empirical orthogonal function (eof) analysis on the o 2 a-band vijay natraj, run-lie shia, xun jiang...
Post on 21-Dec-2015
215 views
TRANSCRIPT
Empirical Orthogonal Function (EOF)
Analysis on the O2 A-bandVijay Natraj, Run-Lie Shia, Xun Jiang and Yuk
Yung
Welcome-2
Rationale
• Multiple Scattering RT calculations time-consuming
• Need a speed improvement of about 1000!
• Solution: make use of redundancies in spectra
– Correlated-k (Lacis and Wang, Lacis and Oinas, Goody et al, Fu and Liou)
– Optical depth binning (Ramaswamy and Friedenreich)
• Problem: assume that atmospheric optical properties spectrally correlated
at all points along optical path
Welcome-3
Rationale (contd …)
• Spectral Mapping (Crisp and West, Meadows and Crisp)
– No assumption about spectral correlation
– Combine only spectral regions that remain in agreement at ALL
points along optical path
– Binning parameters: optical depth, single scattering albedo,
asymmetry parameter, surface albedo
• Problems
– Inadequate speed improvement for OCO precision constraints
– Glitches in partial differentials
Welcome-4
EOF Technique
• Data Set
– Optical properties in M atmospheric layers at N wavelengths
• EOF
– Eigenvectors of covariance matrix of detrended (removed mean) data set
– New basis to represent original data
– No loss of information
• PC
– Projection of original data set onto EOFs
Welcome-12
Statistics
• Total Pixels: 7971
• Total EOF Cases: 131
• 4 RT calls (and 4 calls to a twostream routine) per case
• Speed improvement of at least 10 (conservative estimate)
• Precision of better than 0.5% except in highly saturated regions
• Tunable