---
license: cc-by-4.0
task_categories:
- object-detection
- audio-classification
tags:
- drone-detection
- counter-uas
- acoustic-array
- ptz-tracking
- multimodal
- gps-truth
pretty_name: "nightjar field flight 2026-08-04 — cue chain + first live setpoint-zoom exercise"
---

# nightjar flight — 2026-08-04

One 20.9-minute drone sortie recorded end-to-end by the nightjar rig: PTZ camera under
closed-loop acoustic-cued optical tracking, two microphone arrays, full autopilot telemetry,
and the tracker's own decision log. **GPS truth is exceptionally clean here — 12,447 valid
UTC stamps out of 12,448 rows** (a prior session in this series had exactly 1, which made it
unusable for anything truth-referenced).

Rig, site and method: see the companion sessions in this series and `SENSIBELSPECS.md` /
`SUBHUNTBLACKPAPER.md` in the project.

## Envelope

| | |
|---|---|
| airborne | 1252 s (20.9 min), 12,448 GPS fixes at 10 Hz |
| max height | 276 m |
| max slant range | **473 m** (furthest of the series to date) |
| max horizontal speed | 10.5 m/s (24 mph) |
| path flown | 3021 m |
| window (UTC) | 16:46:25 – 17:07:17 |

## Contents

```
audio/uma16_<epoch>.wav    UMA-16, 16 ch, 48 kHz, S16_LE, 5-min splits
audio/sb_<epoch>.wav       SB-POLARIS, 8 ch, 48 kHz, S32_LE, 5-min splits
audio/cue_log.jsonl        acoustic cue gate: start / cue_candidate / chirp_reject
video_segments.tar         1080p native + 768x432 substream, H.264 -c copy, 60 s MPEG-TS
blackbox/state.jsonl       tracker FSM at ~2.9 Hz: state, pose, focal, error, detection, track
blackbox/*_frames.tar      7,135 substream stills
dji/*.csv                  decoded DJI FlightRecord (CUSTOM.dateTime = true UTC)
dji/*.txt                  original encrypted FlightRecord
```

**Channel identity matters and is not guessable.** UMA-16 0-based channel 9 is a dead
electronic-floor channel — exclude it, run on 15. SB-POLARIS has 3 live capsules of 8, and
**this session they are `[0, 3, 5]`** (measured: live ~−70 dBFS, dead ~−190 dBFS). The live
set has changed between sessions, so detect it by RMS rather than hardcoding. UMA channel
order is serpentine — load the geometry file, never hand-derive it.

⚠ **The two arrays use DIFFERENT sample widths** (UMA S16_LE, SB S32_LE). Reading both as
int16 splits every SB sample into two halves, scrambles channel identity and destroys the
spectrum. That bug produced a since-retracted long-range result in this series; see below.

## Calibration as flown

| | |
|---|---|
| UMA-16 → camera | `az_offset_deg` **300.87**, `invert_az` true — re-solved this morning from the JBL beacon (spread 0.10°, 41 dB); 1.1° drift from 08-03's 299.77 |
| SB-POLARIS → camera | `az_offset_deg` **102.6**, `invert_az` **false** — solved for the first time this morning; two beacons 89.5° apart agreed to 0.9°, run-to-run 0.10°. Rotation only; mic positions are the ring model, not solved. **Nothing consumed SB bearings during this flight** — the cue chain is UMA-only. |
| cue producer | cheap daemon (`SUBHUNT=0`); ft16 starves under live tracker load |
| site notch | 100–200 Hz (widened from 140 Hz before this flight) |
| start pose | pan 45 / tilt 45 |

## Results

### Acoustic cue → optical lock

**20 cues posted, 14 locked (70%)**, 11 chirp-rejects, 50 candidates not posted, 26 TRACK
episodes. Rotor-band specifically: 10/15 locked. Time-to-lock ranged 1.7–41.3 s.

The site-emitter notch was widened to 200 Hz immediately before this flight, and it worked:
**no cue below 222 Hz was posted all session**, where the previous session repeatedly fired
false cues on a fixed 140–170 Hz machinery line and slewed the camera at nothing.

