AERONET Quarterly


Tuesday, June 24, 2003

Dear Colleagues:


Welcome to the occasional AERONET Quarterly.  I have three principle issues to present: current calibration status, the new cimel instruments and the status of the Dubovik inversions plus a few other miscellaneous items.



There are approximately 200 instruments in the network maintained at Goddard and Lille/Carpentras, France.  Langley plots are conducted with four reference instruments cycled through Mauna Loa for Goddard and two at Pic du Midi for the Carpentras  intercomparison.    Sky radiance calibration is achieved with factory calibrated Labsphere spheres at Lille and the 6 foot HARDY sphere at Goddard.  The link between the calibrations is made once every 6 months with a transfer calibration instrument referenced to the Goddard standards and intercompared to the Lille spheres.  A tolerance of <3% is acceptable.   If the limit is exceeded, the calibration of the Lille sphere will be adjusted to conform to the Goddard reference and all affected field instrument’s calibration will be adjusted.  To date this has not occurred.  Because Langley plots are absolute and evaluated for MLO and PdM by the same analyst (Tom Eck), no network intercomparisons are required. 


The Tarbes intercomparison site was phased out in favor of Carpentras (44° N, 5° E) which seems to have many more cloud free days.  The calibration effort under the guidance of Damiri Bahaiddin (Bahy) is running very smoothly.  


We are receiving some queries about the slow calibration process  at Goddard.  Clouds and rain (300 mm above normal precip since the beginning of May) this spring has severely limited our ability to provide timely calibration.  We cannot relax our standards in order to get instruments into the field.  The approach is to stage them in order of receipt in preparation for clear calibration weather.  Despite our poor weather there are still 108 instruments operating in the field.  The sun is shining this week!


New Instrument:

Cimel is manufacturing and selling a new extended wavelength model and an upgraded model for the standard CE318-x  sun & sky scanning radiometer used in the network.  The new model CE318-NE is now officially accepted into the network.  Extensive testing and feed back from our staff to Cimel Electronique over the last 10 months helped identify and resolve software and hardware problems and brought it up the our required standards.  Some issues and decisions still remain but we expect to have it operational in July or August.  The primary new feature is a 1.64 mm band added to the standard suite of wavelengths.  Although the instrument looks the same, the additional band has required numerous optical, electronic, firmware, processing software and data archive changes.  The following features and issues are expected:


*  1.64 mm AOT

*  6 wavelength almucantar  and PP:  (380 (?), 440, 500(?), 675, 870, 1020, 1.64)

            380 almucantar/PP is in the test phase

*  1020 AOD w/ temp invariant InGAS detector

*  Monitor external battery voltage

*  A-D converter in sensor head rather than control box

*  4 wavelength and 6 wavelength inversion products

*  New Data base products


So far the polarization version with the 1.64 mm band has not been tested at Goddard.  The upgraded standard (CE-318-NV) and polarization (CE-318-NP) models appear to be fully functional yet we are waiting for clear skies to evaluate their performance before declaring them ready for field use.  Perhaps this week.


The upgraded polarization instruments have the polarizing filters between the detector and the interference filter thus reducing the incident light on the polarizer and hopefully prolonging the life of the filters. We have no data yet to know if this is an improvement.


Note:  Operating a new instrument does not immediately mean having new or improved products.  All former products will be continued and new products will ~follow the schedule in the next section.



Inversions are operationally computed using the 1996 Nakajima Code, the Dubovik spherical model and the new Dubovik spheroid model for almucantars.  PP inversions are currently being processed for the Dubovik spherical and spheroid models; all historical data will be processed by mid July.  Currently only the Nakajima and Dubovik spherical  and spheroid models are available from the AERONET download tool.  A major revision in the website (just made operational, week of June 23) allows the user to download  data from the browser with full access to all data products generated from the models and measurements.


Level 1:  Does not apply to Inversions.


Level 1.5:  Inversions produced from predeployment calibrations using cloud screened AOT data.


