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16 Nov 2022
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HOW TO USE PERFORMANCE REPORTS

About Performance Reports


Overview of GPS Operations Center Performance Reports

The GPS Operations Center is manned 24/7 and produces both prediction models and post-assessment models of GPS accuracy using the program GIANT (GPS Interference And Navigation Tool). These charts only represent the Signal In Space, or SIS, errors. There are additional sources of position error that the user will encounter that we do not predict such as multipath, ionospheric scintillation, or obscura to name a few. Posting is accomplished daily, and archived products are also available through the website.

Prediction Products

The GPSOC creates prediction analysis for both, PDOP (Position Dilution of Precision) and 95th Percentile Position Error. These analyses are based on a Best-4 Receiver’s logic. All predictions are posted 3 days in advance, or 72 hours into the future. You can use the prediction maps to see what the GPS performance will be in your area of interest. In the PDOP predictions, the color bands indicate the maximum PDOP experienced at each grid point over the course of the day. In the Position Error Predictions, the color bands indicate the 95% percentile position error seen at each grid point over the course of the day. In brief, the 95th Percentile indicates, not the maximum position error, but the most probable range of position errors. As an example, if the chart indicates a color band of 4-8 meters for the 95th percentile (assume 8 meters for simplicity), there is a 95% chance that any position solutions will have 8 meters or less of error.  

Post Assessment Products

The Post Assessment products are based on the observed errors of the GPS constellation by the Master Control Station. The GPSOC produces charts for both the Best-4 satellite receiver, and the All-In-View (generally a 12-channel receiver). The All-In-View post assessments will usually show better performance than a Best-4 post-assessment. The color bands indicate the maximum actual position error (in meters) experienced at each grid point over the course of the day.  


How to Use Reports

All predictions are posted 3 days in advance (24-hour period, 72 hours into the future). The GPSOC is now open 24/7, so posting is accomplished daily. Use the prediction maps to see what the GPS performance will be in your area of interest. In the PDOP Predictions, the color bands indicate the maximum PDOP experienced at each grid point over the course of the day. In the Position Error Predictions, the color bands indicate the 95th Percentile Position Error seen at each grid point over the course of the day. In brief, the 95th Percentile indicates, not the maximum position error, but the most probable range of position errors. As an example, if the chart indicates a color band of 4 - 8 meters for the 95th Percentile (assume 8 meters for simplicity), there is a 95% chance that any position fixes will have 8 meters or less of error. Barring any kind of satellite outage/anomaly, the remaining 5% rarely exceeds 20 meters of error. If you suspect your area may be adversely impacted, SBMCS can be used to create a prediction for your location of interest or you may contact the GPS Operations Center for an analysis/prediction specific to your needs.

The GPS Post-Assessment, Daily Navigation Accuracy Maps are based on observed GPS errors from the GPS Master Control Station. These maps can be used as a quick-look post mission assessment to determine what ACTUAL, past GPS accuracy was like in your area of interest. The color bands indicate the maximum actual position error (in meters) experienced at each grid point over the course of the day. You will need to contact the GPS Operations Center to obtain detailed information on accuracies for a specific location.