Rescue 21 Distress System Coverage

VHF Distress Coverage Charts

Charts showing predicted areas of VHF National Distress System coverage can be downloaded in .jpg format. Coverage plots assume a mobile transmitter power of 1 watt or greater at sea level over water.

Predicted charts were created by C3CEN Remote Missions Systems Product Line using open source software RF Signal Propagation, Loss, and Terrain (RF SPLAT) analysis tool. The software calculates path loss based on the NTIA Longley-Rice Irregular Terrain Model (ITM) as well as the new Irregular Terrain with Obstructions Model (ITWOM v3.0). Terrain data was modeled based on the high resolution 1 arc-sec obtained from NASA’s Shuttle Radar Topography Mission (SRTM) flown in 2000. The coverage plots are displaying predicted regional coverage area based on line of sight between the Regional Fixed Facility VHF receive antenna and an antenna six feet above water level.

Digital Selective Calling

On 20 January 2015 the Coast Guard declared Sea Area A1 in certain areas off the coast of the United States based upon the performance of the Coast Guard's Rescue 21 System in accordance with applicable provisions of the International Convention for the Safety of Life at Sea, 1974 (SOLAS). The Coast Guard defines Sea Area A1 as those areas where more than ninety percent of the area within 20 nautical miles seaward of the territorial baseline along the East, West and Gulf Coasts of the United States, excluding Alaska, and including Hawaii, Puerto Rico, Guam, the Virgin Islands of the United States and the Northern Mariana Islands of Saipan, Tinian and Rota, is within coverage of Coast Guard very high frequency, or VHF Coast Stations that provide both a continuous watch for Digital Selective Calling, or DSC, distress alerts on Channel 70 and a capability to respond to distress alerts. That response would typically be on VHF Channel 16.

Coverage Plots

These coverage plots include distress watchkeeping on both channel 16 voice and channel 70 DSC.