Whitepapers

Solar Cycle Sunspots are temporary areas of the sun, caused by active magnetic flux reducing convection. The more sunspots, the more areas with magnetic activity. These areas can eject particles which add to the solar wind and may be carried to Earth. As more particles hit earth, the layer of atmosphere known as the ionosphere becomes more charged, and the GNSS signal delay resulting from the ionosphere increases. The Sun's magnetic field flips once every 11 years and sunspot activity is correlated with this 11-year cycle. It is difficult to predict the magnitude of the solar cycle. Early models predicted that the maximum in 2025 would be similar to the previous. See the NOAA model above. However, new models and measurements indicate a cycle more similar to the cycle which peaked around 2002. Ionosphere The ionosphere is an ionized layer of the upper atmosphere that has a large number of electrically charged atoms and molecules, which cause a delay in the GNSS signals passing through it. The ionosphere varies over time, with significant differences between night and day, when the solar energy source is present. The impact on radio waves is dependent on frequency. The delay is inversely proportional to the square of the frequency, as a result L1 (at a higher frequency) has less delay than L2. A common metric describing the ionosphere is TEC or Total Electron Content. This is the total number of electrons integrated between two points, e.g., from the receiver to the satellite in a straight line. The units are electrons per meter squared; with the frequency of a signal, this can be converted to an equivalent signa delay. 6 Trimble IonoGuard ™ —Protecting RTK GNSS from Ionospheric disturbances

• Cover