How to estimate atmospheric refraction effects on dish pointing using SatPointer
When a satellite dish is pointed toward a geostationary satellite, the path between the dish and the satellite bends slightly because Earth's atmosphere refracts radio waves. The bending effect, known as atmospheric refraction, can shift the apparent position of a satellite by a small but measurable amount. For installers working in places like the suburbs of Sydney, the tropical coast near Cairns, or a remote camp in the Pilbara, ignoring this shift can leave a dish pointed a fraction of a degree away from the true signal peak.
SatPointer is a free web tool that turns the dish-pointing calculation into a few clicks, and it offers a built-in atmospheric refraction estimate that helps installers anticipate exactly how much bending their local conditions will introduce. By understanding how the tool models refraction, an installer can decide whether the predicted offset is worth correcting or whether the alignment can proceed with the standard settings.
What atmospheric refraction actually does to a satellite signal
Atmospheric refraction occurs because radio waves travel at slightly different speeds as they pass through layers of air with different temperature, humidity, and pressure. When a wave passes from denser, cooler air into thinner, warmer air near the ground, its path curves toward the cooler medium. The result is that a satellite sitting at a true elevation of, say, 30 degrees above the horizon appears to sit a little higher in the sky than it really is.
The amount of bending depends strongly on the elevation angle. At low elevations, around 5 to 15 degrees, the wave passes through a long, slanted slice of the atmosphere and bends by the greatest amount. At elevations above 60 degrees, the wave cuts straight down through the atmosphere and the bending drops to almost nothing. This is why a dish pointed at Optus D3 in Adelaide will be affected more on a humid summer evening than the same dish pointed at a satellite directly above the user's longitude.
For practical work, the effect ranges from roughly 0.1 degree at high elevations to 0.6 degree or more when the satellite sits near the horizon during severe weather. Installers who ignore that range often find that the dish is perfectly centred on the geometry but a touch off the actual signal maximum, leading to reduced carrier-to-noise ratios and dropouts during heavy rain.
How SatPointer incorporates refraction into its pointing math
SatPointer combines Google Maps, the user's selected coordinates, and published orbital elements to draw the precise bearing line between an installation point and a target satellite. Its refraction model uses the standard International Telecommunication Union formula for radio-wave bending, scaled by the local atmospheric conditions entered by the user. Temperature, sea-level pressure, and relative humidity each feed into a correction term that shifts both the azimuth and elevation outputs.
The tool presents the result as a small offset value next to the dish-bearing read-out, so installers can see at a glance how much their local weather is pulling the apparent position. Because SatPointer updates the offset whenever the user changes the location pin on the map, it is straightforward to compare refraction between two nearby sites, such as a coastal suburb and an inland suburb in the same city.
A broader overview of how the tool integrates map data with orbital parameters is well documented on the SatPointer help pages, and many installers cross-check their numbers on the teknisi discussion forum when unusual conditions give unexpected results.
Australian weather patterns and their refraction footprint
Australia covers climates ranging from the wet tropics around Darwin and Cairns to the dry heat of central Queensland and the cool, often cloudy conditions of Tasmania. Each of these produces a different refraction signature, and SatPointer makes the comparison direct. A dish pointed at the same satellite from Townsville and from Alice Springs will experience different bending because the humidity and temperature profiles along the signal path are not the same.
Humidity plays a particularly large role because water vapour changes the refractive index of air more than dry air at the same temperature. Brisbane in late summer routinely records humidity above 80 percent, which can push the refraction offset up by 10 to 15 percent compared with the same dish in Perth during a dry winter morning. Melbourne's reputation for four seasons in a day means the refraction figure can shift several tenths of a degree between a clear morning install and an afternoon storm.
Coastal sites also pick up the temperature inversion that often forms above the ocean in the early evening. When a dish on a rooftop in Coogee is pointed at a low-elevation satellite, the inversion layer can bend the wave path sharply, so the apparent elevation rises more than the standard model predicts.
Step-by-step process for estimating refraction with SatPointer
The estimation process begins by opening the SatPointer map view and dropping a pin on the actual installation location. Once the pin is placed, the tool displays the default bearing values for the selected satellite. Before taking those numbers at face value, the installer should open the weather inputs and enter the current temperature, pressure, and humidity for the site.
