# UV-VIS nadir spectroscopy
*methodologies*

Spectrally resolved nadir measurement of backscattered sunlight, typically from about 300 to 500 nm and down to 270 nm or below on instruments that also retrieve ozone profiles, in contiguous spectra at roughly 0.2 to 1 nm resolution. It retrieves atmospheric columns of NO2, SO2, ozone and other trace gases by differential optical absorption spectroscopy (DOAS) and related spectral fitting. Instruments that also cover the O2 A band near 760 nm add cloud and aerosol layer height. Daylight only. Orbit, swath and pixel size are attributes, not separate methods.

## Specifications
- **family**: Atmospheric spectroscopy
- **requirements envelope**: {"kind":"spectral","spectral_range_nm":{"min":300,"max":500},"calibration_tier_min":"radiometric","daylight_required":true,"cloud_tolerant":false}
- **entity type**: methodology
- **last verified date**: 2026-10-21
- **verified by**: sw
- **claim status**: unclaimed
- **technology**: optical-spectral-sensing

## Editorial
UV-VIS (ultraviolet and visible) nadir spectroscopy retrieves atmospheric columns of nitrogen dioxide (NO2), sulphur dioxide (SO2), ozone and other trace gases from sunlight scattered back to a satellite looking straight down.[^tropomi-eu-products] It uses differential optical absorption spectroscopy (DOAS), which inverts the differential absorption structure left after smooth scattering and continuum components are removed.[^wikipedia] It requires contiguous spectra at roughly 0.2 to 1 nm resolution, typically across about 300 to 500 nm, and works in daylight only. Cloud and coarse pixels limit it.

**Requirements.** Instruments that also retrieve ozone profiles extend the range to 270 nm or below; TROPOMI (TROPOspheric Monitoring Instrument) uses 270 to 329 nm for its profile.[^mettig-2021-o3-profile] OMI (Ozone Monitoring Instrument) covers 270 to 500 nm at 0.42 to 0.63 nm,[^wmo-omi] GEMS (Geostationary Environment Monitoring Spectrometer) covers 300 to 500 nm at under 0.6 nm,[^wmo-gems] and the OMPS (Ozone Mapping and Profiler Suite) nadir mapper covers 300 to 380 nm.[^wmo-omps-nadir] TROPOMI derives NO2 from a fit between 405 and 465 nm.[^vangeffen-2022-no2] Filter imagers such as EPIC (Earth Polychromatic Imaging Camera), with ten discrete filters, lack contiguous sampling and form a different method.[^epic-description]

**Pixels.** Pixel size varies: 3.6 by 5.6 km for TROPOMI NO2,[^vangeffen-2022-no2] 7.5 km for Sentinel-5,[^wmo-sentinel-5] 13 by 24 km for OMI,[^wmo-omi] 13 by 48 km for EMI (Environment Monitoring Instrument),[^wmo-emi] 40 by 40 or 40 by 80 km for GOME-2 (Global Ozone Monitoring Experiment-2)[^wmo-gome2] and under 8 km for geostationary Sentinel-4.[^wmo-sentinel-4]

**Oxygen A band.** Instruments that also reach the O2 A band near 760 nm can add cloud and aerosol layer height: TROPOMI,[^tropomi-eu-l1b] Sentinel-4,[^sentinels-s4-payload] Sentinel-5,[^wmo-sentinel-5] GOME-2,[^wmo-gome2] EMI[^wmo-emi] and TANSO-3.[^wmo-tanso-3] TROPOMI's aerosol layer height works on cloud-free scenes only,[^tropomi-eu-alh] and GOME-2 provides cloud fraction and pressure.[^eumetsat-gome2-factsheet] OMI and GEMS stop at 500 nm.[^wmo-omi][^wmo-gems] The shortwave-infrared modules of TROPOMI and Sentinel-5 belong to shortwave-infrared absorption spectroscopy, not to this method.[^wmo-tropomi][^wmo-sentinel-5]

**Ozone and plumes.** Total ozone columns are a core product;[^nasa-earthdata-omps] nadir viewing gives only coarse profile information, and limb sounding gives finer vertical resolution.[^nasa-earthdata-omps] TROPOMI produces SO2 columns, and its aerosol layer height covers elevated layers such as ash.[^tropomi-eu-products][^tropomi-eu-alh] These signal plumes, not geology.

