---
license: cc-by-4.0
task_categories:
- audio-classification
- object-detection
tags:
- drone-detection
- counter-uas
- acoustic-array
- cue-to-track
- ablation
pretty_name: "nightjar flight 2026-08-06 #2 — chirp guard off: the cue chain closes"
---

# nightjar flight 2026-08-06, session 2 — the fix, and a producer swap mid-session

The "after" half of a same-evening, same-site A/B against `nightjar-flight-20260806-1`, where the
chirp guard vetoed the drone outright. Here the guard is disabled and the gate **cues while the
drone is airborne** (0 → 8). ⚠ **But GPS scoring (added after first publication) shows the
optical "locks" were NOT the drone and most cheap-gate cues were a second site emitter** — see
the scored findings below. An earlier revision of this card claimed "the full chain fires";
that claim is RETRACTED.

⚠ **This session contains TWO different cue producers.** Treat it as two segments, not one:

| segment | UTC | producer | chirp guard |
|---|---|---|---|
| A | 00:25:15 – 00:42:28 | `cue_daemon_subhunt.py` (ft16 neural) | **off** |
| B | 00:42:28 – 00:53:27 | `cue_daemon.py` (cheap gate) | **off** |

The swap was made live because SubHunt was starving the cue rate (below).

## ★ Finding 1 — the chirp guard was real, but it was not the only problem

With `CHIRP_GUARD=0` the gate produces **8 cues coincident with an airborne drone** (session 1:
zero). That part of the fix stands.

⚠ **Scored against the DJI GPS record, most of those cues are NOT the drone either:**

| cue disposition (14 total) | n |
|---|---|
| fired while the drone was **not airborne** | 6 |
| pinned at array az **322.6–323.4** — a **second fixed site emitter** | 6 |
| consistent with the drone | **2** (SubHunt az 184.0 vs GPS 193.0 = **−9.0°**; one cheap az 164.4 vs 208.9 = −44.5°, marginal) |

Best-fit constant-offset residual over the 8 airborne-coincident cues: **56.5° robust sigma,
12% within 10°** — the beamformer mostly locked the loudest static source, not the drone.

⚠ Lesson recorded: **wandering `line_hz` is NOT a drone signature by itself.** The az-323
emitter cluster wanders 363–1166 Hz (the peak-picker hops harmonics on a stationary machine)
while its **bearing stays pinned to 0.8°**. Bearing spread is the discriminator; frequency
spread fooled the first read of this data.

## ★ Finding 2 — SubHunt starves the agreement window on this hardware

| | segment A (SubHunt) | segment B (cheap) |
|---|---|---|
| duration | 17.2 min | 11.0 min |
| cue candidates | **1** | **13** |

The gate needs **4 agreeing bearings inside a 5 s window at ~1 Hz**. SubHunt logged
`analysis behind, skipped ~81 hops` over ~825 hops (~10 %). That rate is the documented
steady-state, **not** the retracted "runaway" — but losing one hop in ten still prevents the
4-of-5 s window from filling. **The 2026-08-05 preallocated-ring fix is real and present**
(1 startup overrun, skips flat); it removed the ALSA overruns but did not make ft16 fast
enough to sustain the gate under a live tracker.

⚠ **Rate is not accuracy.** GPS scoring reverses the quality read: SubHunt's single cue was
the **only clearly drone-consistent bearing of the session** (−9.0° vs truth), while the cheap
gate's 13 cues were dominated by the az-323 emitter and not-airborne false alarms. n=1 proves
nothing about ft16 either — but do not cite this session as "cheap gate beats SubHunt"; on
bearing truth it was the other way around.

## Tracker outcome

| | session 1 (guard ON) | **session 2 (guard OFF)** |
|---|---|---|
| track active | 0.2 % | **5.7 %** |
| frames with detection | 1 | **83** |
| track episodes | 1 (2.0 s) | **22** (longest 7.6 s) |
| max focal | 15.17 mm | 11.59 mm (2.70x) |
| SEARCH | 96.6 % | 89.7 % |

⚠ **The FSM numbers above are NOT drone locks.** Scored against GPS (256 tracked samples with
truth within 2 s): camera-implied bearing vs drone bearing has **27.5° robust sigma after
removing the best-fit constant offset — a time-shuffled placebo scores 27.2°**, i.e. the real
pairing beats exactly 50 % of random pairings. The 22 episodes were clutter (treeline / cloud
edges), indistinguishable from real locks in the FSM but not pointed anywhere near the drone.
An earlier revision of this card counted them as drone acquisitions; that is RETRACTED.

