Low grazing-angle sea surface reverberation patchiness and statistics observed with a high-frequency multibeam sonar
Bibliographic record
Abstract
Sea-surface reverberation, and in particular backscatter from near-surface bubbles, can significantly limit high-frequency (>10 kHz) active sonar performance. While accepted models for near-surface bubble backscatter exist, these have generally assumed horizontally uniform bubble layers. This study presents measurements using a horizontally-oriented 90 kHz multibeam sonar from a moving ship that show significant spatial variability in low grazing angle sea-surface reverberation. The surface scattering strength and scattering amplitude statistics under sea states 3 to 4 conditions are investigated. The time- and spatially-averaged background reverberation levels were in moderate agreement with well-known bubble layer models. However, the instantaneous backscatter amplitudes exhibited localized patchiness and non-Rayleigh statistical distributions, in agreement with either a K-distribution or a Rayleigh-K mixture model. This variability was attributed to scattering patchiness, bubble-induced extinction and refraction, and near-surface processes such as Langmuir circulation. K-distribution shape parameters from 4 to 15 were estimated from the sonar data, increasing with range as predicted by an effective scatter density model. These low shape factors lead to a larger probability of false alarm than might be predicted using Rayleigh models.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 teacher head, 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".