements of the calibration data itself. Abbreviated as IMRAN (Iterative Maximal Residual As Noise), this method is an iteration procedure using least square fitting to calculate the maximum residual of the sensor pixel in question against the rest sensor pixels and to consider this value as the estimated noise. The iteration is continued after subtracting the noise from the raw data of the sensor pixel until the noise estimation gets converged and then the accumulation of the results from each round is the final estimated noise. And this procedure is applied to every sensor pixel. The verification results demonstrated the IMRAN method can effectively estimate the integral noise of pre-launch radiometric calibration data and substantially improve its precision. When the number of radiation level increases, the precision of the estimated noise will be rapidly increased, whereas the number of sensor pixels has no obvious effect. Because this IMRAN method uses the data of every sensor pixel, it is sensitive to the outlier, which can be eliminated by variance detection as part of the IMRAN method.     

A method for the mapping of the apparent ground brightness using visible images from geostationary satellites

Abstract

This paper deals with a method for mapping the apparent ground brightness on a pixel basis. It makes use of geostationary satellite visible data and generalizes the earlier work of Cano (1982). The detection of clouds larger than one pixel is performed in a time series by comparing the cloud-induced sensor response to the signal which would occur if the pixel were cloud-free by means of an iterative and adaptive filtering. To illustrate the method, Meteosat data either received by means of a WEFAX-type receiver connected to a personal computer or provided by ESOC have been processed. Maps of apparent ground brightness are presented for Europe and Africa with 5?km resolution.     

Analysis of a station-keeping maneuver strategy for collocation of three geostationary satellites

A collocation strategy has been planned and analyzed for three geostationary satellites in the same longitude control box. The orbit determination error analysis is performed when only one ground station is used for the angle tracking and ranging. Based on the orbit determination errors, the station-keeping bands are allocated for seven-day East/West and 14-day North/South station-keeping maneuver cycles. The eccentricity control circle and inclination control box for individual satellites are allocated for the collocation. The eccentricity vector and inclination vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. A total of fourteen weeks of station-keeping maneuvers are performed for three KOREASAT satellites, collocated in 116°E±0.05° longitude band.     

An operational radiometric calibration procedure for the Landsat sensors based on pseudo-invariant target sites

The Statewide Landcover and Trees Study (SLATS) use both Landsat-7 ETM+ and Landsat-5 TM imagery to monitor short-term woody vegetation changes throughout Queensland, Australia. In order to analyse more subtle long-term vegetation change, time-based trends resulting from artefacts introduced by the sensor system must be removed. In this study, a reflectance-based vicarious calibration approach using high-reflectance, pseudo-invariant targets in western Queensland was developed. This calibration procedure was used to test the existing calibration models for ETM+ and TM, and develop a consistent operational calibration procedure which provides calibration information for the MSS sensors. Ground based data, sensor spectral response functions and atmospheric variables were used as input to MODTRAN radiative transfer code to estimate top-of-atmosphere radiance. The estimated gains for Landsat-7 ETM+ (1999-2003), -5 TM (1987-2004), -5 MSS (1984-1993) and -2 MSS (1979-1982) are presented. Results confirm the stability and accuracy of the ETM+ calibration, and the suitability of this data as a radiometric standard for cross-calibration with TM. Vicarious data support the use of the existing TM calibration model for the red and two shortwave-infrared bands. However, alternative models for blue, green and near-infrared bands are presented. The models proposed differ most noticeably at dates prior to 1995, with differences in estimated gains of up to 9.7%, 10.8% and 6.9% for the blue, green and near-infrared bands respectively. Vicarious gains for Landsat-2 MSS and Landsat-5 MSS are presented and are compared with those applied by the on-board calibration system. Updated calibration coefficients to scale MSS data to the SLATS vicarious measurements are given. The removal of time based calibration trends in the SLATS data archive will enable the measurement of vegetation changes over the 26 year period covered by Landsat -2, -5 and -7.     

