Open AccessInformation‐rich spectral channels for simulated retrievals of partial column‐averaged methane
Author(s) -
Su Zhan,
Xi Xi,
Natraj Vijay,
Li KingFai,
Shia RunLie,
Miller Charles E.,
Yung Yuk L.
Publication year - 2016
Publication title -
earth and space science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.843
H-Index - 23
ISSN - 2333-5084
DOI - 10.1002/2015ea000120
Subject(s) - methane , channel (broadcasting) , spectral resolution , column (typography) , spectral line , remote sensing , sky , resolution (logic) , a priori and a posteriori , absorption (acoustics) , environmental science , computer science , physics , meteorology , geology , optics , chemistry , telecommunications , philosophy , epistemology , astronomy , artificial intelligence , organic chemistry , frame (networking)
Space‐based remote sensing of the column‐averaged methane dry air mole fraction (XCH 4 ) has greatly increased our understanding of the spatiotemporal patterns in the global methane cycle. The potential to retrieve multiple pieces of vertical profile information would further improve the quantification of CH 4 across space‐time scales. We conduct information analysis for channel selection and evaluate the prospects of retrieving multiple pieces of information as well as total column CH 4 from both ground‐based and space‐based near‐infrared remote sensing spectra. We analyze the degrees of freedom of signal ( DOF ) in the CH 4 absorption bands near 2.3 μm and 1.6 μm and select ∼1% of the channels that contain >95% of the information about the CH 4 profile. The DOF is around 4 for fine ground‐based spectra (resolution = 0.01 cm −1 ) and 3 for coarse space‐based spectra (resolution = 0.20 cm −1 ) based on channel selection and a signal‐to‐noise ratio (SNR) of 300. The DOF varies from 2.2 to 3.2 when SNR is between 100 and 300, and spectral resolution is 0.20 cm −1 . Simulated retrieval tests in clear‐sky conditions using the selected channels reveal that the retrieved partial column‐averaged CH 4 values are not sensitive to the a priori profiles and can reflect local enhancements of CH 4 in different partial air columns. Both the total and partial column‐averaged retrieval errors in all tests are within 1% of the true state. These simulated tests highlight the possibility to retrieve up to three to four pieces of information about the vertical distribution of CH 4 in reality.