| --- |
| 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_<epoch>.wav UMA-16, 16 ch, 48 kHz, S32_LE (32-bit, verified from headers) |
| audio/sb_<epoch>.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. |
| |
