A matched filter approach for the calibration of GRACE and GRACE-FO accelerometers.
Bibliographic record
Abstract
For the accurate determination of the gravity field of the Earth, the accelerometers on board GRACE and GRACE-FO missions need to be calibrated, which is a rather challenging task. In many gravitational field studies, the bias and scale factors are introduced, among others, as unknown parameters in the gravity field recovery process and are estimated concurrently with the gravity field parameters. In other studies, the calibration method makes use of modeled accelerometer data, and the parameters are estimated in a least squares adjustment. Depending on the calibration process, the scale factors and biases may vary significantly. In this study, an alternative calibration method is followed using the matched filter method. This method is widely used in radar applications for scattered signal detection purposes since it maximizes the signal-to-noise ratio. The idea behind this method is that a known signal is transmitted out and the reflected signal is compared to the known transmitted signal. This allows the proposed method to be based only on the satellite measurements. In this study, the total accelerations of the satellite derived from the GPS positions, play the role of the transmitted signal that contains both the gravitational and the non-gravitational accelerations. The penumbra transitions, which appear as jumps (offsets) of very short duration in the accelerometer measurements, are used as the known calibration pulses that need to be detected in the transmitted signal. The process of matching (focusing) the penumbra transition pulse on the GPS accelerations is presented step by step and as a result, 30 daily scale factors are calculated for both missions during different periods of solar activity. The biases of the instrument are calculated daily using a second order polynomial fit. The scale factor and the biases appear to be correlated with the β’ angle variations (the angle that indicates when the satellite is in a full sun orbit). The scale factors of the cross-track component in both missions show the largest variations, since the y-axis of the accelerometer is the least sensitive, while the scale factors in the x-axis show the largest sensitivity due to thermal variations in the atmosphere . The performance of the calibration parameters during high and low solar activity is examined and evaluated.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.005 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".