My interest in weather recording is mainly focused on the technologies required to receive real-time weather images from satellites. For my long range weather insights I use Victoria University Wellington's meteorological forecasting pages, MetVUW .
- From the Weather sub-menus choose WXTOIMG to see thumbnail views of recent weather images.
- Click on a thumbnail to have a larger window pop up.
- Close the pop-up to return to the WXTOIMG page.
- Predicted satellite passes are listed at the bottom of the page.
- From the sub-menu choose MetVUW (Meteorology - Victoria University Wellington) to access their long range forecast service.
- I commonly view the 7-day or 10-day forecasts for the South Island which shows 6-hourly thumbnails of predictions.
- Click on a thumbnail image to have a larger window pop up. Close the large image to get back to the thumbnail page.
- I use MetVUW predictions to support my mountain hiking activities.
A NOAA Waeather Satellite
In 2019 four polar-orbiting satellites provide receivable VHF (very high frequency) direct weather picture broadcasts.
- Three American satellites are NOAA-15, NOAA-18 and NOAA-19 run by the National Oceanic and Atmospheric Administration. [Overview]
- The NOAA satellites continuously scan a broad strip of land beneath them with visible and infra-red sensors. As they move forward over the earth they scan over new land each time. These scan lines build up a picture similar to the line by line scanning of a home picture scanner.
- The satellites transmit frequency modulated radio signals which carry the scanning information in an Automatic Picture Transmission (APT) format
- The APT format was introduced in the 1960s so has been in use for almost 60 years. However, it is still capable of providing beautiful imagery as shown on the WXTOIMG page.
- There is one operational Russian satellite, METEOR-M2. [Overview]
- METEOR-M2 also scans the earth and transmits its information down to ground stations on earth as it passes overhead. Each scan line is 1500km wide, 15.8km apart and it takes about 12 minutes for it to complete an overhead pass as viewed from one groundstation.
- This satellite flys at a higher altitude than NOAA satellites, therefore it can see more of the earth. That means it scans and transmits a wider strip of land as it passes overhead.
- METEOR-M2 was launched in 2014 and is the most modern of the four satellites. It uses a digital system (QPSK - quadrature phase shift keying) to pass higher quality images to ground stations.
- All four satellites are classed as polar orbiting environmental satellites (POES) meaning their orbit path takes them over the north and south poles.
- They travel close to the earth, between 700 - 850 km in altitude, compared to geostationary satellites which are parked above the equator and are 35,800 km in altitude.
- Because polar orbitting satelites are closer to earth their radio signals are relatively strong, making them easier for ground stations to receive. Amateurs and school groups can use simple equipment to receive and process their signals.
- They take between 101 - 102 minutes to circle the earth once. However, as the earth is rotating on its axis during this period, the satellites always observe an adjacent sector of the earth on every pass.
- From New Zealand the four satellites appear to do a series of morning passes coming down from the North Pole and in the afternoon and evening they appear to rise up from the direction of the South Pole.
Below are details of how I receive NOAA weather satellite pictures and display them on my web page.
The hardware required is an aerial to receive the signal, a pre-amplifier to boost that signal, a receiver to convert the radio signal to an audio signal, and a computer to run software to process the signal.
My QFH aerial
- Because the weather satellites may be travelling in any orientation relative to the earth, the polarisation of their signals may be horizontal, vertical or anywhere in-between. That means a circularly polarised aerial is required to receive a steady signal.
- I use a home-built quadrafilar helix antenna (QFH or QHA), a design which allows me to receive a good signal out to the horizon. It is right-hand circularly polarised which prevents signal fades. [Circular Polarisation]
- I use a small pre-amplifier mounted at the aerial to overcome losses in my aerial cable.
I use an Icom PCR-1000 receiver. This is a relatively old receiver, but so is my decoding software and it knows how to automatically tune it to suit whichever satellite is passing overhead.
The PCR-1000 is a small black box with no control knobs on it. All settings are made via an RS232 control cable connected to a computer.
The LNK-137 Preamplifier
I use an LNK-137 preamplifier to boost signal levels from the antenna. My coaxial aerial cable is about 6m of old tv coax. I inject 15v DC onto the coax at the receiver using a bias-T device and this powers the amplifier. The current draw is about 10mA.
I use an old Compaq laptop computer as a dedicated controller. As a guide to processing power, it had previously been used with Windows Vista. I upgraded its memory to 1GB of RAM and replaced the hard disk drive for a silicon SSD. The prime requirement was for a RS232 port. This laptop didn't have one, but a USB-RS232 dongle converter worked well. It has internal WiFi.
My automated weather satellite station.
The aerial cable comes in through the wall, via the Bias-T power unit to the receiver
on the left. The control cable plugs into the USB-RS232 dongle on the side of the
laptop and the audio cable plugs into the front microphone socket.
Wxtoimg shows an un-processed satellite image on the screen.
I installed a Linux operating system on the laptop. This decision was easy to make as I found an open source (free) compilation of Skywave Linux, an amateur radio-focused distribution which included the controller software (Wxtoimg) that I wanted to use. I installed Skywave 3.1.1.
WXTOIMG is a very smart program:
- It predicts the orbits of the three NOAA satellites;
- It tunes my receiver to the correct frequency at the right time for the approaching satellite;
- It converts the satellite audio signal into pictures; and
- It pushes the pictures out via the Internet to my website and displays them beautifully.
The picture choices I have made are for MSA (Multi Spectral Analysis) during daylight passes, MCIR (Multi-channel Infra Red) for night passes with a fallback of a non-colour contrast-enhanced image if either of the first two types aren't processed. I use a licenced version of WXTOIMG.
The modern USA polar weather satellite system which will supercede the old NOAA satellites disappoints me. There is no longer any ability for amateur or educational direct weather collection as their new system requires purpose built earth stations to download data and a distribution centre to pass the weather information to officially approved users. Their website education content appears to be minimal.
Their first new satellite is named Suomi NPP (National Polar-orbiting Partnership), which launched in 2011 as a 'bridging' service supporting transitioning from old to new systems. The new system is called JPSS (Joint Polar Satellite System) with its first launch in 2017 of JPSS-1, renamed NOAA-20 on successful commissioning in space. JPSS-2, 3 and 4 are scheduled for launches in 2021, 2026 and 2031.
The modern Russian weather satellites in the Meteor-M series replace the older Meteor weather satellites which have mostly failed and been turned off. The first Meteor-M1 satellite in the new series has technical problems, so normally is turned off (March 2018). The third satellite in the series was destroyed during launch along with 18 other satellites on that rocket. Apparently old guidance software had been installed in the rocket instead of the well-tested new software needed for rockets departing the new Russian space launch site. Oops! The upper stage and its satellite payload never made it to space and burnt up on re-entry.