bsrn 2002 regina 28.-31. may aerosol optical depth with pfr instruments in gaw trial network...

BSRN 2002 Regina 28.-31. MayAerosol Optical Depth

with PFR instruments in

GAW Trial NetworkChristoph Wehrli

Physikalisch-Meteorologisches ObservatoriumDorfstrasse 33, 7260 Davos Dorf, Switzerland

•Goals of trial network•State of the network•Calibration scheme•Data processing approach•Results from selected stations•Comparison with other data

BSRN 2002 Regina 28.-31. May

GAW/WORCC trial network

Subsequent to the AOD fiasco in BAPMon, WORCC was proposed and established in 1996 at Davos, sponsored by Switzerland.

Goals• Implement AOD measurements at 12 global

observatories with new instrumentation, sound calibration, data quality control and protocols.

• Test and verify new instruments and methods under operational network conditions.

• Train station operators in AOD measurements.

WORCC is assisted by a international group of experts and works in cooperation with GAW QA/SAC SAG/Aerosols assumes these roles.

WMO initiated contacts between potential stations and WORCC for placement of instruments donated by MeteoSwiss. Host stations are to provide tracking facility and limited manpower.


State of trial network

1. Hohenpeissenberg, Germany, Jun.19992. Mace Head, Ireland, Jul. 19993. Boulder, USA, Aug. – Oct. 1999

Mauna Loa, Ha, USA, Nov. 1999 (Aeronet)4. Bratt‘s Lake, Canada, Apr.2001 (BSRN, Aeronet)5. Izaña, Spain, Jun. 20016. Ryori, Japan, Jun. 20017. Alice Springs, Australia, Jul. 2001 (BSRN)8. Ny Ålesund, Norway, Apr. 2002 (BSRN)9. Irkutsk, Russia

10. Bukit Koto Tobang, Indonesia

11. Brazil ? (Acre | Manaos)

12. Africa ? (Lamto)

Jungfraujoch, Switzerland, Mar. since 1999 (CHARM)Davos, Switzerland, Nov. 1998 – Nov. 2000


Precision Filter Radiometer

PFR specifications• Automated, solar spectral radiometer• 4 WMO channels at 862, 500, 412, 368nm

using IAD interference filters• Field of View: ±2.5° , slope angle 0.7°• Dimensions: Ø90 x L300mm, Mass 3 kg• Sensor at 20±0.1°C in range –25 ÷ 35°C

internal shutter; N2 purged, airtight housing• High cadence (2 or 1 min.) measurements• Data logger with 30 day storage capacity, built-

in pressure and pointing sensors

PFR N21 at Ryori, Japan.


WORCC Calibration Hierarchy

• Standard instruments are calibrated at high altitude stations (Jungfraujoch, Mauna Loa) by atmospheric extrapolation methods.

• Working standards are calibrated by com-parison with WORCC standards at Davos or Jungfraujoch.

• Stability of standard instruments is moni-tored by spectral comparison with a metro-logically traceable absolute detector.

• Station instruments are linked to WORCC reference by travelling standards or ex-change of sensors.

• Performance is tested through intercom-parison of field instruments with other co-located networks.


Stratospheric Balloon Flight

• Verification of Langley method by in situ measurements from SIMBA balloon flight in Oct.98

• PFR N01 measurements at 40 km height. Atmospheric transmission corrected by MODTRAN calculation

• PFR N02 mean of 19 refined Langley calibrations, obtained in Dec. 98 and Jan.99 at Jungfraujoch (3580m)

• Comparison between N01 and N02 found agreement to < 1%

• Langley calibration V0 are con-sistently higher than balloon.


