# Presentation: 222021

## BSRN Validation for GEWEX/ISCCP

**R. T. Pinker**
**Department of Meteorology**
**University of Maryland**
**College Park, MD**
**CEOS/WGCV Land Product Validation**
**Workshop on Albedo**
**April 27-28, 2005**
**EGU 2005 Vienna**

## Highlights

-  What is available on global scale from GEWEX
-  Scale issues-same satellites, different spatial
-       gridding
-  Scale issues-different satellites
-  Evaluation of products
**Discussion in context of :**
**CEOS/WGCV Land Product**** ****Workshop**
- Boston, 23-24 October, 2002

## Error budgets

** **
**Scaling may be much larger source of error than **
**       ****calibration or narrow to broadband transformation.**
**What to measure-albedo; reflectance**; **spectral intervals**
**The scientific community has primary interest in the total albedo. Therefore, it is recommended that priority should be given to   measurements of this parameter.**
**There is also interest in spectral albedo, both broadband and narrow band.**
**Broadband intervals of interest are the visible and NIR for which instrumentation of acceptable quality is available.**
**High spectral resolution albedo or BRDF are also of interest in building spectral libraries and for evaluating narrow band albedo  from satellites.   **

## What we do

**Global distribution of surface SW radiation at 0.5 degree, Jan 1992**
**Both downward and upward fluxes are computed, ****allowing derivation of albedo**

_**What we do**_

## Approach to Derive SW

-   **Start with spectral reference albedo models as**
**    ****boundary  conditions**
**  ****Compute surface upwelling and down- welling fluxes:**
**     **
**	****Clear conditions**
**	****All conditions**
**Compute spectrally for:**
**	****diffuse**
**	****total**
**Albedo:**** ratio of upwelling to down -welling flux**

## Narrow to broad band transformations-updates

**To derive angularly and seasonally dependent relationships between narrowband reflectance and broadband albedo, under clear sky  conditions, as observed from the several different satellites.**** The simulations will utilize surface types based on the University of Maryland land cover classifications.**** **

-   **Extensive model simulations with MODTRAN 3.7**
**  ****10 solar zenith angle bins**
**  ****16 gaussian points in zenith and 8 in zenith  direction to obtain the spectral **
**     ****flux**
**  ****20 climatological profiles for temperature, water vapor and ozone in 4   **
**    ****seasons**
**  ****Newly developed spectral surface albedo models**

**Objective**

**Narrow to broadband transformations are based on:**

## Updated Surface Spectral Reflectance ModelsCompatible with Current Global Land Cover Classifications

- Evergreen Broadleaf Forest	 0.83     0.46     0.18        ASTER
- Deciduous Needle leaf Forest	0.74      0.39     0.14        ASTER
- Deciduous Broadleaf Forest	 0.83     0.46     0.18        ASTER
- Mixed Forest		0.79     0.42      0.16        ASTER
- Woodlands			0.35     0.25      0.09        ASTER/Bowker
- Wooded Grasslands		0.36     0.32      0.12        ASTER/Bowker
- Closed Bushland/Shrubland	0.37     0.36      0.13        ASTER/Bowker
- Open Shrubland		0.19     0.22      0.07        ASTER/Bowker
- Grassland			0.07     0.19      0.03        ASTER
- Cropland			0.54     0.51      0.20        ASTER/Bowker
- Barren			0.55     1.35      1.13        ASTER/Bowker
- Urban	   			                   ASTER

**Updated Surface Spectral Reflectance Models****Compatible with Current Global Land Cover Classifications**
**Scaling Factors for the surface types according to UMD land cover classification**

- 		**Ch1****	****Ch2****	****Ch2**		**	****	****	****Scaling  ****	**** Scaling  ****	**** Scaling   Source           ****	****  Surface type****	****factor****	**** factor****	**** factor****	****	****	****	****	****(0.3-0.5)****	**** (1.3-2)****	****(2-4)****	**

## What albedo products are available:*

-  _**At global scale**_
-   ISCCP D1 UMD GEWEX/SRB, 2.5 deg, 1983-2001
-       (There are other estimates based on ISCCP D1, such as: LaRC
-        GEWEX/SRB; ISCCP D1-FD)
-   MODIS 1 deg, UMD SRB model, about 3 years
_**At continental scale**_
- ISCCP DX based estimates, 0.5 deg; 1990-2001
_**At regional scale**_
-   GOES based estimates at 0.5 degree for the US; 1996-current
-  Improved above product for 1996-2000 at 0.5 and 1/8 deg resolution
-  GOES based estimates at 0.5 deg, Amazon basin for 1998-2000.
- * **This is not a comprehensive review of everything available**