### Where each array loses the drone

Per-second channel-agreement detection in the 240–460 Hz rotor band reads 100% at every
range for both arrays — but that number is a trap, because a fixed site harmonic sits inside
the band. **The discriminator is the peak-frequency IQR:** a real drone's rotor line wanders
with throttle (wide IQR); a fixed emitter is pinned (tight IQR).

| range | UMA-16 peak Hz | SB-POLARIS peak Hz |
|---|---|---|
| 0–50 m | 342 IQR[319–357] | 312 IQR[258–342] |
| 50–100 m | 308 IQR[253–346] | 266 IQR[250–344] |
| 100–200 m | 326 IQR[242–348] | 260 IQR[245–324] |
| 200–400 m | **245 IQR[240–274]** | **247 IQR[240–263]** |

Both arrays converge on the same pinned ~245 Hz line beyond 200 m — that is the site
emitter, not the drone. **Neither array demonstrably hears the drone past ~200 m here, and
the SensiBel shows no range advantage over the UMA.**

> **Retraction.** A previous session in this series reported the SensiBel still hearing the
> drone at ~330 m while the UMA had collapsed. That came from the int16/S32 misparse noted
> above. Recomputed with correct parsing, the SB's long-range IQR is tight and pinned, i.e.
> emitter, not drone. Treat any earlier SB-range claim in this series as withdrawn.

### Optical: the zoom bootstrap trap

The camera held a median of **1.01×** even while tracking, reaching 11.3× at most; 73% of
tracked time was still at full wide. Scoring the flight in **pixels on target** (0.35 m
drone, GPS slant range, `deg_per_px` from the blackbox) shows why that is decisive:

| range | median px on target | detection rate | px if held at 120 mm |
|---|---|---|---|
| 0–50 m | 27.1 | **46.6%** | 454 |
| 50–100 m | 3.2 | **1.0%** | 88 |
| 100–200 m | 1.6 | **0.0%** | 44 |
| 200–300 m | 0.7 | 0.0% | 20 |
| 300–500 m | 0.7 | 0.2% | 20 |

Detection collapses exactly where apparent size falls below ~10 px, and the pixel model
predicts the cliff. The counterfactual column is the finding: at the lens's usable tele the
drone would have stayed above the detection floor out to ~300 m instead of dying at 50 m.

It did not, because **zoom is gated on a track that can only exist where zoom is not needed**
— zoom climbs only under an established optical track, tracking requires detection,
detection requires ~10 px, and inside 50 m the target is already 27 px. Outside 50 m there
is no detection, so no track, so no zoom, so there will never be detection. The tracked
median range was 10 m. This dataset is a clean instrumented record of that trap.

## Known issues in this session

* Blackbox logs the zoom *outcome* (`focal_mm`, `zoom_speed`) but not the *decision* — no
  containment ceiling, no σ, no binding axis. Zoom behaviour can be described from this
  session but not fully attributed.
* SB-POLARIS elevation is not calibrated; azimuth registration exists but nothing consumed it.
* `OSD.height` in the decoded CSV is **feet**.
* Blackbox sampling is ~2.9 Hz, well below video frame rate.

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

The rig height in this day's drone-altitude frame (the missing constant that
floored close-range elevation truth at ~25 deg estate-wide) is SOLVED from
this repo's own blackbox TRACK/LOCK poses vs the eval-cache GPS — no
acoustics, no field survey.

- **z_rig = -0.50 m**, el = -1 x tilt + 94.36 deg
- north offset 50.43 deg (pan sign +1), az gate residual 16.4 deg
- med |el residual| **11.25 deg** over 87 camera-on-drone rows, horiz 2-31 m
- per band: 0-30m: 11.43 deg (n=86)
**SUSPECT** — residual above the clean-day range (0.8-1.9 deg); do not use for close-range el truth until lock purity / pixel-offset is investigated.

Artifact: `joshruby/acoustic-knowledge` -> `v3/assets/el_datum/nightjar-flight-20260804.json`.
Tool: `sirch613/subhunt-v2` `v3/fit_el_datum.py`. Derive el truth as
atan2(hgt - z_rig, horiz) — NEVER from raw hgt.