High Altitude Calibration

Sphinx Research Station at Jungfraujoch

Altitude 3580mLatitude 46°32’55” NLongitude 7°59’11” EFully automated domeOperation of 4 PFRs

Jan00 Jan013.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

4.0

4.1

4.2Langley history N24

Date

V0 [

V]

Wavelength : 368 412 500 862 [nm]Langley Vo : 4.009 3.651 3.802 3.505 [V]Stdev Vo : 0.004 0.007 0.007 0.009 [V]Slope/year : -0.00 -0.39 -0.88 -0.52 [%]±Slope : 0.18 0.14 0.14 0.09 [%]


Radiometric Calibration

Spectral irradiance scale based on cryogenic radiometer of PTB (Berlin) transferred via calibrated trap detector (uncertainty <5•10-4)

400 500 600 700 800 90010

-2

100

102

104

Wavelength / nm

Re

sp

on

siv

ity

/ (

V/W

)

PFR radiometric response

Trap Calibration History PFR-N01

0.98

0.99

1.00

1.01

1.02

Jul-98 Jan-99 Aug-99 Feb-00 Sep-00 Mrz-01 Okt-01 Mai-02

Rat

io to

Mea

n(ca

l 3..8

)

Stdeviation <0.33% (0.5%)Annual drift <(0.6±3)•10-3

Bandpass integral deter-mined every 6 months.

Instrument N01 is assumed to be radiometrically stable to <±0.5%

Solar calibration V0 could be determined if an accurate extraterrestrial spectrum was available.


Operations & data processing

• At GAW stations– Periodic download from logger to local PC– Periodic maintenance (cleaning, pointing, clock)– External provision of ancillary data (O3, meteo)– Production of Level2 data, quality control– Upload to WORCC by mail or ftp

• At WORCC– Monthly archive updates– Monthly overview summaries and tests– Production of AOD files

• At WDCA undefined yet


Data Products, Quality control and

ArchivesProducts

• Level1: bulk raw measurements, 1m cadence.

• Level2: daily files in standardized format.• Level3: daily files of derived AOD, 2

releases.

Quality control• Quality flags added to Level2 data on-site

with warning/error messages during processing.

• Preliminary Level3.1 data generated assuming constant calibration.

• Final Level3.2 after assessment of calibration by travelling standard and evtl. re-processing.

Archives and data volume• Level1: GAW-GO, WORCC

~3.5MB/month• Level2: GAW-GO, WORCC <128kB/day• Level3: WORCC WDCA <20kB/day

GAW-GO WDCA (final network)


Level2 Data format• Self-contained daily ASCII files

• Header with keyword = parameter set

• Generated by standardized software

%STATION =MaunaLoa %LATITUDE = 19.5330 %North%LONGITUDE =155.5780 %West%ALTITUDE = 3397.0 %above sea level%ZONE = 0 %UTC=logger time - Zone%STATIDENT = 11%DATE =2000 8 10 %date containing solar noon%AIRPRESS = 666.7 %average Sun above horizon%AIRTEMP = 23.8 %instrument body%OZONE = 277.3 %climatological or actual DU%INSTRUMENT=PFR-N27 %INSTIDENT = 27%NCHANNELS = 4%NREADINGS =1439 %actual number of records%WAVELENGTH= 862.4 501.2 412.0 367.6 %nominal or measured%CALDATE =1999 12 27 %recalibrated at MLO%CALIBRAT = 3.4640 3.8140 3.8070 4.1030 %Extraterrestrial signal%SLOPE = +0.072 +0.050 -0.151 +0.117 %mV per day since CALDATE%O3ABS = 0.0024 0.0340 0.0002 0.0000 %Gueymard, filter averaged%RAYLSCATT = 0.0157 0.1420 0.3186 0.5128 %Bodhain at WAVELENGTH%SUNEARTH = 1.013466 %%DECLINAT = 15.11215%EQOFTIME = 6.882%NOON = 22.487%LOGFILE =H:\WORCC\PFR\MaunaLoa\mlo_n27.LOG%VERSION = 2.80%COMMENT =for column description, see PFRLEV2.HLP%END % UTC SunElv Barom 862 500 412 368 Tsens Tbody PntgV PntgH Flg 17.0000 12.513 666.2 3.2552 2.2998 1.3813 0.8234 20.49 16.11 -5.71 -7.62 0 17.0167 12.744 666.2 3.2598 2.3206 1.4054 0.8460 20.49 16.16 -5.66 -7.59 0 17.0333 12.974 666.1 3.2614 2.3376 1.4279 0.8682 20.49 16.24 -5.73 -7.57 0 17.0500 13.205 666.0 3.2687 2.3592 1.4522 0.8913 20.49 16.29 -5.73 -7.59 0 17.0667 13.435 666.1 3.2739 2.3792 1.4753 0.9146 20.49 16.37 -5.72 -7.55 0 17.0833 13.666 666.2 3.2768 2.3970 1.4984 0.9365 20.49 16.42 -5.77 -7.54 0 17.1000 13.897 666.2 3.2794 2.4140 1.5202 0.9578 20.49 16.50 -5.79 -7.54 0 17.1167 14.128 666.3 3.2809 2.4301 1.5411 0.9794 20.49 16.55 -5.84 -7.54 0 17.1333 14.358 666.2 3.2832 2.4457 1.5626 1.0002 20.49 16.62 -5.88 -7.51 0 17.1500 14.589 666.3 3.2859 2.4614 1.5819 1.0208 20.49 16.68 -5.87 -7.49 0 17.1667 14.820 666.3 3.2911 2.4806 1.6041 1.0432 20.49 16.75 -5.92 -7.46 0 17.1833 15.051 666.3 3.2933 2.4956 1.6246 1.0639 20.49 16.81 -5.93 -7.47 0 17.2000 15.282 666.2 3.2960 2.5105 1.6429 1.0842 20.49 16.86 -5.99 -7.47 0 17.2167 15.514 666.2 3.2971 2.5246 1.6628 1.1044 20.49 16.94 -6.02 -7.40 0 17.2333 15.745 666.3 3.3008 2.5399 1.6827 1.1256 20.49 17.01 -5.98 -7.42 0 17.2500 15.976 666.3 3.3044 2.5541 1.7018 1.1454 20.49 17.07 -6.06 -7.38 0 17.2667 16.207 666.1 3.3050 2.5667 1.7193 1.1645 20.49 17.15 -6.07 -7.38 0 17.2833 16.439 666.3 3.3062 2.5807 1.7371 1.1842 20.49 17.20 -6.05 -7.34 0 17.3000 16.670 666.3 3.3105 2.5960 1.7562 1.2041 20.49 17.27 -6.11 -7.36 0


