One of the key products within the Integrated Terminal Weather System (ITWS) Initial Operating Capability (IOC) product suite is one designed to remove anomalous propagation (AP) ground clutter from the ASR-9 precipitation product. This has been identified as a critical component of ITWS due to the frequent occurrence of AP when storms or outflows move over this sensor. In order to achieve this objective, the algorithm compares the raw ASR-9 weather data to composite maps generated by the Next Generation Weather Radar (NEXRAD) and the Terminal Doppler Weather Radar (TDWR). An editing template, containing regions of AP, is created based on the ASR-9 data collected at the middle of the composite volume scan to minimize the difference in update rates. It is used to edit the ASR-9 scan immediately after the composite map and all subsequent scans until a new composite map is received. The motion of each storm cell is used to ensure that valid weather returns which track into AP regions are not removed.
This algorithm has been shown to perform quite well at removing AP, especially if the weather returns are not co-located with the AP. During the 1994 Demonstration and Validation Operational Test and Evaluation in Memphis and Orlando, the probability of editing AP (PEAP) in the absence of weather was 0.97 for level 2 and greater returns. The probability of editing weather (PEW) for those cases with weather only was quite low, e.g., 0.01. In order to minimize the removal of weather returns in cases where the AP and weather are located in close proximity, the editing thresholds are quite conservative. This is reflected by the 1994 results which show a PEAP of 0.81 and a PEW of 0.02 for this class of event. Besides the conservative threshold, another limiting factor is the fact the AP regions can expand or increase in intensity after the AP editing template is created. This rapid variation frequently occurs with convectively generated AP and can cause the performance of the algorithm to decrease with time until a new template is created.
In this study, we will examine the algorithm failure mechanisms in detail to identify possible site adaptable parameter changes that can be used to improve the performance for the mixed weather/AP events. This is especially germane since the parameter set was not re-evaluated after the TDWR composite map was incorporated in 1995. In the critical region over the airport during hazardous weather conditions, this radar updates more frequently than the NEXRAD. Since the parameters were designed to account for the NEXRAD volume update rate, they are probably too conservative for the current algorithm which uses both composite maps. We will also investigate the utility of updating the AP editing template more frequently to account for the dynamic nature of this phenomena.
* This work was sponsored by the Federal Aviation Administration. The views expressed are those of the authors and do not reflect the official policy or position of the U.S. Government.
+ Opinions, interpretations, conclusions and recommendations
are those of the authors and are not necessarily endorsed by the United
States Air Force
The 8th Conference on Aviation, Range, and Aerospace Meteorology