Hello Everyone. This is a brief informal update of the AERONET activities and developments over the last several months combined with the FY99 annual summary. I’ve added a large number of recipients. If you want your name deleted or someone added to the mailing list please contact Laura East (least@pop900.gsfc.nasa.gov).

Figure 1. (a & b) Bldg. 33, GSFC, construction on the AERONET calibration platform,. (c)The existing platform with AERONET instruments (lower level) and the new platform with benches (upper level).

The international channels have been issued which allows satellite transmission through GMS, GOES and METEOSAT. ID #’s will be coordinated through Luc Blarel (blarel@loa.univ-lille1.fr) for the METEOSAT footprint and Ilya Slutsker (ilya@spamer.gsfc.nasa.gov) for the GOES and GMS footprints. We are just working this system out so we may run into some glitches.

In anticipation of a late July launch of TERRA (now Dec. 16) and various collaborative efforts, we substantially increased our site list including Moldova, S. Korea, Dead Sea, Buenos Aires and Cordoba, Argentina, 3 additional sites in the Amazon basin, Paris, Bandi Bish, UK, Sopot, Poland, Gotland Sweden, Chesapeake Lighthouse. Several more sites are expected to be established before the launch of TERRA.

The AERONET facility at GSFC is nearly complete with a full horizon calibration platform (Fig. 1 c). Completion is expected by November 25^th. The low sun season has caused calibration and instrument evaluation difficulties due to obstructed sky view from the current platform. Please bear with us until construction is complete. Recalibration of field instruments depending on weather is completed in about two weeks. New instrument turnaround is ~6 weeks.

The new Dubovik inversion retrievals now include particle size distribution (including coarse, and fine mode analysis), wavelength dependent complex index of refraction and SSA, phase function, and asymmetry factor are available on the AERONET homepage under 'O Dubovik inversion'. The detailed description of the retrieval algorithms are summarized in the manuscript by Dubovik and King (available on the AERONET homepage). In addition, the sensitivity of the inversion to instrumental offsets, aerosol particle inhomogeneity, nonspeherisity, etc. has been tested. The results of the sensitivity studies are summarized in the manuscript by Dubovik et. al. (available on the AERONET homepage). The Nakajima skyrad.pack size distribution and phase function inversions are still available under 'Nakajima inversion'.

New Cimel software was developed to eliminate ubiquitous cable binding problems. All standard instruments will be upgraded with this software when they are returned for calibration. Polarization upgrades will be available in the near future. New ocean-leaving radiance with sun and sky radiance scenarios is being developed for tower mounted sites. A BRDF version is currently supported for terrestrial tower sites. Complexities of transmitter type and measurement type make this rather complicated at times but your instrument will be automatically upgraded when it is returned to GSFC for calibration and maintenance.

Please remember to remove the Cimel internal battery before shipping an instrument back to us. We have had instruments fry during shipment because the battery is not secure in the control box. Please include the battery pack in the shipment. Please place the sensor head in a clean sealed plastic bag before shipping and don’t touch the windows.

We are replacing all original sensor head cables that are worn. Please let us know if you need a replacement so we can anticipate fabrication requirements (wayne@spamer.gsfc.nasa.gov).

Please return any unused equipment or equipment that has been replaced as soon as possible.

A suggestion box has been added to the homepage. Please add you comments as you see fit on any issue relating to the program.

Calibration/swap out periods have been nominally extended to 9 to 12 months. Several instruments have successfully remained in the field for over 15 months without significant Vo degradation. Tom Eck provides the following analysis on filter stability which will appear in the ‘AERONET climatology paper’:

The stability in time of the Vo values derived from MLO Langley analyses for one of our reference instruments (#101) is shown in Fig. 2. The data in this figure cover the time period of September 30, 1997 to September 11, 1999, a nearly 2 year interval. The filters in use for this instrument and all others in the AERONET network from 1997 onward were ion assisted deposition interference filters. We computed the average yearly change in Vo from a linear regression of Vo versus time for the entire 711 day data record. As depicted in Fig 2, there are varying rates of change for the different wavelengths, ranging from 0.24%/ yr for 870 nm to -3.90%/yr for 675 nm. The change in Vo with time show in general a linear tendency, with the exception of the 940 nm filter. This is due to a much larger uncertainty in Vo determination for the 940 nm channel as a result of water vapor variability at MLO as contrasted with a very stable aerosol environment. The repeatability of morning Langley derived values of Vo for aerosol channels at MLO, from typically 5 to 15 mornings, is excellent with a coefficient of variability (standard deviation/mean) averaging only 0.3-0.5% while the value for the 940 nm channel averages 2.2%.