Note: Level 1.5 inversions will be post field calibrated if the instruments have been returned for post field calibration.


Level 2 inversion products:  The data have been post field calibrated and cloud screened, inversion screening criteria are applied to raise selected data to ‘Quality Assured’ status.


We’ve examined strategies for Level 2 inversion products all winter and spring for the spherical and spheroid model inversions.  Since the products are a solution to an inversion and because the products represent column integrated values, there is no absolute validation data base to compare our results, thus we must develop strategies that are limited by questionable input data (cloud contamination & viewing geometry for example), residuals between modeled and measured radiances and unrealistic results (ultra fine accumulation  mode during dust events) etc.  The website download tool now (beginning the week of June 23)  has our best determination of quality assured inversion products from almucantars for the spherical and spheroid models.  The screening criteria for Level 2 is available on the ‘Download tool’ under ‘Data Descriptions’.  


The Data base is being upgraded again to accommodate the increased number of products from the various processing models and in anticipation of new processing strategies.  Our best chronological guess for availability through the AERONET website follows:


Nakajima (Level 1.5)-current

Dubovik spherical & spheroid 4 almucantars (Level 1.5 & 2)-Week of June 23

Dubovik spherical & spheroid 4 PP (Level 1.5)-July

% Polarization from  PP @ 870 nm (Level 1.5)-July

Dubovik spherical & spheroid 6 almucantar , 6 PP (Level 1.5)–Sept.

Dubovik spherical & spheroid 6 almucantar UV (Level1.5)-Dec.?



We’ve greatly increased our processing and storage capacity with an SGI Origin 300 workstation that has now (beginning the week of June 23) taken over the processing and web server load. The old AERONET server provides a backup role as well as research number crunching.


Several AERONET sites were co-located to support GLAS validation and a small network of 7 instruments were deployed in Thailand and Vietnam for the spring biomass burning season.  Three instruments remain as permanent sites.


Plans to expand in Russia, Ireland and Africa have been delayed by Goddard’s cloudy spring weather and the long development process of the new instrument.  My apologies to everyone expecting an AERONET site before now.  Given that we are now into the historically poor calibration conditions of summer, it may be fall before we can expect to catch up to our commitments.  The network is still closed to new AEROENT sites in N. and S. America and Europe.  New sites in Asia, Africa, the oceans and high latitudes will be accepted by myself if Goddard resources are required or by Philippe Goloub for PHOTON resources in France.


Dr. Alexander Sinyuk joined the AERONET staff in May and will be working most closely with Oleg Dubovik to develop improved inversions.   In the short term he will be combining almucantar and PP data sets into the retrieval scheme.


Terry Aquino is continuing to improve our photo gallery.  Please notify her of errors and omissions and send in pictures of the site and site managers and PI’s if they are missing.



Considerable research inside and out of AERONET is being conducted using the AERONET data-base.  Much of it will be published in the Safari2000 and Ace Asia special issues.  Eck and Smirnov have highlighted  aerosol characterization (biomass burning, marine aerosols and diurnal variations) and Dubovik radiative forcing and advanced inversions.  Validation continues as an important aspect of the program with particular emphasis on Remer’s MODIS aerosol validation investigation.  Please see the AERONET publication list for the latest papers.  If you see missing papers, errors or omissions in our citations please notify me with the proper reference. 


Staff Contacts:


Brent Holben                              

Tom Eck                                    

Ilya Slutsker                               

Wayne Newcomb                      

Alexander Smirnov                     

Oleg Dubovik                             

Mikhail Sorokine                        

Anne Vermeulen                         

Don Ho                                      

Amy Kley                                   

Dave Giles                                  

Terry Aquino                              

Alexander Sinyuk                       



Philippe, Gouloub                       

Luc Blarel                                   

Thierry  Podvin                           

Damiri  Bahaiddin                       

Francois Lavenu (CESBIO)        

Bernadette Chatenet  (LISA)      



All the best,


Brent Holben