--- license: cc-by-4.0 task_categories: - audio-classification - object-detection tags: - drone-detection - counter-uas - acoustic-array - self-calibrating-threshold - cue-to-track pretty_name: "nightjar flight 2026-08-13 — first sortie with a self-calibrated presence threshold" --- # nightjar flight 2026-08-13 — self-calibrated presence gate, fast cue chain First field session where the acoustic presence threshold was **measured from the site's own drone-free preroll** instead of using the 2026-07-27 constant. Also the first with a fast-reaction cue gate. Both arrays recorded at full native depth. ## ★ Headline: the presence threshold was ~8 dB too strict, and it is not static Calibrated live from 151 drone-free ambient blocks (150 s, band 100–1200 Hz): ``` TRACK 8.87 dB (p99) was 14.6 ambient median 3.67, max 10.98 SEARCH 6.93 dB (p95) was 10.0 not clamped ``` The shipped 14.6 dB constant was this site's p99 on **2026-07-27**. Today's site measures 3.67 dB median — the gate was roughly 8 dB above where the noise actually sits, which is why earlier sorties detected on so few windows. ⚠ **And the ambient does not hold still.** `ambient_drift` telemetry (a rolling p95, logged once a minute, 20 samples) ranged **7.15 → 15.75 dB**, wandering up to **8.82 dB** from the frozen 6.93 preroll value. That is far past the ~2 dB that would justify rolling recalibration. ⚠⚠ **BUT do not read that as pure ambient drift.** The drone was airborne for much of this session, and `ambient_drift` measures the rolling p95 of the presence statistic *whatever the source* — a loud drone inflates it directly. This log therefore **cannot separate ambient non-stationarity from the drone's own contribution**. The honest next step is a drone-free recording of similar length; until then the 8.82 dB figure is an upper bound on drift, not a measurement of it. ## Cue chain | | | |---|---| | candidates | 132 | | **posted** | **50** | | az-masked (site emitters suppressed) | 16 | | cue az | median 144.9, sd 44.8 | | presence at cue | median 12.0 dB, min 7.7 | Mid-session the gate was retuned live for reaction speed (daemon restarted into the same session; video/blackbox never stopped): ``` M_AGREE 4 -> 3 agreement window fills a second sooner CUE_MIN_PERIOD_S 12 -> 4 corrections every 4 s instead of 12 PRESENCE_DB pinned 8.87/6.93 (skips the 150 s preroll on restart) ``` Measured effect: posts began landing at the **4 s floor** (gaps 4.0, 5.0, 4.0 s) versus ~20 s before. The pre-change timeline is in the log: first faint contact at t+359 s, first POST at t+367 (**8 s**, dominated by the 4-of-5 s agreement gate), second POST at t+381 (the 12 s refractory). Longer gaps afterwards are `CUE_SUPPRESS_DEG` correctly staying quiet while the camera was already on target — not a failure. `AZ_MASK="281-297,319-335"` suppressed the utility-pole transformer (array az 289.2) and emitter-B (327.5). ⚠ The mask is expressed in ARRAY azimuth while the emitters are fixed in the WORLD, so it silently stops working after any registration change — see `~/Desktop/TRANSFORMERS.md`. ## Tracker (blackbox, 21.6 min, 3,763 samples) ``` SEARCH 1750 | TRACK 809 | COAST 365 | ACQUIRE 250 | IDLE 571 | REACQUIRE 18 track active 1431 samples (38%), of which 937 YOLO-vouched pick source while tracking: blob 520 | yolo 289 focal while tracking: median 9.2 mm, max 83.1 mm (19x) ``` ⚠ **No GPS truth was captured for this session** (no DJI FlightRecord exported at time of writing), so **none of the tracking above is confirmed to be the drone**. On 2026-08-12 an identical-looking 38%-tracked session turned out to be on-drone only inside ~25 m and 0% on-drone beyond it. Do not cite these numbers as detection performance without scoring them. The test that settles it is differential — correlate CHANGES in tracker bearing against CHANGES in GPS truth bearing; absolute-error scoring is circular. ## Registration in force ``` UMA-16 az_offset 302.2 invert_az true (JBL far-anchored, 42 dB SNR) SB-POLARIS az_offset 339.55 invert_az FALSE (2 beacons, handedness margin 2.45 vs 50.85) ``` ## Contents ``` audio/uma16_.wav UMA-16, 16 ch, 48 kHz, S32_LE (32-bit, verified from headers) audio/sb_.wav SB-POLARIS, 8 ch, 48 kHz, S32_LE audio/cue_log.jsonl every candidate, mask event, presence_cal and ambient_drift record audio/uma.log daemon log incl. the calibration line video_segments.tar 1080p native + 768x432 substream, H.264, 60 s MPEG-TS blackbox/state.jsonl tracker FSM ~3 Hz: state, pose, focal, detection, track, blob_seeded blackbox/frames.tar 9,495 substream stills ``` ⚠ **Both arrays are S32_LE.** Reading them as int16 splits every sample, scrambles channel identity and destroys the spectrum. The UMA16v2 is natively 32-bit; every wav banked before 2026-08-09 was silently truncated to the top 16 bits. **Channel identity is not guessable.** UMA-16 0-based channel 9 is a dead electronic-floor channel — exclude it, run on 15. Load the serpentine geometry from `uma16_geom.json`. ## Known-good replay reference Presence detection replayed over two GPS-truthed flights, channel-agreement gate applied: | threshold | flight A | flight B | |---|---|---| | 14.6 (old constant) | 3.8% | 16.6% | | 6.55 | 67.6% | 66.3% | | 4.71 | 84.1% | 79.9% | These are **window-level presence detections**. A posted cue must additionally clear bearing consistency, the az mask and the refractory, so cue availability sits at or below these figures.