基于红外地中基准的自旋稳定卫星姿态控制修正方法

针对自旋稳定卫星采用红外地中基准进行姿态控制时控制结果偏差较大的问题,首先对等倾角控制原理进行了说明,分析了太阳基准和红外地中基准在姿态控制时的主要区别,并分析了红外地中基准控制偏差较大的主要原因,提出了采用执行角补偿修正的方法。经仿真验证,通过执行角修正,有效提高了控制精度。     

基于工作流的星载SAR辐射定标系统研究与设计

在对原有星载SAR辐射定标处理系统的开发和认识的基础上,分析星载SAR辐射定标处理系统的领域需求及辐射定标数据的处理流程,并对工作流技术及工作流管理系统机制进行研究.在现有的SAR辐射定标处理系统中引入工作流技术及设计思想,实现系统处理的控制逻辑与具体的实现逻辑分离,及辐射定标数据处理的自动化或半自动化,提高数据处理的效率以及系统的灵活性和适应性.     

红外目标模拟器校准装置构建和校准技术研究

在对传统红外目标模拟器校准装置分析的基础上,结合辐射照度校准理论、方法和误差来源三方面,构建了红外目标模拟器校准装置,开展了辐照度测量系统内部杂散辐射建模仿真和抑制的研究、红外大气传输修正方法的研究和测试结果数据拟合算法的研究,分别提出了基于复合蒙特卡洛法的内部杂散辐射数学模型、基于编码器-解码器结构的卷积神经网络红外辐射大气传输校准算法和基于粒子群优化的极限学习机算法,并在实验室条件下进行了辐照度计量校准实验。分别验证了在追迹光线数相等的情况下复合蒙特卡洛法的精度更高,复合蒙特卡洛法标准偏差为6.1940×10-8,平均误差为0.19293,且仿真结果体现了红外辐射计各部分杂散辐射对探测器入瞳面接收到的杂散辐射造成的影响;基于编码器-解码器结构的卷积神经网络算法能够较好的预测大气透过率和大气程辐射,在三个波段下的平均误差为3.0783%,3.8186%,5.3452%,低于传统方法,降低了大气透过率和大气程辐射的影响;通过与GA-ELM模型、ELM模型进行对,验证了与传统数据拟合方法相比,基于PSO-ELM的方法在1μm~3μm、3μm~5μm、8μm~14μm三个波段下的拟合精度都有所提高,决定系数分别为0.9925、0.9913、0.9814,平均相对误差分别为0.1242%、0.7157%、0.7471%有效提高了红外辐射测量准确度。     

An automatic model calibration method for occupant restraint systems

Computer models are widely used to simulate dynamic systems in automobile industry. It is imperative to have high quality CAE models with good predictive capability. This requires CAE engineers to conduct model calibration with physical tests. The challenges in the occupant restraint system model calibration are: (1) the dynamic system usually consists of multiple responses, (2) most of the responses are functional data or time histories, and (3) the traditional trial-and-error calibration approach is time consuming and highly depends on analyst??s expertise. These call for the development of an automatic and effective model calibration method. This paper presents a newly developed automatic model calibration method, based on the Error Assessment of Response Time Histories (EARTH) metric. The EARTH metric is used to perform model assessment on various important features of the functional responses. A new multi-objective optimization problem is formulated and solved by a Non-dominated Sorting Genetic Algorithm to automatically update CAE model parameters. A real-world example is used to demonstrate the use of the proposed method.     

An efficient camera calibration method for vision-based head tracking

The aim of this study is to develop and evaluate an efficient camera calibration method for vision-based head tracking. Tracking head movements is important in the design of an eye-controlled human/computer interface. A vision-based head tracking system is proposed to allow the user's head movements in the design of the eye-controlled human/computer interface. We propose an efficient camera calibration method to track the three-dimensional position and orientation of the user's head accurately. We also evaluate the performance of the proposed method and the influence of the configuration of calibration points on the performance. The experimental error analysis results showed that the proposed method can provide more accurate and stable pose (i.e. position and orientation) of the camera than the direct linear transformation method which has been used in camera calibration. The results for this study can be applied to the tracking of head movements related to the eye-controlled human/computer interface and the virtual reality technology.     