Cloud Filtering

Cloud flags for individual high cadence samples1. Harrison & Michalsky algorithm, modified for air

masses <22. Aeronet algorithm applied as moving filter on

continuous samples3. Optically thick (OD>3) clouds

6 8 10 12 14 160.0

0.5

1.0

1.5

2.0

2.5

3.0

Time [GMT]

Sig

na

l [V

]

Eithe r H a rris onSm irnovC le a rs ky


Instrument health control

-30 -20 -10 0 10 20 30-30

-20

-10

0

10

20

30Pointing

arcminutes -30 -20 -10 0 10 20-15

-10

-5

0

5

10

15

T(body-head)

Pe

ltie

r p

ow

er

0 10 20 30

870

880

890

900

910

920

930

940

Day

atm

. p

res

su

re [

hP

a]

HK-Overview HPB N06 for APR02

Date: 23-May-2002 ChWFile: monthlyHK2.m

Mean pointing : 12.2± 8.5 [arcmin]

Peltier cntrl :-0.505*dT -0.37 [W] Mean pressure : 902.2± 7.9 [hPa] Temperature :Thd= 20.5±0.0; Tbd= 10.2± 3.8; Tlg= 34.0± 0.6; [°C]

0 10 20 30

-20

-10

0

10

20

30

40

Day

Te

mp

era

ture

s [

°C]


