Dobrin M B
Appl Opt. 1969 Aug 1;8(8):1551-7. doi: 10.1364/AO.8.001551.
When coherent light from a laser beam is passed through a transparency on which pictorial information is impressed, the information itself acts as a complex grating to produce a Fraunhofer diffraction pattern which is the two-dimensional Fourier transform, or power spectrum, of the information in the picture. By properly obstructing the light in the transform, one can filter out undesired spatial frequencies or directions of inclinations in the original picture. The most widespread commercial application of this principle has been to the analysis and filtering of seismic reflection records made in exploration for oil. Removal of undesired noise from seismic recordings can often be accomplished more economically by optical filtering than by more conventional digital and electrical analog techniques. Examples are demonstrated where optical filters have substantially improved the quality of seismic data. Use of optical transforms for analysis and solution of geological problems is also illustrated. The most unique advantages of optical processing are in economy, flexibility, and convenience of monitoring. Principal disadvantages are limited dynamic range, and difficulty in constructing filters that behave as gradational rather than step functions.
当来自激光束的相干光穿过印有图像信息的透明片时，信息本身就像一个复杂的光栅，产生夫琅禾费衍射图样，该图样是图像中信息的二维傅里叶变换或功率谱。通过适当地遮挡变换中的光，可以滤除原始图像中不需要的空间频率或倾斜方向。这一原理最广泛的商业应用是对石油勘探中制作的地震反射记录进行分析和滤波。通过光学滤波去除地震记录中不需要的噪声，往往比采用更传统的数字和电模拟技术更经济。文中展示了一些例子，说明光学滤波器如何显著提高了地震数据的质量。还阐述了利用光学变换分析和解决地质问题的情况。光学处理最独特的优点在于经济性、灵活性和监测的便利性。主要缺点是动态范围有限，以及难以构建表现为渐变而非阶跃函数的滤波器。