Figure 2 Vo stability for reference instrument 101 for two years of continuous operation with BARR IAD filters

In addition, the newest batch of 340 nm filters from Barr exhibit rapid degradation in Vo, on the order of 3-4% per month. We are not installing these in any more instruments but some field sites have these filters and thus will not have usable data for this wavelength.

Ilya Slutsker has completed extensive testing and elimination of all Y2K bugs in the AERONET processing software. Testing of the cimel software showed it to be bug free.

Several instruments have been incorrectly processed assuming an erroneous elevation resulting in excessive Rayleigh optical depth corrections and so far undetermined perturbations in the Dubovik retrievals. The sites include Sede Boker, Banizoumbo, and Creteil (Paris). The data have been or are being reprocessed. We are currently checking all instrument coordinates but please check this before you use any data. Please notify Ilya (ilya@spamer.gsfc.nasa.gov) if you spot an error. I apologize for this problem.

Anne Vermeulen has officially joined the program specifically to work on polarization issues including an instrument/data quality status and development of inversion products. Anne will work closely with Oleg Dubovik. Polarization has been largely ignored on this side of the lake so Anne’s presence will help bring ~ 30% of the data base into greater use.

Data base Quality Assurance: Currently we have two types of data sets A) Real time prefield calibration applied no cloud screening or QA; and after an instrument is returned a pre and post field calibration but no cloud screening or QA ; B) Level II Pre and post field calibration applied and manually evaluated plus automatic cloud screening and QA. : Alexander Smirnov has raised all historic data sets to level II status. We are considering offering a cloud screened data set that does not meet the level II QA criteria.

International agreements are currently being developed with collaborators in Morocco, Taiwan, S. Korea, Singapore, Botswana, Namibia and Australia. These agreements are necessary for NASA equipment to be installed in any country. Approximately 25 agreements have been completed to date. Agreements are not necessary for non-NASA instruments.

PHOTON (Didier Tanre): The CNRS/CNES/Lille PHOTON network operates approximately 15 instruments in Europe, W. Africa and N. America. Didier Tanre heads the program which has emphasized the polarization instruments for validation of the Polder instrument products. A complete renovation and recalibration last year and early this year created long data gaps however redeployment this year has provided overall higher quality data. Increased support has added Luc Blarel to the staff, including Bernadette Chatenet and F. Lavenu. A field experiment was conducted during the summer for monitoring urban pollution in Paris. A lidar was deployed in conjuction with a sunphotometer (collaborative effort with LMD, Laboratoire de Meteorologie dynamique, in Paris). In addition, one instrument was operating in Puy de Dôme at an altitude of 1600m for studying aerosols in the 'free troposphere' (collaborative effort with LAMP, Laboratoire de Meteorologie Physique, in Clermont-Ferrand)

A fair amount of effort was put into improving the AEROCAN "duty cycle" during the summer and the results indicate a significant increase in database size and more importantly in data quality at virtually all stations. From 1997 to 1999 the average number of (non-cloud screened) optical depth summer time spectra measured / day / station increased from about 6.7 to 7.5 to 9.1 (12% from 1997 to 1998 and 21% from 1998 to 1999). More importantly we feel that the data quality, a somewhat more difficult parameter to quantify increased substantially. The current sites are Saturn Island B.C., Bratt's Lake, Saskatchewan, Egbert, Ontario, Sherbrooke, Québec, and Kajimkujik, Nova Scotia. Thompson Manitoba and Waskesiu Saskatchewan are AERONET sites which are "on loan" to AEROCAN but which are still ably monitored by AERONET staff. Just recently the last sunphotometer was installed at Churchill Manitoba (on the shore of Hudson's Bay). For a variety of birthing pain reasons (including polar bears running interference) this instrument has yet to make any measurements.

