High range resolution radar techniques and the wavelet transform

Modern radar systems now require more information on a target object than that supplied by a simple radar plot. Techniques are now available that can supply detailed information on a target's characteristics. One of these is to generate a high range resolution profile on a target object. From this range profile, characteristics of the target object can be determined. These have traditionally be used for air breathing targets but they are now being utilised for space borne objects too. Conventional techniques for target discrimination by high resolution, however, show severe disadvantages when faced with space borne objects. High range resolution (HRR), for example, usually applies to a single, isolated target that moves with almost constant velocity. Space borne targets are often multiple and tend not to move uniformly, so, for these targets, the usual HRR techniques must be adapted. This paper considers new methodologies for stepped frequency waveforms that have been designed to cope with space borne object's characteristics. The principal characteristic of interest in the wavelet context is the objects rotational motion. A major problem, in generating the range profile of the target, is the need to compensate for motion. This problem is at its most acute when the target is tumbling. Tumble distorts the range profile unless the dwell time is short. This compromises the design of the profile by making it short too. In the space borne scenario the profile is likely to have not only tumbling objects but also to contain a number of objects travelling at different rates with respect to one another. Techniques ate presented here that enable the extraction of objects motion characteristics for different types of motion both linear and rotational by using Wavelets. The wavelet transform provides an additional dimension that enables the objects individual scattering centres to be tracked in range as they progress during the radar's dwell time. From this the objects linear motions can be estimated and any rotational motions can be seen as characteristic features that enable parameters such as tumble rate to be deduced. Lastly an approach is presented that would facilitate a performance enhancement of the radar when wavelets are used in conjunction with a high resolution range profile mode for space borne targets.