OMI Aerosol Products: A tutorial ARSET Applied Remote SEnsing Training A project of NASA Applied Sciences

Aerosol Index (AI) o Qualitative Indicator of the presence of absorbing aerosols: smoke, desert dust, volcanic ash. o It is calculated using observations at two wavelengths in the range nm. o Values > 2 means indicates and enhances layer of Absorbing aerosols. o Useful for tracking long-range transport of volcanic ash, smoke and dust over clouds and snow/ice, and through mixed cloudy scenes. OMI Near UV Aerosol Products (388 nm) OMI Aerosol Products

Aerosol Extinction - Also called Aerosol Optical Depth (AOD) or Thickness (AOT) o The extinction is a measure of radiation extinction due to aerosol scattering and absorption. o It is related to the total column amount of aerosol particles in the atmosphere. o A unitless quantity ranging from 0- to. 1= lots of aerosols, 0=none o AOD is available through Giovanni at a number of wavelengths between 342 and 500 nm from Aura/OMI. OMI Aerosol Products con’t

Aerosol Absorption Optical Depth, AAOD in the near-UV (NOT to be confused with AOD) o A measure of concentration of near-UV absorbing aerosol particles such as smoke and mineral dust. o Contains information on the aerosol concentration. Quantitative estimates of AAOT can be made only in relatively cloud-free scenes. o It is calculated as: AAOD = AOD x (1.0 – Singe Scattering Albedo) OMI Aerosol Products con’t

NASA A-Train and Terra observations of the 2010 Russian wildfires J. C. Witte, A. R. Douglass, A. da Silva, O. Torres, R. Levy, and B. N. Duncan Atmos. Chem. Phys., 11, , Summer Russian Fires OMI Aerosol Products con’t Single Scattering Albedo, SSA o A measure of the fractional extinction due to scattering of incident solar radiation. Varies between 0 (all absorption, no scattering) and 1 (all scattering, no absorption) o Typical variability range (0.6 to 1.0)

There are 2 OMI Aerosol Products OMAERUV – NASA/GSFC near-UV retrieval algorithm Uses a set of aerosol models to obtain aerosol products from the UV to blue ( nm) wavelength range and reports values at 388 nm, and 500 nm OMAERO – KNMI Multi-wavelength aerosol retrieval algorithm The multi-wavelength algorithm is based on the reflectance spectral information in the near UV and the visible reporting values at 5 wavelength: nm, 388 nm, 442 nm, 463 nm, and nm. Row anomalies NOT filtered in the OMAEROG 0.25x0.25 degree gridded product

-Sensitivity to aerosol layer height -Cloud contamination associated with large footprint (instrument limitation) -Works best under conditions of minimum cloud contamination and large scale aerosol events (desert dust and smoke plumes) Current Limitations

L2 Swath to gridded L2G, L3 data are readily available at the Goddard Data Information Service Center (DISC). One can also use Giovanni to view L3, L2G gridded products and download subset data in HDF, NetCDF, KMZ, or ASCI formats.

Validation tool for transport models Separation of carbonaceous from sulfate aerosols Identification of aerosols above PBL (i.e., PBL aerosols are not detectable by OMI) Tracking of aerosol plumes above clouds and over ice/snow Transport around the globe of a high altitude smoke layer generated by the Australian fires in December Numbers indicate the day of the month. Applications

-Positive values for UV-absorbing particles: desert dust, smoke, volcanic ash -Negative values for small size (less than 0.2 microns) non-absorbing particles -Magnitude of positive AI depends mainly on aerosol absorption optical depth and height of aerosol layer. Also depends on aerosol microphysical properties. -Detects absorbing aerosols over all surface types: ocean, vegetated surfaces, deserts, snow/ice, etc - Detects absorbing aerosols under partial cloudiness conditions and above clouds -Aerosol Index yields near-zero values for clouds. -Aerosol Index is insensitive to carbonaceous aerosols (smoke) below ~ 2km -Larger sensitivity to low altitude desert aerosols (~ 0.5 km) -Direct conversion of AI to any quanitatively meaningful parameter is not possible because of multiple dependencies (AOD, SSA, height, etc). OMI AI Summary

Introducing VIIRS aerosol products Lorraine A. Remer JCET UMBC VIIRS Cal/Val Team: Istvan Laszlo, Co-Chair (NOAA-STAR) Shobha Kondragunta, Co-Chair (NOAA-STAR) Hongqing Liu(IMSG NOAA) Jingfeng Huang (ESSIC NOAA) Ho-Chun Huang (ESSIC NOAA) Hai Zhang(IMSG NOAA) Sid Jackson (Northrup-Grumann) Edward Hyer (NRL) Min Oo (SSEC U.Wisc.) Andrew Sayer (USRA NASA) N. Christina Hsu (NASA-GSFC) Robert Holz (SSEC U.Wisc.) 11

VIIRS is a multiwavelength imager, like MODIS with similar wavelength bands in the aerosol range MODISVIIRS Orbit altitude 690 km824 km Equator crossing time 13:30 LT Granule size5 minutes86 seconds swath2330 km3000 km Pixel nadir0.5 km0.75 km Pixel edge2 km1.5 km 12

VIIRS granule VIIRS 0.67 – 0.55 – 0.49 µm 2 Sep :24:27.8 UTC MODIS 0.66 – 0.55 – 0.47 µm 2 Sep :40 UTC 13 NASA MODIS AtmospheresSSEC PEATE

Don Hillger, NOAA 14

MODIS swath edge ‘bowtie’ effect VIIRS doesn’t have this 15 From NASA LANCE

MODISVIIRS Product resolution nadir 10 km 3 km 6 km 0.75 km Product resolution edge 40 km 12 km 1.5 km Products land , Angstrom exponent, (suspended matter) Products ocean , fine mode fraction , Angstrom exponent, (suspended matter) Angstrom exponent over land and suspended matter not ready for public use 16

VIIRS AOT 550 nm 4 July 2012 IP 750 m 17 Kondragunta

VIIRS AOT 550 nm 4 July 2012 VIIRS RGB 4 July :07 UTC 18

VIIRS RGB 4 July :07 UTC MODIS RGB 4 Jul :40 UTC 19

VIIRS AOT 550 nm 4 July 2012 IP 750 m MODIS AOT 550 nm 4 July 2012 Aqua L2 Col51 10 km 20 Kondragunta NASA MODIS Atmospheres

Suspended matter is just another way to say “aerosol type” Dust, smoke, sea salt, volcanic ash 21

Kondragunta/Liu 22

Kondragunta/Liu 23

Take home messages: 1.VIIRS and VIIRS aerosol products follow from MODIS heritage 2.Progression of improvement, from Beta to Provisional. 3.Now, Land AOT is very good. 4.Ocean AOT is excellent 5.Suspended matter needs an iteration 6.Use Quality Flags 24

IDEA Site with sample VIIRS Data