Measurements of signal coherence for high and low duty cycle sonars in a shallow water channel
Notice bibliographique
Résumé
Military sonars must detect, localize, classify, and track submarine threats from distances safely outside their circle of attack. However, conventional Pulsed Active Sonars (PAS) have duty cycles on the order of one percent which means that 99% of the time, the track is out of date. In contrast, High Duty Cycle (HDC) sonars have duty cycles approaching 100% which enable near-continuous updates to the track. If one can overcome technical challenges such as the high dynamic range required by the receiver, then HDC should significantly improve tracking performance in the (approximately) free-field environment that one encounters in the deep ocean. Improvements in tracking performance in shallow water, however, are not assured since both targets and clutter will be tracked continuously and HDC may increase false tracks to an unacceptably high level — essentially continuously tracking the clutter. Furthermore, one would typically want to maintain the same bandwidth for an HDC system as for the PAS system it might replace. This will provide a significant increase in the time-bandwidth product, but may not produce the increase in gain anticipated if there are coherence limitations of the acoustic channel that result from environmental variability. To compare performance of HDC with conventional PAS in the littorals, a set of experiments was conducted as part of the Target and Reverberation Experiment (TREX) in spring 2013. This was one of the first scientifically controlled experiments conducted in the littorals to compare environmental effects on these two active sonar techniques. In most active sonar experiments, the source, receiver, and target are moving so that one cannot cleanly isolate the impact of platform motion from that of environmental variability. In the experiment discussed in this paper, however, R/V SHARP was fixed in a four-point mooring, and a free-flooding ring transmitter and a horizontal line array receiver were deployed from the deck and mounted a few meters above the seabed. The target, an air-filled hose, was deployed approximately 3 km away and anchored to the seabed with minimal surface expression, thereby drastically reducing its motion. This fixed-fixed geometry provided an opportunity to examine the effect of the acoustic channel on signal coherence. An initial examination of the echo levels from an air-filled passive target shows that there is very little difference in the coherence loss of HDC and PAS pulses. However, the standard deviation of the HDC echo levels is about 0.1 dB lower than PAS under similar environmental conditions; this may be because the longer HDC pulses provide some averaging of the effect of surface roughness on the coherent gain.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».