**Carbon dioxide.** The method does not measure CO2. NO2 serves as a co-emitted plume tracer: a Berlin simulation for the Copernicus anthropogenic CO2 monitoring mission found an NO2 instrument detecting about 35 of 50 observable plumes a year, against 6 and 16 for CO2.[^kuhlmann-2019-co2m]

**Aerosol.** The UV aerosol index is a residual from Rayleigh-only reflectance at 340/380 nm and 354/388 nm.[^nasa-gesdisc-s5p-ai] Near-UV retrievals add single-scattering albedo: OMI's OMAERUV assumes one of three aerosol types, each with a fixed bimodal spherical size distribution and an assumed refractive index,[^torres-2013-omaeruv] and GEMS fits three types.[^gems-aerosol-amt-2024] Both prescribe fixed aerosol models, so they indicate absorption, not size distribution or refractive index.

**Status as of 21 October 2026.** TROPOMI operational products include NO2, SO2, ozone, aerosol index and aerosol layer height.[^tropomi-eu-products] GOSAT-GW, carrying TANSO-3 with a band near 0.45 micrometres for NO2, launched on 29 June 2025; the NO2 Level 2 product is planned, not yet demonstrated.[^wmo-tanso-3][^nies-gosat-gw]

## Sources
- [wikipedia] | Wikipedia: Differential optical absorption spectroscopy | https://en.wikipedia.org/wiki/Differential_optical_absorption_spectroscopy | tier=community | accessed=2026-10-21
  Re-read 2026-10-21. Supports only the statement that DOAS exploits differential absorption structures: smooth scattering and continuum components are removed (polynomial) and the remaining differential structure is inverted for trace gas amounts. Ground-based focus; no satellite, instrument, wavelength or product claim is supported.
- [wmo-tropomi] | WMO OSCAR instrument record: TROPOMI | https://space.oscar.wmo.int/instruments/view/tropomi | tier=agency-doc | accessed=2026-10-21
  270-495 nm 1200 ch 0.55 nm SNR 1000; 710-775 nm 0.55 nm; 2305-2385 nm 0.25 nm; 7 km at SSP; 2600 km swath.
- [ceos-veefkind-s5p] | Veefkind (KNMI) CEOS ACC presentation: Sentinel-5P TROPOMI | https://ceos.org/document_management/Virtual_Constellations/ACC/Meetings/AC-VC-12/Day%201/4.%20Veefkind%20-%20S5P-Tropomi.pdf | tier=agency-doc | accessed=2026-10-21
  Design band plan 270-320, 320-495, 675-775, 2305-2385 nm at 0.49, 0.54, 0.38, 0.25 nm; products include UV aerosol index and aerosol layer height. Text read via pdftotext.
- [tropomi-eu-l1b] | TROPOMI Level-1B radiance product page (tropomi.eu) | https://www.tropomi.eu/data-products/l1b-radiance | tier=agency-doc | accessed=2026-10-21
  Calibrated band edges 267-300, 300-332, 305-400, 400-499, 661-725, 725-786, 2300-2343, 2343-2389 nm; resolution table garbled in extraction, values 0.45-0.65 nm for UV and UVIS.
- [tropomi-eu-products] | TROPOMI Level-2 data product list (tropomi.eu) | https://www.tropomi.eu/data-products | tier=agency-doc | accessed=2026-10-21
  Operational: AER_AI, AER_LH, CO, CLOUD, HCHO, CH4, NO2, O3 total/tropospheric/profile, SO2. Under development: AER_OT, BRO, OCLO, CHOCHO, KD, SIF, UV, TCWV.
