A METHOD FOR THE RETRIEVAL OF AEROSOL OPTICAL THICKNESS ON CBERS DATA FROM TOP-OF-ATMOSPHERE RADIANCE

Zhang Xin, Zhao Xiang, Liu SuhongBeijing Normal University

CONTENTS

BACKGROUND

METHOD

VALIDATION

SUMMARY

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).

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

0.4 0.5 0.6 0.7 0.8 0.9

表观反射率大气纠正反射率波谱仪实测反射率

Vegetation 0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.4 0.5 0.6 0.7 0.8 0.9

表观反射率大气纠正反射率波谱仪实测反射率

Water

BACKGROUND

Some algorithms only retrieval one result on every image, it is hard to fulfill the Correction accuracy

Some algorithms currently require visible to short-wave spectral bands (400-2500nm)

Some algorithms need densely vegetated area we have developed

a novel retrieval algorithm only use

the visible and near-infrared (VNIR)

spectral bands and have a high-

accuracy

BACKGROUND

This method is design for CBERS CCD Image.

24 June 2007(Path 8/Row 61) , Shanxi Province, China

Sensor Name CCD

Sensor Type Push-broom

Band information 1： 450～ 520nm2： 520～ 590nm3： 630～ 690nm4： 770～ 890nm5： 510～ 730nmResolution 19.5 m

METHODThis retrieval work is designed to obtain the main atmospheric parameters from the image itself.

METHOD

CalibrationL=DN/K

(http://www.cresda.com/)Grid divison The image is divided in 10KM*10KM cells.Selecting the suitable pixels by Cv

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,).

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.

Method

VALIDATION

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Real AOD(Cv=0.2, 0.5, 0.8)

Retr

ieve

d AO

D

y = 1.1135x + 0.0493R² = 0.9498RMSE=0.14

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Real AOD(Cv=0.5, 0.7, 0.9)

Retr

ieve

d AO

D

y = 1.1125x - 0.0416R² = 0.9818RMSE=0.055

Surface reflectance AOT Apparent reflectance

Retrieval AOD

VALIDATION

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Real AOT（ 0.5、 0.6、 0.7、 0.9）

Retr

ievi

ng A

OT

y = 1.1638x - 0.0801R² = 0.9696RMSE=0.068

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Real AOT (0.5、 0.6、 0.7、 0.8、 0.9）

Retr

ievi

ng A

OT

y = 1.1152x - 0.0427R² = 0.9786RMSE=0.055

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 0.0000 0.0035

VIS(KM) 15 16 17 18 19 20 25 40 65 AVG

RMSE 0.0000 0.0000 0.0000 0.0000 0.0017 0.0037 0.0066 0.0038 0.0000 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.

VALIDATION

Before After

VALIDATION

AND

SUM

MARY

The result after correction is much closer to the real spectrum.

Vegetation Water

SUMMARY

The shortage of current work:1. 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.

2. The vegetation coverage also has some error when VIS is small. We want to find a new algorithm to calculate it.

Thank you!