Detecting and Tracking Airborne Volcanic Ash with WSR-88D Radars

Of the 169 geologically active volcanoes in the USA, 54 volcanoes have the USGS threat levels of "high" or worse. Seven from the ten most dangerous volcanoes in the US are located in the highly-populated states of Washington, Oregon, and California. The other three are in Alaska and Hawaii.  WSR-88Ds are located in all the volcanic areas and can be used to detect explosive eruptions, estimate the amount of ash erupted, and track the volcanic plumes. These radar capabilities can be used to estimate the hazard for the general public and aviation. The estimated erupted volcanic mass can be used by atmospheric transport models to predict propagation of ash plumes at large distances from volcanoes.  The majority of previous world-wide radar observations of airborne volcanic ash have been conducted with C-band weather radars although there are a few reports on using X- and S-band systems, including two with WSR-88Ds. Comparisons of sensitivity of radars that have been used to observe volcanic ash with that of the WSR-88D show that the latter has better sensitivity to detect the ash. The WSR-88Ds are capable of detecting explosive eruptions at distance at least 320 km. Polarization properties of the ash are discussed and compared with the ones of wild fire ash. Some signal processing techniques to enhance detectability of radar echoes are considered. Recommendations are made about radar parameters to best observe airborne volcanic ash with the WSR-88Ds.  It is hoped that future observations might help with development of a Volcanic Ash Detection Algorithm.