Recently the AEROCAN network was awarded a three year "extension" via a grant from NSERC (the Canadian equivalent to the NSF). Alain Royer put a proposal together with the help of Norm O’Neill and Phil Teillet; it is Norm's considered opinion that AERONET's reputation, support and years of in kind help most likely had a direct influence on the decision of the evaluation committee). This award gave some impetus to an idea that has been kicking around about the expansion of AEROCAN to St. Anicet Québec and Alert N.W.T. (the latter site, on Ellesmere Island is the "most northern permanently inhabited settlement in the world." see http://webhome.idirect.com/~jbuchan/cfs/index.html). However the financing is not in place for this yet.

A network of 12 ocean color instruments were purchased and hardened for the marine environment in support of ocean color calibration and validation. The hardening process was not without problems but has resulted in 10 island or coastal sites including Wallops Island VA; Amynom, Island S. Korea; Enstitusu Turkey, Tahiti; Lanai, Hawaii; Ascension Island; Azores and Perth Australia (waiting on agreement) and Patagonia, Argentina (?). Two instrument will be used for swapouts.

COLORS (Giuseppe Zibordi): The ocean color program supports Venice and JRC in Italy and is due to expand by 4 to North Sea sites. A new downward looking protocol is under consideration.

DOE/ARM (Rangasayi N. Halthore): Three sites are supported: Southern Great Plains Cart Site OK, Nauru S. Pacific and Barrow AK. All sites are heavily instrumented with flux sensors and lidars.

LTER (John Vande Castle): This is a well functioning network of 4/5 US sites: Sevietta, NM, Bonanza Creek, AK, , HJ Andrews, OR, USA and Chalengua, WI, USA. A fifth site at Oyster VA is operated in federation with PHOTON. During the Antarctic summer the LTER support an instrument in the Dry Vallies.

CONAE (Ida Nollmann): Argentine Space Agency collaboration with AERONET for Buenos Aires and Cordoba with possible Simbios collaboration. CONAE enthusiastically embraced the program and has plans for 2 CONAE instruments.

INPE/USP/NASA-LBA (Holben): 5 instruments established in Brazilian Amazon basin. USP to establish 4 additional sites in Brazil.

Univ of Wits/RSA (Harold Annagarn): Coordination of southern. Africa network. 2 sites established in RSA. 6 expected in region prior to SAFARI campaign.

Many other organizations and collaborators are participating in this program that will not be mentioned in this report. I’d like to express my thanks to all those who have joined this effort to make AERONET a globally distributed network. Certainly NASA scientists and individual PIs have benefited from their individual measurements. I think more importantly the experiment that is a federation and open data archive has proved a huge benefit to the scientific community. A special thanks goes to Michael King and Bob Curran for supporting the AERONET portion of the program through this rapid growth phase and to Diane Wickland for providing the initial support for the project in 1991. As always thanks to the AERONET staff which actually does the work and produces the products and the following research papers.

Christopher, S.A., X. Li, R.M. Welsh, J.S. Reid, P.V. Hobbs, T.F. Eck, B.N. Holben, Estimation of surface and top-of-atmosphere shortwave irradiance in biomes burning regions during SCAR-B, Journal of Applied Meteorology, in press, 1999.

Dubovik, O., B.N. Holben, Y. J. Kaufman, M. Yamasoe, A. Smirnov, D. Tanré, I. Slutsker, "Single-scattering albedo of smoke retrieved from the sky radiance and solar transmittance measured from ground", J. Geophys. Res., 103, 31903- 31924, 1998.

Dubovik, O.and M.D.King, A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements, submitted to J. Geophys. Res.

Dubovik, O., A.Smirnov, B.N.Holben, M.D.King, Y.J. Kaufman, T.F.Eck, and I.Slutsker, Accuracy assessments of aerosol optical properties retrieved from AERONET Sun and sky-radiance measurements, submitted to J. Geophys. Res

Eck T.F., B.N. Holben, J.S. Reid, O. Dubovik, A. Smirnov, N.T. O'Neill, I. Slutsker, and S. Kinne, Wavelength Dependence of the Optical Depth of Biomass Burning, Urban, and Desert Dust Aerosols, Journal of Geophysical Research, in press, 1999.

