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Retrieval of Atmospheric Concentrations for Ecosystem Studies. Jiabin Liu 1 , Le Kuai 1 , Run-Lie Shia 1 , Qiong Zhang 1 , Dejian Fu 2 , Stanley P. Sander 2 , Harmut Aumann 2 , Thomas Pongetti 2 , Yuk L. Yung 1 1.California Institute of Technology, Pasadena, California, USA

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Retrieval of Atmospheric Concentrations for Ecosystem Studies

Jiabin Liu1, Le Kuai1, Run-Lie Shia1, Qiong Zhang1, Dejian Fu2, Stanley P. Sander2, Harmut Aumann2, Thomas Pongetti2, Yuk L. Yung1

1.California Institute of Technology, Pasadena, California, USA

2.Jet Propulsion Laboratory,Pasadena, California, USA

Sensitivity Studies of the Retrieval

Introduction

Remote sensing of Earth’s atmosphere is a powerful tool to investigate various ecosystem structures. The forest canopy structure, in particular, influences the water vapor and CO2 in the atmosphere and has impact on the solar radiance of satellite measurements. In this study, we use the Line-by-line Radiative Transfer Model (LBLRTM) to retrieve the water vapor, temperature, and CO2 in the boundary layer. Jacobian values, as sensitivity studies of the retrieval, are calculated to show the efficiency of vertical profile retrieval for each gaseous species. Further work will be done on more species and potentially with another model under different circumstances. .

  • The Jacobianvalues, calculated in the retrieval process, provide the sensitivity of the forward model to the current state vector of the retrieved species. Here we show the Jacobians of the retrieved temperature at one certain level and all levels. Similar studies are performed for water.
  • A sensitivity peak for temperature, shown in red, centers around 650 – 800 cm-1. A clear sensitivity peak is shown at 909 cm-1 for water, and optimal retrieval should focus around this value. The two wings at the side of the peak are due to pressure broadening.

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Line-by-line Radiative Transfer Model

  • The Line-by-line Radiative Transfer Model (LBLRTM) is an efficient and flexible line-by-line model and provide accurate spectral radiance calculations. It exploits Voigt line shape at all levels and utilizes a temperature-dependent absorbing coefficient. The information of species is based on the Hitran 2004 database.
  • In this study, LBLRTM provides the user-defined upwelling spectrum. For user-defined upwelling, the two figures show the radiance as well as brightness temperature at designated spectral window.
  • The LBLRTM specializes in the thermal and we use the window from700 cm-1 to 900 cm-1 for the retrieval.

Summary and Future

The line-by-line radiative transfer model is a powerful tool to accurately calculate the spectral radiance and serves as a good forward model for retrieval studies of greenhouse gases.

In the retrievals using LBLRTM, the sensitive window of gaseous species can be calculated to determine where the optimal results of retrieval can be made. Also, Jacobians can suggest the appropriate resolution for the measurements to take place as no important features should be lost.

The sensitivity information in the retrieval can help future designs to make more efficient observations. In particular, the retrieval needs to have a certain resolution in order not to lose important features of the spectrum.

In the future, a two-stream model will be incorporated to account for the solar radiation scattered by clouds.

Acknowledgement

Keck Institute for Space Studies (KISS) Grant P721546