Bratt’s Lake

Apr01 Jul01 Oct01 Jan02 Apr02 Jul020.00

0.10

0.20

0.30

Date

AO

D 5

00

nm

0 0.05 0.1 0.15 0.2 0.250

10

20

30

40

50

60

70

AOD 500nm

Nu

mb

er

of

ca

se

s

AOD summary REG-N23

Date: 24-May-2002 ChWfile: AODstat2.m

272 selected clear days

Avg( ) =0.089±0.055; Median( )=0.072 Avg( ) =1.24 ±0.368; Median( )= 1.31

Gmean( )=0.075*1.8± 1

Filter: >0 & <0.3 & 0.00< <0.29

0 0.1 0.2 0.30

0.5

1

1.5

2

2.5

3

AOD 500nm

Ån

gs

trö

m


Hohenpeissenberg

Jan99 Jan00 Jan01 Jan020.00

0.05

0.10

0.15

0.20

0.25

0.30

Date

AO

D 5

00

nm

0 0.1 0.2 0.30

10

20

30

40

50

60

AOD 500nm

Nu

mb

er

of

ca

se

s

AOD summary HPB-N06




Gmean( )=0.084*2.0± 1

Filter: >0 & <0.3 & 0.00< <0.31

0 0.1 0.2 0.30

0.5

1

1.5

2

2.5

3

AOD 500nm

Ån

gs

trö

m


Sahara Dust event

6 8 10 12 14 160.00

0.20

0.40

0.60

0.80

AO

D &

Ån

gs

trö

m

VBGR: 367.6 412.1 501.0 863.1 nm

HOHENPEISSENBERG PFR-N06 06-Jul-2001

Date: 24-May-2002 ChWFile: AerosolOD2.m; opt=2

Wl: 368 412 501 863 nm

V0: 4.218 3.825 3.837 3.370 V

<AOD>: 0.498 0.460 0.399 0.284 < >= 0.970, < >=0.2600press: 902.9 hPa; Ozone: 327.9 DU

6 8 10 12 14 16

0.5

1

1.5

2

2.5

Ån

gs

trö

m

Time [GMT]


Mace Head

Jan01 Apr01 Jul01 Oct01 Jan02 Apr020.00

0.05

0.10

0.15

0.20

0.25

0.30

Date

AO

D 5

00

nm

0 0.1 0.2 0.30

10

20

30

40

50

60

AOD 500nm

Nu

mb

er

of

ca

se

s

AOD summary MHD-N02




Gmean( )=0.110*1.6± 1

Filter: >0 & <0.3 & 0.00< <0.31

0 0.1 0.2 0.30

0.5

1

1.5

2

2.5

3

AOD 500nm

Ån

gs

trö

m


MLO Comparison 2000

Methodology

• AERONET/CIMEL and WORCC/PFR data compared at individual samples level

• Aeronet Level2 data†as published on web• WORCC/PFR with interpolated calibration

• CIMEL channels are interpolated to WMO wavelengths of PFR by Ångström’s law

• PFR one minute samples are interpolated in time to CIMEL observation scheme

• Data gap in PFR from late May to early July

† with kind permission of Dr. Brent Holben, Aeronet PI, NASA/GSFC

BSRN 2002 Regina 28.-31. MayMLO Comparison 2000

Aerosol Optical Depths

0 0.05 0.1 0.150

0.05

0.1

CIM

EL

0 0.02 0.04 0.06 0.08 0.10

0.02

0.04

0.06

0.08

0.1

0 0.02 0.04 0.06 0.08 0.10

0.02

0.04

0.06

0.08

0.1

CIM

EL

PFR

Date: 23-May-2002 ChWuse of Aeronet data kindly permitted by Brent Holben, NASA/GSFC

Wavelength : 367.6 412.0 501.2 862.4

Mean slope : 1.0941 1.1056 1.0678 1.0531Mean bias : -0.0002 0.0001 -0.0005 0.0002RMS diff. : 0.0055 0.0043 0.0030 0.0026N = 4705

0 0.02 0.04 0.06 0.08 0.10

0.02

0.04

0.06

0.08

0.1

PFR


MLO Comparison 2000 Ångström α

Q1-00 Q2-00 Q3-00 Q4-00 Q1-010.0

1.0

2.0

3.0

4.0

5.0

Ån

gs

trö

m

green: Aeronet; black: GAWnet

0 1 2 3 40

0.5

1

1.5

2

2.5

3

3.5

4Ångström

PFR

Cim

el

Date: 23-May-2002 ChWuse of Aeronet data kindly permitted by Brent Holben, NASA/GSFC

Alpha PFR :1.63±0.26

Alpha Cimel :1.69±0.46; Aeronet 1.83±0.30(2000)Aeronet :1.66±0.24; (climatological)

0 0.05 0.1 0.15 0.20

0.5

1

1.5

2

2.5

3

3.5

4

AOD500

Ån

gs

trö

m

bsrn 2002 regina 28.-31. may aerosol optical depth with pfr instruments in gaw trial network...

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