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Frequently asked questions

National Weather Service River Forecast Center

National Weather Service Weather Forecast Office

National Weather Service

Web Map Services, Internet accessible services that provide map layers. Contrail integrates these services as map layers within the Contrail pan and zoom map display.

Next Generation Weather Radar

ITS stands for Intelligent Transportation Systems and is the field that all Road Weather solutions fits in with.

TDMA is time division multiple access. It is one of the transmission modes available for ALERT2 using the RF AirLink layer. In this mode, each transmitter takes turns talking on a specified schedule. Using this mode eliminates data loss due to two sites transmitting over each other.

NTCIP is National Communications for ITS Protocol. It is a set of protocols that are defined by a standards body for road weather information systems.
RWIS stands for Road Weather Information Systems.

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.

SHEF is the Standard Hydrologic Exchange Format. This format was defined to give standards to how hydrologic data is exchanged between agencies and computer systems. The SHEF format is used to transfer data from individual local government data collection systems into the MADIS system where it is collected and redistributed to all of the various NWS around the U.S.

Reed Solomon encoding stores bytes of checksum data and allows for the correction of blocks of data that might be caused by a noise burst. This method also can determine if the data is in error and is uncorrectable. This method of data correction compliments Forward Error Correction(FEC), the former correcting burst errors, and the latter correcting individual bit errors.
Forward error correction is a method in which binary data is encoded using additional bits. This method of error correction can correct individual bit errors in an RF data transmission. It is not capable of correcting many bit errors together.