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on mountain edge tops and one in a valley bottom 365 m (1,200 ft) below. Each panel is <br />approximately 250 m (830 ft) wide. <br />A line-of-sigh[ path between each remote data acquisition node and a data processing site was <br />required for [he 2.4-GHz spread-spectrum transceivers employed. Tests of wireless LAN repeaters <br />were also made. The repeaters were found to reduce overall data processing rates to unacceptable <br />levels in certain data acquisition modes. Both continuous and event-triggered seismic data file <br />collection and transmission modes were investigated. Due [o the high sampling rates, [he data <br />acquisition platforms created an irreversible backlog of data files when a repeater was used <br />between a data acquisition node and [he main processing node. Thus, when a repeater was <br />required, i[ was necessary to collect data in event-triggered mode. <br />North ridge array <br />Valley array <br />LEGEND South ridge array <br />Sensor <br />Q Wireless network node <br />Q Data processing node <br />Figure 5. Bowie No. 2 Mine network. <br />EXAMPLE SEISMIC MONITORING RESULTS <br />Examples of seismic event locations are shown in Figures 6 and 7. Relative seismic even[ <br />magnitude is indicated by the size of [he symbols, with the largest event shown having an <br />approximate magnitude of 2. The processing procedures performed for the event locations were <br />completely software automated without human interaction. <br />Seismicity associated with 7 m (23 fr) of retreat of the D-2 longwall coal panel a[ [he Willow <br />Creek Mine is shown in Figure 6. The abundant seismic activity is a product of strong, competent <br />