Spectral Canopy Array
Gimbal-mounted hyperspectral and thermal imaging across the greenhouse grid. Resolves VIS/NIR/SWIR/thermal radiance into per-specimen vegetation indices for stress detection ahead of any visible symptom.
1. Overview
The array comprises 28 ceiling-gantry imaging heads plus 6 mobile-rail heads. Each head sweeps a push-broom hyperspectral line scanner co-bored with a long-wave thermal microbolometer. Output is a registered radiance cube per zone, from which CHLORA derives vegetation indices and feeds the control plane. The array complements the point measurements of the PhytoSense Mesh with full spatial coverage.
2. Spectral Bands & Resolution
| Domain | Range | Bands | Spectral Res. | Spatial GSD | Primary Use |
|---|---|---|---|---|---|
| VIS | 380–700 nm | 64 | 5 nm | 1.2 mm | Pigments, chlorosis, anthocyanin |
| NIR | 700–1300 nm | 96 | 6 nm | 1.2 mm | Biomass, cell structure, NDVI |
| SWIR | 1300–2500 nm | 64 | 10 nm | 2.4 mm | Leaf water content, lignin/cellulose |
| Thermal (LWIR) | 8–14 µm | 1 (broadband) | — | 4.0 mm | Canopy temp, stomatal/transpiration |
Radiometric depth 14-bit; thermal NETD ≤ 40 mK; geometric registration of thermal-to-hyperspectral ≤ 0.5 px after orthorectification.
3. Computed Indices
| Index | Formula | Detects | Alarm Band |
|---|---|---|---|
| NDVI | (NIR − Red) / (NIR + Red) | Vigor / biomass | < 0.55 → CAUTION |
| PRI | (R₅₃₁ − R₅₇₀) / (R₅₃₁ + R₅₇₀) | Photosynthetic light-use efficiency | Δ > 0.03 drop → watch |
| Chlorophyll (CIre) | (NIR / RedEdge) − 1 | Chlorophyll content, N status | < 1.8 → nutrient flag |
| Water-stress (NDWI) | (NIR − SWIR) / (NIR + SWIR) | Leaf water content | < 0.20 → irrigation cue |
| CWSI (thermal) | (T_canopy − T_wet)/(T_dry − T_wet) | Crop water-stress index | > 0.6 → CRITICAL |
4. Scan Cadence & Positioning
- Full-grid pass — all 14 zones imaged in ≤ 6 h; staggered so each zone is refreshed every 90 min.
- Targeted re-scan — on alarm, a head re-tasks to the cluster within 120 s at 4× spatial oversampling.
- Night fluorescence pass — dark-adapted SIF (solar-induced fluorescence analog) sweep at 02:00 UTC.
4.1 Gimbal / Positioning
| Attribute | Specification |
|---|---|
| Gimbal axes | 3-axis (pan ±170°, tilt ±95°, roll ±20°) brushless, harmonic drive |
| Pointing accuracy | ±0.02° absolute; ±0.005° repeatability |
| Stabilization | IMU-fused, < 12 µrad RMS jitter during scan |
| Mobile rail heads | 6 units on overhead monorail, 0.4 m/s traverse, ±2 mm positioning |
| Scan geometry | Push-broom line at 200 Hz; nadir ± 30° off-nadir tasking |
5. Calibration Targets
- White reference — 99% Spectralon panel imaged at start of every pass for flat-field/gain.
- Dark reference — shuttered dark frame for offset; updated every 30 min for thermal drift.
- Spectral — Hg/Ar pencil lamp lines verify wavelength registration monthly (≤ 0.5 nm tolerance).
- Thermal — two-point blackbody at 20.0/40.0 °C; accept ≤ ±0.3 °C.
- Geometric — fixed fiducial grid per zone for orthorectification; re-survey quarterly.
6. Data Products
| Product | Level | Contents | Retention |
|---|---|---|---|
| Raw radiance cube | L0 | 14-bit DN, per-head, uncorrected | 14 days (warm tier) |
| Calibrated reflectance | L1 | White/dark corrected, orthorectified | 90 days |
| Index rasters | L2 | NDVI/PRI/CIre/NDWI/CWSI GeoTIFF per zone | 2 years |
| Specimen rollups | L3 | Per-cluster index time series → CHLORA | Indefinite (cold tier) |
L2/L3 products are queryable through the MDF telemetry API and surfaced on the Monitoring status board. Index thresholds map to alarms in VC-ENG-2400 and units in Botanical Metrics.