Improved Detection of Optically Thin Cirrus Clouds Using CrIS Double CO2 Bands

Lin Lin1,2 and Fuzhong Weng2

1 I. M. Systems Group, Inc.2 NOAA Center for Satellite Applications and Research pp

Presented at 14th JCSDA Technical Review Meeting & Science Workshop on Satellite Data Assimilation, Moss Landing, California, May 31 – June 2, 2016

Outline

1. Major Issues for CrIS Data Assimilation (DA)

- Issues related to simulations of shortwave channels- Misclassification of thin cirrus cloud in DA

2. Improve CrIS Quality Control

Cl d d t ti l ith i d bl CO2 b d- Cloud detection algorithms using double CO2 bands

- Cloud Scattering and Emission Index (CESI)

3. Summary and Conclusions

4 Future Work

2

4. Future Work

2012 NCEP t k i 934 HWRF

A Baseline HWRF System for Satellite Data Assimilation

• 2012 NCEP-trunk version 934 HWRF (three nested domains)

• System ModificationsModel Domains

- Higher model top (0.5 hPa, 61 levels)- Warm start- Asymmetric vortex initializationAsymmetric vortex initialization

• Advanced POES and GOES DA- POES sounding instruments:

AMSU ATMS C IS IASI AIRSInner

domain

Outerdomain

AMSU, ATMS, CrIS, IASI, AIRS- New quality control (QC) for MHS- GOES-13/15 imager radiance

Th t l i d l d i

Middledomain

- POES microwave imager radiance(AMSR2, GMI)

- Surface sensitive channels through

Three telescoping model domains:Outer domain: 27 km (fixed) Middle domain: 9 km (moving)I d i 3 k ( i )g

Community Surface Emissivity Model (CSEM)

Inner domain: 3 km (moving)

3

CrIS Weighting Function

— LWIR— SWIR

— MWIR

a)re

ssur

e (h

PaPr

WF (hPa-1) WF (hPa-1)

WFs of 399 CrIS channels selected for CrIS data assimilation in GSI:— 184 (713) LWIR channels— 87 (159) SWIR channels— 128 (433) MWIR channels 4

Impacts of CrIS and ATMS DA on Hurricane Forecasts

Control Run Control Run +ATMS Control Run +CrIS

• Unlike ATMS data assimilation of CrIS radiance observations in HWRF degraded• Unlike ATMS data, assimilation of CrIS radiance observations in HWRF degraded the forecasts of Superstorm Sandy tracks.

• Assimilation of CrIS and ATMS data results in 30% and 70% gains of ACC at 500 hPa for the five day global forecast using the NCEP global system respectively

5

Some fundamental issues related to QC of CrIS data are yet to be resolved!

hPa for the five day global forecast using the NCEP global system, respectively.

5

QC in Current GSI for CrIS

include: remove data with quality flags from b d d FOV5 d t l ti d

11 top-level QC checks

bad scan and FOV5; data locations and observation times must be within valid range; data must within analysis time window, etc.

Further QC checksrelated to:(1) QC for shortwave IR observations

during daytime(2) QC for observations within high

topography(3) QC for cloud contamination(4) QC for clear-sky observations that

fail to pass temperature/emissivity checks

(5) QC for observations with large radiance observation departures

6

Impact of Solar Reflection on Daytime CrIS Shortwave Measurements

• Currently, CrIS surface-sensitive shortwave channels whose wavenumbers being larger than 2400 cm-1 are all removed from assimilation.

• Not all CrIS pixels of these shortwave channels are affected by Sun glint.

Si l t d d b d l k C IS b i ht t tPercentage VIIRS pixels affected by

p y g• A Sun glint correction on CrIS observations is incorporated in the CRTM version

released in 2014 (Chen et al., 2013)

Simulated and observed clear-sky CrIS brightness temperature Percentage VIIRS pixels affected by Sun glint at collocated CrIS FOV

Channel 1293 (2520 cm-1)

7Chen, Y., Y. Han, P.-V. Delst, and F. Weng, 2013: Assessment of shortwave infrared sea surface reflection and NLTE effects in CRTM using IASI data. J. Atmos. Oceanic Tech., 30, 2152-2160.

Impact of NLTE on Daytime CrIS Shortwave Measurements

• Non-Local Thermaldynamic Equilibrium (NLTE) emission occurs in the upper t h ( b 40 k ) h th

CrIS O-B Biases w/o NLTE CorrectionAscending node, clear-sky data over ocean at 1800 UTC during 22-29 October, 2012

atmosphere (above 40 km), where the rates of creation and annihilation of photons due to solar pumping are greater than the rate of collisions.

