Rutherford Appleton Laboratory Requirements Consolidation of the Near-Infrared Channel of the GMES-Sentinel-5 UVNS Instrument: Study Overview R.Siddans PM1: RAL, 9 July 2013

O 2 A-band O 2 A-band contains optically thick molecular absorption lines →Effective scattering altitude of photons (viewed in nadir) varies with wavelength →O 2 mixing ratio known therefore measurements can be used to infer scattering profile. Amount of information depends critically on spectral resolution but also on random and systematic instrumental and forward model errors Wavelength / nm 0.3 nm resolution 0.06nm resolution Sun-normalised radiance

Overview Study to consolidate requirements for Sentinel-5 NIR channel Application areas to be addressed: Height resolved aerosol from O2-A (and B) bands (RAL) Scattering correction for DOAS retrievals UV/VIS/NIR (RAL) Scattering correction for full-physics retrievals from SWIR+NIR joint retrieval (Univ Leicester) Water vapour retrievals (Univ Bremen) Impact of vegetation fluorescence to be taken into account in deriving requirements (and retrieval simulations) Input from FU-Berlin consultant

Consortium Retrieval Schemes RAL height-resolved aerosol scheme OE scheme largely developed for Eumetsat and ESA studies (MTG UVS, Capacity, Camelot) Retrieves aerosol extinction profile, integrated to layer amounts Instrumental errors quantified by linear mapping Non-linear version used to test impact of realistic cloud distributions Leicester OCO full physics retrieval scheme Retrieves CO2, CH4 from SWIR band, jointly fitting NIR band, and internally representing aerosol as either extinction profile or parameterised profile shape. Bremen Optimal Estimation DOAS (BESD) scheme Devloped for full physics SWIR retrievals, to be applied for H2O from NIR, exploiting O2-B for implicit scattering correction.

Treament of Cloud (errors from NIR fit on other L2) 1.UV/VIS species: As in Eumetsat A-band study. 1.Realistic cloud scenarios defined (model or CALIPSO/CloudSat) 2.NIR radiances simulated 3.Cloud parameters (fraction layer height, reflectance or optical depth) retrieved from A and/or B band. 4.UV/VIS AMF computed for true and retrieved state 5.Linear mapping used to propagate instrumental errors through SWIR species Full physics approach from sub-set of UV/VIS set (cirrus, aerosol low cloud fraction) 3.NIR-H2O Full physics approach from sub-set of UV/VIS set

Organisation of study Task 1: First Analysis of the NIR Band of the S-5 UVNS Instrument – Initial Trade-off. Task2: Refinement of NIR Specifications Task 3: Conclusions NB Task 2.6 runs during Task1, to define its scope by MTR Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

Task1: First Analysis of the NIR Band of the S-5 UVNS Instrument – Initial Trade-off. Focus on threshold and goal requirements for spectral resolution and coverage in the region of the O2-A and O2-B(+H2O) bands. User requirements + basic instrument performance will be taken from the MRTD + updates from ESA. Performance for NIR-1 and NIR-2 bands reported for resolutions of 0.4,0.2,0.12 and 0.06nm, for each application. Based on existing simulations where possible. Limited new simulations if not. It will be stated which L2 requirements can be met by a NIR channel which covers nm at the threshold resolution (0.4nm) Threshold resolution for aerosol profile identified. Output: TN1, describing the NIR band specifications linked to user service requirements. Task limited to resolution / noise / bandwidth trade-off. Impact of other errors only where overriding considerations identified previously.

Task 2: Refinement of NIR Specifications Task : Retrieval simulations to consolidate requirements for each application area. Task 2.5: Co-registration requirements Assess impact of co-registration errors on utility of NIR band scattering profile characterisation Based on CloudSat/CALIPSO + RT calculations to generate statistics of AMF errors as fn of co-location error. Task 2.6: Definition of geophysical scenarios and instrument assumptions Define scope of Task 2 simulations Geophysical scenarios Key instrument requirements to be consolidated via retrieval simulation Study resources limit number of different types of error to ~5 Discussion with SWIR contractor to align simulation work & define baseline for SWIR channel to be assumed here.

Deliverables KO=April KO + 4 months = end July’13 TN1, describing the NIR band specifications linked to user service requirements KO + 11 months = end Feb’14 TN2: describing the refined NIR band specifications linked to user service requirements KO + 12 months = end March’14 Final Report, Executive Summary + Technical Data Package ?