Acoustic near field effects for the Simrad–Mesotech SM 2000 multibeam sonar
Bibliographic record
Abstract
Targets quantitatively observed with a multibeam sonar based on a truncated circular arc transducer geometry, focused at infinity, display anomalous apparent target strengths at short measurement ranges. Three near field mechanisms, affecting both the sonar transmit and receive responses, are identified: (1) Anomalous inter-elemental differential phase shifts, (2) inter-elemental differential spreading losses, (3) shifts in elemental viewing aspect. With reference to a commercial 200 kHz Simrad–Mesotech SM 2000 multibeam sonar, the relative importances of the three mechanisms are numerically examined at a 1-m target range. Combined effects in both transmit and in receive are further evaluated for target ranges between 0.5 and 20 m. For the instrument considered, near field effects are significant at ranges of 5 m and less and are characterized by systematically reduced target amplitudes after the application of ‘‘normal’’ sonar time variable gain. Systematic broadening of combined transmit–receive response patterns at short target ranges result in target defocusing in sonar imaging applications. Experimentally measured responses are presented for comparison with theory. [Work supported by the DFO National Hydroacoustic Program and generous access to the Defence Research & Development Canada—Atlantic acoustic calibration facilities.]
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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 | 0.000 | 0.001 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 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".