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Weather electronics move into mainstream

Jan 1, 2003

Getting weather information offshore means being able to receive voice-based forecasts, text broadcasts, weatherfax charts, and satellite images. These various sources when used together provide an excellent picture of ever-changing offshore weather.

These types of weather data came via different means. Voice broadcasts can be received with an HF SSB transceiver or a receive-only radio that can tune to the HF band: e.g., the Si-Tex NAV-FAX 100 and 200 radios. If you're unfamiliar with the format of voice offshore weather it's a good idea to record the broadcasts on tape. Then you can play them back several times to make sure you get all the information.

Navtex (an automated text-based weather forecast and notice to mariners system) can be received with a dedicated navtex radio/printer or a radio like the NAV-FAX 100 or 200 and a laptop computer. Navtex is a great service, but it isn't well supported everywhere, and in those countries where it is broadcast it's only available in coastal areas. Navtex receivers are offered by Furuno and Simrad, among others.

Weatherfax charts can be received with a dedicated weatherfax receiver. This typically is a unit with a built-in HF SSB radio that connects to an antenna tuner. It can be set with a timer to tune to a weatherfax frequency and receive a chart or charts, which are usually printed on thermal paper. An example of this type of receiver is the Furuno FAX 207.

Another approach to receiving and manipulating weatherfax charts is to use a laptop, a modem, and weatherfax software (you also need a radio) for receiving charts. With this system, you tune the radio to the correct frequency, the chart is converted into a digital file by the modem, and then you see the chart on screen. This approach allows you to skip the paper stage entirely. If an image is valuable, you can save it to disk or print it out. If the image is poor quality, most weatherfax software allows you to process an image, often improving it. If the image is not wanted, it can simply be deleted. There is no waste of paper using this approach.

Two companies that sell weatherfax software for running on a PC are Weatherfax for Windows by Coretex, and PC HF Facsimile by Software Systems Consulting.

In addition to weatherfax charts, satellite images are also broadcast from land-based weatherfax radio stations. These charts have been received from satellites, cleaned up a bit, gridded with lat/long lines and a coastal outline, and then sent out over HF. The only downside to this process is that the satellite pictures are several hours old when you receive them on board your vessel. However, it's possible to get these images directly off the satellite.

As polar-orbiting weather satellites sail along at about 500 miles above the earth, they are constantly taking pictures, one scan line at a time. The satellites broadcast each scan line as it is received. Thus, if you had a VHF receiver on board that could decode these images, you could pick up satellite pictures as the weather birds flew overhead. This is exactly what various satellite reception products allow you to do. Equipped with a helix antenna, image capture receiver, and software, you get pluck these images directly off the satellite. And the software can clean the image up, add grids and coastlines, and false color the images for easier analysis. In order to perform this amazing feat, you do need to tell the software where you are (this can be obtained via NMEA 0183 interface with your GPS), what the time is in GMT, and what the orbital parameters are for the two NOAA polar-orbiting weather satellites. This orbital or ephemeris data can be downloaded off the web. You could also have it sent to you if you have Inmarsat C or if you have an HF e-mail system like PinOak Digital. If you are unable to get updated ephemeris data, these programs will still receive the satellite pictures and grid them, but the gridding feature will get less accurate. Most of these programs will allow you to slew the lat/long grid around so you can match it up with a major land feature whose lat/longs are known.

Examples of this type of gear include Weathertrac by SFWX, Inc., and SeaStation Mariner by Ocens, Inc.

The downside to these systems is that they add coast and another layer of complexity to your electronic systems. For the long-term voyager, however, it's a big plus to get satellite weather images anywhere in the world.


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