Relative Growth Rate (RGR)
VC-MET-009 — the rate of canopy height/extension gain over a rolling window, the slow-cadence integral of vitality that confirms whether favourable physiology is translating into biomass.
Definition
Relative Growth Rate (RGR) here is the canopy linear extension rate — the gain in mean canopy height (or leading-shoot length) per day, in mm·day⁻¹ — derived from the structured-light and stereo-photogrammetry channels of the Spectral Canopy Array over a rolling multi-pass window. It is the facility's productivity confirmation signal: where instantaneous physiology says a plant can grow, RGR says whether it is.
Why it matters
RGR is the slowest, most integrative vitality channel and the one that catches chronic, sub-alarm problems — a plant whose photosynthesis and turgor look acceptable yet quietly stops extending is in trouble that fast sensors will not flag. CHLORA uses RGR to schedule training, pruning, and harvest, and to validate that CVI-favourable conditions are actually producing biomass. A stall is a strong precursor to senescence onset.
Formula
RGR = (H_t − H_{t−Δ}) / Δ (linear form, mm·day⁻¹)
where:
H_t = canopy height estimate at time t (mm)
H_{t−Δ} = canopy height one window earlier
Δ = window length (days), default 1.0 d
canopy height (Spectral Canopy Array):
H = P95(point-cloud elevation) − bench datum
P95 = 95th-percentile elevation (suppresses outliers)
point cloud from structured-light + stereo pass
smoothing:
H is a 4-pass (24-h) moving median before differencing
to reject single-pass photogrammetry noise.
Reported to 0.1 mm·day⁻¹.
Inputs
| Symbol | Quantity | Reference Band | Source |
|---|---|---|---|
| H_t | Canopy height (P95) | per cultivar stage | Spectral Canopy Array |
| Datum | Bench reference elevation | fixed survey | Spectral Canopy Array |
| Δ | Differencing window | 1.0 d | Derivation |
| Stage | Phenological stage (band select) | veg / flower / mature | Cultivation Records |
Units & Scale
mm·day⁻¹, reported to 0.1. Nominal bands are stage-dependent — the 3.0–9.0 envelope applies to the vegetative stage; flowering and mature stages carry lower expected bands stored in the cultivar profile. Aggregated per cohort as the median; facility value is cohort-count-weighted. Confidence degrades when fewer than three passes contribute to the height median or when occlusion exceeds 25%.
Sampling & Source
- Derived every 6 hours from Spectral Canopy Array photogrammetry passes.
- Height smoothed over a 24-h (4-pass) moving median before differencing.
- Nominal band selected by cultivar phenological stage.
- Stale handling: flagged STALE after 2 missed passes; high-occlusion passes excluded.
Thresholds
OK
Active extension for stage. No action.
WARN
Growth slowing; CHLORA advisory, investigate chronic stress.
CRIT
Growth stalled; auto-dispatch, senescence precursor.
Recent Trend
Facility cohort-weighted RGR (vegetative cohorts), last 14 windows:
Interpretation Guidance
| RGR Band | Reading | Likely Driver | Action |
|---|---|---|---|
| 7.0–9.0 | Vigorous | Optimal vegetative growth | Schedule training/pruning. |
| 3.0–6.9 | Healthy | Normal stage growth | None; normal range. |
| 1.5–2.9 | Soft slowdown | Mild chronic stress or stage shift | Confirm stage; check A (VC-MET-008). |
| 0.5–1.4 | WARN slowing | Chronic stress, N limit, root issue | Cultivation investigation. |
| < 0.5 | CRIT stalled | Severe stress or pre-senescence | Auto-dispatch; check senescence (VC-MET-011). |
Related Metrics
Net Photosynthetic Rate
Carbon supply that funds growth.
VC-MET-010Leaf Area Index
Structural growth partner.
VC-MET-011Senescence Fraction
Opposing end-of-life signal.
VC-MET-001Canopy Vitality Index
Growth confirms favourable CVI.
VC-MET-014Root Electrical Capacitance
Root capacity behind growth.
VC-MET-105CO₂ Concentration
Enrichment driver of growth.
Related SOPs
- SOP Library — photogrammetry datum survey & stage-band assignment.
- Growth-stall investigation & WARN/CRIT triage — Operations SOP set in the SOP Library.
- Training/harvest scheduling & alarm escalation — Monitoring Systems.