Study Of Method Of Altitude Measurement In VHF Radar And Complex Topographic Influence

Problems of altitude measurement based on a type of VHF radar are discussed in this paper. The beam of meter-wave radar is rather wide, and the reflection from ground results in beam split. Several antennas with different height are adopted to acquire a group of radar echoes, which have certain relationship of phases among them. The correlation of different beams can be used to determine elevation code which represents the region in which target located. Then the method of amplitude comparison can be applied to altitude measurement. The above process to obtain the altitude of objects is called the method based on beam split to measure height in VHF radar. MUSIC algorithm, one of the basic algorithms of array high-resolution based on the eigenvalue decomposition, will be ineffective on coherent multi-path signals. An improved MUSIC algorithm through reconstructing a special Toeplitz matrix can be used to estimate properly the DOA of coherent and uncorrelated signals. This new algorithm can be theoretically applied to estimating coherent multi-path echoes of meter-wave radar. The new method does not adapt for this type of radar because of the size of its antennas and some other conditions. The method based on beam split to measure height fits for this type of VHF radar rather than the improved MUSIC algorithm. There are many factors which can affect the accuracy of altitude measurement. Horizontal and vertical polarization with various reflection properties is presented with emphasis. For horizontal polarization the reflections from different soils and sea water will influence the elevation measurement. Ground surface fluctuations that can change VHF radar echoes are discussed. The accuracy of altitude measurement can be ensured by modifying theoretical model according to topographic survey on slope. Finally the experimental results of altitude measurement in this type of radar are presented, and the method based on beam split to measure height is proved to be effective.