diff --git a/algo.md b/algo.md
index 67ff07fd..ee159613 100644
--- a/algo.md
+++ b/algo.md
@@ -1297,25 +1297,125 @@ For each band:
 | Signal prediction floor | +/- 2-3 dB | Measured from link data |
 | CW bandwidth advantage | ~7 dB | 10*log10(2700/500); 24% range increase |
 
-## ITU-R References
+## ITU-R Recommendations
 
-- P.453-14: Radio refractivity
-- P.525: Free-space path loss
-- P.676-13: Gaseous absorption (O2 + H2O)
-- P.838-3: Specific rain attenuation
-- P.526: Diffraction
-- P.452: Interference between stations
+The following ITU-R Recommendations provide the physics models underlying the scoring algorithm. All are publicly available from the ITU Radiocommunication Sector (https://www.itu.int/rec/R-REC-P/en).
 
-## Data References
+| Recommendation | Title | Used For |
+|----------------|-------|----------|
+| ITU-R P.453-14 | The radio refractive index: its formula and refractivity data | Surface refractivity N calculation, refractivity gradient |
+| ITU-R P.525-4 | Calculation of free-space attenuation | Free-space path loss baseline |
+| ITU-R P.676-13 | Attenuation by atmospheric gases and related effects | O2 and H2O absorption coefficients per band |
+| ITU-R P.838-3 | Specific attenuation model for rain for use in prediction methods | Rain attenuation coefficients (k, alpha) per band |
+| ITU-R P.526-15 | Propagation by diffraction | Knife-edge and terrain diffraction loss |
+| ITU-R P.452-17 | Prediction procedure for the evaluation of interference between stations on the surface of the Earth | Clear-air propagation modeling framework |
+| ITU-R P.835-6 | Reference standard atmospheres | Standard atmosphere profiles for baseline |
+| ITU-R P.530-18 | Propagation data and prediction methods for terrestrial line-of-sight systems | Multipath fading and enhancement statistics |
 
