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Data Collection To devise effective ionospheric mitigation methods in GNSS RTK receivers, Trimble engineers require data gathered from areas where the issue is prevalent. Trimble R&D facilities are generally concentrated in mid latitudes where disturbance is low. Collecting code and carrier measurements in addition to raw radio frequency (RF) data for all GNSS frequencies during high periods of solar activity is a logistically difficult exercise. In previous solar cycles, Trimble constructed specialized RF recorders that were bulky and necessitated frequent replacement of storage media. Fortunately, contemporary recorders are significantly smaller and have the ability to capture extended data periods directly on their internal storage. Trimble installed both online continuously operating receivers and RF recorders at multiple equatorial and high latitude locations. The recorders captured large amounts of regular seasonal ionospheric activity in addition to during some major solar storm events. This data provided the basis for R&D development. Signal processing techniques and RTK algorithms are tuned using replayed data. Updated firmware is then loaded into onsite receivers for real time evaluation. Trimble IonoGuard Ionospheric mitigation features have been included and improved in Trimble receivers over the last three solar cycles. To ensure preparation for the current and future solar maximums, the data collection exercise was leveraged to develop next generation Trimble IonoGuard technology. Signal Processing Mitigation During ionospheric storms, there can be significant frequency-dependent differences in the phase and group delay through the ionosphere. It is therefore important for the receiver not to be dependent on any one frequency for operation. Trimble's GNSS signal processing has been updated to track signals independently. The exception to this is the L2 code measurement on GPS satellites launched before 2005. Unlike the newer L2C signals, these require L1 to assist tracking. To account for this, IonoGuard adjusts the signal processing on these channels during ionospheric events to minimize tracking error. RTK algorithms rely on carrier phase measurements from all frequencies. During extreme ionospheric events, the receiver can lose lock on the carrier for brief periods, often for just a few seconds. Phase tracking algorithm improvements with IonoGuard technology has reduced the time taken to recover carrier phase tracking and minimize potential disturbances. ProPoint is also agnostic to the signals tracked, e.g. it can operate with any combination of triple, dual, or single frequency measurements. Trimble ProPoint RTK Mitigation Trimble IonoGuard has been tightly integrated into the Trimble ProPoint RTK engine. Optimum performance is achieved when IonoGuard is enabled at both the base and rover receivers. With IonoGuard enabled at the base station, ionospheric information for each satellite is transmitted via CMRx or RTCM MSM protocols to rover receivers. IonoGuard rover receivers utilize this information together with their own ionospheric measurements to optimize the computed positions. If IonoGuard is not enabled at the base receiver then an IonoGuard rover will analyze the standard base messages and determine if ionospheric adjustments are necessary. These adjustments are then used to improve positioning performance. This method is not as rigorous as having the more detailed ionospheric information sent from the base but can assist when using a non Trimble ProPoint receiver or 3rd party base receiver. 10 Trimble IonoGuard ™ —Protecting RTK GNSS from Ionospheric disturbances

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