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  • William Hunt MBE

What is the Kp Index and How Does it Affect Drones?

Updated: Jun 13, 2020

The Kp Index is a measurement of global geomagnetic activity. The index is expressed by a measurement the ranges from 1 (weakest) to 9 (strongest). Generally, anything below 4 is known as ‘quiet’, if the index is at 4 is is ‘disturbed’ and anything above 4 indicated a magnetic storm.

The Kp-index is the global geomagnetic activity index that is based on 3-hour measurements from ground-based magnetometers around the world. Each station is calibrated according to its latitude and reports a certain K-indice depending on the geomagnetic activity measured at the location of the magnetometer. The K-index itself is a three hour long quasi-logarithmic local index of the geomagnetic activity at the given location and time compared to a calm day curve. A magnetometer measures the maximum deviation of the horizontal component of the magnetic field at its location and reports this. The global Kp-index is then determined with an algorithm that puts the reported K-values of every station together. The Kp-index ranges from 0 to 9 where a value of 0 means that there is very little geomagnetic activity and a value of 9 means extreme geomagnetic storming.

The geomagnetic activity can affect your drone and it’s Global Positioning Systems (GPS) in 2 ways: 1. It decreases the signal-to-noise ratio and affects carrier frequency. This will cause the receiver to loose lock on some satellites. Instead of 9 satellites, you might lock only 6, or the number might fluctuate from second to second. This can make your GPS less accurate.

2. It changes the propagation delay through the ionosphere, making GPS positioning inaccurate even if the receiver has all satellites "locked".

This means that during times with a moderate Kp Index (5-7), a few things might happen: - Your aircraft may take longer to acquire GPS fix. - Your home/RTH position may not be as precise. - You may lose GPS entirely and be forced into ATTI mode.

Again, with a moderate Kp Index, these effects will be pretty minor and you might not even notice. However, once they get a bit higher (7-9) you could see location errors as large as 100ft. It should be noted though, that Kp Indices in that range are considered a major geomagnetic storm and are very rare. The best things you can do to prevent a Kp Index related mishap are to be aware of the Kp Index and to practice ATTI mode regularly, if your drone supports it. If your GPS signal degrades or fails entirely, you will be forced to complete the mission in ATTI mode. You want to ensure you are comfortable navigating and landing your aircraft in this mode, even with high winds.

To avoid this potential issue, monitor the Kp index through an app such as UAV Forecast. If its above 5, dont fly unless you flight mission is ATTI mode.

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