S-Pol Range and Azimuth Checks for MAP

The S-Pol site during the MAP field program presented a challenging situation for analyzing tower data, due to the complex terrain. The problem was two-fold: first, the numerous hills made it difficult for the radar to see towers at all and be able to distinguish them from the hillside; second, the dense vegetation, hills, and winding roads made driving to the towers extremely difficult

After several tries, we located two towers that matched well with radar observations. Figure 1 shows the radar observations of power (dBM) at elevation angles of a) 1.5°, b) 1.3°, and c) 1.1°. Notice that the towers are stationary over the three scans. The radar cooridinates (azimuth and range) for the GPS unit and S-Pol are listed in Table 1. It can be seen that the GPS and S-Pol ranges agree quite well. However, the azimuths differ by an average of ~ 1.25 °.

Please note that an azimuth correction of +1.25° will be incorporated into the final, distributed S-Pol datasets.

Verifying the pointing and ranging at different times during the project was particularly important during MAP because of the relatively soft ground at the landfill site. The pedestal was levelled after each operational period to minimize the effects of the radar settling. In order to verify that no changes occurred in the pointing and ranging calibration, we compared ground clutter patterns (in the absence of precipitation) at various times throughout the project. The results show consistent clutter locations, implying that no changes occured in the range and azimuth estimates during MAP. Figure 2 shows S-Pol power measurements of ground clutter targets northeast of the radar for 4 different days throughout the deployment. Although the propagation (and thus clutter) characteristics are different on the different days, the location of the ground echos remain highly consistent.

Special clutter scans were used to reach the conclusions shown in Table 1. For these scans, the antenna was moved very slowly, producing a spacing between beam centers of about 0.2°. Occasionally throughout the project, other groups of such scans were performed. Those occasions are listed in Table 2.