Post on 30-Dec-2015
description
1Mark.Weber@iup.physik.uni-bremen.de
GOME2 Error Study
WP 210: Spectral Aliassing
PM2 10/2001
Spectral Aliassing
I. “Bad Case Scenario”
R. De Beek, M. Weber, R. Siddans (RAL), B. Latter (RAL)
all albedo sequences were analysed to identify worst case scenario from LANDSAT/artificial albedo perturbation provided by RAL
worst case scenario was defined by maximum variance of differential albedo error spectra
definition of differential albedo error spectra:
I() – P() = Wa()(a()/a) – P()
I() relative intensity perturbation due to albedo variation P() fitted quadratic (cubic) polynomial Wa() albedo weighting function (SCIATRAN) a() albedo sequence with mean albedo subtracted a mean albedo of sequence
2Mark.Weber@iup.physik.uni-bremen.de
GOME2 Error Study
WP 210: Spectral Aliassing
PM2 10/2001
Gas Position StDev StDev mean albedo sequence file Scan (1m) (IFOV) albedo
O3 536 0 5.7e-04 3.6e-05 0.46 syn3/pix80_nd3_p1_10_1m_box_80_spec.sav NO2 509 0 3.0e-03 1.3e-04 0.51 syn10/pix80_nd10_p0_10_1m_box_80_spec.sav BrO 529 0 6.7e-04 6.3e-06 0.47 syn3/pix80_nd3_p1_10_1m_box_80_spec.sav
OClO 438 0 2.0e-03 8.3e-05 0.51 syn10/pix80_nd10_p0_10_1m_box_80_spec.sav
worst case scenario from 1m box artifical albedo perturbation
IFOV convolution reduces StDev by a factor of 15-100
albedo error spectra applied to biomass burning (No. 1) and ozone hole scenario (No. 2)
Results:
4Mark.Weber@iup.physik.uni-bremen.de
GOME2 Error Study
WP 210: Spectral Aliassing
PM2 10/2001
Results from weighted intensities using weights
determined from averaging a=0.05 and a=0.8 to obtain
mean albedo
Results from fits to I(a=0.05)
5Mark.Weber@iup.physik.uni-bremen.de
GOME2 Error Study
WP 210: Spectral Aliassing
PM2 10/2001
Results from weighted intensities using weights
determined from averaging a=0.05 and a=0.8 to obtain
mean albedo
Results from fits to I(a=0.05)
7Mark.Weber@iup.physik.uni-bremen.de
GOME2 Error Study
WP 210: Spectral Aliassing
PM2 10/2001
Results from weighted intensities using weights
determined from averaging a=0.05 and a=0.8 to obtain
mean albedo
Results from fits to I(a=0.05)
8Mark.Weber@iup.physik.uni-bremen.de
GOME2 Error Study
WP 210: Spectral Aliassing
PM2 10/2001
Results from weighted intensities using weights
determined from averaging a=0.05 and a=0.8 to obtain
mean albedo
Results from fits to I(a=0.05)
9Mark.Weber@iup.physik.uni-bremen.de
GOME2 Error Study
WP 210: Spectral Aliassing
PM2 10/2001
Preliminary Conclusion for IT=0.1875ms and readout of 46ms:
errors on the order of less than 0.1% (O3), 80% (NO2), 11% (BrO), 5% (ozone hole OClO) have been observed for albedo variations of less than 0.04 (very small albedo variations!)
spatial aliassing equivalent noise is a dominant error source for current IT and readout time settings
larger albedo variations leads to variability of reference slant column and air mass factor (additional error source). DOAS assumes unique slant column within the window
fits will be repeated for intensities with proper mean albedo (a=0.46 and a=0.5)
additional case studies and error checking on current approach is planned.