• If the atmosphere is assumed to be in a local thermodynamic equilibrium (LTE), then the local kinetic temperature is defined as the Plank temperature of the radiation field, which is invalid in the IR short wavelengths for the upper atmosphere where NLTE emission occurs in the strong 4.3 m CO2

• NLTE effect leads to a significantly larger observed satellite radiance than that computed from an LTE approach

absorption band.

computed from an LTE approach.

Chen, Y., Y. Han, P.-V. Delst, and F. Weng, 2013: Assessment of shortwave infrared sea surface reflection and NLTE effects in CRTM using IASI data. J. Atmos. Oceanic Tech., 30, 2152-2160.

8

Issues with the CurrentGSI Cloud DetectionGSI Cloud Detection

• The IR semi-transparent thin cirrusclouds are poorly detected by thecurrent GSI QC scheme and thus thecloud-affected CrIS radiances couldbe treated as clear-sky radiances andbe treated as clear sky radiances andassimilated wrongly into GSI.

• Compared with VIIRS cloud products, both CrIS cloud fraction and cloud top pressure derived in the current GSI are significantly biased

• A new cloud detection algorithmneeds to be developed for betterdiscrimination of the optically thin

9

p ycirrus clouds within CrIS FOVs

9

CrIS Channels and SDR NSR Data Quality

BandSpectral Range

(cm-1)Number of

ChannelSpectral

Resolution (cm-1)

LWIR 650 to 1095 713 0.625

MWIR 1210 to 1750 433 1.25

i i (bl ) ifi i ( )

SWIR 2155 to 2550 159 2.5

BandNEdN

@287K BBRadiometric Uncertainty

FrequencyUncertainty

GeolocationUncertainty

SDR uncertainties (blue) vs. specifications (green)

a d @ 87mW/m2/sr/cm-1

U ce a y@287K BB (%)

U ce a y(ppm)

U ce a y(km)

LW 0.098 (0.14) 0.12 (0.45) 3 (10) 0.2 (1.5)

MW 0.036 (0.06) 0.15(0.58) 3 (10) 0.2 (1.5)

SW 0.003 (0.007) 0.2 (0.77) 3 (10) 0.2 (1.5)10

CRTM Model Simulation of CrIS Channels

)m

pera

ture

(K)

ghtn

ess T

em

Wavenumber (cm-1)

Bri

LWIR MWIR SWIR

Locations of 80ECMWF Profilesl US t d d

6354

26-31

plus a US standardprofile in green

63

54

2423

(29.8oN, 116.0oW)(28 7oN 149 8oE)54

138

(28.7oN, 149.8oE)(47.3oS, 116.5oW)

11

Four Input Profiles for CrIS Radiance Assimilationa)

Pres

sure

(hPa

T (K) q (g kg-1) O3 (ppmv) CO2 (ppmv)

hPa)

— US standard profile

Pres

sure

(h US standard profile———

ECMWF profilesN2O (ppmv) CO (ppmv) CH4 (ppmv)

12

CrIS Sensitivity to Ice Cloud Microphysics ) — Clear-sky

R 60 IWP 5 / 2 CRTM Simulation Scenarios:• Doubled and halved particle size

with fixed IWP• Doubled and halved IWP with fixedm

pera

ture

(K) y

— Re = 60 m, IWP = 5 g/m2

— Re = 30 m, IWP = 5 g/m2

— Re = 15 m, IWP = 5 g/m2

Doubled and halved IWP with fixed particle size

Layer top : 230 hPaghtn

ess T

em

y pLayer bottom : 280 hPaLayer thickness: 1.5 km

Bri

) — Clear-sky Re = 30 m IWP = 10 g/m2

Sensitivities • Simulated BT increases with

increased particle size• Si l t d BT d ithm

pera

ture

(K) — Re = 30 m, IWP = 10 g/m2

— Re = 30 m, IWP = 5 g/m2

— Re = 30 m, IWP = 2.5 g/m2

• Simulated BT decreases with increased IWP

• CRTM is sensitive to both ice particle size and ice water path gh

tnes

s Tem

13Wavenumber (cm-1)

Brig

Physical Basis for CrIS Double CO2 Cloud Detection Algorithmg

Simulated CrIS Brightness Temperatures

Clear sky

scattering of clouds

Cirrus cloud

Clear-sky

Emission & scattering of clouds

Paired channels

• The CrIS BTs at both LW (e.g., 670-750 cm-1) and SW (e.g., 2200-2400 cm-1) CO2( g , ) ( g , ) 2channels display different responses to the changes of cloud vertical structures.

