1. Near UV aerosol products
TEMPO Aerosols Workshop
Near UV aerosol products
Omar Torres, Changwoo Ahn, Hiren Jethva
NASA-Goddard Space Flight Center
Greenbelt, MD, 20771, USA
September 11, 2017

2. Satellite Aerosol Remote Sensing
In aerosol remote sensing, measured reflectances depend on multiple aerosol properties:
Particle size: particle size distribution
Fine and coarse modes, std. dev., coarse mode fraction: at least 5 parameters
-Particle shape: aspect ratio, 1 parameter
-Particle composition: Complex refractive index (wavelength dependent), 2 parameters
-Extinction Optical Depth, AOD , 1 parameter
Aerosol vertical distribution (stronger in the UV)
Other requirements:
-Surface reflectance must be characterized
-Cloud-free conditions
State-of-the-art satellite aerosol sensors use VIS/near IR observations to retrieve
multi-spectral AOD, and Angstrom Exponent, a qualitative indicator of particle size.

3. Use of near UV Satellite Observations for retrieving aerosol properties
Observations in the nm range can be used to derive aerosol properties
Advantages:
Low surface albedo at all terrestrial surfaces (.01 to .03 for vegetation; deserts)
Sensitivity to aerosol absorption.
Negligible gas absorption interference.
Disadvantages:
Ocean color interference
Aerosol absorption detection is aerosol layer height sensitive.
Historically, near UV measurements have been associated with coarse spatial resolution sensors (TOMS, OMI) primarily designed for trace gas retrieval.
At these multi-kilometer resolution sub-pixel cloud contamination (SCC) is the most important error source in aerosol remote sensing.
Full exploitation of this retrieval technique awaits the development of high spatial resolution UV instruments that can minimize cloud contamination effects.

4. Spectral range of observations (nm)
Improvements in spatial resolution of near UV measurements
Agency
Sensor
Satellite
Spectral range of observations (nm)
Resolution
Period
KNMI/NASA/FMI
NOAA-NASA
NASA
EU (Copernicus)
KARI
JAXA-NIES
NASA-SAO
ESA
NASA-JPL
OMI
OMPS
EPIC
TROPOMI
GEMS
CAI-2
TEMPO
UVN
MAIA
Aura
Suomi-NPP
DSCOVR
Sentinel 5 P.
GKOMPSAT2
GOSAT-2
TBD (GEO)
Sentinel 4
TBD (LEO)
(Hyp.)
340, 388
; & (Hyp.)
(Hyp.)
343, 380
& (Hyp.) ,
360, 380
13x24 km
50 km
~ 10 km
3.5X7 km
7x7 km
0.5x0.5
2.1x4.7km
3.5x7
1.0X1.0km
2005-Present
2011-Present
2015-Present
2017 (Sched.)
2019 (Sched.) ?
2020 (Sched.)
TEMPO will be, at launch, the highest spatial resolution space borne hyper-spectral
sensor ever built

5. One of four sensors on the
Ozone Monitoring Instrument (OMI)
An international project: Holland, USA, Finland
Nadir solar backscatter spectrometer nm
13X24 km footprint
2600 km swath width
Launched on
One of four sensors on the
EOS-Aura platform
(OMI,MLS,TES, HRDLS)
Retrieval Products:
Radicals: Column O3, NO2,
BrO, OClO
O3 profile
Tracers: Column SO2
Cloud top pressure
Aerosols (OMAERUV)
OMI is part of the A-train
A global 13-year record of AOD/SSA has been produced from OMI’s near UV observations

6. OMAERUV Retrieval Procedure
Level2 calibrated radiances at 354 and 388 nm
Surface Albedo
(OMI Climatology)
Radiative Transfer Calculations
Absorbing Aerosol Index
-AIRS CO data:
Three aerosol types:
Desert Dust
Carbonaceous aerosols
Weakly absorbing
Seven aerosol models per type
(varying ω0)
-Surface Type
Aerosol Type
Cloud Screening
CALIOP Climatology
GOCART Climatology
Aerosol Layer Height
Assumed aerosol parameters:
-Particle size distribution
-Real comp. refractive index
-Relative spectral dep. of imag. refractive index.
Inversion Scheme
Extinction optical depth
Single Scattering Albedo
Lookup Tables
Plans to apply the OMI near UV algorithm to TEMPO observations are in place.

