The Environmental message is intended for a wide variety of environmental data, including: current flow, water level, water temperature, visibility, and air gap. The message has the ability to provide both real-time and forecast data. In order to maximize flexibility, this message can be used to transmit from 1 to 8 sensor reports (a 1 sensor report uses 1 slot while a message with 8 sensor reports requires 5 slots). These sensor reports can be data from one location or from multiple locations. In addition, the data does not need to be sent at the same update rate allowing data that changes more rapidly to be sent more often than slowly changing data. Static data such as sensor position can be sent even less frequently.

Usage Notes:

• The sensor reports are a combination of dynamic and static information; the static information such as location and identification should be transmitted less often than the dynamic information (sensor readings).
• The desired frequency of transmissions is an operational decision based upon how frequently the data is updated (for example, this is 6 minutes for NOAA PORTS data) and the maximum time that a new user should expect to wait to receive the data.
• Old data should never be transmitted if newer data is available. Data should also not be transmitted past the data expiration time.
• Presentation software should automatically update the data display upon receiving new data and should also show the time of the data so that users know the epoch of the data.
• Up to 5-slot messages can be created, but messages with more than 3 slots should be avoided as messages with more slots are less likely to be received due to RF noise or packet collision.
• The Sensor ID is used to link the site location, identification, and sensor data. A single location may have multiple physical sensors at that location, generating a variety of data elements, allowing for the creation of multiple sensor reports from that location.
• From 1 to 8 sensor reports can be assembled into a message; these can be from the same site or multiple sites. The number of reports assembled into a message is an operational decision based upon the maximum number of slots that are desired to be used for a single message. A single slot message can be created by using just one sensor report while it takes 5 slots to send a message with 8 sensor reports.
• This can also be used to link additional text (e.g., a separate text message). However, the same source MMSI needs to send both the Environmental Message and additional Text Description message (See Text Description Message).