GOES-16 Magnetometers Anomaly Solar-Angle-Based Characterization and Correction

The GOES-16 observatory is a member of the NOAA GOES-R Series constellation of weather satellites and was launched on 19 November 2016. The GOES-16 magnetometers post-launch testing and checkout began on 7 December 2016 during magnetometer boom deployment. The magnetometer boom hosts the GOES-16 inboard and outboard magnetometers. Post-launch tests revealed anomalous measurements from the observatory magnetometers as determined by the diurnal difference between the inboard and outboard magnetometer measurements. The anomaly resulted in magnetometer measurement diurnal difference variations and excessive inboard magnetometer shadowing sensitivity. Identifying the inboard and outboard magnetometers individual contribution to the measured anomalous diurnal difference result was a nontrivial exercise in the absence of geomagnetic field truth sources to compare against at the geosynchronous checkout orbit location. To assist with identifying the individual inboard and outboard magnetometer contribution to the measured anomalous diurnal difference result, a solar angle based mathematical model was developed that allocated individual anomalous behavior to the inboard and outboard magnetometer model results in such a way to agree with the flight measured magnetometer diurnal difference result. The flight data indicated that during certain hours of the day, the inboard magnetometer has greater detrimental performance impact resulting from an anomalous source. A principle component driving the anomalous inboard magnetometer measurement shadowing sensitivity is thought to be temperature sensitive magnetic contamination near the inboard magnetometer. Inboard magnetometer shadowing occurs when this magnetometer’s view to the Sun is obscured by either the observatory or the Earth during eclipses. A study was performed to characterize the magnetometers anomalous behavior as a function of solar-angle and to develop a solar-angle based correction algorithm for magnetometer performance recovery. This paper describes key results from the magnetometer measurement anomalous behavior characterization and the algorithm-based magnetometer measurement performance recovery. GOES-NOP constellation flight data was used as the validated truth source for identifying the GOES-16 observatory magnetometers measurement uncertainty. A month period of having the GOES-13 and GOES-16 observatories collocated in the GOES East orbit slot permitted validating that GOES-13 was a trustworthy measurement of the geomagnetic field environment at geosynchronous orbit. In an effort to derive a geomagnetic field truth source at the GOES-16 observatory Checkout location, a study was undertaken using the GOES-NOP constellation magnetometer hardware assets. In so doing, a validated truth source for the GOES-16 checkout location was derived based on time and geomagnetic field bias shifting of the GOES-NOP East observatory (GOES-13) magnetometer measurements to the GOES-NOP Checkout observatory (GOES-15) magnetometer measurements. GOES-15 was independently validated as a good truth source of the geomagnetic field at geosynchronous orbit. Magnetometer anomalous measurement behavior sensitivity to season and observatory location within its orbit box are discussed. The magnetometer anomalous measurement behavior is shown to be repeatable to within ~0.75 nT. The magnetometer measurement uncertainty requirement is given as +/-1.7 nT per axis. In the presence of the GOES-16 magnetometer anomaly, the magnetometer flight data measurement uncertainty is ~+/-10 nT. The developed correction algorithm decreases the measurement uncertainty to ~+/-2.5 nT. The correction algorithm uses the Sun pointing vector in the respective magnetometer sensor reference frame as input and provides three degree-of-freedom magnetometer measurement corrections in the corresponding reference frame as output. Implementing magnetometer sensor axes referenced solar-angles as the basis for the correction algorithm development permits correction algorithm independence from sidereal drift, orbit box drift, and GOES observatory orbit slot location (i.e. East, West, Storage, and Checkout) during nominal flight operations. The mathematical analysis model that replicates the magnetometer anomalous measurements was developed to assist with correction algorithm development, to support anomalous behavior repeatability assessments, and to support anomalous behavior root cause investigation. The correction algorithm was tuned using approximately a yearlong GOES-16 magnetometer flight data set and validated against an independent half-year duration GOES-16 magnetometer flight data set. The GOES-16 magnetometers solar-angle based correction algorithm tuning and trending are currently on-going.