Frequency diversity for image enhancement

Abstract

Methods for improving the availability of information derived from signals received from an object irradiated with coherent pulses of any form of radiation that exhibits a wave nature are disclosed. A method for reducing speckle derives separate component noncoherent signals from the received signals, and combines these separate noncoherent signals to form improved composite noncoherent signals. Weighting and processing of component signals can be applied as a function of time, frequency, and signal amplitude to optimize speckle reduction in all or a critical part of the signal by compensating for the range and frequency dependence of attenuation and the frequency dependence of scattering phenomena. In a method for enhancing resolution, separate component coherent signals are derived from the received signals, weighted and processed, and combined to form improved composite coherent signals; then noncoherent signals are derived from the improved composite coherent signals. In both methods, signals can be processed either in the analog or digital domains or in hybrid analog/digital domains. The apparatus for performing each method also is disclosed.

We claim: 
     
       1. A method of reducing speckle in signals received from an object irradiated with finite-bandwidth, coherent pulses of any form of radiation that exhibits a wave nature comprising: generating finite-bandwidth, coherent pulses and transmitting said pulses toward an object:   receiving the signals scattered by said object .Iadd.to develop a broadband electrical signal .Iaddend. device .[.therefrom.]. .Iadd.from said broadband electrical signal .Iaddend.separate, component, noncoherent signals, each representative of the components of said scattered signals in component frequency bands within said finite bandwidth; and   combining the component, noncoherent signals to obtain composite noncoherent signals, wherein the degradation of the signals due to speckle is less than in noncoherent signals derived directly from the original received signals.   
     
     
       2. .[.The method as set forth in claim 1.]. .Iadd.A method of reducing speckle in signals received from an object irradiated with finite-bandwidth, coherent pulses of any form of radiation that exhibits a wave nature, comprising: generating finite-bandwidth, coherent pulses and transmitting said pulses toward an object;   receiving the signals scattered by said object to derive therefrom separate, component, noncoherent signals, each representative of the components of said scattered signals in component frequency bands within said finite bandwidth;   combining the component, noncoherent signals to obtain composite noncoherent signals, wherein the degradation of the signals due to speckle is less than in noncoherent signals derived directly from the original received signals; and .Iaddend.   wherein the step of receiving comprises:   receiving the signals scattered by said object with a coherent receiver;   filtering said received signals to obtain separate, component, coherent signals having different frequency content; and   deriving separate noncoherent signals from the separate coherent signals.   
     
     
       3. The method as set forth in claim 2 further including, after the step of filtering, the step of weighting and processing said component, coherent signals separately as a function of such parameters as time, frequency content and signal amplitude. 
     
     
       4. The method as set forth in claim 2 further including, after the step of deriving separate noncoherent signals, the step of weighting and processing said component noncoherent signals separately as a function of such parameters as time, frequency content, and signal amplitude. 
     
     
       5. The method as set forth in claim 1 further including the step of transforming said composite noncoherent signals into a set of composite signals that map the irradiated object into a form suitable for inspection, such as an image. 
     
     
       6. The method as set forth in claim 2 wherein the steps of filtering, deriving separate noncoherent signals, and combining are performed on signals in the analog domain. 
     
     
       7. The method as set forth in claim 2 further including the step of digitizing the received signals, and wherein the steps of filtering, deriving separate noncoherent signals, and combining are performed on signals in the digital domain. 
     
     
       8. The method as set forth in claim 2 wherein the step of filtering comprises passing the received signals through at least two band-pass filters having substantially nonoverlapping, adjacent and equal pass bandwidth characteristics to obtain at least two filtered signals having different frequency content. 
     
     
       9. The method as set forth in claim 2 wherein the step of filtering comprises passing the received signal through at least two band-pass filters having substantially nonoverlapping adjacent passbands and about equal Q factor. 
     
     
       10. The method as set forth in claim 2 further including the step of normalizing the received signals to compensate for characteristics in system components to provide signals containing information more accurately representing information from said scattering object. 
     
     
       11. The method as set forth in claim 1 further including the steps of separately mapping the irradiated object from each of the separate noncoherent signals, separately processing each of said mappings, and combining the separate mappings into a composite mapping, wherein the degradation of the mapping due to speckle is less than in a mapping of noncoherent signals derived directly from the original received signals. 
     
     
       12. A method of enhancing resolution in signals received from an object irradiated with a finite-bandwidth, coherent pulse of any form of radiation that exhibits a wave nature, comprising: generating finite-bandwidth, coherent pulses and transmitting said pulses toward an object;   receiving the signals scattered by said object with a coherent receiver;   filtering said received signals to obtain separate, component, coherent signals having different frequency content;   weighting said component, coherent signals separately as a function of frequency content;   combining said component, coherent signals to obtain composite coherent signals; and   deriving noncoherent signals from said composite coherent signals, wherein the resolution of the noncoherent signals is enhanced compared to noncoherent signals derived directly from the original received signals.   
     
     
       13. The method as set forth in claim 12 wherein the step of weighting comprises processing said component, coherent signals separately as a function of such parameters as time, frequency content and signal amplitude. 
     
     
       14. The method as set forth in claim 12 further including the step of transforming the derived noncoherent signals into signals that map the irradiated object into a form suitable for inspection, such as an image. 
     
     
       15. The method as set forth in claim 12 wherein the steps of filtering, weighting.Iadd., .Iaddend.deriving noncoherent signals, and combining are performed on signals in the analog domain. 
     
     
       16. The method as set forth in claim 12 further including the step of digitizing the received signals, and wherein the steps of filtering, weighting, deriving noncoherent signals, and combining are performed on signals in the digital domain. 
     
