NEXUS – The Acoustic Bubble: Interim Report (v1.0)

Stationary ultrasonic detectors are routinely used in bat research, yet the influence of microclimatic conditions on detection range has not been systematically quantified. This interim report presents empirical evidence for the "acoustic bubble"—a weather-dependent detection zone around stationary ultrasonic sensors caused by atmospheric attenuation. Over 19 valid recording nights at 10 sites in the Paderborn region (February–July 2026; 21 of 30 planned nights completed), a self-contained microclimate monitoring system (NEXUS: Seeed XIAO ESP32S3 Sense, BME680, AIR530, SparkFun SEN-15901) was operated alongside a TeensyBat T4.1 ultrasonic detector. A within-session fixed-effects approach with cluster-robust standard errors—controlling for habitat-specific confounders—demonstrates a significant relationship between the theoretical bubble radius and the detection rate (Pearson r=0.621, R²=0.386, p=0.0006, n=73 bins, 19 nights); this result is robust according to a leave-one-session-out jackknife analysis (coefficient range: 1.78–2.16). Species-specific bubble radii align with attenuation laws defined by ISO 9613-1. Bioacoustic species identification was performed using dual-CNN cross-validation (BatDetect2 + BattyBirdNET, confidence ≥ 0.85), confirming five species as the "gold standard" (560 detections, 10 sites). A full analysis incorporating the remaining nine recording nights will be presented in the final version.