1. GAW2005 Workshop, Geneva, 14.-16. March 2005 Christoph Wehrli Physikalisch-Meteorologisches Observatorium Dorfstrasse 33, 7260 Davos Dorf, Switzerland WORCC tasks assigned in 1995: Development of a radiometric reference for Sunphotometry Development of new instrumentation, algorithms and QC/QA Implementation of a global demonstration network  Summary of global AOD networks World Optical depth Research and Calibration Center, WORCC

2. GAW2005 Workshop, Geneva, 14.-16. March 2005 Radiometric Calibration of 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% Top_of_Atmosphere calibration V 0 could be determined in laboratory, if an accurate (<1%) extraterrestrial solar spectrum was available.

3. 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

4. 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

5. 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

6. GAW2005 Workshop, Geneva, 14.-16. March 2005 GAWPFR: results 2003 Forest fires SiteAnnual MLO0.022 IZN0.024 JFJ0.030 ASP0.049 NAS0.089 HPB0.104 MHD0.116 BLO0.119 RYO0.208

7. GAW2005 Workshop, Geneva, 14.-16. March 2005 AOD Comparison Results  FRC-I Davos, 2 days, fall 2000 10 radiometers at 7, given calibration2  <0.016  Mauna Loa, 1 year 2000 AERONET – GAWPFR at 4, in-situ cal.U95  0.007,  (  )<0.95  Alice Springs, summer 2000 3+1 radiometers, 2-4, in-situ calibrationU95 0.02)  Bratt’s Lake, summer 2001 5 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.

8. GAW2005 Workshop, Geneva, 14.-16. March 2005 Ground based global AOD Networks “are currently mostly un-coordinated” Latitudinal distribution Polar regions: 4 Midlatitude North:50 Tropics:26 Midlatitude South:10 Total 90 Major data gaps Africa, Asia, India, Polar region and Oceans International: AERONET, BSRN, GAWPFR, SKYNET National: Australia, China, Finland, Germany, Japan, Netherlands, Russia, USA(4)

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