ALERT stands for Automated Local Evaluation in Real-Time. It is a radio protocol developed by the NWS in the late 1970s for transmitting hydrometeorological data. Some of the hallmarks of ALERT are:
- 300 BAUD
- Sensor IDs from 1 – 8192
- Sensor values are integers from 0 to 2047
- ALOHA transmissions – They speak when they have something to say and they don’t know if their data was received
- More than one base station can receive transmissions
- Transmission is four (4) bytes of data per transmission, with three (3) bytes of content and the rest of the bits are marker bits.
- Data can be lost because two sites can transmit at the same time causing a collision
- Rain count protocol is resilient, if we miss a transmission, we catch up with the total on the next transmission
This protocol is used widely in the U.S. and Australia. In Australia, they call it ERRTS.