     
       17. The method as set forth in claim 12 wherein the step of filtering comprises passing the signals through at least two band-pass filters having substantially nonoverlapping, adjacent and equal pass bandwidth characteristics to obtain at least two filtered signals having different frequency content. 
     
     
       18. The method as set forth in claim 12 wherein the step of filtering comprises passing the signals through at least two band-pass filters having substantially nonoverlapping adjacent passbands and about equal Q factor. 
     
     
       19. The method as set forth in claim 12 further including the step of normalizing the received signals to compensate for characteristics in system components and to provide signals containing information more accurately representing information from said scattering object. 
     
     
       20. Apparatus for reducing speckle in signals received from an object irradiated with a finite-bandwidth, coherent pulse of any form of radiation that exhibits a wave nature, comprising: means for generating finite-bandwidth, coherent pulses and transmitting said pulses toward an object;   means for receiving the signals scattered by said object .Iadd., for developing a broadband signal .Iaddend.and for deriving .[.therefrom.]. .Iadd.from said broadband signal .Iaddend.separate, component, noncoherent signals, each representative of the components of said scattered signals in component frequency bands within said finite .[.bandwith.]. .Iadd.bandwidth; .Iaddend.and   means for combining said component, noncoherent signals to obtain composite noncoherent signals, wherein the degradation of the signals due to speckle is less than in noncoherent signals derived directly from the received signals.   
     
     
       21. Apparatus .[.as set forth in claim 20.]. .Iadd.for reducing speckle in signals received from an object irradiated with a finite-bandwidth, coherent pulse of any form of radiation that exhibits a wave nature, comprising: means for generating finite-bandwidth, coherent pulses and transmitting said pulses toward an object;   means for receiving the signals scattered by said object and for deriving therefrom separate, component, noncoherent signals, each representative of the components of said scattered signals in component frequency bands within said finite bandwidth;   means for combining said component, noncoherent signals to obtain composite noncoherent signals, wherein the degradation of the signals due to speckle is less than in noncoherent signals derived directly from the received signals; and .Iaddend.   wherein the means for receiving and deriving comprises:   means for receiving the signals scattered by said object with a coherent receiver;   means for filtering said received signals to obtain separate, component, coherent signals having different frequency content; and   means for deriving separate noncoherent signals from the separate coherent signals.   
     
     
       22. Apparatus as set forth in claim 21 further including means for weighting and processing said component, coherent signals separately as a function of such parameters as time, frequency content, and signal amplitude. 
     
     
       23. Apparatus as set forth in claim 21 further including means for weighting and processing said component noncoherent signals separately as a function of such parameters as time, frequency content, and signal amplitude. 
     
     
       24. Apparatus as set forth in claim 20 further including means for transforming said composite noncoherent signals into a set of composite signals that map the irradiated object into a form suitable for inspection, such as an image. 
     
     
       25. Apparatus as set forth in claim 21 further including means for digitizing said received signals, and wherein the signals filtered, derived and combined are digital signals. 
     
     
       26. Apparatus as set forth in claim 21 wherein the means for filtering comprises at least two band-pass filters having substantially nonoverlapping, adjacent and equal pass bandwidth characteristics to thereby obtain at least two filtered signals having different frequency content. 
     
     
       27. Apparatus as set forth in claim 21 wherein the means for filtering comprises at least two band-pass filters having substantially adjacent passbands and about equal Q factor. 
     
     
       28. Apparatus as set forth in claim 20 further including means for normalizing the received signals to compensate for characteristics in system components and to provide signals containing information more accurately representing information from said scattering object. 
     
     
       29. Apparatus as set forth in claim 20 further including means for separately mapping the irradiated object into a form suitable for inspection, such as an image, from each of the separate noncoherent signals, means for separately processing each of said mappings, and means for combining the separate mappings into a composite mapping, wherein the degradation of the composite mapping due to speckle is less than in a mapping of noncoherent signals derived directly from the received signals. 
     
     
       30. Apparatus for enhancing resolution in signals received from an object irradiated with a finite-bandwidth, coherent pulse of any form of radiation that exhibits a wave nature, comprising: means for generating finite-bandwidth, coherent pulses and transmitting said pulses toward an object;   means for receiving the signals scattered by said object with a coherent receiver;   means for filtering said received signals to obtain separate, component, coherent signals having different frequency content;   means for weighting said component, coherent signals separately as a function of frequency content;   means for combining said component, coherent signals to obtain composite coherent signals;   means for deriving noncoherent signals from said composite coherent signals, wherein the resolution of the noncoherent signals is enhanced compared to noncoherent signals derived directed from the original received signals.   
     
     
       31. Apparatus as set forth in claim 30 wherein the means for weighting comprises means for processing said component, coherent signals separately as a function of such parameters as time, frequency content and signal amplitude. 
     
     
       32. Apparatus is set forth in claim 30 further including means for transforming the derived noncoherent signals into signals that map the irradiated object into a form suitable for inspection, such as an image. 
     
     
       33. Apparatus as set forth in claim 30 further including means for digitizing said received signals, and wherein the signals filtered, weighted, combined, and derived are digital signals. 
     
     
       34. Apparatus as set forth in claim 30 wherein the means for filtering comprises at least two band-pass filters having substantially nonoverlapping, adjacent and equal pass bandwidth characteristics to obtain at least two filtered signals having different frequency content. 
     
     
       35. Apparatus as set forth in claim 30 wherein the means for filtering comprises at least two band-pass filters having substantially nonoverlapping, adjacent passbands and about equal Q factor. 
     
     
       36. Apparatus as set forth in claim 30 further including means for normalizing the received signals to compensate for characteristics in system components and to provide signals containing information more accurately representing information from said scattering object.