Thursday, December 23, 2010

Specific Area Message Encoding

Specific Area Message Encoding,
Specific Area Message Encoding or SAME is the protocol used to encode the Emergency Alert System (EAS) and NOAA Weather Radio's Public Warning System in the U.S. and Weatheradio Canada in Canada.


From the 1960s to the 1980s, a special feature of the NOAA Weather Radio system was the transmission of a single tone at 1050 Hz prior to the broadcast of any message alerting the general public of significant weather events. This became known as the Warning Alarm Tone (WAT). Although it has served NOAA Weather Radio well, there were many drawbacks: without staff at media facilities to manually evaluate the need to rebroadcast a Weather Radio message using the Emergency Broadcast System (EBS), automatic rebroadcasting of all messages preceded by just the WAT was unacceptable and impractical. Even if stations and others with that type of 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.
In 1985, the National Weather Service forecast offices began experimenting with putting 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 Weather Radio messages. The NWS started implementing SAME on the full NOAA Weather Radio system in 1988. The SAME technique was later adopted by the FCC for regular broadcasters on radio, television, and cable, as well as by Environment Canada for its Weatheradio Canada service. Much like the original EBS alert tone, this produces a distinct sound which is easily recognized by most Americans due to its use in weekly and monthly broadcast tests, and in weather emergencies. During the said events, viewers and/or listeners will hear these digital codes in the form of buzzes, chirps, & clicking sounds (or what broadcast engineers affectionately call "duck farts")just before the attention signal is sent out and at the conclusion of the voice message.


A sample SAME transmission

An example of SAME, with the header decoded as follows:
"A Required Weekly Test has been issued for the following counties/areas: Hillsborough FL, Manatee FL, Pasco FL, Pinellas FL, and Sarasota FL at 12:15 am EDT on October 5 effective until 12:45 am EDT. Message from WTSP/TV."
Problems listening to this file? See media help.
In the SAME system, messages are constructed in four parts, the first and last of which are digital. The first part is a header message, which 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.
The header is an AFSK data burst, with each individual bit lasting 1920 μs (1.92 ms) each, giving a bit rate of 5205⁄6 bits per second. A mark bit is four complete cycles of a sine wave, translating to a mark frequency of 20831⁄3 Hz, and a space bit is three complete sine wave cycles, making the space frequency 1562.5 Hz.
The data is encoded in 7-bit ASCII but uses all 8 bits, with no parity bit and no stop bit ("8-N-0"). The least-significant bit of each byte is transmitted first, including the preamble.
The text of the header code is a fixed format of Preamble-ZCZC-org-eee(up to 32 of -pssccc)+tttt-jjjhhmm-llllllll:
A preamble of binary 10101011 (0xAB in hex) repeated sixteen times, used for "receiver calibration" (i.e., clock synchronization), then the letters ZCZC as an attention to the decoder
org: Originator code; programmed per unit when put into operation
EAN - Emergency Action Notification Network (President or other authorized national officials. No longer officially used)
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 (or Environment Canada. Any weather-related alert)
EAS - Broadcast station or cable system (Broadcasters. Generally only used with test messages)
eee: Event code; programmed at time of event
pssccc: Location codes (up to 31 locations); programmed at time of event
In the United States, designated by FIPS state code and indicating the county (parish in Louisiana, borough or census area in Alaska), but which may be designated for the whole state by using county number 000
In Canada, designated by Canadian Location Code, which corresponds to a specific forecast region as used by the Meteorological Service of Canada
tttt: Duration of alert in the format hhmm, normally in increments of 15 minutes from time of issue
jjjhhmm: Exact time of issue, in UTC, without time zone adjustments
jjj is the Ordinal date day of the year, with leading zeros
hhmm is 24-hour hours and minutes, in UTC, with leading zeros
Eight-character station callsign identification, with / used instead of - (such as the first eight letters of a cable headend's location, WABC/FM for WABC-FM, or KLOX/NWS for a weather radio station programmed from Los Angeles).
Each field of the header code is terminated by a dash character.

