Specific Area Message Encoding


Specific Area Message Encoding is a protocol used for framing and classification of broadcast emergency warning messages. It was developed by the United States National Weather Service for use on its NOAA Weather Radio network, and was later adopted by the Federal Communications Commission for the Emergency Alert System, then subsequently by Environment Canada for use on its Weatheradio Canada service. It is also used to set off receivers in Mexico City and surrounding areas as part of the Mexican Seismic Alert System.

History

From the 1960s to the 1980s, a special feature of the NOAA Weather Radio system was the transmission of a single attention tone prior to the broadcast of any message alerting the general public of significant weather events. This became known as the Warning Alarm Tone. Although it served NWR well, there were many drawbacks. Without staff at media facilities to manually evaluate the need to rebroadcast an NWR message using the Emergency Broadcast System, automatic rebroadcasting of all messages preceded by just the WAT was unacceptable and impractical. Even if stations and others with the need were willing to allow for this type of automatic capture, assuming the events for activation were critical, there was no way for automated equipment at the station to know when the message was complete and restore it back to normal operation.
SAME had its beginnings in the early 1980s when NOAA's National Weather Service began experimenting with system using analog tones in a dual-tone multi-frequency format to transmit data with radio broadcasts. In 1985, the NWS forecast offices began experimenting with placing special digital codes at the beginning and end of every message concerning life- or property-threatening weather conditions targeting a specific area. The intent of what became SAME was to ultimately transmit a code with the initial broadcast of all NWR messages. However, the roll-out moved slowly until 1995, when the U.S. Government provided the budget needed to develop the SAME technology across the entire radio network. Nationwide implementation occurred in 1997, when the Federal Communications Commission adopted the SAME standard as part of its new Emergency Alert System. In 2003, NOAA established a SAME technology standard for weather radio receivers.
The SAME technique was later adopted by the U.S. Federal Communications Commission in 1997 for use in the EAS as well as by Environment Canada for its Weatheradio Canada service in 2004. Much like the original EBS dual-tone, this produces a distinct sound which is easily recognized by most individuals due to its use in weekly and monthly broadcast tests, as well as weather alert messages. During the said events, viewers and/or listeners will hear these digital codes in the form of buzzes, chirps, and clicking sounds just before the attention signal is sent out and at the conclusion of the voice message.

Format of digital parts

In the SAME system, messages are constructed in four parts, the first and last of which are digital and the middle two are audio. The digital sections of a SAME message are AFSK data bursts, with individual bits lasting 1920 μs each, giving a bit rate of 520 bits per second. A mark bit is four complete cycles of a sine wave, translating to a mark frequency of 2083 Hz, and a space bit is three complete sine wave cycles, making the space frequency 1562.5 Hz.
The data is sent isochronously and encoded in 8-bit bytes with the most-significant bit of each ASCII byte set to zero. The least-significant bit of each byte is transmitted first, including the preamble. The data stream is bit and byte synchronized on the preamble.
Since there is no error correction, the digital part of a SAME message is transmitted three times, so that decoders can pick "best two out of three" for each byte, thereby eliminating most errors which can cause an activation to fail.

Header format

The text of the header code is a fixed format:
ZCZC-ORG-EEE-PSSCCC+TTTT-JJJHHMM-LLLLLLLL-
This is broken down as follows:
1. A preamble of binary 10101011 repeated sixteen times, used for "receiver calibration", then the letters ZCZC as an attention to the decoder.
2. ORG — Originator code; programmed per unit when put into operation
  • PEP – Primary Entry Point Station
  • *President or other authorized national officials
  • CIV – Civil authorities
  • *i.e. Governor, state/local emergency management, local police/fire officials
  • WXR – National Weather Service
  • *Any weather-related alert
  • EAS – EAS Participant
  • * Broadcasters. Generally only used with test messages.
  • EAN – Emergency Action Notification Network
  • * Used to send Emergency Action Notifications.
3. EEE — Event code; programmed at time of event
4. PSSCCC — Location codes, each beginning with a dash character; programmed at time of event
  • In the United States, the first digit is zero if the entire county or area is included in the warning, otherwise, it is a non-zero number depending on the location of the emergency. The remaining five digits are the FIPS state and county code. The entire state may be specified by using county code 000.
  • In Canada, all six digits make up a Canadian Location Code, which corresponds to a specific forecast region as used by the Meteorological Service of Canada. All forecast region numbers are six digits with the first digit always zero.
5. TTTT — Purge time of the alert event
  • In the format hhmm, using 15 minute increments up to one hour, using 30 minute increments up to six hours, and using hourly increments beyond six hours. Weekly and monthly tests sometimes have a 12-hour or greater purge time to assure users have an ample opportunity to verify reception of the test event messages; however; 15 minutes is more common, especially on NOAA Weather Radio's tests.
  • For short term events this value could be set to 0000, which will purge the warning immediately after the message has been received. However, this is not typical, and FCC guidelines suggest a minimum of 15 minutes purge time.
  • The purge time is not intended to coincide with the actual end of the event. Longer events that may not end for days may have a purge time of only a few hours. That an event message has been purged does not indicate or imply that the threat has passed.
6. JJJHHMM — Exact time of issue, in UTC,.
  • JJJ is the Ordinal date of the year, with leading zeros
  • HHMM is the hours and minutes, in UTC, with leading zeros
7. LLLLLLLL — Eight-character station callsign identification, with "/" used instead of "–".
Each field of the header code is terminated by a dash character, including the station ID at the end; individual PSSCCC location numbers are also separated by dashes, with a plus separating the last location from the purge time that follows it.

