# Presentation: 693700

## Aerosol Properties over “Bright-Reflecting Source Regions”: The Deep Blue Algorithm and its Applicability to MODIS

_***N. Christina Hsu***_* ****and***
***S.-C. Tsay******, M. D. King, Y. J. Kaufman, J. R. Herman***
***University of Maryland, Baltimore County &***
***NASA Goddard Space Flight Center***
***Greenbelt, Maryland  USA***

## Asian Dust (+ microbes?): Long Range Transport

- Asian Dust (+ microbes?): Long Range Transport

## Rationale

*•**  ****Climate Forcing****:** requires *_***aerosol properties near source regions***_* to achieve a complete picture of aerosol information from source to sink;*
*•**  ****Carbon Cycle****:** tracks *_***iron sources***_* from windblown dust for stimulating ****plankton**** growth in the open ocean;  *
*• ** ****Aerosol Transport Modeling****:** needs accurate and realistic *_***dust source***_* locations; and*
*•  ****Visibility and Adverse Health Effects****:** **demands timely *_***atmospheric turbidity***_* information over affected regions.*

## Slide 4

## Principle of Aerosol Retrievals*

***Non-absorbing aerosols make ***_***contrast apparent reflectance***_*** diminished faster for brighter surface.***
*** ******Absorbing aerosols make apparent reflectance ******brighter****** (or darker) for darker (or ******brighter******) surface.***
*** ******The dashed lines denote the critical values of surface reflectance where the presence of aerosol ******CANNOT****** be detected by that particular spectral wavelength.***

***Principle of Aerosol Retrievals**********

**********Hsu, Tsay, King, and Herman, 2004: Aerosol properties over bright-reflecting source regions, IEEE TGRS, 42, 557-569.***

## MODIS Visible & NIR Bands: 

***superimposed on the GOME spectral ***
***reflectance taken over ******the Sahara***

## March 2001

**Gobi**

**Taklamaken**

**Inner Mongolia**

**African desert**

## Nadir

***Fine-grain sands***

***Coarse-size gravel***

**10 May 2001, 11:03 MT**
***The Great Gobi, Dunhuang, China***

**Nadir**

## Flowchart for Deep Blue Algorithm

***Flowchart for Deep Blue Algorithm***

**Radiances**
**412, 490, 670 nm**

## Phase Function for Dust Model

***Phase Function for Dust Model***

## Deep Blue Algorithm for SeaWiFS/MODIS

***Deep Blue Algorithm for SeaWiFS/MODIS***

** ****Utilize solar reflectance at ********= 412, 490, ****and**** 670 nm**** to retrieve aerosol optical thickness (********a****) and single scattering albedo (********o****).**
** ****Less sensitive to aerosol ****height****, compared to UV methods.**
** ****Works well on retrieving aerosol properties over various types of  surfaces, including very ****bright desert****.**

******0****(dust****670nm****)=1.0**

********

********

******a**

******a**

## Asian Dust Outbreak

***Asian Dust Outbreak***
***6 April 2001***
***  ******Deep Blue Algorithm:***

*  **Cloud mask works very well *
*  **Aerosol retrievals indicate dust*
*    **storms originated from Gobi*
*    **and Inner Mongolia regions*
*  **Single scattering albedos are *
*    **quite different between these*
*    **two regions*

- SSA (412nm)

**0.85**

**1.0**

**0.90**

**0.95**

## Slide 13

## Perfect Dust Storm

**Perfect Dust Storm**
**7 April 2001**

******a**

****

## Comparisons with AOT

- from Sun Photometers
- in China during ACE-Asia

## Aerosol Optical Thickness Retrieved from Deep Blue Algorithm:

- Dust plumes in Africa

******a**

## Validation: Comparisons with AERONET 

***Aerosol Optical Thickness***

## Slide 18

## Summary

* ****It ******works******!**** *
***Deep-Blue Algorithm***** *****well***** for SeaWiFS measurements**
**Compared *****well***** with surface/aircraft products**
**Separate dust *****well***** from other anthropogenic sources**

* ****We ******expect******:**** *
**Implement *****Deep-Blue Algorithm***** *****soon***** for MODIS**
**Produce new MODIS products over bright-reflecting surfaces, and integrate into operational MODIS products**

## Backup Slides

## Aerosol retrievals use an Aerosol Index:

**absorbing and non-absorbing aerosols:**

**I****meas****   = Radiance measured by the satellite at 412 or 490 nm**
**I****calc      ****= Radiance calculated using a radiative transfer model**

**Large AI’s are caused by high AOT or by highly absorbing aerosols.**
**As with UV wavelengths, the visible AI is also a function of altitude.**

***Aerosol retrievals use an Aerosol Index:***

## Properties of Aerosol Index*

**The dependence of AI with both AOT and absorption is confirmed by simulations we performed using aerosols of different types**

*******The properties of blue water were assumed in this simulation**

***Properties of Aerosol Index****

## In areas of mixed aerosol types, we linearly mix radiances from the dust aerosol model, Rdust, with those from the smoke aerosol model, Rsmoke 

**Aerosol**
**Mode**l

******412**

******470**

******490**

******470**

**Refractive Index**
**412 nm**

**Refractive Index**
**490 nm**

******0**
**412 nm**

******0**
**490 nm**

**Dust**

**Smoke**

**1.00**

**1.00**

**1.55 – 0.020i**

**1.55 – 0.022i**

**1.55 – 0.008i**

**1.55 – 0.026i**

**0.91**

**0.96**

**0.89**

**0.90**

**1.30**

**0.92**

**The aerosol characteristics used to generate the simulated radiances in these two figures are shown below**

**In areas of mixed aerosol types, we linearly mix radiances from the dust aerosol model, R****dust****, with those from the smoke aerosol model, R****smoke**** **

**= aR****dust**** + (1-a)R****smoke**

**Gaussian distribution with a peak at 3 km and a width of 1 km was assumed**