A new composite display for polarimetric radar measurements

The application of polarimetric radar is one of hottest points in weather radar research. As the development in hardware and signal processing, recent polarimetric radars can output more and more types of measurements, which implicate more information of the targets, however, complicate the image analysis in operational use meanwhile, then forecasters would face more and more screens and shift their focuses between more and more images of variables, so it is an important work to set up a composite display technique to indicate more properties of the targets with only one figure.

In the field of satellite remote sensing, fake color composite images created by the different channels data as the RGB data are frequently used in the qualitative analysis of clouds, for example, the VVI images built with the data of visible and infrared channel in the processing of cloud classification can be used to identify the high cirrus and low liquid clouds, which could be referred in the application of polarimetric radar, a fake color composite image of radar composed of proper combination of radar measurements could show more information than that from any single image of radar basic variable, which would simplify the process of radar data analysis.

Using the different combinations of the radar reflectivity Zh, differential reflectivity Zdr and linear depolarization radio LDR in RHI and PPI of S-band polarimetric weather radar scaled to 0-255 linearly as the RGB channel data, a mass of radar composite images are created. The compare shows that the image formed by the sequential combination of Zh, Zdr and LDR can take on more abundant information, which not only retains the reflectivity structure characters in smooth changing of colors and brightness, but also implicates the properties from the polarimetric measurements, for example, the ground clutter can be easily recognized because of its striking bright green color. So the composite image of Zh, Zdr and LDR orderly as the RGB data can be directly used in the qualitative analysis of echo types. And a great deal of tests show that the combination of reflectivity multiplied by a scale factor of 1.2 and the original Zdr and LDR will make better image containing more comfortable color and stronger contrast between meteorological echoes and ground clutter echoes which can be used for operational work.