Flux Tower Data Dictionary - What Each CSV Column Means

Plain-language definition of every column in the 8 tower CSVs Shell sent us, pulled from Shell's own student data guide (full file is in Resources). Read this before writing any ingestion or chart code - it tells you what each field means, its unit, and what it's actually good for.

• Sign convention: negative NET_CARBON_DIOXIDE_FLUX (NEE) means the land is absorbing CO2 (a "sink," good); positive means it's releasing CO2 (a "source").
• NET_CARBON_DIOXIDE_FLUX / NEE (umol CO2/m2/s): net CO2 exchange - the core "is this plot healthy" number.
• GPP (umol CO2/m2/s): total CO2 pulled in by photosynthesis - a calculated value, not a raw sensor reading.
• RECO (umol CO2/m2/s): CO2 released by plant + soil respiration - also calculated, not raw.
• EVAPOTRANSPIRATION / ET (g/m2/s): water lost to the air from soil + plants - good for drought/irrigation dashboards.
• LATENT_HEAT_FLUX (W/m2): energy used evaporating water - tracks closely with ET, use it as a quality check.
• SENSIBLE_HEAT_FLUX (W/m2): heat moving between ground and air with no phase change.
• SOIL_HEAT_FLUX (W/m2): energy moving into or out of the soil.
• NET_RADIATION + incoming/outgoing shortwave & longwave (W/m2): sunlight in, heat out - good for day/night detection and as model inputs.
• AIR_TEMPERATURE, AIR_PRESSURE, RELATIVE_HUMIDITY: basic weather context variables.
• VAPOUR_PRESSURE_DEFICIT / VPD (kPa): how "thirsty" the air is - higher VPD means drier air and more plant stress.
• SOIL_TEMPERATURE, SOIL_MOISTURE (fraction, e.g. 0.25 = about 25%): soil condition - drives respiration, GPP and ET with a time lag.
• RAINFALL (mm per interval): precipitation for that 30-minute or daily window.
• WIND_SPEED / WIND_DIRECTION: matters because a tower's "footprint" (the area it's actually measuring) shifts with the wind.
• *_FLAG columns and "NA": quality flags - filter these out before charting or training, never plot raw numbers blindly.
• Two files per tower: a 30-min file (finest detail, ~15MB each) and a daily file (rolled up, ~150-250KB) - use daily for overview charts, 30-min for zoomed-in detail views.
• Build-responsibly rules straight from Shell's guide: preserve timestamps/timezones, handle NA values, use the QC flags, split any forecast model's train/test data by time (not randomly), and don't treat a tower as one fixed plot since its coverage footprint moves with wind and weather.