• A new cloud detection algorithm will be developed using the two CrIS CO2 bands.14

Flow Chart Describing LWIR/SWIR Pairing Procedure

SW CO2 channels2200-2400 cm-1

LW CO2 channels670-750 cm-1

1) WF peak model level difference less than 22) WF peaking height within the height range [0, 12 km]

3) Determine the lowest cloud-sensitive levels 4) The lowest cloud-sensitive model level difference less than 2

5) The final pair is selected by choosing a single SWIR channel that has the smallest standard deviation of BTs from the “paired” LWIR channel from steps 1-4 over 80 ECMWF profiles.

15

Paired LWIR and LWIR

Ch80Ch81Ch83Ch85Ch87Ch88

Steps 1-2

SWIR Channels Whose Model Level

Difference of WF sure

(hPa

)

Ch88Ch89Ch93Ch95Ch96Ch99Ch101Difference of WF

Peak Is Less than 2 Pres

s Ch102Ch104Ch106Ch107Ch111Ch147

SWIR

Ch148

Ch1170WFs of 19 LWIR (upper

panel) and 13 SWIR

re (h

Pa)

Ch1170Ch1171Ch1172Ch1177Ch1178Ch1179Ch1180

panel) and 13 SWIR channels (lower panel) whose WF peaks are within 150 - 500 hPa

Pres

su

Ch1180Ch1181Ch1187Ch1189Ch1190Ch1239Ch1241

within 150 500 hPa.

WF (hPa-1)

Ch1241

16

Paired LWIR and LWIR

Ch116Ch120Ch123Ch124Ch125Ch126

Steps 1-2

SWIR Channels Whose Model Level

Difference of WF sure

(hPa

)

Ch130Ch132Ch133Ch136Ch137Ch138Ch142Difference of WF

Peak Is Less than 2 Pres

s Ch142Ch143Ch144Ch145Ch151Ch153 Ch165

SWIRWFs of 22 LWIR (upper panel) and 10 SWIR

Ch168Ch216Ch238

re (h

Pa)

panel) and 10 SWIR channels (lower panel) whose WF peaks are within 500 - 800 hPa

Ch1164Ch1165Ch1166

Pres

su

within 500 800 hPa. Ch1166Ch1167Ch1168Ch1169Ch1173Ch1174Ch1175

WF (hPa-1)

Ch1175Ch1242

17

Paired LWIR andLWIR

Steps 1-2

Paired LWIR and SWIR Channels

Whose Model Level Diff f WF su

re (h

Pa) Ch150

Ch154Ch157Ch158Ch159Ch160Difference of WF

Peak Is Less than 2 Pres

s Ch160Ch163Ch164Ch166Ch170

SWIRWFs of 10 LWIR (upper panel) and 10 SWIR

re (h

Pa)

panel) and 10 SWIR channels (lower panel) whose WF peaks are

within 900 - 1000 hPa

Ch155Ch161Ch162Ch171

Pres

su

within 900 1000 hPa. Ch173Ch175Ch208Ch228Ch236Ch667

WF (hPa-1) 18

Steps 3-4RLWIR

RcloudyLWIR Rclear

LWIR

RclearLWIR

Determining Cloud Sensitivity Height

RLWIR Rcloudy

LWIR RclearLWIR

RclearLWIR

RSWIR RSWIR

Sensitivity Measure:RSWIR

RcloudySWIR Rclear

SWIR

RclearLWIR

Thresholds:

RSWIR Rcloudy

SWIR RclearSWIR

RclearLWIRRLWIR

cloud sensitive heigh 0.01, RSWIR

cloud sensitive height 0.1

Pa)

Peak W

Pres

sure

(hP W

F

19A total of 14 LWIR (solid) and 12 SWIR (dashed) channels whose peak WF is above 500 hPa

RLWIR (solid) and RSWIR (dashed)

Selecting the SWIR Channel that has the S ll t Std f BT

Step 5

Smallest Std. of BTsne

ls (K

)

SWIR

SWIR

Cha

nnW

avenun

LWIR

& S um

ber (cm-1

MSD

bet

wee

n 1)

LWIR

RM

Channel Number

20

1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 19 Pairs:

19 LWIR/ SWIR Pairs and an Example Scatter Plot for a Pair

Pair 412

) BT

(K)

34567

ress

ure

(hPa

)

SWIR

B FOR1 or 303 or 285 or 267 or 249 or 22

89101112

Pr 9 or 2211 or 2013 or 1815 or 16

1314151617

Scatter plots of CRTM-simulated brightness temperature with input from 80 ECMWF

LWIR BT (K)1819

21

LWIR SWIR

temperature with input from 80 ECMWF profiles with six zenith angles (0 o, 36.87o,

48.19 o, 55.15 o, 60.0 o, and 63.61o).

