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with battery storage. Seismic data are transferred to data processing workstations on the network <br />via 2.4-GHz, direct-sequence, spreadspec[rum wireless transceivers. <br />While the PC-I04 computers can operate the four- and eight-channel A/D boards under <br />Windows95/98/NT, DOS, and Linux, Linux was selected as [he operating system of choice <br />because laboratory tests showed [hat it allows the fastest error-free sampling rates. Samba, an <br />open-source file system server, was used to give Microsoft Windows-based network nodes access <br />to files on the Linux PC-I04 units. The 486-100 MHz PC-l04 computers are placed at the point of <br />signal digitizing to alleviate a data transmission bottleneck encountered in some applications of <br />method 2. <br />In method 2, seismic data are continuously sampled and transmitted back to a centralized <br />processing computer on [he network, where they are examined for discrete seismic "events." The <br />number of channels that can be recorded at [he high sampling rates is limited by the available <br />bandwidth of the spread-spectrum radio network. Adding additional channels reduces the <br />maximum possible sampling rate. To increase the number of stations providing data via radio link <br />without reducing [he sampling rates, the distributed PC-104 approach was developed. <br />Continuously sampled seismic data are examined by the embedded processor and discarded, if so <br />desired, when [rigger conditions are not met. Data files meeting the trigger criterion are locally <br />saved to disk and/or pulled off the remote node with [he wireless network connection. Providing <br />[he task load is not too great on [he remote computer, additional processing may also be done. <br />Work is currently underway [o use [he networked PC-104 platforms with inexpensive single- <br />frequency Global Positioning System (GPS) receivers for continuous measurements of subsidence <br />and other factors of importance in mine safety studies (Swanson et al., 2001). <br />Time Base Synchronization <br />Each data acquisition system records a common timing signal derived from GPS satellites. <br />Underground data acquisition systems receive these time codes via copper or fiber cables. During <br />[he initial part of the data processing cycle, [he timing signals are decoded and the time base of <br />each seismic record is adjusted. <br />SOFTWARE <br />Networking <br />Several different types of networking and operating system software were examined during <br />system development. As the initial data acquisition systems were restricted to DOS, peer-[o-peer <br />networking to the data processing platforms was achieved using [he NetBEUI protocol available in <br />Workgroups Add-On for DOS. TCP/IP protocol is used to connect to Linu1<based data acquisition <br />PC's. The main seismic data processing PC's use either W indows9x or NT operating systems. <br />Use of mining companies' general-purpose LAN's for seismic data acquisition and processing <br />has me[ with mixed success. If there is no one on site to [end [o [he monitoring system on a regular <br />basis, astand-alone, or isolated, LAN is preferred. This avoids problems associated with many <br />diverse users, corporate firewalls, and other security issues. If [he corporate system administrator <br />is on site and attuned [o the needs of [he seismic monitoring system, problems can be minimized. <br />By isolating [he data acquisition nodes onto a separate LAN, these problems can be largely limited <br />to periodic temporary disruption of the automated data processing. <br />