Weather satellite image

Weather satellite images received on board via VHF radio

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Weather information is complex

The most important question of the sailor, the answer to which decides the weal and woe of the ship and crew, is still today: “How will the weather be?” Every skipper is inevitably more or less happy to be a meteorologist and cobbles together his personal prognosis depending on skills, sources and experience.

The data available from various channels for weather forecasting must be filtered, evaluated, compared and interpreted. Purely computer-generated data in GRIB format are easily available on the basis of various calculation models. They can be displayed on a computer, tablet, smartphone or plotter with the appropriate software.

However, GRIB data only represent part of the weather information – albeit a very widespread one. Depending on the situation, weather faxes, local weather news from the newspaper or the radio, farmers’ rules, mobile phone apps and satellite images are also used. The satellite photos in particular are a great aid for weather interpretation and forecasting. With them you can classify the current weather situation even better.

One way of getting satellite photos is to get the relevant images via the Internet or a weather app. However, internet access is not always available on board a long-haul yacht. However, it is possible to access the satellite images. And it’s easy and cheap! I would like to show you how this works.

Weather satellite image 2

Reception of the satellite images on board

The still active weather satellites NOAA 15, 18 and 19 circle the earth in time with the sun and take photos with various sensors. These data are transmitted line by line via VHF radio as a tone signal (acoustically similar to a fax) to earth. The satellites rise on the horizon, continuously scan line by line what is below them and transmit the result as a sound via VHF radio. The satellite is like a fax machine flying in space. 🙂

Since these satellites speed around 850 kilometers above the earth’s surface and VHF can be received as a quasi optical signal in a direct line thousands of kilometers, it is possible to pick up the signal. This process only takes a few minutes – depending on the elevation angle. This works best when the satellite is just above your head. Then you are in the center of the area shown and the signal strength is highest.

The technical components

The following components are required to receive weather satellite images:

  1. A VHF radiotelephone system that is used on almost every sailing yacht. Ideally, the antenna is on the top of the mast.
  2. A laptop or computer with a reasonably acceptable sound card. Suitable sound cards for retrofitting with a USB connection are now available for a few euros in online shops.
  1. A special VHF receiver on which the exact frequency can be set up to the third decimal place. The device must be able to output the received signal as an audio signal in the best possible quality. Such devices cost around 180 euros. Two devices that can be considered are:
    a) the APT-06 – Weather Satellite Receiver or
    b) the R2FU (click on the image)

Satellite photos can be received with a special FM receiver.

  1. An antenna splitter or switch for the antenna line. In this way, the sensitive receiver can be separated from the VHF marine radio. The price of a simple coax manual switch is around 35 euros and various providers such as Albrecht or Daiwa produce something like this. (You can click on the image for more infos)

For safety reasons, it should be possible to bypass this switch or splitter in a few simple steps, as the radio must run even if the switch or splitter is defective.

  1. A sound cable with a mass separation filter. The filter defuses potential differences between computer / laptop and receiver. The cable costs around 12 euros and is available from various providers. For example Monacor (cable: FGA-35).
  1. A software to make the data visible. Unfortunately, what I think is the best program for this is no longer being developed. However, it is still available as a full version for free! I am very grateful for that, as the program is considered the Rolls Royce of decoding programs!

The program is called WXtoIMG (Wetter [WX] zum [to] Bild [IMG]) and can be downloaded for Windows, Mac and Linux from https://wxtoimgrestored.xyz/. The appropriate license key is:

Full name: Kevin Schuchmann
Email address: Your email address
Upgrade key: CGHZ-PP9G-EAJZ-AWKK-NDNX

This data is legal and was disclosed by the author of the software.

Assembling the components

The installation does not require a lot of work, only the very small receiver and the switch / splitter have to be installed and connected with cables. Then the sound cable is plugged into the receiver and connected to the computer.

In the next step the mentioned software WXtoIMG is installed and the mentioned upgrade key is entered (Help -> Enter Upgrade Key). Now the satellite data must be updated (File -> Update Keplers) and your own location must be entered (Options -> Ground Station). If a GPS mouse is connected or the position data is available via NMEA at a port, this can be configured as a GPS source, which makes entering the position data obsolete.

Tip: I recommend using a GPS mouse that can receive both GPS signals and Russian GLONASS data. If OpenCPN is then installed on the computer, a second chart plotter and a redundant, independent position data receiver can be installed on board relatively inexpensively. The GPS mouse usually has a very good reception so that it also works inside a GRP yacht and receives an exact position from the Russian or American systems within seconds.

Once all components have been connected, the system is switched on or started up. Finally, the audio source is configured in the software under “Options -> Recording Options”. Then everything is ready.

Reception of the satellite images

Now that everything is ready on the receiving end, a nice overflight of a weather satellite must be awaited. In the software under “File -> Satellite Pass List” you can see when the next overflights are expected. The elevation angle of the satellite should be greater than 20 degrees. Receiving flatter overflights makes little sense – the reception would be too poor.

Next, the frequency that matches the satellite must be set on the receiver. For the NOAA 19 satellite, for example, this would be 137,100 Mhz.

Note: The corresponding frequencies and flight data are conveniently displayed in the WXtoIMG program at the bottom.

The recording of the data is started in the software under “File -> Record” via “Manual Test” or “Auto Record”. The decoding takes place automatically. To check the reception quality of the first attempts, it is advisable to also listen to the received audio signal acoustically. Either through the loudspeakers of the laptop or headphones.

The audio signal from the satellites sounds like a fax-like “ping, ping, ping”, which is lost again and again in the noise and can be heard differently and clearly depending on the position of the satellite in the sky.

Satellite images: reception in practice

Since the existing VHF antenna is usually shaped as a simple, straight metal wire pointing directly upwards, it is not the ideal antenna for receiving a satellite overflight, as the satellite also flies directly over your head and therefore unfavorably in the ” Extension ”of the antenna. Nevertheless, the signal can usually be received sufficiently well.

If the first attempts are made in the harbor, it is important to note that the area and the other masts and rigs can interfere with reception. Then only patience helps. I gave up myself after the first few attempts. At sea it looked very different.

If the reception is successful, the recording is analyzed, decoded and displayed by the software. The data, which are the most important, can be displayed in different ways via the menu item “Enhancements”

  • visible light
  • infrared (at night)
  • water temperature
  • thunderstorm activity
  • humidity

Conclusion

All these evaluations were made at the push of a button and are not rocket science. There are also a few other “enhancements” available depending on the satellite. The handling is child’s play after a short “getting to know the system” and shouldn’t put anyone off.

The images above were received with a simple VHF antenna in the harbor. The sturgeon streaks were most likely caused by the rigs of the other ships.

If the system is installed and reception is good, the software can be set to “Auto Record”. Then all usable satellite overflights are automatically recorded. Any automatic frequency switching that is required for this can be implemented with a few receivers. And with the “WetterFax” plug-in, the images received can be displayed in OpenCPN in the appropriate scale over the maps.

In summary, it can be said: With an existing VHF antenna and computer, a simple weather satellite receiver system can be set up for around 200 euros, the images of which can be used free of charge for trip planning.

The system works worldwide, free of charge and without internet! Especially in the middle of the ocean. For me, the attraction of using it lies in the mixture of exciting technology on the one hand and the feeling of independence on the other. The readers of this site presumably value independence in particular 🙂

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