---
license: cc-by-4.0
task_categories:
- object-detection
- audio-classification
tags:
- drone-detection
- counter-uas
- acoustic-array
- ptz-tracking
- multimodal
- gps-truth
- low-altitude
pretty_name: "nightjar field flight 2026-08-04 #4 — longest tracked sortie of the day"
---

# nightjar flight — 2026-08-04, fourth sortie

Last sortie of a four-flight day, and **the one with the most time under an optical track**.
Same rig and site as the other 2026-08-04 sessions. GPS truth: **3,572 valid UTC stamps of
3,573**.

| | |
|---|---|
| airborne | 357 s |
| max height | 26 m |
| max slant range | 244 m |
| median elevation angle | **5°** |
| path flown | 894 m |

## The interesting number

**53 cue candidates, and 43 of them were evaluated at the 14.6 dB threshold.** The deployed
presence gate is state-dependent — strict (14.6 dB) while nightjar reports TRACK, relaxed
(10.0 dB) while it is searching — so a candidate stamped 14.6 means the tracker *was locked at
that moment*. Only 10 candidates saw the relaxed threshold. Compared with the third sortie,
where all 8 candidates were at 10.0 dB and the tracker was never locked when a cue was
evaluated, this session spent substantially more of its life holding a track.

That is a suggestive contrast, not a controlled one: the two sorties differ in duration
(357 s vs 200 s), range (244 m vs 142 m) and path length (894 m vs 357 m) as well.

`audio/cue_log.jsonl` stamps `thr_db` and `nj_state` on every candidate, so each cue is
attributable to the threshold in force. 4 chirp-rejects. Two `start` records appear because
the cue daemon was restarted into the session after a device-contention race at launch (the
daemon *is* the UMA recorder — the array is single-open).

## Caveat that applies to the whole day

⚠ **26 m altitude at 244 m range is a ~5° elevation angle** — the drone was on the treeline,
against foliage rather than sky. Three of the day's four sorties flew this profile. It is a
hard background for the detector and it sits at the null of a horizontal array's elevation
response (sensitivity goes as sin(el), so ~0 at the horizon). The 50–150 m detection question
that motivated the day's work therefore remains unexercised.

## Contents / gotchas

```
audio/uma16_<epoch>.wav   UMA-16, 16 ch, S16_LE     audio/sb_<epoch>.wav  SB-POLARIS, 8 ch, S32_LE
audio/cue_log.jsonl       cue gate log (thr_db, nj_state per candidate)
video_segments.tar        1080p native + 768x432 substream, 60 s MPEG-TS
blackbox/state.jsonl      tracker FSM ~2.9 Hz    blackbox/frames.tar  2,856 stills f<epoch_ms>.jpg
dji/*.csv, *.txt          decoded + original FlightRecord (CUSTOM.dateTime = true UTC)
```

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; detect them by RMS (live ~−70 dBFS, dead ~−190) rather
than hardcoding. ⚠ **The arrays use different sample widths** — UMA S16_LE, SB S32_LE; reading
both as int16 scrambles SB channel identity and destroys its spectrum.

Calibration as flown: `az_offset_deg` **301.37**, `invert_az` true. Cue producer: cheap daemon
(`SUBHUNT=0`). Site notch 100–200 Hz. Start pose pan 178.9 / tilt 45, pointed at the JBL
beacon. Cue-gated blob seeding was present in the build but **disabled** for this flight.

## GPS-referenced pixel work

Placing the drone in the image from GPS reaches a floor of about **5° of bearing error** on
this rig's data — the DJI's own ±2–5 m of position is 4–9° of bearing at the 20–45 m ranges
where the optical correspondences live. Treat any in-frame or pixel-level claim derived from
GPS here as approximate.

## 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 = +1.70 m**, el = -1 x tilt + 75.38 deg
- north offset -64.56 deg (pan sign -1), az gate residual 3.4 deg
- med |el residual| **1.10 deg** over 187 camera-on-drone rows, horiz 12-14 m
- per band: 0-30m: 1.10 deg (n=187)

Artifact: `joshruby/acoustic-knowledge` -> `v3/assets/el_datum/nightjar-flight-20260804-4.json`.
Tool: `sirch613/subhunt-v2` `v3/fit_el_datum.py`. Derive el truth as
atan2(hgt - z_rig, horiz) — NEVER from raw hgt.