Full message breakdown

An EAS message contains these elements, in this transmitted sequence:
Attention signal: Sent if any message is included (normally sent with all messages except RWT on commercial radio/TV); must be at least eight seconds long
Single 1050 Hz (help·info) audio tone for Weatheradio
Combined 853 and 960 Hz (help·info) tones for commercial radio/TV
Message - audio, video image or video text
Tail: (Preamble) NNNN (EOM)
There is one second of blank audio between each section, and before and after each message.

Event codes

There are about 80 different event codes currently used in EAS. Originally, all but the first six of these were 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.
Key for event code type field:
M mandatory code
O1 original optional code
O2 optional code added in 2002
Type Code Description
M EAN Emergency Action Notification (Begins a nationwide EAS activation)
M EAT Emergency Action Termination (Ends a national activation)
M NIC National Information Center statement (Used to follow up an EAN)
M RMT Required Monthly Test
M RWT Required Weekly Test
M NPT National Periodic Test
O1 BZW Blizzard Warning
O1 CEM Civil emergency Message
O1 CFA Coastal flood watch
O1 CFW Coastal flood warning
O1 DMO Demonstration message
O1 EVI Evacuation immediate
O1 FFA Flash flood watch
O1 FFS Flash flood statement
O1 FFW Flash flood warning
O1 FLA Flood watch
O1 FLS Flood statement
O1 FLW Flood warning
O1 HUA Hurricane watch
O1 HUW Hurricane warning
O1 HWA High wind watch
O1 HWW High wind warning
O1 SPS Special weather statement
O1 SVA Severe thunderstorm watch
O1 SVR Severe thunderstorm warning
O1 SVS Severe weather statement
O1 TOA Tornado watch
O1 TOR Tornado warning
O1 TRA Tropical storm watch
O1 TRW Tropical storm warning
O2 ADR Administrative message
O2 AVA Avalanche watch
O2 AVW Avalanche warning
O2 BHW Biological hazard warning
O2 BWW Boil water warning
O2 CAE Child abduction emergency
O2 CDW Civil danger warning
O2 CHW Chemical hazard warning
O2 CWW Contaminated water warning
O2 DBA Dam break watch
O2 DBW Dam break warning
O2 DEW Contagious disease warning
O2 DSW Dust storm warning
O2 EQW Earthquake warning
O2 EVA Evacuation watch
O2 FCW Food contamination warning
O2 FRW Fire warning
O2 FSW Flash freeze warning
O2 FZW Freeze warning
O2 HLS Hurricane local statement
O2 HMW Hazardous materials warning
O2 IBW Iceberg warning
O2 IFW Industrial fire warning
O2 LAE Local area emergency
O2 LEW Law enforcement warning
O2 LSW Landslide warning
O2 NAT National audible test
O2 NMN Network message motif
O2 NST National silent test
O2 NUW Nuclear plant warning
O2 POS Power outage statement
O2 RHW Radiological hazard warning
O2 SMW Special marine warning
O2 SPW Shelter in place warning
O2 TOE 911 telephone outage emergency
O2 TSA Tsunami watch
O2 TSW Tsunami warning
O2 TXB Transmitter backup on
O2 TXF Transmitter carrier off
O2 TXO Transmitter carrier on
O2 TXP Transmitter primary on
O2 VOW Volcano warning
O2 WFA Wildfire watch
O2 WFW Wildfire warning
O2 WSA Winter storm watch
O2 WSW Winter storm warning
O2 ??A Unrecognized watch
O2 ??E Unrecognized emergency
O2 ??S Unrecognized statement
O2 ??W Unrecognized warning

SAME on weather radio receivers

An example of a SAME alert weather radio receiver.
There are many weather/all-hazards radio receivers that are equipped with the SAME alert feature. It 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 (Examples given: If a person were to live in Irving, Texas, he or she would program a FIPS code for Dallas County. However, if he or she needs to be in the know of severe weather from the west and northwest ahead of time, the user would program additional FIPS codes for Denton and Tarrant Counties. 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(s), 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 (in MHz): 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. 

SAME in popular culture

The SAME EOM (end of message) tone was heard in the movie trailer for Knowing, where its familiar emergency use and its increasing cadence create a sense of foreboding.


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