-- ARRL Microwave Contest QSO database: 58,282 total, 57,488 tropospheric with distance (1992-2024)
-- IEM ASOS observations: 1,299 stations, 58,398 surface observations
-- IEM RAOB soundings: 112 stations, 3,901 soundings
-- IEMRE gridded hourly: 3,675 observations at 0.125° resolution
-- HRRR model profiles: 4,522 profiles with refractivity, BL depth, PWAT
-- Terrain profiles: 58,276 QSO paths (97.2% blocked, avg 36.2 dB diffraction)
-- Commercial link data: 7 links at 11/24/68 GHz near DFW, SNMP-polled
-- Solar indices: 9,586 daily values (1998-2026) — reserved for future use
+## Data Sources
+
+### Primary QSO Dataset
+
+**ARRL Microwave Contest Results (1992-2024)**
+- Source: Contest log submissions compiled from ARRL contest results
+- Volume: 58,282 total QSOs across 13+ bands (10 GHz through 403 GHz)
+- Usable subset: 57,488 tropospheric QSOs after filtering 4 EME contacts (QRA64D/JT4F modes >3,000 km)
+- Fields: station callsigns, Maidenhead grid squares, timestamp, mode (CW/SSB/FM/FT8), band
+- Grid-to-coordinate conversion: gridmap.org API for Maidenhead → lat/lon
+- Distance: Haversine great-circle calculation from grid square centers
+
+### Surface Weather Observations (ASOS)
+
+**Iowa Environmental Mesonet (IEM) — Automated Surface Observing System**
+- API: `https://mesonet.agron.iastate.edu/cgi-bin/request/asos.py`
+- Network discovery: `https://mesonet.agron.iastate.edu/api/1/network.py`
+- Station count: 2,922 total, 1,299 with observations matched to QSOs
+- Observation count: 58,398 surface observations
+- Fields: temperature (°F), dewpoint (°F), relative humidity (%), wind speed (kts), wind direction (°), sea level pressure (mb), sky condition (CLR/FEW/SCT/BKN/OVC), precipitation (inches/hour), weather codes
+- Temporal matching: ±2 hours around QSO timestamp
+- Spatial matching: nearest station within 150 km of QSO path endpoints
+- No authentication required
+
+### Upper-Air Soundings (RAOB)
+
+**Iowa Environmental Mesonet (IEM) — Radiosonde Observations**
+- API: `https://mesonet.agron.iastate.edu/json/raob.py`
+- Station count: 346 sounding stations total, 112 with data matched to QSOs
+- Sounding count: 3,901 vertical profiles
+- Standard times: 00Z and 12Z (bracketing QSO timestamps)
+- Spatial matching: nearest station within 300 km of QSO path
+- Raw profile: pressure, temperature, dewpoint, height per level
+- Derived parameters (computed at ingestion by `SoundingParams.derive/1`):
+  - Surface refractivity (ITU-R P.453-14 formula)
+  - Minimum refractivity gradient (N/km) — primary ducting indicator
+  - Boundary layer depth (m)
+  - Precipitable water (mm)
+  - K-index, Lifted index — atmospheric stability
+  - Ducting detection and duct characteristics (height, strength in M-units)
+
+### HRRR Model Data
+
+**NOAA High-Resolution Rapid Refresh (HRRR)**
+- Source: AWS S3 public bucket `https://noaa-hrrr-bdp-pds.s3.amazonaws.com`
+- Format: GRIB2 files, hourly cadence, 3km horizontal resolution
+- Profile count: 4,522 profiles matched to QSO/grid locations
+- Pressure levels extracted: 1000, 975, 950, 925, 900, 850, 800, 700 mb
+- Surface fields: temperature (°C), dewpoint (°C), pressure (mb), HPBL (boundary layer height, m), PWAT (precipitable water, mm), 10m wind components (u, v), cloud cover (%), precipitation (mm)
+- Per-level fields: temperature, dewpoint, geopotential height
+- Derived: refractivity profile, min gradient, ducting detection (same as sounding derivation)
+- Batch optimization: groups multiple grid points by HRRR hour to download GRIB2 once per time step
+
+### IEMRE Gridded Hourly Weather
+
+**Iowa Environmental Mesonet Reanalysis (IEMRE)**
+- API: `https://mesonet.agron.iastate.edu/iemre/hourly/{date}/{lat}/{lon}/json`
+- Resolution: 0.125° (~14 km) gridded
+- Observation count: 3,675 gridded hourly observations
+- Fields per hour: air temperature (°F), dewpoint (°F), sky cover (%), wind components (u/v, m/s), hourly precipitation (inches), solar radiation
+- Used for: weather at QSO endpoint grid points, more granular than nearest-ASOS matching
+- Status: ingested but not yet integrated into scoring factors
+
+### Terrain Elevation Data
+
+**SRTM (Shuttle Radar Topography Mission)**
+- Primary source: AWS S3 `https://elevation-tiles-prod.s3.amazonaws.com/skadi` (local tile cache)
+- Resolution: 90m (SRTM3, 3 arc-second)
+- Tile format: `.hgt` binary, 3601×3601 samples, 16-bit signed big-endian
+- Fallback APIs (when tiles unavailable):
+  - Open-Meteo: `https://api.open-meteo.com/v1/elevation`
+  - OpenTopography: `https://api.opentopodata.org/v1/srtm90m`
+- Profile method: 64 elevation samples per QSO path (great-circle interpolation)
+- Path count: 58,276 QSO paths profiled
+- Results: 56,658 BLOCKED (97.2%, avg 36.2 dB diffraction), 1,277 CLEAR (2.2%), 341 FRESNEL_PARTIAL (0.6%)
+- Analysis: max elevation, min Fresnel clearance, knife-edge diffraction loss, obstruction count
+
+### Commercial Link Validation Data
+
+**Ubiquiti airFiber and airFiber 60 links near Princeton, TX**
+- Link count: 7 commercial microwave links
+- Frequencies: 11 GHz (AF11X, dual-chain), 24 GHz (AF11X), 68 GHz (AF60, single-chain)
+- Polling: SNMP at 5-minute intervals (rx_power_0, rx_power_1 for dual-chain; rx_power for single)
+- Weather correlation: KTKI ASOS station
+- Historical dataset: March 14-29, 2026 (18,540 samples)
+- Validated coefficients: 11 GHz and 24 GHz gaseous absorption, 68 GHz O2 band wing absorption (0.1 dB/km per g/m³ measured on 2.8 km path)
+- Live polling: active for ongoing validation
+
+### Solar Indices
+
+**GFZ German Research Centre for Geosciences**
+- Source: `https://kp.gfz.de/app/files/Kp_ap_Ap_SN_F107_since_1932.txt`
+- Volume: 9,586 daily values (1998-2026)
+- Fields: Solar Flux Index (F10.7), adjusted SFI, sunspot number, Ap index, Kp values (3-hourly)
+- Status: ingested but NOT used in tropospheric scoring — reserved for potential VHF/sporadic-E extension
+
+### Live Scoring Data
+
+**Propagation Grid Scores**
+- Coverage: CONUS grid at 0.125° resolution
+- Update cadence: hourly (HRRR-based via `PropagationGridWorker`) + 10-minute ASOS adjustments (`AsosAdjustmentWorker`)
+- Per grid point: composite score (0-100), 9 individual factor scores, valid_time
+- Bands scored: all configured bands (10, 24, 47, 68, 75, 122, 134, 142, 241 GHz)
+- Retention: 2 most recent valid_times kept, older data pruned automatically
 
 ## Known Data Quality Issues
 
@@ -1324,3 +1424,5 @@ For each band:
 - **Sounding data recency**: Latest soundings are from Sep 2024. Ingestion pipeline may need restart for live enrichment.
 - **Surface obs density**: Historical obs are sparse (~1 per 4.7 days per station) because they were fetched per-QSO-window. Live polling is now active for continuous coverage.
 - **Weather codes (wx_codes)**: Stored in surface_observations but unused by scoring. Direct fog/thunderstorm/freezing-rain detection could supplement indirect inference from Td depression and sky condition.
+- **Contest bias**: 97% of QSOs are from August-September ARRL Microwave Contest. Seasonal and regional statistics may not generalize to year-round conditions.
+- **Rain model unvalidated**: ITU-R P.838-3 rain attenuation coefficients are theoretical — no rain events occurred in the commercial link validation dataset.