1. Zhang Xin, Zhao Xiang, Liu Suhong Beijing Normal University
A METHOD FOR THE RETRIEVAL OF AEROSOL OPTICAL THICKNESS on CBERS data from top-of-atmosphere radiance
Zhang Xin, Zhao Xiang, Liu Suhong
Beijing Normal University

2. CONTENTS
Background
Method
Validation
Summary

3. Background
The atmospheric influence is strong enough to substantially modify the electromagnetic signal, causing the loss or the corruption of part of the carried information about the observed target. It is important to retrieve the Aerosol Optical Thickness (AOT).
Vegetation
Water

4. Some algorithms need densely vegetated area
Background
we have developed a novel retrieval algorithm only use the visible and near-infrared (VNIR) spectral bands and have a high-accuracy
Some algorithms need densely vegetated area
Some algorithms currently require visible to
short-wave spectral bands ( nm)
Some algorithms only retrieval one result on
every image, it is hard to fulfill the
Correction accuracy

5. 1：450～520nm 2：520～590nm 3：630～690nm 4：770～890nm 5：510～730nm
Background
This method is design for CBERS CCD Image.
Sensor Name
CCD
Sensor Type
Push-broom
Band information
1：450～520nm 2：520～590nm 3：630～690nm 4：770～890nm 5：510～730nm
Resolution
19.5 m
24 June 2007(Path 8/Row 61) ,
Shanxi Province, China

6. METHOD
This retrieval work is designed to obtain the main atmospheric parameters from the image itself.

7. METHOD Calibration L=DN/K (http://www.cresda.com/) Grid divison
The image is divided in 10KM*10KM cells.
Selecting the suitable pixels by Cv

8. METHOD 1. We set the surface reflectance values as the follow equation
2. C is the vegetation coverage which is decided by the Atmospherically Resistant Vegetation Index (ARVI, Kaufman and D. Tanre,).

9. Method 1. We set the surface reflectance values as the follow equation
The ρ is calculated through AOT and the apparent radiance L by using radiative transfer equation.
A one - dimensional search method was used to get the optimal solution.

10. Method

11. Validation
Surface reflectance
AOT
Apparent reflectance
Retrieval AOD

12. Validation

13. Validation
VIS(KM) 5 6 7 8 9 10 11 12 13 14
RMSE
0.0000
0.0108
0.0065
0.0044
0.0078
0.0062
0.0028
0.0049
0.0035 15 16 17 18 19 20 25 40 65
AVG
0.0017
0.0037
0.0066
0.0038
0.0033
When we get the AOT, do a atmospheric correction to get the surface reflectance. Calculate the RMSE between the retrieval reflectance and the real reflectance. The result is shown on the form.

14. Validation
Before After

15. Validation AND Summary
Vegetation
Water
The result after correction is much closer to the real spectrum.

16. Summary The shortage of current work:
We don’t do a lot of validation on this method, especially on CBERS image. In the next work we will download a lot of CBERS image to validation and improve this method.
The vegetation coverage also has some error when VIS is small. We want to find a new algorithm to calculate it.

17. Thank you!