7. Aerosol Type Determination
OMAERUV uses real-time AIRS CO data for aerosol type identification [Torres et al., AMT, 2013]
UVAI0 = 0.8 over land
UVAI0 = 1.0 over ocean
COI = CO /10^18
During TEMPO operation CO measurements will likely be available from CrIS measurements on the S-NPP
and JPSS-1 platforms. It may also be available from GeoCARB.
The use of TEMPO’s formaldehyde product as smoke tracer is under study.

8. Combined use of OMI and AIRS observations for smoke-dust separation
CALIOP
OMI
AIRS
The combined use of AI and CO allows the identification of smoke layers over arid areas on July 7, 2006.
- Torres, O., C. Ahn, and Z. Chen, Improvements to the OMI Near UV aerosol algorithm using A-train CALIOP and AIRS observations, Atmos. Meas. Tech., 6, , 2013

9. OMAERUV Retrieval Procedure
Level2 calibrated radiances at 354 and 388 nm
Surface Albedo
(OMI Climatology)
Radiative Transfer Calculations
Absorbing Aerosol Index
-AIRS CO data:
Three aerosol types:
Desert Dust
Carbonaceous aerosols
Weakly absorbing
Seven aerosol models per type
(varying ω0)
-Surface Type
Aerosol Type
Cloud Screening
CALIOP Climatology
GOCART Climatology
Aerosol Layer Height
Assumed aerosol parameters:
-Particle size distribution
-Real comp. refractive index
-Relative spectral dep. of imag. refractive index.
Inversion Scheme
Extinction optical depth
Single Scattering Albedo
Lookup Tables

10. Cloud Screening Scheme
OMI: Pixel-by-pixel basis
TEMPO: Spatial Homogeneity
At TEMPO’s higher (than OMI’s) spatial resolution, spatial homogeneity analyses can be applied to deal with cloud contamination.

11. OMAERUV Retrieval Procedure
Level2 calibrated radiances at 354 and 388 nm
Surface Albedo
(OMI Climatology)
Radiative Transfer Calculations
Absorbing Aerosol Index
-AIRS CO data:
Three aerosol types:
Desert Dust
Carbonaceous aerosols
Weakly absorbing
Seven aerosol models per type
(varying ω0)
-Surface Type
Aerosol Type
Cloud Screening
CALIOP Climatology
GOCART Climatology
Aerosol Layer Height
Assumed aerosol parameters:
-Particle size distribution
-Real comp. refractive index
-Relative spectral dep. of imag. refractive index.
Inversion Scheme
Extinction optical depth
Single Scattering Albedo
Lookup Tables

12. CALIOP-based Aerosol Height Climatology
OMAERUV uses a CALIOP-based Absorbing Aerosol Layer Height Climatology Torres et al, AMT, 2013
January
April
Aerosol Layer Height (km)
July
October

13. Near UV Inversion Scheme
354/388 radiance ratio
388 nm radiance
For a given aerosol type and layer height, satellite measured radiances at 354 and 388 nm are associated with a set of AOD and SSA values.

14. AOD Validation
With AERONET

17. Summary OMI TEMPO Nadir Native Resolution Cloud Masking Approach
Nadir Product Resolution
Aerosol Typing
Resolution Surface Albedo climatology
13X24 km
Single pixel thresholds
UVAI, CO (AIRS)
0.25°x 0.25° (~ 25 km)
2.1x4.7 km
Spatial homogeneity (8 pixels)
8.4X9.4 km
UVAI, CO {CrIS (S-NPP, JPSS-1)}
CO (GeoCARB) ?
CH2O (TEMPO) ?
CAI ?