Remote sensing in the O2 A band
Cloud retrievals from
GOME-2/SCIAMACHY using
oxygen absorption and its
applications
Ping Wang
Gijs Tilstra
Olaf Tuinder
Maarten Sneep
Piet Stammes
KNMI, De Bilt
Overview
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FRESCO surface solar radiation product
Detect volcanic ash height and optical
thickness using FRESCO
FRESCO for TROPOMI
FRESCO-B
FRESCO surface solar radiation product
Broadband surface solar irradiance (240-4600nm)
the Heliosat method
METEOSAT data
n = (R-Rmin)/(Rmax–Rmin)
Rmax = 0.95
Rmin = Rclear(As)
Transmission
G = k*Gclear
k = 1-n
Cloud index n
Calculate n using METEOSAT
visible channel, no absorption
Cano et al., Solar Energy, 1986
Mueller et al., 2004
Effective cloud fraction
Scattering cloud
Lambertian cloud
R = (1-ceff)Rclr + ceffRc
T = (1-ceff)Tclr
Tc = 0
Ceff = (R- Rclear)/(Rc-Rclear)
n = (R-Rmin)/(Rmax–Rmin)
Choose proper Rc(Ac) and Rmax
The definition of effective cloud
fraction (Ceff) and cloud cover index
(n) in the Heliosat method is similar.
Stammes et al., JGR, 2008
SCIAMACHY effective cloud fraction and
broadband surface solar irradiance
BSRN stations used for the validation of SSI
Baseline Surface Radiation Network
OMI and SCIAMACHY SSI for all data in 2008
SCIAMACHY
Wang et al., 2011, 2014
OMI
OMI and SCIAMACHY SSI data are
at www.temis.nl
Statistics of OMI and SCIAMACHY SSI validation
OMI
SCIAMACHY
BSRN Mean global
irradiances [W/m2]
554.3
509.0
Mean differences
(SSI-BSRN) [W/m2]
Standard deviation
[W/m2]
-4.7
-4.2
99.6
101.1
Correlation
0.937
0.932
Number of data
5651
1006
Volcanic ash plume detection GOME-2 image
20120606
AAI depends on
aerosol height,
type, optical
thickness
Assume aerosol
type, get aerosol
height from
FRESCO
Use a look-up
table to derive
AOT.
Wang et al., 2012
Volcanic ash plume height and optical thickness
Assume the AOD and height of the
plume did not change during the day
Balis et al., 2016
FRESCO for TROPOMI
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Retrieve effective cloud fraction, cloud
pressure, scene pressure, scene albedo
Use actual snow/ice detection.
Use surface pressure from ECMWF
Use GMTED2010 surface height database
Include wavelength calibration
Will be used in the aerosol height retrieval
and the trace gas retrievals.
FRESCO-B
Retrieve scattering cloud properties from the
O2 A and B bands
Use scattering cloud model
Derive cloud top height and cloud geometric
thickness, and cloud optical thickness.
A postdoc position for two years.
Yang et al., 2013
Reflectance spectra measured by GOME-2B
O2 B
O2 A
FRESCO-B flowchart
Different cloud heights in O2 A and B bands
Cloud 1 km thick
Red: cloud layer 1-2 km
Green:
5-6 km
Blue:
9-10 km
Dot COT = 35
Star COT = 15
Square COT = 5
SZA = 60 degree
VZA = nadir
hsum = ha+hb
hdiff = ha-hb
Summary
• The surface solar irradiance products from
SCIAMACHY and OMI have good agreement with
ground-based measurements.
• FRESCO volcanic ash plume height and aerosol
optical thickness values are reasonable for thick
volcanic ash plumes.
• FRESCO algorithm has been implemented in
TROPOMI processor in KNMI. The FRESCO cloud
product will be used in the trace gas retrievals
and aerosol height retrievals.
• The FRESCO-B project will start in autumn. We
are going to derive scattering cloud parameters.