The Geophysics Program Seismology Group has recently implemented several methods of continuous digital data telemetry from remote sites to the UW seismology recording lab. The digital data is 24bit, either 3 or 6 channel, from strong motion accelerometers or broad-band seismometers recorded by Terra Technology IDS24 and IDS20 digital recorders and Reftek modified 72AXX recorders. Data is sampled at either 100 or 50 s/s.
The first method has been in operation for several years. This is a one-way only transmission using a proprietary modem system over UHF radios from a remote site (TTW) to the UW. This system is prone to data dropouts due to RF interference or problems of atmospheric attenuation, and the inability to request a retransmit of lost data.This method has been mostly reliable.
Next, we use dial-up telephones and standard modems to request the download of selected data from triggered events or a time window from continuously recorded data to the UW for analysis. We have been using this method for our broad-band reftek recorded data for several years. This method has been very reliable.
We purchased a pair of Freewave Spread Spectrum data radios and have used them in several test transmissions of continuous data in house and plan to install them at a strong motion recording site to radio directly to the UW soon. These radios can also be combined with the following lease-line modems for a more remote site if necessary.This method has proved reliable locally.
There are five strong-motion + broad-band stations sending data to the UW by lease-line modems using several media for communicating. We use a Power Co. microwave communication channel for several sites which then bridge to a lease-line or a T1 channel into the UW. We are using Motorola V.3400 lease-line modems for transfering either 3 or 6 channels of data. These same sites we have set up to record triggered events and we have a 33.6 modem at the site in case we need to reset the equipment or download events if the continuous telemetry fails. We could also go to the site and retrieve the data. This method has proved reliable and when combined with a remote power switch to reset the remote modem has proved very reliable.
The most recent attempt at continuous telemetry has been to utilize the internet. We have installed a terminal server which interfaces our recorder's serial port to the internet. The terminal server is assigned an IP address and our recorder computer polls it frequently to send data. Requires a connection to a highspeed trunk.This method has proved mostly reliable although a connection we have made is not at a high speed junction.
