Detecting aerosol layer height over coastal regions using

Detecting aerosol layer height over coastal regions using OCO-2 O 2 A measurements Zhao C. Zeng (Caltech) with Vijay Natraj (JPL), Stanley P. Sander (JPL), and Yuk L. Yung (Caltech) OCO 2 Science Team Meeting Oct 23 -25, 2018

Why aerosol layer height? Continuum 1. Atmospheric aerosols scatter photons back to space and therefore reduce the chance of the photons being absorbed by the oxygen. 2. Photons scattered by higher aerosol layers undergo shorter absorption paths, thereby enhancing the reflectivity within the O 2 absorption band. gas absorption 3 Scenarios: Same amount of total AOD; But at different altitudes. 3. Uncertainty on gas column density retrievals if the aerosol layer height is not well constrained.

Constraining aerosol vertical structure using O 2 band Zeng et al. (2018), Constraining Aerosol Vertical Profile in the Boundary Layer Using Hyperspectral Measurements of Oxygen Absorption, Geophysical Research Letters, published. Validation: CALIPSO aerosol profile CLARS-FTS source: earthobservatory. nasa. gov Mt Wilson 1. 67 km OCO-2 tracks (Nadir mode) over the coastal region of Sahara desert. (Ocean surface is relatively dark and its BRDF effect is relatively well known)

A strong dust plume going out of Sahara

Low (~1. 5 km) Spectral sorting for Aerosol Layer Height High (~2. 5 km) Clear 1. Low and high aerosol layer height (same total AOD~0. 5); 2. Relatively higher radiance for high aerosol layer height; 3. Spectral sorting technique (for clouds: Liou 2002; Richardson et al. 2017). Two advantages over a conventional fitting scheme: (1) absolute radiance as well as the shape can be used; (2) the spectral regions with the largest sensitivity can be identified. Aerosol Layer Height Total AOD

Retrieval of total AOD and effective aerosol layer height 1. Retrieval algorithm (Zeng et al. , 2018, GRL) (a) Look-up table based on the sorted spectra (b) Simple assumption of dust optical properties and ocean surface BRDF (Cox-Munk; constant wind speed of 10 m/s); Land Cloud 2. The total AOD and effective ALH can be very well constrained; Decreased accuracy for ALH retrieval with lower AOD. 3. Larger uncertainty around cloud regions. Land Cloud

Conclusions 1. OCO-2 O 2 A band nadir measurements show potential to constrain the vertical structure over the coastal regions On land, especially over dirty urban areas, need further investigation(due to the complex BRDF effect) 2. A “Divide and Conquer” strategy for gas retrievals (1) Constrain the aerosol vertical structure and optical properties using O 2 A band; (2) Gas retrievals with the constrained aerosol inputs in RT.

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