The honest statement: the guard fix restored *cueing*; nothing in this session demonstrates a
verified optical lock on the drone. (Caveat on the scoring itself: rig position was taken from
the 07-27 survey and the rig moved 08-05 — at 24–83 m slant a ~10 m rig-position error is up
to ~13° of bearing, which inflates the residuals but cannot produce a placebo-level track
result or the pinned az-323 cue cluster.)

⚠ **`cue.blob_seed: true` was enabled for the first time on 2026-08-06 and is present in both
sessions. It is NOT yet validated** — no analysis here separates blob-seeded acquisitions from
YOLO-seeded ones. Do not credit it for the improvement above; the controlled variable between
the two sessions is the chirp guard, not blob seeding.

## Drone truth — two flights

`dji/` holds both records. **Flight A spans the session boundary**; flight B is wholly inside.

| | flight A `[20-15-21]` | flight B `[20-37-43]` |
|---|---|---|
| airborne | 00:15:21 – 00:28:10 UTC | 00:37:43 – 00:50:47 UTC |
| captured here | 00:25:15 – 00:28:10 (**175 s**) | **784 s** (all) |
| also in | session 1 (287 s) | — |
| max slant | 84 m | **138 m** |
| max height | 51 m | 47 m |
| elevation | median 17, p90 31 deg | median 26, p90 44 deg |
| bearing from rig | 172 – 264 deg | 166 – 302 deg |

Operator notes the drone flew approximately the same positions in both sorties, which is what
makes the session-1 / session-2 comparison fair.

⚠ **DJI stamp sparsity: 5 of 7,846 rows (flight B) and 7 of 7,694 (flight A) carry a valid
`CUSTOM.dateTime`.** Anchor ONCE off the first valid stamp and derive every row from
`OSD.flyTime`.

⚠ **Timezone:** Jetson clock is Denver (MDT); DJI wall-stamps are US Eastern. Filename
`[20-37-43]` is 00:37:43 UTC the next day.

## Configuration in force

```
cue producer      SubHunt (ft16) then cheap gate - SEE SEGMENT TABLE ABOVE
chirp guard       OFF  (CHIRP_GUARD=0; no KT pinger was running)
detector.mode     day
yolo_engine       nightjar_v3.pt   (yolo_conf 0.15 / seed 0.45 / imgsz 1280)
cue.blob_seed     true   (unvalidated)
search.scan_enabled  false  - SEARCH holds for a cue, it does not sweep
UMA-16            az_offset_deg 297.644   invert_az true
SB-POLARIS        NOT RECORDED
```

⚠ **SB-POLARIS produced no audio**: the card dropped off the USB bus before session 1 and did not
return. **UMA-16 only** for both sessions of 2026-08-06.

## Contents

```
audio/uma16_<epoch>.wav   UMA-16, 16 ch, 48 kHz, S16_LE, 5-min splits
audio/cue_log.jsonl       every candidate and reject, both producers
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
blackbox/frames.tar       1,760 substream stills
dji/                      both DJI FlightRecords (txt + decoded csv + geojson)
```

**Channel identity is not guessable.** UMA-16 0-based channel 9 is dead — exclude it, run on 15.
Load the serpentine geometry from `uma16_geom.json`.

## Open questions this session raises

1. **Tune the chirp guard rather than disabling it.** Reject records now log `hi` and `hi_med`, so
   an absolute floor (or the cheap gate presence-override) can be fitted instead of `CHIRP_FACTOR`
   alone. Porting `chirp_ovr` into the SubHunt daemon is the obvious fix.
2. **The az-323 emitter needs suppression** (survey it; a bearing mask now exists in the cheap
   daemon: `AZ_MASK="315-331"`, logging `ev:az_masked`).
3. **A verified drone lock is still outstanding** — next session runs a truth-scored look-away
   drill (hovering drone at a surveyed station) instead of free flight, so every cue and every
   lock is scored against a fixed truth pose at the moment it happens.
4. **Fresh rig GPS fix needed** — all bearing scoring above leans on the 07-27 rig position.

## Companion

* `nightjar-flight-20260806-1` — same evening, guard ON, the negative control.

## Elevation datum (fit_el_datum, 2026-08-16)

**Status: FEW_ON_DRONE** — this day's elevation datum is honestly UNSOLVABLE from
banked data (camera never/rarely locked on the drone).
Close-range elevation truth for this day remains datum-limited (~25 deg
floor). Tool: `sirch613/subhunt-v2` `v3/fit_el_datum.py`; summary:
`joshruby/acoustic-knowledge` -> `v3/assets/el_datum/SUMMARY.json`.