A New Cloud Index for CrIS DA QC Using CrIS Double CO2 Bands

A linear regression is established between the paired CrIS SWIR and LWIR channels:

Tb,SWIRregression Tb,LWIR

obs

JJ

where the regression coefficients and are obtained by minimizing the following cost function

min J( i , i ) Tb,SWIRregression (i, j)Tb,SWIR

CRTM (i, j) 2

j1

JJ

(Clear pixels)

An empirical cloud emission and scattering index (CESI) is defined for cloud detection at various altitudes

22

obsb,SW

regb,SW TTCESI

Relationship between Double CO2 Channels in Clear Sky

229 hP 280 hP 321 hPa

T (K

)

229 hPa 280 hPa 321 hPa

SWIR

BT

469 hPa 790 hPa 972 hPa

T (K

)

469 hPa 790 hPa 972 hPa

FOR

SWIR

B 1 or 303 or 285 or 267 or 249 or 2211 or 20

23LWIR BT (K) LWIR BT (K) LWIR BT (K)

11 or 2013 or 1815 or 16

Regression Coefficients for 19 Pairs

Mean over 30 FORsMean over 30 FORs

g

Mean over 30 FORs

PairPair

CrIS FORCrIS FOR

0.9 1.0 1.1 1.2 1.3 1.4 -90 -75 -60 -45 -30 -15 0 15 30

24

The regression coefficients and for the 30 FORs of the 19 pairs show not only strong channel dependence but also weak scan angle dependence.

Brightness Temperatures for Paired LWIR/SWIR Ch l ( 310 hP )Channels (~310 hPa)

LWIR channel SWIR channel

215 220 225 230 (K) 220 225 230 235 240 245 (K)

The depression in brightness temperature seems to be more widespread in the

25

The depression in brightness temperature seems to be more widespread in the SWIR channel than in the LWIR channel.

Validation of CESI by GOES Cloud Products

Reflectance of VIS Channel Cloud Types Cloud Top Pressure

(K) (K)

fog water scwt op-ice cirrus overlap oversht 230 375 520 655 800 945 (hPa)0.03 0.12 0.21 0.30 0.39 0.4 0.57 0.66

CESI at 310 hPa CESI at 469 hPa

(K) 26

(K)

Summary and Conclusions

• Assimilation of CrIS radiance in GSI requires improved quality control of thin cirrus clouds

• Some degradation may be associated with an inadequate quality• Some degradation may be associated with an inadequate quality control of thin cirrus clouds, resulting taking some cloudy radiance data affected by thin cirrus clouds as clear-sky radiances

• Cirrus cloud microphysical parameters have strong impacts on CrISspectral radiances. IWP and particle size are sensitive parameters in forward simulationsforward simulations

• A pairing of CrIS CO2 channels between LWIR and SWIR bands can resolve the cirrus clouds due to their differential responses

• A new CESI is developed to detect the vertical distribution of non-opaque clouds

• Spatial distribution of thin cirrus detected by CrIS CESI is• Spatial distribution of thin cirrus detected by CrIS CESI is consistent with GOES derived cloud products

27

Future Work• Collocate CrIS data with CALIPSO and VIIRS for validation of CESI and

understanding of the GSI QC performance of cloudy radiance• Extend the current work for the normal spectrum resolution (NSR) to the full p ( )

spectrum resolution (FSR) SDR data, which allow for more paired channels and higher vertical resolutions of detected clouds

• Assimilate CrIS NSR and/or FSR radiances in HWRF for improved CrISpdata assimilation and hurricane forecasts

SNPP CrIS Full vs. Normal Resolution SDRs

BandSpectral Range

(cm-1)Number of

ChannelSpectral

Resolution (cm-1)

LWIR 650 to 1095 713 0.625

MWIR 1210 to 1750 433 (865) 1.25 (0.625)

SWIR 2155 to 2550 159 (633) 2.5 (0.625)

28