Development of GEMS Cloud Data Processing Algorithm Yong-Sang Choi 1, Bo-Ram Kim 1, Heeje Cho 2,...
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Development of GEMS Cloud Data Processing Algorithm Yong-Sang Choi 1, Bo-Ram Kim 1, Heeje Cho 2, Myong-Hwan Ahn 1 (Former COMS PI), and Jhoon Kim 3 (GEMS
Development of GEMS Cloud Data Processing Algorithm Yong-Sang
Choi 1, Bo-Ram Kim 1, Heeje Cho 2, Myong-Hwan Ahn 1 (Former COMS
PI), and Jhoon Kim 3 (GEMS PI) 1 Ewha Womans University, Seoul 2
Seoul National University, Seoul 3 Yonsei University, Seoul
Slide 2
Clouds significantly affect gas/aerosol retrievals! Cloud
contamination causes errors in air mass factor, and errors in
gas/aerosol retrievals. 2
Slide 3
Comparison of UV cloud products InstrumentWavelength
regionProducts GOME-2300 800 nmO 3, NO 2, BrO, SO 2, H 2 O, HCHO,
and OClO OMI280 500 nmO 3, aerosols, surface UV irradiance, NO 2,
BrO, SO 2, HCHO, and OClO SCIAMACHY240 2380 nmO 3, SO 2, NO 2, BrO,
HCHO, OClO, H 2 O, CO, CH 4, CO 2, and clouds TROPOMI270 500 nm,
675 775 nm, 2305 2385 nmO 3, SO 2, NO 2, HCHO, H 2 O, CO and CH 4,
and clouds and aerosols 3
Slide 4
223 253 283 876543210876543210 460 a 465 a 470 a 475 a 480 485
a 490 O 2 -O 2 absorption band (Acarreta, Haan, and Stammes 2004
JGR) Absorption cross-section of the O 2 -O 2 collision complex
near 477 nm, based on measurements by Newnham and Ballard [1998] at
283 K (red curve) and 223 K (blue curve). The curve for 253 K
(green) was obtained by interpolation. (adopted from OMI ATBD)
4
Slide 5
GEMS cloud algorithm will provide CH and CF by using O 2 -O 2
absorption. Main cloud products: - Cloud height ( z c ) - Effective
cloud fraction ( c f ) Main bands: -O 2 -O 2 absorption band
(460490 nm) 5
Slide 6
GEMS cloud algorithm will provide CH and CF by using O 2 -O 2
absorption. Main cloud products: - Cloud height ( z c ) - Effective
cloud fraction ( c f ) Main bands: -O 2 -O 2 absorption band
(460490 nm) 6 ISSUE: How to build DOAS and LUT
Slide 7
DOAS-calculated O 2 -O 2 absorption factors (Rc and Ns) are
compared with LUT, to get cloud products. LUT variables (7D or 8D)
Radiance spectra Solar zenith angle Viewing zenith angle Relative
azimuth angle Surface altitude Surface albedo Absorption cross
section RcRc NsNs 7 Calculation of Rc and Ns Temperature
profile?
Slide 8
DOAS-calculated O 2 -O 2 absorption factors (Rc and Ns) are
compared with LUT, to get cloud products. Radiance spectra Solar
zenith angle Viewing zenith angle Relative azimuth angle Surface
altitude Surface albedo Absorption cross section RcRc NsNs 8 LUT
variables (7D or 8D) Temperature profile? Calculation of Rc and Ns
ISSUE: How to effectively extract cloud fraction and cloud height
from LUT fitting?
Slide 9
C Sequence of cloud height ( z c ) and cloud fraction ( c f )
retrievals zczc OBS DB 9 Cloud height for C f (Albedo = 0.8) Cloud
fraction
Slide 10
C Sequence of cloud height ( z c ) and cloud fraction ( c f )
retrievals zczc OBS DB 10 Cloud height for C f (Albedo = 0.8) Cloud
fraction zczc
Slide 11
Generation of GEMS synthetic cloud- radiation data TOA UV
Radiance (Reflectance) Forward RT simulation Cloud Information 3D
NWP model Retrieval Algorithm 11
Slide 12
Data and models Cloud-to-radiance conversion SCIATRAN (ver 3.1)
Cloud properties WRF model simulation* of Case: Typhoon Muifa (
03UTC, August 6, 2011 ) *by Prof. S.-Y. Hongs team in Yonsei Univ.
WRF output Geometry Liquid & ice water contents Centroid cloud
height 12
Slide 13
Assumptions Standard atmosphere McLinden climatology Surface
albedo based on WRFs land category Cloud water droplet size = 10 m
Cloud ice particle size = 50 m of fractal shape 13
Slide 14
A test for c f retrieval R clear clear sky simulation R cloud
overcast simulation assuming Lambertian reflector ( A g = 0.8) R
meas Synthetic data 14
Slide 15
A test for c f retrieval R clear clear sky simulation R cloud
overcast simulation assuming Lambertian reflector ( A g = 0.8) R
meas Synthetic data 15
Slide 16
Relation between effective cloud fraction and cloud optical
thickness in synthetic data 16 1% of cloud pixels exceed c f value
of 1. These clouds are optically thick ( c 25), having albedo over
0.8.
Slide 17
Error analysis with synthetic data Errors in cloud height
Errors in effective cloud fraction 1%0.06% 10%0.1% 50%0.4%
Artificial errors were given to cloud height, and then the
sensitivity to errors in effective cloud fraction were tested with
our synthetic data. Results show that the sensitivity is fairly
small, meaning that cloud height limitedly affects the retrieval
accuracy of effective cloud fraction. 17
Slide 18
C Sequence of cloud height ( z c ) and cloud fraction ( c f )
retrievals zczc OBS DB 18 Cloud height for C f (Albedo = 0.8) Cloud
fraction zczc Probably Fine How about this?
Slide 19
Error analysis with synthetic data Errors in cloud height
Errors in effective cloud fraction 1%0.06% 10%0.1% 50%0.4%
Artificial errors were given to cloud height, and then the
sensitivity to errors in effective cloud fraction were tested with
our synthetic data. Results show that the sensitivity is fairly
small, meaning that cloud height limitedly affects the retrieval
accuracy of effective cloud fraction. 19
Slide 20
Future study topics and call for In-depth discussion issues in
Cloud/aerosol breakout session in GEMS International Science
Workshop (October 2013, Korea) Cloud/aerosol effects on various gas
retrievals Accuracy of cloud/aerosol products Validation plans for
cloud/aerosol products Synthetic cloud-radiation simulators
Comparison of algorithms using different bands: O 2 -A, O 2 -B, O 2
-O 2, Raman scattering Etc. 20 Yong-Sang Choi ([email protected])