An alternative stochastic sensitivity analysis method for RBDO

Structural and Multidisciplinary Optimization - A new method, which is an alternative to the score function method, is developed. Unlike the score function from the literature, this proposed method...     

An alternative method of curve interpolation

Given a point data set that contains several fairly unevenly distributed random points, this paper presents a new paradigm of curve interpolation to fit a curve to the data with end tangent vector constraints. The method uses a base curve, which is subjected to constrained shape manipulations to achieve interpolation, while maintaining end point and end tangent constraints. The algorithm is not sensitive to the distribution or to the randomness of the data, as long as the points represent fairly simple shapes, as in reverse engineering of properly segmented points, or in shape design using simple segments. The method is iterative in nature and allows various forms of adjustments to achieve good results.     

A model for the estimation of the daily global sunshine duration from meteorological geostationary satellite data

In this research a simple model was proposed for the estimation of daily global sunshine duration and constructing spatially continous sunshine duration map from meteorological geostationary satellite sensor data. First cloud cover index and then daily mean cloud cover index value for each pixel were computed using a time‐series of Meteosat C3D visible type images. The statistical relationship between daily mean cloud cover index and measured bright sunshine duration values was tested and found to be linear. Using regression parameters daily sunshine duration of each pixel was calculated and then daily sunshine duration and monthly mean daily sunshine duration maps were constructed. It was shown that, by using the suggested model it is possible to calculate daily sunshine duration values over a large area where the sunshine duration data are not available and construct spatially continious long‐term sunshine duration maps.     

An automatic method for the calibration of time-series of Meteosat images

A method is described for the automatic calibration of the successive operational Meteosat sensors in the visible range since 1985. As a starting point, the absolute vicarious calibration for only one image in the whole time-series is needed, which can be provided by previous published works. The automatic method performs on a daily basis and is based on a statistical analysis of two images, one when the Sun illuminates the entire field of view of Meteosat, the other during night-time. This approach does not require any information about atmospheric and surface parameters, and therefore can be easily performed either on archived data, or in quasi-real time when receiving the images. Our results are fully consistent with previous studies. Several tests have been performed to validate the method and check its robustness and reliability.     

基于角度不变的线阵推扫式CCD相机几何畸变在轨检校方法

对航天遥感相机进行在轨检校,是提高卫星产品质量,扩大产品应用效果的重要技术内容.文中研究了一种基于角度不变的线阵推扫式CCD相机几何畸变在轨检校方法.该方法利用相机外方元素对于相机视向量夹角角度影响比较小的原理,根据地面控制点和一级产品图像,求解相机视向量夹角,从中提取相机光学部件的畸变模型参数,从而实现相机内外方元素解耦.相机畸变模型采用一维3阶多项式,对焦距和主点等引起的低阶误差能够很好地吸收.该方法用在HJ-1A/B卫星的宽幅盖CCD相机几何畸变校正上,检校误差残留在2—6个像元,和参考数据精度相似,表明取得了很好的校正效果.     

An evaluation of digitized APT data from the TIROS-N/NOAA-A, -J series of meteorological satellites

The TIROS-N/NOAA-A, -J series of meteorological satellites transmit imagery data to the Earth in both digital and analogue formats. The analogue data are a processed subset of the digital data and have lower resolution. A quantitative evaluation of a post-reception digitized version of this is made using the corresponding digital data as a standard. In nine comparisons the calibration of the infrared sensor on board was within 001°C. Sea surface temperature estimates from APT data were 0.3°C below the corresponding digitally transmitted data. The albedo estimates were within 0.2 per cent. Processed APT data are adequate for many mesoscale measurements in the fields of oceanography and meteorology and are more readily accessible than the digitally transmitted data.