Research On Theory And Methods Of Doppler Weather Radar Resolution Improvement

The resolution improvement of Doppler weather radar will be helpful to enhancethe detecting ability for these small-scale disaster weather systems, to acquire muchfiner echo structures and to provide more precise radar data for forecasting and earlywarning.To improve the range resolution and angular resolution of weather radar,the directmethods are to increase the radar signal bandwidth and increase the diameter of antenna.However, This methods will be related to a great deal of hardware modifications ofradar transmitter, receiver and antenna, which will result in much longer alterationperiod and huge cost of reconstruction, thus it can be not feasible for theoperation-working weather radar networks of CINRAD. This dissertation will befocused on the research of methods to enhance weather radar resolution through theimprovements of signal processing or data processing at the back-end of radar receiver.The main work and contribution of this dissertation are as follows.(1) The antenna motion combined with time averaging in the spectral estimation ofDoppler weather radar will create an effective broadened beamwidth, which is widerthan that of determined by radar antenna diameter and radar wavelength, and results inthe degradation of effective azimuthal resolution. This dissertation investigates thetheoretical computation method of antenna effective beamwidth for scanning weatherradar and theoretically calculates the effective beamwidth under different volumecoverage patterns (VCP); investigates two methods of decreasing the radar azimuthalsampling interval, overlapping radials and data weighting to decrease the broaden ofeffective beamwidth and improve the azimuthal resolution of weather radar,experimental results from radar simulation and actual radar data have proved theavailability of these two methods.(2) Aiming at the actual problems of the errors in the spectral processing due to thedecrease of pulse average number and signal to noise ratio, this dissertation gives theprocessing methods of combining the methods of range oversampling and whiteningfilter with the ones of overlapping radials and data weighting, which can both enhancethe azimuthal resolution and also improve the accuracy of spectral estimation.Theoretically analyzes their detailed performance of improvement degree, and teststheir availability from radar simulation and actual data. Experimental results indicate that these methods can remedy the accuracy decrease due to the processing of azimuthalresolution and meet the need of radar operation application.(3) Combined with the echo signal model of weather radar and the technique ofrange oversampling, This dissertation builds on the mathematical model for higherrange resolution reconstruction, which divides the basic cell of range resolution intomuch smaller cells and it is equivalent to the divisions for the distributed weather scattercenters in one range resolution cells along range direction. Based on the investigation ofthe algorithm of minimum variance distortionless response (MVDR), this dissertationdevelops a robust MVDR algorithm based on the steepest descent method to realize theecho signal reconstruction of higher range resolution. Experimental results indicate thatfor the target objects and asymmetrical weather objects, these methods can reconstructthe gradient changes of echo power and radial velocity for the scatter centers within therange resolution cell and can improve the range resolution of radar.(4) Aiming at the resolution improvement of weather radar reflectivity factor, thisdissertation derives a mathematical model between reflectivity factor and radar echopower based on the radar meteorology equation and a matrix equation is set up for theimprovement of range and azimuthal resolution, and then an oversampling technique inrange and angular is proposed to acquire multiple partially correlated measurements inphysical weather radar system, and two regularization algorithms of one and twodimensional truncated singular value decomposition (TSVD) and Tikhonovregularization are first provided to be applied in weather radar resolution improvementof reflectivity factor. Experiments results have shown that the proposed methods basedon regularization algorithm are efficient for range and angular resolution enhancementof reflectivity factor and can reconstruct much finer weather echo structure.