# Presentation: 444890

## Near Constant Contrast (NCC) Methodof Atmospheric Correction over Land

*Purely mathematical approach: one way to complete the system of equations*
*	**	**is to process two images simultaneously.*
*	**	**	*
*	**	**	****Introduce two generic assumptions:***
*	**- the surface properties do not change in small time intervals;*
*	**- far from sources, aerosols vary slowly on short distances (3-5 km)*
*	**	**(mesoscale range of aerosol variability is 20-60 km).*
*	**	**	**	****What does it give?***
*Divide the image into small boxes with size N**2** with constant AOT;*
*For two images for any given box, there are 2N**2** measurements and N**2** + 2 *
*	**    **unknowns (N**2** albedo and 2 AOT values for 2 days) for any spectral band;*
*NCC method is not constrained by DDV; No assumption on spectral regression;*
*Retrievals are done separately for each band (robustness check for AOT).*
*	**	**	**	****Requirements***
*SZA**1** **** SZA**2** to avoid effect of surface BRF (for ETM+);*
*Sufficient surface contrast (variable surface);*
*Stable instrument calibration.*

*Near Constant Contrast (NCC) Method**of Atmospheric Correction over Land*

*A. Lyapustin, GEST UMBC/NASA GSFC*

## Examples: LUT-based AOT Retrievals

**Figure 1**. The variability of spectral extinction for different aerosol models. The two models (solid and dashed lines) are formed of the same fine (F) and coarse (C) fractions, but with different relative concentrations C/F=0.1, 1. The lines show the spectral dependence of AOT for three LUT entries specified at 0.44 m (=0.25, 0.3 0.35). The vertical lines show the centers of the ETM+ blue (B1) and red (B3) bands.

*Examples: LUT-based AOT Retrievals*

_***LUT Specification***_
*  **Aerosol model is based on  **	**AERONET GSFC model*
*  **The step in AOT is 0.02 in the **	**Blue band*
*  **The ratio AOT**Bn** /AOT**B1**  is:*
*1; 0.775; 0.598; 0.456; 0.226; 0.199.*

_***NCC Algorithm***_

*(albedo) is calculated with 3D RT theory*

## Example 1

*2000-10-02*

*2001-10-05*

***Example 1***

## Processing Sequence

*Covariance*

*F**min*

*Cloud Mask*
*(covariance, BT, Reflectance)*

*Clouds are indicated by black color*

***Processing Sequence***

## Aerosol Retrieval Sequence

*2000-10-02*

*DDV *

*2001-10-05*

*NCC** *

*NCC *

***Aerosol Retrieval Sequence***

*AOT bin size is 0.02 in the blue band. AOT band ratio is 0.775; 0.598; 0.456; 0.226; 0.199.*

*Final AOT *

*Final AOT *

## Result of Atmospheric Correction:

_*Result of Atmospheric Correction:*_
*2000-10-02*
*Surface Albedo,B1*
*Scale 1000*

## Example 2

*2003-04-02*

*2000-03-24*

*Artifacts caused by *
*    **cloud shadows*

***Example 2***

## Example 2: Illustration of Relative Information

*2003-04-02*

*2000-03-24*

*DDV*

*NCC*

*Current DDV Alg.*
* ****7**<0.2*

*NCC*

*DDV*

***Example 2: Illustration of Relative Information***
***Content of DDV and NCC Methods***

*Few DDV pixels *
*are available for*
*accurate AOT *
*retrievals*

## Result of Atmospheric Correction:

_*Result of Atmospheric Correction:*_
*2003-04-02*
*Surface Albedo,B1*
*Scale 1000*

## Example 3

*2002-05-01*

*2001-04-28*

***Example 3***

## Result of Atmospheric Correction:

_*Result of Atmospheric Correction:*_
*2001-04-28*
*Surface Albedo,B1*
*Scale 1000*

## ... to be completed for ETM+

*Refine CM over snow*
*Add cloud shadows (filtering or separate processing without direct **	**irradiance)*
*Extensive testing and validation:*
*	**- AOT retrievals (against AERONET measurements)*
*	**- Surface albedo (against ASRVN albedo: 36 subsets from LEDAPS)*
*	**   **(ASRVN is AERONET-based Surface Reflectance Validation Network)*
*	**- Testing on continental/global scales*
*	*
***Issues for MODIS ****(Research stage)*
*1.  Gridding of TOA reflectance (to ensure the same footprint at different view angles)*