joshruby/nightjar-flight-20260804

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.