# Presentation: 206667

## MODIS/Meteosat/MISR  Surface Albedo Comparison Exercise

- B. Pinty (1), M. Taberner (1),
- S. Liang (2), Y. Govaerts (3), J.V. Martonchik (4), Lattanzio (5), C. Barker Schaaf (6),
- M. M. Verstraete (1), R. E. Dickinson (7),
- N. Gobron (1),  and J-L. Widlowski (1)
*(1) Institute for Environment and Sustainability of EC-JRC, Ispra (VA) Italy*
*(2) University of Maryland, College Park, USA*
*(3) EUMETSAT, Darmstadt, Germany*
*(4) Jet Propulsion Laboratory, Caltech, Pasadena, USA*
*(5) Makalumedia gmbh, Darmstadt, Germany*
*(6) Boston University, Boston, USA*
*(7) SEAC, Georgia Institute of Technology, Atlanta, USA*

**2nd CEOS/WGCV/LPV Workshop on Albedo Products, **
**      ****Vienna, April 27-28, 2005**

## Various types of Surface albedo (1)

- BHR : Bi-Hemispherical Reflectance is the ratio between the upward and the downward radiant fluxes, that is, accounting for the downwelling diffuse intensities from the sky.

- Depends on both surface and ambient atmospheric radiative properties and ...the Sun angle.

- All quantities can be defined monochromatic or broadband

## Various types of Surface albedo (2) 

- DHR: Directional Hemispherical Reflectance is the ratio between the upward flux and the downward collimated flux coming thus from one single direction (Black sky).

- Depends on surface radiative properties and ...the Sun angle.

- All quantities can be defined monochromatic or broadband

- BHR*iso*: If the downwelling diffuse intensities from the sky is assumed fully **isotropic **then the BHR is equal to the integral of the DHR over all incoming directions (White sky).

- Depends on surface radiative properties only.

## Surface albedo products from space agencies

-  MODIS delivers DHRs (Black sky) and BHR*iso *(White sky)

-  MISR delivers DHRs and BHRs as flux ratios but under ambient conditions and for the Sun illumination conditions at time of observations

-  EUMETSAT delivers DHRs for a fixed Sun angle

- and all information needed to reconstruct the DHRs and BHRiso

- and all information needed to reconstruct the DHRs at any other Sun angle as well as the  BHRiso

- to reconstruct the BHRs may require some investments or some level of assumption

- The albedo products may also differ wrt the spectral bands of integration they refer to.

## Parameterization of  the surface-atmosphere radiative coupling 

- Assuming that the field of downwelling diffuse intensity reaching the surface is PERFECTLY isotropic yields a convenient parameterization for the  *BLUE SKY ALBEDO*

- Surface level

- Sun angle

- Atmospheric optical depth (type of atmosphere)

- Surface BRF (amplitude and shape)

- ratio of direct to total downward flux

- ratio of diffuse to total downward flux

- with

- Pinty et al., JAS, 2005

## Surface albedo comparison

- Perform a comparison between MODIS-Meteosat-MISR surface albedo products : a user perspective.
- Compare similar physical quantities, e,g., BHRs, BHRiso, DHRs.
- Based on year 2001 products: latest public version available.
- For two large geographical regions : Africa-Southern Europe and North-East Europe.

## Comparison of Surface BHRiso products from MODIS/Meteosat/MODIS 

-  Select the same period of time and identical geographical regions

-  Achieve the needed transformations (e.g., BHRs, spectral conversions) to ensure comparison of physical quantities having same meaning

-  Identify the product values showing appropriate QA

##  Albedo comparison for an ‘Ideal’ Band (0.4-1.1μm) 

## Govaerts, pers. Com

## Slide 10

## Spectral Correction for the Meteosat large band effects

## Spectral conversion to the ‘Ideal’ Band (0.4-1.1μm) 

- Spectral conversion to the ‘Ideal’ Band (0.4-1.1μm)

- Meteosat

- MISR

## Slide 13

## January 2001

## MISR low & MODIS high

- MISR high & MODIS low

## January 2001

## Histogram of BHRiso differences

## (MISR-MODIS) Albedo 

- (MISR-MODIS) Albedo

## June 2001

- January 2001

- Using Shunlin’s conversion factors

- Using Yves’s conversion factors

## January 2001

## Mean BHR values over common area with valid values from one of the two other sensors

## Ratio of the mean values

## Primary Eigenvectors

## Correlation between pairs of samples

## Results for year 2001 Shortwave domain (0.3-3.0 μm) 

- Africa –Southern Europe

## Primary Eigenvectors

## October 2001

## Results for year 2001 Visible domain (0.3-0.7 μm) 

## Slide 29

## Results for year 2001 Near-infrared domain (0.7-3.0 μm) 

## Slide 31

## Results for year 2001 Shortwave domain (0.3-3.0 μm) 

- Northern –Eastern Europe

## Slide 33

## Slide 34

## Full inversion

- Magnitude inversion

- Backup solution

## Mean BHR values over common area with valid values from one of the two other sensors

- Full inversion

## Slide 37

## Slide 38

## Primary Eigenvectors

- Full inversion

## Northern –Eastern Europe

- Hexadecad 6: End of March 2001

## Slide 41

## Slide 42

## Issues and caveats

- An error was recently identified in the MISR processing code: BHRs tend to be biased high by  about 2 to 3% on average (season & latitude dependent).
- The nominal spectral conversion formulae (from Liang and Govaerts) agree well.
- MODIS BHRs are off when estimated from the backup algorithm.

## Africa –Southern Europe

## Magnitude inversion

- January 2001

- June 2001

## Northern –Eastern Europe

## Magnitude inversion

- January 2001

- June 2001

## Conclusions and Perspectives

- Albedo (BHRiso) comparison reveals very good agreement between MODIS-MISR-Meteosat (high QA) products.
- Extend the comparison exercise globally.
- Repeat the exercise for DHRs.