- [tropomi-eu-alh] | TROPOMI aerosol layer height product page (tropomi.eu) | https://www.tropomi.eu/data-products/aerosol-layer-height | tier=agency-doc | accessed=2026-10-21
  O2 A band, optimal estimation, cloud-free only, plume mid-pressure for elevated layers (dust, ash, smoke); also gives height context for the UV aerosol index.
- [nasa-gesdisc-s5p-ai] | NASA GES DISC: Sentinel-5P TROPOMI Aerosol Index L2 (S5P_L2__AER_AI) | https://data.nasa.gov/dataset/sentinel-5p-tropomi-aerosol-index-1-orbit-l2-7km-x-3-5km-v1-s5p-l2-aer-ai-at-ges-disc | tier=agency-doc | accessed=2026-10-21
  UV aerosol index is a residual from Rayleigh-only reflectance at wavelength pairs 340/380 nm and 354/388 nm; the page does not state aerosol type sensitivity.
- [vangeffen-2022-no2] | van Geffen et al. 2022, TROPOMI NO2 retrieval v2.2 (AMT 15, 2037) | https://amt.copernicus.org/articles/15/2037/2022/ | tier=peer-reviewed | accessed=2026-10-21
  DOAS fit 405-465 nm; cloud pressure from FRESCO-wide using the O2 A band near 758 nm; pixel 3.6 km across, 5.6 km along since 2019-08-06.
- [theys-2017-so2] | Sulfur dioxide retrievals from TROPOMI onboard Sentinel-5 Precursor: algorithm theoretical basis (AMT 10, 119, 2017) | https://amt.copernicus.org/articles/10/119/2017/ | tier=peer-reviewed | accessed=2026-10-21
  Full text read. SO2 DOAS windows 312-326 nm (baseline), 325-335 nm and 360-390 nm; SO2 absorption in the 310-326 nm range can be three orders of magnitude weaker than ozone.
- [wmo-omi] | WMO OSCAR instrument record: OMI | https://space.oscar.wmo.int/instruments/view/omi | tier=agency-doc | accessed=2026-10-21
  270-314 (390 ch, 0.63 nm), 306-380 (390 ch, 0.42 nm), 350-500 nm (780 ch, 0.63 nm); 13 x 24 km; 2600 km swath.
- [wmo-gome2] | WMO OSCAR instrument record: GOME-2 | https://space.oscar.wmo.int/instruments/view/gome_2 | tier=agency-doc | accessed=2026-10-21
  240-315, 311-403, 401-600, 590-790 nm; 1024 ch each; 0.24-0.53 nm; 40 x 40 or 40 x 80 km.
- [eumetsat-gome2-factsheet] | EUMETSAT GOME-2 Factsheet v4F | https://www-cdn.eumetsat.int/files/2022-02/GOME-2%20Factsheet_v4F.pdf | tier=agency-doc | accessed=2026-10-21
  240-790 nm, 0.26-0.51 nm, 4096 spectral points; products include O3, NO2, tropospheric NO2, SO2, HCHO, BrO, absorbing aerosol index; FRESCO+ cloud fraction and top pressure in level 1b. Text read via pdftotext.
- [wmo-sentinel-4] | WMO OSCAR instrument record: Sentinel-4 | https://space.oscar.wmo.int/instruments/view/sentinel_4 | tier=agency-doc | accessed=2026-10-21
  305-400 (0.5 nm), 400-500 (0.5 nm), 755-775 nm (0.2 nm); under 8 km at 45N; 60 min repeat.
- [sentinels-s4-payload] | Copernicus Sentinels: Sentinel-4 instrument payload | https://sentinels.copernicus.eu/missions/sentinel-4/instrumental-payload | tier=agency-doc | accessed=2026-10-21
  UV 305-400, VIS 400-500, NIR 750-775 nm; 0.5 nm UV-VIS and 0.12 nm NIR; 8 x 8 km.
- [wmo-sentinel-5] | WMO OSCAR instrument record: Sentinel-5 | https://space.oscar.wmo.int/instruments/view/sentinel_5 | tier=agency-doc | accessed=2026-10-21
