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WATER VAPOR RETRIEVAL OVER CLOUD COVER AREA ON LAND

WATER VAPOR RETRIEVAL OVER CLOUD COVER AREA ON LAND. Dabin Ji, Jiancheng Shi, Shenglei Zhang Institute for Remote Sensing Applications Chinese Academy of Sciences, China. Outline. Introduction Basic Theory Water Vapor Retrieval Validation. Introduction. Introduction.

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WATER VAPOR RETRIEVAL OVER CLOUD COVER AREA ON LAND

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  1. WATER VAPOR RETRIEVAL OVER CLOUD COVER AREA ON LAND Dabin Ji, Jiancheng Shi, Shenglei Zhang Institute for Remote Sensing Applications Chinese Academy of Sciences, China

  2. Outline • Introduction • Basic Theory • Water Vapor Retrieval • Validation

  3. Introduction

  4. Introduction • Current methods overland. 1. Neural Network. 2. Two frequency ratio of polarization difference of Tb (ΔTb18.7/ΔTb23.8, Deeter et al., 2007, Wang et al., 2010) • In this study: Based on method ΔTb18.7/ΔTb23.8 with improvement on surface emissivity estimation

  5. Basis of Two Frequency ratio of Polarization Difference (1) ε: Surface emissivity t: Transmittance P: Pressure T: Temperature Subscript v: Frequency, p: Polarization, s: Surface. Brightness received by Microwave sensor [Jones, A. S, 1990; Liou K. N, 2004]

  6. Basis of Two Frequency ratio of Polarization Difference (2) Ratio of ΔTb at two frequency (3) Understanding： Δε18.7 and Δε23.8 are well correlated for land surface conditions. In previous study (Wang et al., 2010), the first part Δε18.7/Δε23.8 in Eq (3) is equal to a constant. Polarization difference of Tb

  7. Basis of Two Frequency ratio of Polarization Difference • Both ΔTb18.7/ΔTb23.8and ΔTb36.5/ΔTb89are more sensitive than single Tb. • ΔTb36.5/ΔTb89 will not be used in the retrieval due to its sensitivity to cloud liquid water. The second part on the right of Eq.(3) is a function of water vapor (wv).

  8. Sensitivity Analysis Using MODIS water vapor products (MOD07) under clear sky condition, the surface emissivities can be derived Relationships of surface emissivity at frequency 18.7 and 23.8GHz estimated from the South Great Plain in USA. Jan, 2007 H-POL V - H V-POL

  9. Sensitivity Analysis July, 2007 H-POL V - H V-POL Mean and variance of Δε18.7/Δε23.8 have significant change over seasons The assumption of Δε18.7/Δε23.8 might result in a significant error in atmospheric water vapor estimation

  10. Water Vapor Retrieval with AMSR-E Ratio of ΔTb at two frequency (3) From measurements of ΔTb18.7/ΔTb23.8, if Δε18.7/Δε23.8and Surface temperature (Ts) are known, then water vapor can be estimated.

  11. Estimation of Surface Temperature with AMSR-E (4) Tb36.5V is AMSR-E vertical polarization brightness temperature at frequency 36.5GHz Ts is estimated using Eq.(4) [Holmes, T. R. H., 2008].

  12. Atmospheric profiles Parameter of Microwave Radiometer Surface temperature Cosmic T(2.7K) Atmospheric parameter calculating Eddington two stream calculation Simulated Microwave Brightness Temperature Water Vapor Retrieval with LUT Input Calculate Output MODEL: 1-D Microwave Radiative Transfer Model (1DMRTM), (Olson, William S, 2001) used to build LUT for estimating emissivity.

  13. Estimation of Δε18.7/Δε23.8 Data used: • AMSR-E brightness temperature • MODIS-MYD07 (atmospheric profiles and surface temperature) EstimatingΔε18.7/Δε23.8at clear sky. For cloudy, it’s estimated using 7-day average data.

  14. Water Vapor Retrieval Summary Outline of the retrieval: Re-project AMSR-E TB and MYD07 into 0.25°-0.25° grid image. Calculate ΔTb18.7/ΔTb23.8 using AMSR-E TB. Estimating Ts in cloudy condition using Eq. (4). Estimating Δε18.7/Δε23.8. Using LUT to estimate water vapor

  15. Comparison with GPS Estimation GPS retrieved water vapor from SuomiNet was used for comparison Water vapor in Jan. 2007 was retrieved over cloud cover area in South Great Plain of USA.

  16. Possible Errors • Uncertainty of Δε18.7/Δε23.8 in cloudy condition due to precipitation event and other events changing surface emissivity. • 1D atmospheric Microwave RT model itself • Surface temperature estimation • Spatial scale difference of the retrieved water vapor and GPS water vapor.

  17. THANK YOU FORYOUR ATTENTION!

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