## Examples of low resolution albedo products

## Based on GOES pixel level data; available for 1998-2000

**Based on GOES pixel level data; available for 1998-2000**

##  Both observed and satellite derived albedo are generally lower in dry and   higher in    wet months.

|  |  | Annual mean | Variability among sites | Seasonal variability |
| --- | --- | --- | --- | --- |
| Forest | Obs | 0.133 | 0.122-0.147 | Weak, higher in dry, lower in wet season |
|  | GOES | 0.088 | 0.079-0.104 | Very weak |
|  | DX | 0.113 | 0.103-0.129 | Lower in Jun/Jul/Aug |
| Pasture | Obs | 0.176 | 0.169-0.193 | Stronger,
Lower in dry season |
|  | GOES | 0.090 | 0.075-0.100 | Very weak |
|  | DX | 0.116 | 0.102-0.127 | Lower in Jun/Jul/Aug |

**Analysis**** ****based on Berbet, M. et al. (2003);  observations  made in 1990-1993 (Culf et al., 1996).  The observation uncertainty of the order of 0.006 (Wright et al. 1996).  GOES and DX estimates are available from 1998/03 – 2001/02, and from 1998/07 – 2001/02, respectively.**

-  ***Both observed and satellite derived albedo are generally lower in dry and   higher in    wet months.***
*** ******Satellite driven albedo show smaller difference between the vegetation cover, and weak seasonal variability******.  ***

## Based on GOES pixel level

**Based on GOES pixel level**

**1/2 deg**

**1/8****th**** deg**

## GOES  1/8th

- ISCCP DX, 0.5 deg

## Albedo  based on MODIS using ratio of surface fluxes

**The surface parameters used to calculate spectral surface albedo needed in the inference scheme for SRB were taken from the MODIS Bidirectional Reflectance Distribution Function (BRDF) and Albedo Product (MOD43B) at the 0.25° resolution (Lucht et al., 2000; Schaaf et al., 2002).**
**The three weighting parameters associated with the RossThickLiSparseReciprocal BRDF model that best describes the anisotropy of each pixel are provided for each of the MODIS spectral bands as well as for the three broad bands (0.3-0.7 μm, 0.7-5.0 μm, and 0.3-5.0 μm). **
**For two broad bands (0.3-0.7 μm, 0.7-5.0 μm), these parameters were used with simple polynomials to estimate the white sky albedo and the black sky albedo for the monthly mean solar zenith angle.**
** **

## Auxiliary information for driving SRB model:  

**Level-3 MODIS Atmosphere Monthly Global Product at 1° x 1° resolution, processed with the latest collection 4 algorithms for:**
-  **Cloud_Fraction_Total, Cloud_Optical_Thickness_Combined,Optical_Depth_Land_And_Ocean aerosol, Total_Ozone, and Atmospheric_Water_Vapor**
-  **Missing aerosol optical depths over arid areas were filled from the MODIS-GOCART integrated monthly aerosol optical depth data, School of Earth and Atmosphere Sciences, Georgia Institute of Technology. Missing cloud optical thickness values were replaced by interpolated values**.

## One degree spatial resolution

## From MODIS, V004 product

## MODIS swath data at highest resolution

## Evaluation of GOES surface albedos against SURFRAD stations during summer and winter, Fort Pack, MT (0.5 degree)

**Evaluation of GOES surface albedos against SURFRAD stations during summer and winter, Fort Pack, MT (0.5 degree)**

## Evaluation os GOES surface albedo against SURFRAD stations during summer and winter Goodwin Creek,  MS (0.5 degree)

**Evaluation os GOES surface albedo against SURFRAD stations during summer and winter Goodwin Creek,  MS (0.5 degree)**

## Evaluation

**Comparison between the derived broadband surface albedo and broadband surface observations** - The methodology will be tested with ground observations at the semi-arid USDA-ARS Walnut Gulch Experimental Watershed in Arizona. The surface observations started in July 1999 and continue up to now. Total short-wave, infrared and PAR upward and downward fluxes are measured at 5 minute intervals.
**Comparison between the derived broadband albedo from GOES and broadband albedo observed from a satellite with broad band sensor  **–

**Evaluation**

## Semi-Arid region: Walnut Gulch, AZ

**Semi-Arid region: Walnut Gulch, AZ**

## Ongoing observations in sub-Sahel

**Ongoing observations in sub-Sahel**

- Need for ground truth on surface albedo

## No information on savannah type vegetation

## Slide 25

## Summary

**Summary**
**  ****Global products of spectral and total surface albedos are available**
**  ****As yet, not fully evaluated**
**  ****Usefulness of ground observations for evaluation of low resolution **
**    ****products not obvious-preferably, consistency among satellites**
**     ****important**
**  ****Ground observations of albedo important, but should not be**
**     ****expected to match the satellite based albedos**
**  ****Documentation of the annual cycle for different surface types **
**    ****important for benchmarking**