An Improved Retrieval Algorithm of Aerosol Optical Depth

He Tao; Zhao Fengsheng

Vol.22, NO.6, 2011

Article Contents

Article Navigation > Journal of Applied Meteorological Science > 2011 > 22(6): 663-672

He Tao, Zhao Fengsheng. An improved retrieval algorithm of aerosol optical depth. J Appl Meteor Sci, 2011, 22(6): 663-672.

Citation:

He Tao, Zhao Fengsheng. An improved retrieval algorithm of aerosol optical depth. J Appl Meteor Sci, 2011, 22(6): 663-672.

He Tao, Zhao Fengsheng. An improved retrieval algorithm of aerosol optical depth. J Appl Meteor Sci, 2011, 22(6): 663-672.

Citation:

He Tao, Zhao Fengsheng. An improved retrieval algorithm of aerosol optical depth. J Appl Meteor Sci, 2011, 22(6): 663-672.

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An Improved Retrieval Algorithm of Aerosol Optical Depth

He Tao^1,2,3,
Zhao Fengsheng^{2
,
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1.
Chinese Academy of Meteorological Sciences, Beijing 100081
2.
National Satellite Meteorological Center, Beijing 100081
3.
Jinan Environmental Monitoring Center, Jinan Environmental Protection Bureau of Shandong Province, Jinan 250014

Received Date: 2010-11-10
Rev Recd Date: 2011-08-03
Publish Date: 2011-12-31

Abstract

Abstract

The algorithm to retrieve the aerosol optical depth over land has been completely restructured to produce the collection 005 products based on the algorithm by Levy et al. But the accuracy of the MODIS aerosol optical depth (AOD) products still has very large differences for different seasons and geographic locations in China. In order to improve the accuracy of aerosol retrieval products, an easier and faster algorithm for retrieval of aerosol optical depth over land with MODIS 1B data is introduced. This algorithm deals with the surface reflectance relationships is the same way as MODIS V5.2 algorithm.In order to better represent aerosol properties in China, the size distribution and refractive index of aerosol have been improved. Considering the fine structure of the aerosol size distribution has a little effect on satellite remote sensing of aerosol optical depth, this algorithm use the Junge aerosol size distribution to approximate the aerosol size distribution in an actual atmosphere. The real and imaginary index of refractive is 1.5 and 0.005, respectively.The complex refractive index is assumed for all wavelengths (0.47, 0.55, 0.66 μm and 2.1 μm). In order to verify the accuracy and regional applicability of this algorithm, aerosol optical depth is derived with this algorithm using the MODIS 1B data at Taihu and Xianghe, and this retrieval result is compared with equivalent measurements from AERONET (AErosol RObotic NETwork) site (Level 2.0 data). The MODIS/AOD product and 1B data from September 2006 to June 2008 at Taihu (MODISI/AOD product and 1B data from May 2008 to July 2009 at Xianghe) has been matched with L2.0 AOD product from AERONET stations during the same period. Data from the AERONET are averaged within 30 min before and after the satellite's passing, and the MODIS data are averaged over a 10 km (15 km at Xianghe) area centered at the ground stations. The comparison results show that the standard deviation of the new algorithm inversion results and L2.0 AOD product at Taihu is 0.429. The standard deviation of the MODIS/AOD product and L2.0 AOD product at Taihu is 0.693. Accordingly, the standard deviations of two comparison experiment at Xianghe are 0.493 and 0.542, respectively. These results show that this algorithm retrieval results have good consistency with the sun photometer observational results at Taihu and Xianghe. The retrieval algorithm is more accurate than the current MODIS aerosol algorithm and its inversion results are reasonable. In addition, the settings for aerosol model and optical properties are simple and convenient in the new algorithm, which can effectively reduce the computational time for looking-up table and the iteration time for solving equations.
- MODIS;
- 6S;
- remote sensing;
- aerosol optical depth (AOD)

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References(21)

Figures and Tables

图 1 不同季节1°×1°格点的MODIS全球陆地球形粒子气溶胶模型

(红色和绿色区域代表吸收型和非吸收型气溶胶，其余地方为中等吸收型气溶胶)

