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Chapter 3:
Use of Coherent Fields and Images to Determine the Dynamic Parameters of Remote Objects
3.1 Introduction This chapter describes particular methods of obtaining information about the motion and deformation of objects that use coherent fields scattered by these objects and their coherent images. The object under investigation should have a statistically rough surface. The result is that the field at particular points of the reception plane and the image plane is produced by waves coming from different surface points. If the object is illuminated by monochromatic radiation, then interference of these waves forms scattered coherent fields and coherent images with random speckle structure—the speckle pattern. This structure can give us information about the parameters that describe the object's motion. Indeed, the motion of the object changes the phase difference between the waves coming from adjacent surface areas. This, in turn, brings to motion some fragments of the speckle pattern in the reception plane of the scattered field and the image plane. As a result, the speckle pattern brightness is varied. We will use this to estimate the parameters of the object's motion: the vector of linear velocity and the angular velocity of rotation. We will also use these variations to estimate the parameters of surface deformations, such as changes of components of unit vectors normal to particular areas of the object's surface. The concept of using coherent fields and images to determine the dynamic parameters of remote objects has drawn considerable interest. However, investigators dealing with the subject usually give neither explicit algorithms for estimating these parameters nor relationships for determining the accuracy of the estimation. In this chapter we will fill that information gap. The approach we suggest here is applicable to most of the known coherent-image methods for estimating the parameters of remote objects, and it allows us to estimate the parameters with high accuracy by relatively simple and reliable technical means. The methods considered in this chapter use no reference beam and therefore can be used with short-coherence-length sources, e.g., less than 1 m.
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