Arbitrary Baseline Radar Reflectivity Vertical Cross Section Algorithm

Reflectivity vertical cross section is an effective tool to monitor and analyze severe convection weather and identify convective and stratiform cloud. A one-time request can be issued by the PUP (Principle User Processor) user to the RPG (Radar Product Generator) for the product whose vertical resolution is 0.5 km in new generation weather radar system. But this manner isn't convenient to generate the product from historical volume scan radar data, and its vertical resolution is not high. Therefore, a high-resolution reflectivity vertical cross section algorithm based on volume scan radar data has been developed. The algorithm has three steps. First, a random beeline is drawn by mouse on radar image on computer screen, the distance from radar and the azimuth from the begin-point to the end-point and all the other points with 1 km spacing on the beeline are calculated. Second, the elevation angle, azimuth and slant range of any grid point on reflectivity vertical cross section on the space location in radar polar coordinates is calculated. Last, the analysis value of grid point is obtained by using an objective analysis method. In view of the function of reflectivity vertical cross section for analyzing the three dimension structure of severe convective weather, the reflectivity analysis field obtained by the objective analysis method is required to be spatially consecutive while high-resolution structure comparable to the raw volume scan radar data is retained as much as possible. A linear interpolation in vertical direction combined with a nearest neighbor scheme on range-azimuth planes is used. Two schemes are employed for linear interpolation in vertical direction. In the first scheme, two reflectivities in dBZ of the same azimuth-range bin between adjacent tilts are averaged with distance-weight. In the second scheme, firstly reflectivity in dBZ is converted into reflectivity in mm⁶ /m³. Then two reflectivities in mm⁶/m³ between adjacent tilts are averaged with distance weight. Last, reflectivity in mm⁶/m³ is converted into reflectivity in dBZ again. Through comparison between reflectivity PPI and vertical cross section, it's found that the echo intensity and space position in reflectivity vertical cross section generated using the algorithm is reasonable. Through image continuity examination, it's found that the reflectivity analysis field obtained using interpolation with reflectivity in dBZ is spatially consecutive, but the reflectivity analysis field obtained using interpolation with reflectivity in mm⁶/m³ is inconsecutive in vertical direction. Through comparison between reflectivity analysis values and observations, it's found that reflectivity analysis values obtained using interpolation with reflectivity in dBZ are more close to observations than in mm⁶/m³. Because the space between adjacent tilts in low elevation angles is lesser than that of high elevation angles, the interpolation results in low elevation angles are better than that of high elevation angles.