Products from the OMPS Limb Profiler (LP) instrument on the

Suomi NPP Satellite

Pawan K. Bhartia Earth Sciences Division- AtmospheresNASA Goddard Space Flight Center

Greenbelt, Maryland, USA

Limb Scattering Technique

Line of sightTangent point

Tangent heightDiffuse upwelling radiation

Solar Radiation

OMPS LP Standard Products• Products from V2 O3 Algorithm

– Density vs alt profiles from cloud-top to 60 km– Converted into MR profiles using T/P profiles from

GMAO at NASA/GSFC.– Also provides Aerosol Scattering Index (ASI) @ 673 nm

to map aerosols, PMC, PSC and cirrus clouds. Aerosol extinction profiles are no longer produced by the O3 algorithm.

– 2 years of data planned to be released by the end of this month.

• Aerosols Products- produced separately– Currently under evaluation. Data should be released

in 2-3 months.

Aerosol Scattering Index (ASI)

ASI= ln(Im/Ic)

Where Im is the measured radiance, and Ic is calculated radiance assuming no aerosols scattering, both normalized at 45 km to unity to remove calibration and DUR effects, i.e., ASI is forced to be zero at 45 km.

Note: This concept is conceptually similar to TOMS UVAI, except that UVAI is based on radiance ratios at two wavelengths, and UVAI is normalized to zero using a different method.

ASI at 673 nm

Using SAGE aerosol climatology From OMPS LP data

• ASI is produced by two effects: aerosol scattering & Rayleigh attenuation• Rayleigh attenuation becomes important below 20 km• It will be difficult to retrieve aerosol profiles from LP in the SH

Cause of Hemispherical Asymmetry in ASI

• Aerosol/Rayleigh scattering phase function ratio changes by a factor of 40 between 25S and 80N

Key Features of V2 O3 algorithm

• Profiles between 28 and 60 km are derived using 40 wavelengths in the 290-325 nm range.– Radiances are normalized to unity at 65 km to remove (alt-

ind) calibration and DUR effects.– Each wavelength is paired with 353 nm to remove errors in

P/T profiles and to reduce aerosol effects.

• Profiles below 27 km are derived using 19 wavelengths in the 549-633 nm range.– Radiances are normalized at 45 km. – Each wavelength is combined with 510 and 637 nm into a

triplet to remove linearly varying aerosol effects.

LP/MLS Comp of sample V2 profiles

2S 76S

LP/MLS Comparison SummaryAverage of 1 day/month “golden” days on which SNPP

and Aura orbits overlap

Aerosol Error in V2 O3 Data

• Estimated using SAGE climatology- so it may be somewhat of an overestimate• Error is caused by attenuation of Rayleigh by aerosols, not by aerosol scattering• 1e-4 /km aerosol vertical extinction produces ~1% ozone error

Altitude Registration• Rayleigh Scattering Attitude Sensing (RSAS)

– Proposed by Bhartia in 1992, tested on Space Shuttle– Uses 350 nm radiance at 20 km normalized at 35 km, which

varies by ~14%/km. – Not affected by calibration error, but affected by cloud

inhomogeneity and aerosols. Currently limited to Antarctica.– Detected 1.8 km error in mounting the instrument on S/C.

• 290 nm/55 km method– Radiance varies by ~14%/km.– Not affected by O3, aerosols (except PMC) or DUR but requires

absolute radiometric calibration.– Requires accurate pressure profiles in the 55- 65 km range.– Results show variation of TH error along the orbit is <300 m, but

further analysis is req’d.

Synergy with other sensors• Limb and nadir data can be combined to produce

trop O3 column, as was done for MLS & OMI.

• Assimilation of limb and nadir data may provide vertically resolved trop O3 information.– Besides OMPS, nadir sensors include CrIS, IASI, GOME-2,

TropOMI, and later TEMPO, GEMS and Sentinel 4.

• Combination with SAGE III data (to be launched on ISS next year) should provide information about aerosol size distribution.

• SAGE III may help improve/validate LP altitude registration scheme.

Summary & Plans

• V2 O3 profiles are of high quality but they are affected by aerosols (<10% error) in the UTLS and by PMCs in the mesosphere (in polar summer only)– V3 is planned to be released by 1/1/17, though some

improvements to V2 may be released sooner.

• Alt registration is accurate to ~300 m– Further improvements are possible

• Aerosol products need improvement– Aerosol extinction profiles is best derived at ~750 nm to

minimize Rayleigh effects. – Angstrom exponent information is likely to be limited to

northern hemisphere only.