Full message format

An EAS message contains these elements, in this transmitted sequence:
  1. Header.
  2. Attention signal — Sent if any message is included ; must be at least eight seconds long.
  3. *Single audio tone for Weatheradio.
  4. *Combined tones for broadcast radio/TV.
  5. Message — Audio, video image or video text.
  6. Tail — NNNN.
There is one second of blank audio between each section, and before and after each message. For those used to packet communications systems where each packet has a checksum, note that there is no checksum used in the message format. Each message is supposed to be transmitted 3 times, and the receiver is obliged to implement columnar parity correction.
The combined tones date back to 1976 when they were made part of the Emergency Broadcast System, the EAS' predecessor.

Event codes

There are roughly 80 different event codes that are used in EAS. These codes are defined federally by the FCC for use in the EAS system and publicly by the Consumer Electronics Association standard for SAME protocol weather radio receiver decoder units.
All but the first six of these used to be optional and could be programmed into encoder/decoder units at the request of the broadcaster. However, a July 12, 2007 memo by the FCC now requires mandatory participation in state and local level EAS by broadcasters. Furthermore, the creation and evolution of a voluntary standard by the CEA in December 2003 has provided participating manufacturers of weather radio receivers a single definitive reference to use when designing and programming receivers. In addition, some receiver manufacturers have added an additional layer as to whether or not an event code can be user-suppressed or will never be allowed to be suppressed.
The FCC established naming conventions for EAS event codes. The third letter of the code must be one of the following.
The exception to this convention is for "TOR", "SVR", "EVI", the EAS national activation codes, and administrative messages.

On weather radio receivers

There are many weather/all-hazards radio receivers that are equipped with the SAME alert feature, which allows users to program SAME/FIPS/CLC codes for their designated area or areas of their interest and/or concern rather than the entire broadcast area.
On a more specialized receiver, a user has the option to eliminate any SAME alert codes that may not apply to their area such as a "Special Marine Warning" or a "Coastal Flood Warning". Once the SAME header is sent by NOAA/NWS and if it matches the desired code, the receivers then decode the event, scroll it on their display screens, and sound an alarm.
Receivers receive on one of the following National Weather Service network frequencies : 162.400, 162.425, 162.450, 162.475, 162.500, 162.525, and 162.550. The signals are typically receivable up to 40 miles from the transmitters.

In popular culture

  • The Iowa State Cyclones football sports program uses a SAME tone at the end of the pregame video before the football team takes the field. The SAME message is followed by the following narration: "This is a Cyclone Weather Alert! Ladies and Gentlemen, radar has indicated a strong storm approaching Jack Trice Stadium. High winds and low visibility are expected. fans in the area should seek immediate cover...."
  • The EOM tone was heard in the movie trailer for Knowing and in the series Jericho in which its familiar emergency use and its increasing cadence create a sense of foreboding.
  • It was used in the movie trailer for Olympus Has Fallen and The Purge. The uses have since been heavily discouraged on air by the Federal Communications Commission, and stations and networks using them in advertising or promotions have been fined for doing so.
  • The SAME tones can be heard in the Impractical Jokers episode "Virtual Insanity".
  • A Trevor Henderson creature, named Siren Head uses this sound, but it can send much more EAS sounds than that through it's rusty speakers.