GAW2005 Workshop, Geneva, 14.-16. March 2005

Christoph WehrliPhysikalisch-Meteorologisches ObservatoriumDorfstrasse 33, 7260 Davos Dorf, Switzerland

WORCC tasks assigned in 1995:Development of a radiometric reference for SunphotometryDevelopment of new instrumentation, algorithms and QC/QAImplementation of a global demonstration network

Summary of global AOD networks

World Optical depth Research and Calibration

Center, WORCC

GAW2005 Workshop, Geneva, 14.-16. March 2005

Radiometric Calibrationof WORCC reference standards

• Spectral radiance SI scale based on the cryogenic radiometer of PTB (Berlin), transfer via calibrated trap detector

• Radiometric response of PFR deter-mined every 6 months by spectral comparator facility.

Reference instrument N01 assumed to be radiometrically stable to <±0.5%

Trap Calibration History

0.98

0.99

1.00

1.01

1.02

Jan-99 Jan-00 Dez-00 Dez-01 Jan-03 Jan-04 Dez-04R

ati

o t

o M

ea

n

Top_of_Atmosphere calibration V0 could be determined in laboratory, if an accurate (<1%)

extraterrestrial solar spectrum was available.

GAW2005 Workshop, Geneva, 14.-16. March 2005

Precision Filter Radiometer Network Specifications

Classic sun-pointed filter radiometer, custom built 4 simultaneous channels at 368, 412, 500 and 862nm Thermostatic operation, minimized filter exposition Internal Sun-pointing and pressure sensors for QC 1 minute sampling rate for hourly/daily statistics

Weekly/monthly data transmission, central processing Cloud screening algorithms Data products: AOD, Ångström (no inversions) Continuous in-situ and/or (annual) centralized calibration based on

high altitude reference, linear interpolation in time

GAW2005 Workshop, Geneva, 14.-16. March 2005

GAWPFR: global extent

2004: 9 GAW stations operational, 4 stations pending deployment, 5 additional PFRs operated by FMI, DWD, ETHZ

Mauna Loa

Bukit Kototabang

Tamanrasset

Izaña

Cape Point

Ny Ålesund

Mace Head

Polar Circle

HohenpeissenbergJungfraujoch

Bratts Lake

Ryori

Alice Springs

Waliguan

Sodankylä

Marambio

Summit

Jokioinen

Lindenberg

GAW2005 Workshop, Geneva, 14.-16. March 2005

GAWPFR: temporal extent

6 stations with 4 years at >50% coverage

4 stations with 20% cloud free samples

Data available at WDCA up to 2003

STN Sunshine 1999 2000 2001 2002 2003 2004ASP 44% 9 12 12BLO 24% 8 12 12 10HPB 11% 5 12 12 11 11 12IZN 33% 7 12 12 12JFJ 15% 12 12 12 12 12 12MHD 7% 2 8 12 12 10 12MLO 28% 2 11 12 12 12 12NAS 12% 5 7 6RYO 12% 9 12 12

data months 21 43 63 94 100 100

GAW2005 Workshop, Geneva, 14.-16. March 2005

GAWPFR: results 2003

0.0

0.1

0.2

0.3

0.4

0.5

0.6A

OD

500

Monthly means 2003

Forest fires

Site Annual

MLO 0.022

IZN 0.024

JFJ 0.030

ASP 0.049

NAS 0.089

HPB 0.104

MHD 0.116

BLO 0.119

RYO 0.208

GAW2005 Workshop, Geneva, 14.-16. March 2005

AOD Comparison Results

FRC-I Davos, 2 days, fall 200010 radiometers at 7, given calibration 2<0.016

Mauna Loa, 1 year 2000AERONET – GAWPFR at 4, in-situ cal. U950.007, ()<0.95

Alice Springs, summer 20003+1 radiometers, 2-4, in-situ calibration U95<0.010, (2 instr. >0.02)

Bratt’s Lake, summer 20015 radiometers, 4 networks, 5, given cal. 2<0.010, U95()<0.25

WMO goal of AOD uncertainty <0.02 OD is achieved in routine network operations.

GAW2005 Workshop, Geneva, 14.-16. March 2005Ground based global AOD

Networks“are currently mostly un-coordinated”

Global AOD Network Long-term Sites4+ years in operation, >50% coverage

Total count = 90 GAW PFR SIBRAD SURFRAD/ARM JMA SKYNET BoM AERONET-LT CMDL/STAR DW D

Latitudinal distributionPolar regions: 4Midlatitude North:

50Tropics: 26Midlatitude South:

10Total 90

Major data gapsAfrica, Asia, India, Polar region and Oceans International: AERONET, BSRN, GAWPFR, SKYNET

National: Australia, China, Finland, Germany, Japan, Netherlands, Russia, USA(4)

GAW2005 Workshop, Geneva, 14.-16. March 2005