After entering the conditions, the refraction offset appears next to the elevation and azimuth read-outs. A good practice is to note the offset, then change the time-of-day slider by an hour or two and observe how the offset moves. If the figure stays roughly constant, refraction will not affect the install significantly. If it moves by 0.2 degree or more, the installer should plan to fine-tune the dish once the real-time signal meter is attached.
For installers who want to work without a handheld compass, the compass-free alignment method shows how the tool's map overlay can be aligned with known landmarks such as the Sydney Harbour Bridge or a particular street, removing the need for a magnetic compass that might be disturbed by metal roofing.
Adjusting elevation and azimuth to compensate
When the predicted offset is large enough to matter, the installer can apply it directly to the elevation read-out. If SatPointer shows a refraction correction of plus 0.25 degree at 18 degrees apparent elevation, the true elevation of the satellite is 17.75 degrees, so the dish should be set to that lower value before signal fine-tuning. The azimuth correction is usually smaller because refraction bends the wave mostly in the vertical plane, but at very low elevations the horizontal shift can still be a few hundredths of a degree.
For satellites that sit close to the horizon for Australian users, such as those covering Asia or the Middle East, the corrections become more important. Installers working with AMOS satellites over Africa and Europe from a Perth rooftop can follow the AMOS dish alignment guide to combine the refraction correction with the standard low-elevation adjustments, ensuring the dish ends up on the actual signal peak rather than the geometric centre.
Common Australian install scenarios and how they differ
A small domestic Foxtel or VAST install on a suburban home in Adelaide typically points at a high-elevation satellite, so the refraction offset is only a few hundredths of a degree and rarely worth manual adjustment. By contrast, a remote NBN Sky Muster terminal near Bourke or a mining camp in the Pilbara is often aimed at a lower-elevation satellite to keep the dish size manageable, and there the refraction offset becomes part of the daily alignment checklist.
Another common case is the marine or caravan install, where the dish sits close to sea level and is aimed at a satellite hugging the horizon. Salt-laden air and temperature gradients over the water push refraction to its maximum, and the SatPointer offset can climb above 0.5 degree on a still, warm afternoon.
Installers who prefer to follow guided videos rather than text guides often look for multilingual install walkthroughs to refresh their technique in their preferred language before a tricky install.
Comparing refraction behaviour at Australian latitudes
The values shown below summarise the typical behaviour seen across the country, with refraction offsets estimated using SatPointer's built-in weather inputs.
| Location | Typical elevation to Optus D3 | Average humidity | Typical refraction offset | Practical impact |
|---|---|---|---|---|
| Sydney (coastal) | ~38° | 65–75% | 0.10–0.15° | Minor |
| Brisbane (humid subtropical) | ~42° | 70–85% | 0.12–0.20° | Minor |
| Cairns (wet tropics) | ~52° | 75–90% | 0.05–0.10° | Negligible |
| Perth (dry Mediterranean) | ~16° | 50–65% | 0.30–0.45° | Noticeable |
| Hobart (cool temperate) | ~32° | 65–80% | 0.15–0.25° | Minor to moderate |
| Alice Springs (arid inland) | ~25° | 25–40% | 0.20–0.30° | Moderate |
Seasonal swings matter just as much as geography. A dish in Hobart aligned in January will see a different refraction figure than the same dish aligned in July, because the cold winter air has a different refractive index profile than the milder summer air. The figures above show that low-elevation, humid sites produce the largest offsets, while tropical sites with high elevation angles produce the smallest. Installers can use SatPointer to test their own postcode against this pattern.
Practical recommendations for accurate refraction-aware alignment
- Always enter the current temperature, pressure, and humidity into SatPointer rather than accepting the default values, even for a quick install.
- Compare the refraction offset between morning and afternoon before final tightening, especially in coastal or tropical locations.
- Apply the offset as a subtraction from the displayed elevation when the satellite sits below 30 degrees.
- Re-check the offset whenever the dish is realigned for a different satellite, because a satellite at a different elevation will produce a different correction.
- For marine or caravan installs, expect the offset to be near the upper end of the SatPointer range and budget extra time for fine-tuning.
- Keep a small notebook of offset values for repeat customers, which helps spot seasonal trends and unusual atmospheric events.
When the next alignment is on the schedule, run through the refraction inputs on the SatPointer tool before stepping onto the roof, and the dish will land closer to the signal peak on the first attempt.