Botswana Seismic Network
The seismic network consists of 6 permanent stations situated around the Okavango delta in the northern part of Botswana.
Each of the stations is equipped with a Kinemetrics Altus-K2 strong motion accelerograph system with internal episensor.
Time keeping is done by GPS and power is provide by a solar energy.
Previously data storage was done on internal PCMCIA data storage card. Due to the limited space, the system was used in a triggered mode only. Nowadays data storage is not a issue any more so we developed a small system, we call it K2 logger or K2L, that can store continues data coming from the Altus-k2.
The K2L data logger
Data from the Altus K2 is send out serial at a rate of 100 Hz to the K2L system. Incoming data is converted in to miniSEED format which is common used in exchange of earthquake data. Status data, also send by the Altus K2, is logged as well and stored in daily status files. Data storage is done on internal USB stick, which act as circular buffer, and at the same time to external USB stick. Alternatively the external USB connection can be used for sending data over a modem connection. A power management system is taking care for starting up and shutting down the K2L computer in case the voltage drops below a preset value. Communication with the K2L is done by network connection using SSH.
The embedded computer in the K2L is the Raspberry pi model B with 512MB memory. Big advantage is the low power consumption, availability world wide and low price. Unfortunately the Raspberry has no real RS232 interface neither a real time clock that keeps the time when off power. However, there is an GPIO (general purpose input/output) connector that can be used to make those two option. So on the Raspberry board you will find a small board (power monitor) mounted that holds a real RS232 interface, a real time clock with battery backup and a micro controller that takes care for starting up and shutting down the system. The controller is also checking if the system is up and running by sending regularly signals that has to be answered by software running on the Raspberry. In case of no acknowledge the controller will force a reboot in an attempt to get the system running again.
Above pictures shows the field setup of a BSN station with the K2L connected. The small gray tube contains the secodary USB stick with seismic data.