  UV-1 270-310 (1.0 nm, SNR 100), UV-2 300-370 (0.5 nm), VIS 370-500 (0.5 nm), NIR-1 685-710, NIR-2 755-773 (0.4 nm), SWIR-1 1595-1675, SWIR-2 2305-2385 nm; 7.5 x 7.5 km; 2670 km swath.
- [wmo-gems] | WMO OSCAR instrument record: GEMS | https://space.oscar.wmo.int/instruments/view/gems | tier=agency-doc | accessed=2026-10-21
  300-500 nm, resolution under 0.6 nm, sampling under 0.2 nm, 5 km over Korea.
- [gems-aerosol-amt-2024] | GEMS aerosol algorithm AERAOD and validation (AMT 17, 4369, 2024) | https://amt.copernicus.org/articles/17/4369/2024/ | tier=peer-reviewed | accessed=2026-10-21
  Optimal estimation from normalized radiances at 354, 388, 412, 443, 477, 490 nm; products AOD and SSA at 443 nm, ALH, UVAI; three aerosol types (highly absorbing fine, dust, non-absorbing); AOD R=0.792 vs AERONET; SSA within 0.03 for 42.76 percent at AOD over 0.4; ALH mean difference -0.225 km vs CALIOP, 55.3 percent within 1 km; 477 nm O2-O2 band carries height information.
- [wmo-emi] | WMO OSCAR instrument record: EMI | https://space.oscar.wmo.int/instruments/view/emi | tier=agency-doc | accessed=2026-10-21
  240-315, 311-403, 401-600, 590-790 nm; 0.3 to 0.5 nm; 13 x 48 km; 2500 km swath.
- [wmo-omps-nadir] | WMO OSCAR instrument record: OMPS nadir | https://space.oscar.wmo.int/instruments/view/omps_nadir | tier=agency-doc | accessed=2026-10-21
  Mapper 300-380 nm, profiler 250-310 nm, resolution 1 nm with 0.42 nm sampling. No channel count on the OSCAR record; see cisess-omps-performance.
- [nasa-earthdata-omps] | NASA Earthdata: OMPS instrument | https://www.earthdata.nasa.gov/data/instruments/omps | tier=agency-doc | accessed=2026-10-21
  Nadir mapper, nadir profiler and limb profiler; 250-420 nm; total column and profile ozone.
- [wmo-tanso-3] | WMO OSCAR instrument record: TANSO-3 | https://space.oscar.wmo.int/instruments/view/tanso_3 | tier=agency-doc | accessed=2026-10-21
  Band 1 about 0.45 um for NO2 (under 0.5 nm), band 2 about 0.76 um O2, band 3 about 1.6 um CO2 and CH4; 10 km wide or 1-3 km focus; 911 km or 90 km swath.
- [nies-gosat-gw] | NIES GOSAT-GW TANSO-3 page | https://gosat-gw.nies.go.jp/en/gosat-gw02.html | tier=agency-doc | accessed=2026-10-21
  Launched 2025-06-29; NO2 column to be calculated by the conventional DOAS approach; NIES plans monthly Level 2 products including NO2 (planned wording).
- [kuhlmann-2019-co2m] | Kuhlmann et al. 2019, Quantifying CO2 emissions of a city with the Copernicus anthropogenic CO2 monitoring satellite mission (AMT 12, 6695) | https://amt.copernicus.org/articles/12/6695/2019/ | tier=peer-reviewed | accessed=2026-10-21
  Berlin simulation: NO2 instrument detects about 35 of 50 observable plumes per year vs 6 and 16 for CO2; NO2 retrievals tolerate more cloud; abstract read only.
- [nasa-gesdisc-omaeruv-v4] | NASA GES DISC: OMI/Aura Near UV Aerosol OD and SSA L2 V004 (OMAERUV) | https://www.earthdata.nasa.gov/data/catalog/ges-disc-omaeruv-004 | tier=agency-doc | accessed=2026-10-21
  AOD, SSA, absorption AOD, UV aerosol index and above-cloud AOD at 354, 388, 500 nm; 24 x 13 km.
