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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.
|