pressure, and field conditions can be obtained from most  types of broadcast weather services. Broadcast weather  can be transmitted to the aircraft in radio voice format or  digital format, if it is available, via an ACARS system.  Automatic terminal information service (ATIS) is the  continuous broadcast of recorded non-control information  in selected high activity terminal areas. Its purpose is to  improve controller effectiveness and to relieve frequency  congestion by automating the repetitive transmission  of essential but routine information. The information is  continuously broadcast over a discrete very high frequency  (VHF) radio frequency or the voice portion of a local NAVAID.  ATIS transmissions on a discrete VHF radio frequency are  engineered to be receivable to a maximum of 60 NM from  the ATIS site and a maximum altitude of 25,000 feet above  ground level (AGL). At most locations, ATIS signals may be  received on the surface of the airport, but local conditions  may limit the maximum ATIS reception distance and/or  altitude. Pilots are urged to cooperate in the ATIS program  as it relieves frequency congestion on approach control,  ground control, and local control frequencies. The CS  indicates airports for which ATIS is provided.  ATIS information includes the time of the latest weather  sequence, ceiling, visibility, obstructions to visibility,  temperature, dew point (if available), wind direction  (magnetic), velocity, altimeter, other pertinent remarks,  instrument approach and runway in use. The ceiling/sky  condition, visibility, and obstructions to vision may be  omitted from the ATIS broadcast if the ceiling is above  5,000 feet and the visibility is more than five miles. The  departure runway will only be given if different from the  landing runway except at locations having a separate ATIS  for departure. The broadcast may include the appropriate  frequency and instructions for VFR arrivals to make initial  contact with approach control. Pilots of aircraft arriving or  departing the terminal area can receive the continuous  ATIS broadcast at times when flight deck duties are least  pressing and listen to as many repeats as desired. ATIS  broadcast will be updated upon the receipt of any official  hourly and special weather. A new recording will also be  made when there is a change in other pertinent data, such  as runway change and instrument approach in use.  Automated weather reporting systems are increasingly  being installed at airports. These systems consist of  various sensors, a processor, a computer-generated voice  subsystem, and a transmitter to broadcast local, minute­ by-minute weather data directly to the pilot.  At many locations, ASOS/AWSS signals may be received  on the surface of the airport, but local conditions may  limit the maximum reception distance and/or altitude.  While the automated system and the human may differ  in their methods of data collection and interpretation,  both produce an observation quite similar in form and  The automated surface observing system (ASOS)/  automated weather sensor system (AWSS) is the primary  surface weather observing system of the United States. The  program to install and operate these systems throughout  the United States is a joint effort of the NWS, the FAA, and  the Department of Defense (DOD). AWSS is a follow-on  program that provides identical data as ASOS. ASOS/AWSS  is designed to support aviation operations and weather  forecast activities. The ASOS/ AWSS provides continuous  minute-by-minute observations and performs the basic  observing functions necessary to generate a aviation  routine weather report (METAR) and other aviation weather  information. The information may be transmitted over a  discrete VHF radio frequency or the voice portion of a local  NAVAID. ASOS/AWSS transmissions on a discrete VHF radio  frequency are engineered to be receivable to a maximum of  25 NM from the ASOS/AWSS site and a maximum altitude  of 10,000 feet AGL.  The automated weather observing system (AWOS)  observations include the prefix “AUTO” to indicate that  the data are derived from an automated system. Some  AWOS locations are augmented by certified observers who  provide weather and obstruction to vision information in  the remarks of the report when the reported visibility is  less than seven miles. These sites, along with the hours of  augmentation, are published in the CS. Augmentation  is identified in the observation as “OBSERVER WEATHER.”  The AWOS wind speed, direction and gusts, temperature,  dew point, and altimeter setting are exactly the same as  for manual observations. The AWOS also reports density  altitude when it exceeds the field elevation by more than  1,000 feet. The reported visibility is derived from a sensor  near the touchdown of the primary instrument runway.  The visibility sensor output is converted to a visibility value  using a 10-minute harmonic average. The reported sky  condition/ ceiling is derived from the ceilometer located  next to the visibility sensor. The AWOS algorithm integrates  the last 30 minutes of ceilometer data to derive cloud layers  and heights. This output may also differ from the observer  sky condition in that the AWOS is totally dependent upon  the cloud advection over the sensor site.  Automated Weather Observing System  Automated Terminal Information Service (ATIS)  Automated Surface Observing System (ASOS)/  Automated Weather Sensor System (AWSS)  Automated Weather Observing Programs  4-5 