Viallefont-Robinet Françoise, Helder Dennis, Fraisse Renaud, Newbury Amy, van den Bergh Frans, Lee DongHan, Saunier Sébastien
Opt Express. 2018 Dec 24;26(26):33625-33648. doi: 10.1364/OE.26.033625.
A sensor's spatial resolution has traditionally been a difficult concept to define, but all would agree that it is inextricably linked to the Ground Sampling Distance (GSD) and Instantaneous Field of View (IFOV) of an imaging sensor system. As a measure of the geospatial quality of imagery, the Modulation Transfer Function (MTF) of the system is often used along with the signal-to-noise ratio (SNR). However, their calculation is not fully standardized. Further, consistent measurements and comparisons are often hard to obtain. Therefore, in the Infrared and Visible Optical Sensors (IVOS) subgroup of the Working Group on Calibration Validation (WGCV) of the Committee for Earth Observation Satellites (CEOS), a team from various countries and professional entities who are involved in MTF measurement was established to address the issue of on-orbit MTF measurements and comparisons. As a first step, a blind comparison of MTF measurements based on the slanted edge approach has been undertaken. A set of both artificial and actual satellite edge images was developed and a first comparison of processing results was generated. In all, seven organizations contributed to the experiment and several significant results were generated in 2016. No single participant produced the best results for all test images as measured by either the closest to the mean result, or closest to the truth for the synthetic test images. In addition, close estimates of the MTF value at Nyquist did not ensure the accuracy of other MTF values at other spatial frequencies. Some algorithm results showed that the accuracy of their estimates depended upon the type of MTF curve that was being analyzed. After the initial analysis, participants were allowed to modify their methodology and reprocess the test images since, in several cases, the results contained errors. Results from the second iteration, in 2017, verified that the anomalies in the experiment's first iteration were due to errors in either coding or methodology, or both. One organization implemented a third trial to fix software errors. This emphasizes the importance of fully understanding both methodology and implementation, in order to ensure accurate and repeatable results. To extend this comparison study, a reference data set, which is composed of edge images and corresponding MTF curves, will be built. A broader audience will be able to access the edge images through the CEOS CalVal Portal (http://calvalportal.ceos.org/). This paper, which is associated with the reference data set, can serve as a new tool to either implement or check, or both, the MTF measurement that relies on the slanted edge method.
传统上，传感器的空间分辨率是一个难以定义的概念，但所有人都认同它与成像传感器系统的地面采样距离（GSD）和瞬时视场（IFOV）有着千丝万缕的联系。作为衡量图像地理空间质量的指标，系统的调制传递函数（MTF）通常与信噪比（SNR）一起使用。然而，它们的计算并未完全标准化。此外，往往难以获得一致的测量结果和进行比较。因此，在对地观测卫星委员会（CEOS）校准验证工作组（WGCV）的红外和可见光光学传感器（IVOS）子组中，成立了一个由来自不同国家和专业实体、参与MTF测量的团队，以解决在轨MTF测量和比较的问题。作为第一步，已基于倾斜边缘法对MTF测量进行了盲测比较。开发了一组人工和实际卫星边缘图像，并生成了处理结果的首次比较。总共有七个组织参与了该实验，并在2016年产生了一些重要结果。就最接近平均结果或最接近合成测试图像的真实值而言，没有一个参与者在所有测试图像上都取得了最佳结果。此外，奈奎斯特频率处MTF值的相近估计并不能确保其他空间频率处其他MTF值的准确性。一些算法结果表明，其估计的准确性取决于所分析的MTF曲线类型。在初步分析之后，允许参与者修改其方法并重新处理测试图像，因为在某些情况下，结果包含错误。2017年第二次迭代的结果证实，实验第一次迭代中的异常是由于编码或方法，或两者的错误所致。一个组织进行了第三次试验以修复软件错误。这强调了全面理解方法和实现的重要性，以确保获得准确且可重复的结果。为了扩展这项比较研究，将构建一个由边缘图像和相应MTF曲线组成的参考数据集。更广泛的受众将能够通过CEOS校准验证门户（http://calvalportal.ceos.org/）访问边缘图像。与该参考数据集相关的本文可作为一种新工具，用于实施或检查，或同时用于这两者，即依赖于倾斜边缘法的MTF测量。