- [torres-2013-omaeruv] | Torres et al. 2013, Improvements to the OMI near-UV aerosol algorithm using A-train CALIOP and AIRS observations (AMT 6, 3257) | https://amt.copernicus.org/articles/6/3257/2013/ | tier=peer-reviewed | accessed=2026-10-21
  Full text read. OMAERUV assumes one of three aerosol types (desert dust, carbonaceous, sulfate-based), each with a fixed bimodal spherical size distribution from AERONET statistics, an assumed spectral imaginary refractive index (354-388 nm), seven sub-types by k at 388 nm, 21 aerosol models in look-up tables over geometry, AOD, SSA and layer height; type chosen from UV aerosol index, AIRS CO and IGBP scene type; layer height prescribed from a CALIOP climatology.
- [omaero-amt-2017] | OMI multiwavelength aerosol retrieval: Bayesian aerosol model selection and AOD (AMT 10, 4079, 2017) | https://amt.copernicus.org/articles/10/4079/2017/ | tier=peer-reviewed | accessed=2026-10-21
  Abstract read. Concerns OMAERO (KNMI multi-wavelength algorithm), not OMAERUV: precalculated aerosol microphysical models in look-up tables, model selection by Bayesian evidence, cloud-free over-land pixels. Do not cite for OMAERUV.
- [desmedt-2018-hcho] | De Smedt et al. 2018, Algorithm theoretical baseline for formaldehyde retrievals from S5P TROPOMI and from the QA4ECV project (AMT 11, 2395) | https://amt.copernicus.org/articles/11/2395/2018/ | tier=peer-reviewed | accessed=2026-10-21
  Full text read via PDF. HCHO DOAS fitting interval 1: 328.5-359 nm (BrO fitted jointly), interval 2: 328.5-346 nm.
- [mettig-2021-o3-profile] | Mettig et al. 2021, Ozone profile retrieval from nadir TROPOMI measurements in the UV range (AMT 14, 6057) | https://amt.copernicus.org/articles/14/6057/2021/ | tier=peer-reviewed | accessed=2026-10-21
  Spectral data between 270 and 329 nm are used; UV penetration depth is lower at shorter wavelengths, which permits profile retrieval; vertical resolution about 6-10 km above 18 km and 15-25 km below. Introduction cites a GOME-2 method taking the stratospheric profile from the Hartley band (266-307 nm). Abstract and introduction read.
- [cisess-omps-performance] | CISESS/UMD: Performance Evaluation of OMPS | https://cisess.umd.edu/performance-evaluation-of-omps | tier=agency-doc | accessed=2026-10-21
  Nadir mapper 300-380 nm with 196 spectral channels; nadir profiler 250-310 nm with 146 channels; spectral sampling 0.4 nm and 1 nm FWHM resolution.
- [epic-description] | DSCOVR EPIC instrument description (NASA AVDC) | https://avdc1.gsfc.nasa.gov/pub/DSCOVR/EPIC_NISTAR_Documents/DSCOVR-EPIC-Description.pdf | tier=agency-doc | accessed=2026-10-21
  Ten filters in 12-position dual filter wheels (5 filters per wheel plus an open position), CCD focal plane; the channel table itself was not machine-readable in the PDF.

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Source: https://eo-atlas.org/topics/methodologies/uv-vis-nadir-spectroscopy
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