# Presentation: 002426

## Improved aerosol retrieval from combined

- OMI-MODIS observations

- S.K. Satheesh1, O. Torres3, L.A. Remer2
- S. S. Babu**4**, V. Vinoj**1**, T.F. Eck**5,2 ****, **R.G. Kleidman**6,2** and B.N. Holben**2**
**1**Indian Institute of Science, Bangalore, India.
**2**NASA Goddard Space Flight Center, Maryland, USA
**3**Department of Atmospheric and Planetary Sciences,
- Hampton University, USA
**4**Space Physics Laboratory, Vikram Sarabhai Space Centre,
- Thiruvananthapuram, India
- 5 Goddard Earth Science and Technology, UMBC
- 6 Science Systems and Applications Inc.

## A tale of 2 sensors...

- OMI: hyperwavelength capability from the VIS to the UV
-          standard aerosol retrieval uses 354 and 388 nm
-          13 x 24 km (nadir) pixel size
-          aerosol signal is deviation from Rayleigh scattering
-          sensitive to aerosol layer height
-          sensitive to aerosol absorption
- MODIS: 36 wavelength channels from 441 nm to thermal infrared
-               traditional aerosol retrieval uses 7 channels 466 to 2130 nm
-               500 m (nadier) pixel size
-               aerosol signal is derived from deviation from assumed
-                    surface reflectance
-               sensitive to aerosol particle size
-               not sensitive to either layer height or absorption

## Sensitivity study

- wavelength

- 

- 

- Particle
- size

- base

- The UV is sensitive to absorption.  The midIR to size.

- Work by
- Viktor Zubko

- We will combine OMI and MODIS to cover this range.

- _Sensitivity study_

- 0.4

- 0.6

- 0.8

- 1.6

- 1.8

- 2.0

- 2.2

## Standard OMI retrieval:

- Retrieves aerosol optical depth (AOD)
-           and aerosol single scattering albedo (o)
- For 5 different assumptions of aerosol layer height

| z1 | AOD1 | o1 |
| --- | --- | --- |
| z2 | AOD2 | o2 |
| z3 | AOD3 | o3 |
| z4 | AOD4 | o4 |
| z5 | AOD5 | o5 |

## Standard OMI retrieval:

- Then assumes an aerosol layer height from climatological
-      considerations, and returns the most likely
-      AOD and single scattering albedo

| z1 | AOD1 | o1 |
| --- | --- | --- |
| z2 | AOD2 | o2 |
| z3 | AOD3 | o3 |
| z4 | AOD4 | o4 |
| z5 | AOD5 | o5 |

## Combined OMI-MODIS retrieval:

- We will fix the AOD from the MODIS retrieval and return
-        the aerosol height and single scattering albedo

| z1 | AOD1 | o1 |
| --- | --- | --- |
| z2 | AOD2 | o2 |
| z3 | AOD3 | o3 |
| z4 | AOD4 | o4 |
| z5 | AOD5 | o5 |

## First, can MODIS AOD retrieval

-   (466 to 2130 nm) be extrapolated
-    to the UV wavelength of 388 nm?

- MODIS extrap 380 nm AOD

- AERONET measured 380 nm AOD

- Ascension Island

- AERONET - MODIS AOD 380

- Linear extrap

- AOD470 -AOD870

- Simple linear extrapolation (log-log)
- is good, but not adequate.
- Deviations from linear can be
- explained by the difference in
- AOD at 440 and 870 nm

- Satheesh et al. (to be submitted)

## Linear extrapolation

- With curvature correction

- Satheesh et al.
- (to be submitted)

## RMS difference between MODIS extrapolation and AERONET

- At 7 island stations

- Satheesh et al. (to be submitted)

## Areas of study

- Satheesh et al. (to be submitted)

## Atlantic Ocean

**Atlantic Ocean**

**Arabian Sea**

- AOD380
- OMIstd - OMIMOD

- Months in 2006

- Months in 2006

- 0.15

- 0.3

- All data

- o380
- OMIstd - OMIMOD

- -0.1

- Height (km)
- OMIstd - OMIMOD

- -0.03

- 2

- -3.5

## Validating height retrieval

- In Arabian Sea

## No similar validation of o but higher correlations with absorbing index using joint absorption than with OMI alone.

- No similar validation of o but higher correlations with absorbing index using joint absorption than with OMI alone.

- Satheesh et al.To be submitted

## Monthly mean values

- of AOD, o and layer
- height for the months
- of Jan 06 and Mar 06
- for the 3 regions

- Satheesh et al.
- To be submitted

## Constraining the OMI retrieval with MODIS AOD

- Results in a better retrieval of aerosol absorption
-         and height
- Next step,
- Further constrain OMI with information of aerosol type,
-       (determine if aerosol is dominated by dust or smoke)

## OMI/MODIS

- Ratio  of OMI to MODIS reflectance
- As a function of MODIS reflectance (MODIS band 3)

- 3

- Aqua-MODIS
- Spectral response

- MODIS spatially collocated
- To OMI footprint
- OMI spectrally convolved
- To MODIS band 3

- Systematic offset for darker
- targets

## OMI cross track position (not view angle)

- OMI/MODIS

- Refl <0.4

- Refl > 0.4