Viallefont-Robinet Françoise
ONERA DOTA Toulouse, 2, av. E. Belin 31055 Toulouse, France.
Opt Express. 2010 Sep 27;18(20):20845-51. doi: 10.1364/OE.18.020845.
In the earth observation domain, two classes of sensors may be distinguished: a class for which sensor performances are driven by radiometric accuracy of the images and a class for which sensor performances are driven by spatial resolution. In this latter case, as spatial resolution depends on the triplet constituted by the Ground Sampling Distance (GSD), Modulation Transfer Function (MTF), and Signal to Noise Ratio (SNR), refocusing, acting as an MTF improvement, is very important. Refocusing is not difficult by itself as far as the on-board mechanism is reliable. The difficulty is on the defocus assessment side. Some methods such as those used for the SPOT family rely on the ability of the satellite to image the same landscape with two focusing positions. This can be done with a bi-sensor configuration, with adequate focal plane, or with the satellite agility. A new generation of refocusing mechanism will be taken aboard Pleiades. As the speed of this mechanism will be much slower than the speed of the older generation, it won't be possible, despite the agility of the satellite, to image the same landscape with two focusing positions on the same orbit. That's why methods relying on MTF measurement with edge method have been studied. This paper describes the methods and the work done to assess the defocus measurement accuracy in the Pleiades context.
在对地观测领域，可以区分出两类传感器：一类传感器的性能由图像的辐射精度驱动，另一类传感器的性能由空间分辨率驱动。在后一种情况下，由于空间分辨率取决于由地面采样距离（GSD）、调制传递函数（MTF）和信噪比（SNR）构成的三元组，作为一种MTF改进手段的重新聚焦非常重要。只要机载机制可靠，重新聚焦本身并不困难。困难在于散焦评估方面。一些用于SPOT系列的方法依赖于卫星用两个聚焦位置对同一地貌成像的能力。这可以通过双传感器配置、配备合适的焦平面或利用卫星的敏捷性来实现。新一代重新聚焦机制将搭载于昴宿星卫星上。由于该机制的速度将比老一代慢得多，尽管卫星具有敏捷性，也不可能在同一轨道上用两个聚焦位置对同一地貌成像。这就是为什么研究了依靠边缘法进行MTF测量的方法。本文描述了在昴宿星卫星的背景下评估散焦测量精度的方法和所开展的工作。