Fig. 1 Spherical aerosol model type designated at 1° ×1° gridbox of each season

(red and green areas represent absorbing and non-absorbing models, respectively; neutral is assumed everywhere else)

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Fig. 2 Flowchart illustrating the derivation of aerosol over land

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图 3 2006年9月6日—2008年6月10日

(a) 本算法反演结果与地面资料的对比，(b) 对应的MODIS产品与地面资料的对比

Fig. 3 The comparisons between AOD derived by the improved algorithm and MODIS products with measurements at Taihu from 6 September 2006 to 10 June 2008

(a) AOD derived by the improved algorithm and measurements at Taihu, (b) MODIS products and measurements at Taihu

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图 4 2008年5月20日—2009年7月6日气溶胶光学厚度反演结果、MODIS产品与香河站观测值的对比图

(a) 本算法反演结果与地面资料的对比，(b) 对应的MODIS产品与地面资料的对比

Fig. 4 The comparisons between AOD derived by the improved algorithm and MODIS products with measurements at Xianghe from 20 May 2008 to 6 July 2009

(a) AOD derived by the improved algorithm and measurements at Xianghe, (b) MODIS products and measurements at Xianghe

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图 5 2009年5月20日02：50气溶胶反演结果与卫星产品的对比图

(a) 本算法利用Terra卫星2009年5月20日02:50的MODIS数据反演的550 nm通道的气溶胶光学厚度，(b) 同时刻卫星产品

Fig. 5 The comparisons between AOD derived by the improved algorithm and MODIS products

(a) AOD at 550 nm channel derived by the improved algorithm in terms of MODIS data at 02:50 20 May 2009, (b) the satellite products at the same time

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Fig. 6 The contribution of atmospheric and surface to the apparent reflectance and the contribution rate of surface to the apparent reflectance in different aerosol optical depth when the wavelength is 550 nm and the scattering angle is 120°

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Table 1 The setting of parameters about the looking-up table using 6S radiative transfer model

变量名	个数	取值范围
通道	4	MODIS 1，3，4，7通道，中心波长分别为 0.646 μm，0.466 μm，0.553 μm，2.119 μm
太阳天顶角/(°)	9	0, 6, 12, 24, 36, 48, 54, 60, 66
观测天顶角/(°)	16	0, 6, 10, 14, 18, 22, 26, 30, 34, 38, 42, 46, 52, 56, 60, 66
相对方位角/(°)	16	0, 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144, 156, 168, 180
光学厚度	5	0.01, 0.25, 0.5, 1.0, 2.0
地表反射率	3	0.0, 0.1, 0.25
气溶胶粒子半径/μm		0.01~15.0

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Table 2 The statistical average of Angstrom440_675 at part of AERONET sites

站点	时间段	平均值
香河	2001-03-20—2009-07-07	1.127
兴隆	2006-02-19—2008-05-22	1.157
太湖	2005-09-01—2008-10-02	1.196
合肥	2005-11-17—2008-11-20	1.470
杭州	2007-08-08—2007-11-14	1.291

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Table 3 The average statistical of single scattering albedo using AERONET data of different channels

地点	AOD	单次散射比				时间段
地点	AOD	440 nm	675 nm	870 nm	1020 nm	时间段
太湖	0.5 < τ < 1	0.887	0.908	0.905	0.902	2005-09-06—2009-12-05
	1 < τ < 1.5	0.903	0.920	0.916	0.915
	τ > 1.5	0.921	0.936	0.935	0.936
香河	0.5 < τ < 1	0.881	0.908	0.905	0.901	2001-03-20—2009-07-02
	1 < τ < 1.5	0.899	0.925	0.923	0.919
	τ > 1.5	0.921	0.939	0.937	0.934
兴隆	0.5 < τ < 1	0.917	0.936	0.931	0.926	2006-02-20—2008-05-21
	1 < τ < 1.5	0.922	0.936	0.933	0.932
	τ > 1.5	0.942	0.957	0.951	0.948

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