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Frequency And Temporal Compounding Of Partially Correlated Signals: Speckle Suppression And Image Resolution

This work presents the results of first principle calculations of the effects of frequency and temporal compounding on speckle contrast and axial (range) resolution. Frequency compounding corresponds to the process in which a coherent pulse of a specific bandwidth is passed through a filter bank which divides the pulse into a number of sub-bands. The image is formed by incoherently summing (compounding) the intensities of the individual sub-bands. Temporal compounding falls into the category of non-linear multirate signal processing as the final pixel intensity is made up of the intensity of samples which were sampled initially at rates equal to or higher than the pulse bandwidth. The intensities of the samples are then compounded to form the final image. In the limit of infinite sampling rate, temporal compounding is equivalent exactly to analog integrated backscatter where the sensor continuously integrates the intensity of the incoming signal. The speckle contrast reduction and the decrease in resolution for these processes are discussed. These results apply to generic coherent imaging systems which can access both the amplitude and phase of signals.