AIRS (Atmospheric Infrared Sounder)

NASA’s hyperspectral infrared sounder on Aqua — 2378 thermal-IR channels at high spectral resolution provide vertical profiles of atmospheric temperature, water vapor, and trace gases that drive numerical weather prediction at major operational centers worldwide. Continuous since September 2002; one of the longest hyperspectral records anywhere.

What it sees

• 2378 channels from 3.7 µm to 15.4 µm; resolving power ~1200 — captures discrete CO₂, H₂O, O₃, CH₄, CO absorption features for retrieval inversions
• AMSU companion microwave sounder (15 channels, 23-89 GHz) — penetrates clouds, fills in temperature/humidity profile retrievals where IR is blocked
• 45 km horizontal pixel; 2 daily global cycles
• Vertical profiles from surface to ~70 km altitude

Why it matters

• AIRS data drives numerical weather prediction. ECMWF, NCEP, UKMO, JMA assimilate AIRS radiances; the impact-per-bit is among the highest of any satellite observation.
• 20+ year continuous record of atmospheric water vapor + temperature — climate-quality data record (CDR) for trend analysis.
• Trace gases — AIRS captures CO₂, CH₄, CO, O₃ as derived products. Pre-OCO-2 it was the only space-based CO₂ source.
• Volcanic SO₂ + ash detection — AIRS thermal-IR signature is operationally used for aviation hazard advisories.

Where to get the data

• earthaccess Python: short_name="AIRS3STD" (daily L3), AIRX2RET (L2 with AMSU), AIRS3STM (monthly L3)
• GES DISC: disc.gsfc.nasa.gov (AIRS data) + Giovanni for interactive analysis
• AIRS at JPL portal: airs.jpl.nasa.gov/data
• NRT product AIRS_NRT for operational weather-forecasting consumption

What it enables

• Atmospheric water vapor + temperature profile climatology
• Weather forecast verification + impact assessment
• Climate-trend studies (water vapor, upper-troposphere temperature, CH₄)
• Volcanic ash + SO₂ plume tracking (aviation hazards)
• Polar regions vs tropics atmospheric-state comparison
• Stratosphere-troposphere exchange (paired with MLS on Aura)
• Inputs to assimilated reanalyses (MERRA-2, ERA5)

Gotchas

• AIRS L2 retrievals are NOT independent measurements at each footprint. They are model-constrained inversions of measured radiances. Use radiances + your own inversion for advanced users; use L2/L3 only with care.
• Cloud contamination is a real concern. AIRS sees only IR; cloudy pixels yield degraded retrievals. AMSU+IR fusion partly mitigates but not for thick clouds.
• 45 km is the native footprint — don’t expect mesoscale spatial detail.
• Aqua is aging. Expected end-of-mission ~2027; AIRS data ends with Aqua. No direct successor; CrIS on Suomi NPP + JPSS-1/2 is the operational continuation but with different spectral coverage + resolution.
• The 2002-2003 calibration epoch is different. AIRS data prior to ~2003 needs special handling for climate-data-record work.

Related missions

• CrIS (Cross-track Infrared Sounder) on JPSS-series + Suomi NPP: AIRS’s operational successor (NOAA’s NUCAPS retrievals).
• IASI (EUMETSAT MetOp series): European hyperspectral IR sounder; complementary + operationally assimilated.
• MLS on Aura (s17 →): stratospheric chemistry profiles — complementary to AIRS’s tropospheric focus.
• MODIS on Aqua (s04 →): same platform; AIRS radiances + MODIS imagery are commonly co-analyzed.

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