Tech Chat | How do solar storms affect RTK surveying?

For sophisticated surveyors, you may have experienced a time when RTK equipment suddenly became difficult to fix, even with perfect equipment in an open sky view. After that everything went back to normal. This is most likely caused by a solar storm.

Recently, you may also feel that RTK devices have become difficult to fix around the world, such as Vietnam and India. Because it is currently the active period of solar storms.

So how do solar storms affect RTK surveying? What's the impact of 2023 solar storms? In such a special period, what should we do to make the measurement results reliable?

What is the Ionosphere Error?

In RTK measurement, the satellite signal will pass through the atmosphere and be received by the receiver, and various errors will occur in the process. Among them, due to the active ionospheric high-energy particles, it will have a double impact on satellite signals, which can not only change the propagation time of the signal, but also affect the propagation path of the signal.

The ionosphere is constantly changing. The ionosphere consists of particles that are ionized by solar radiation, so the ionosphere changes with sunrise and sunset. At night, when it is not exposed to the sun, the previously ionized particles recombine to become neutral particles and the ionosphere becomes less concentrated. In addition to solar radiation, the ionosphere is subject to many unpredictable changes from various sources of perturbation in space and on Earth itself, which makes it impossible to accurately determine the ionospheric pattern at a particular time.

In RTK algorithms, ionospheric delay can be eliminated by double difference, which is based on the assumption that the delay from the satellite transmitting end to the ground base station receiving end and the satellite transmitting end to the ground mobile station receiving end are consistent, and the consistency between them will become worse as the baseline grows and the ionospheric activity increases. In the long baseline RTK calculation, the currently popular linear combination of ionosphere-free can eliminate the influence of the ionospheric first-order term, but at the same time amplify the noise and multi-path effect; in the virtual reference station algorithm of network RTK, there are also studies of interpolation model algorithms based on baseline length and ionospheric activity, but when the ionosphere is overly active, the accuracy of the virtual reference station data will The accuracy of VRS data is greatly reduced when the ionosphere is overactive.

How Do Solar Storms Affect RTK?

As mentioned earlier, the ionosphere consists of particles that are ionized by solar radiation. Therefore, during the active period of the solar storm, the ionosphere will be highly active due to its influence, which will increase the RTK measurement error, make it difficult to fix, and reduce the accuracy.

Impact of Solar Storms on GNSS in 2023

When judging the impact of solar storms, we usually use the index F10.7, which is the solar 10.7cm radio flux (10-22w.m-2.Hz-1), which is used to represent the heating and ionization effect.

The Space Environment Prediction Center regularly releases F10.7 index short- and medium-term forecast products and evaluates and validates the F10.7 index short-term forecast results. The forecast quantity evaluated is the F10.7 forecast value for the next three days, and the measured value is the observed daily value from the Penticton station in Canada.

The figure below shows that the F10.7 value of the Earth’s ionosphere will reach a peak in April-June 2023, which will affect the navigation, positioning and timing of areas affected by solar storms.

Figure1: Solar Cycle F10.7cm Radio Flux Progression
Data from (Space Environment Prediction Center Chinese Academy of Sciences)

What Should We Do During Solar Storm?

In order to reduce the impact of ionospheric errors on satellite signals. BeiDou Navigation Satellite System broadcasts ionospheric parameters in the navigation message to facilitate users to correct ionospheric delay errors. B1I/B3I signals provide Klobuchar model parameters. B1C/B2a signals provide BDGIM ionospheric model parameters.

Using global observation data to solve the precise ionospheric delay can achieve higher accuracy (2-9TECU).

Figure 2: Global Ionosphere Map
Data from (Test and Assessment Research Center of China Satellite Navigation Office)

The following charts provide the ionosphere-influenced positioning accuracy of the three major GNSS - GPS, BDS and Galileo on a global scale.

Figure 3：Current BDGIM Ionospheric Correction Accuracy of BDS at 07:00 on 23th April

Figure 4：Current NeQuick Ionospheric Correction Accuracy of GALILEO at 07:00 on 23th April

Figure 5：Current Klobuchar Ionospheric Correction Accuracy of GPS at 07:00 on 23th April
Data from (International GNSS Monitoring & Assessment System)

In addition to the ionospheric parameters of the navigation system, for individuals, we can also avoid the impact of solar storms through the following methods:

• The activity of the ionosphere is mainly affected by solar radiation, and we can choose to work at night when the solar activity is relatively less intense.
• During daytime operation, in the case of a very active ionosphere, short baselines between base stations and rovers are a relatively reliable way to work.
• Choose a powerful RTK receiver to help you get high-precision measurements during active solar storms. Learn about SingularXYZ GNSS RTK products:
  https://www.singularxyz.com/Y1.html
  https://www.singularxyz.com/Sfaira_One.html
  https://www.singularxyz.com/SV100.html