Eck, T.F., B. N. Holben, I. Slutsker, and A. Setzer, Measurements of Irradiance Attenuation and Estimation of Aerosol Single Scattering Albedo for Biomass Burning Aerosols in Amazonia, Journal of Geophysical Research, 103, 31865-31878, 1998.

Ferrare, R., S.Ismail, E.Browell, V.Brackett, M.Clayton, S.Kooi, S.H.Melfi, D.Whiteman, G.Schwemmer, K.Evans, P.Russell, J.Livingston, B.Schmid, B.Holben, L.Remer, A.Smirnov, and P.Hobbs, Comparison of aerosol optical properties and water vapor among ground and airborne lidars and sun photometers during TARFOX, Journal of Geophysical Research, 1999 (accepted).

Hsu, N.C., J.R. Herman, O. Torres, B.N. Holben, D. Tanré, T.F. Eck, A. Smirnov, B. Chatenet, and F. Lavenu, Comparisons of the TOMS Aerosol Index with Sun-photometer Aerosol Optical Thickness: Results and Applications, Journal of Geophysical Research, 104, 6269-6279, 1999.

O'Neill, N. T., Eck, T. F., Holben, B. N., Smirnov, A., Dubovik, O., A. Royer, (1999), Uni and bi-modal size distribution influences on the variation of Angstrom derivatives in spectral and optical depth space, (submitted to JGR).

Reid, J.S., P.V. Hobbs, C. Liousse, J. Vanderlei Martins, R.E. Weiss, and T.F. Eck. Comparisons of Techniques for Measuring Shortwave Absorption and the Black Carbon Content of Biomass-Burning Aerosols", Journal of Geophysical Research, 103, 32031-32040, 1998.

Reid, J.S., T.F. Eck, S.A. Christopher, P.V. Hobbs, and B.N. Holben, Use of the Angstrom Exponent to Estimate the Variability of Optical and Physical Properties of Aging Smoke Particles in Brazil", Journal of Geophysical Research, in press, 1999.

Romanov, P., O'Neill, N. T., Royer, A., McArthur, B., (1999), Simultaneous Retrieval of Aerosol Refractive Index and Particle Size Distribution from Ground Based Measurements of Direct and Scattered Radiation (Applied Optics, accepted for publication).

Schmid, B., J. Michalsky, R. Halthore, M. Beauharnois, L. Harrison, J. Livingston, P. Russell, B. Holben, T. Eck, and A. Smirnov, Comparison of aerosol optical depth from four solar radiometers during the Fall 1997 ARM intensive observation period, Geophysical Research Letters, 26, 2725-2728. 1999.

Smirnov A., B.N.Holben, T.F.Eck, O.Dubovik, I.Slutsker, Cloud screening and quality control algorithms for the AERONET data base, Remote Sensing of Environment, 1999 (resubmitted).

Smirnov, A., B.N.Holben, O.Dubovik, N.T.O'Neill, L.A.Remer, T.F.Eck, I.Slutsker, and D.Savoie, Measurement of atmospheric optical parameters on US Atlantic coast sites, ships and Bermuda during TARFOX, Journal of Geophysical Research, 1999 (accepted).

Tanré D., L.R.Remer, Y.J.Kaufman, S.Mattoo, P.V.Hobbs, J.M.Livingston, P.B.Russell, and A.Smirnov, Retrieval of aerosol optical thickness and size distribution over ocean from the MODIS airborne simulator during TARFOX, Journal of Geophysical Research, 104, 2261-2278, 1999.

Tarasova, T.A., C.A. Nobre, B.N. Holben, T.F. Eck, and A. Setzer, Assessment of smoke aerosol impact on surface solar irradiance measured in the Rondonia region of Brazil during Smoke, Clouds, and Radiation - Brazil, Journal of Geophysical Research, 104, 19161-19170, 1999.

Welton, E.J., K.J.Voss, H.R.Gordon, H.Maring, A.Smirnov, B.N.Holben, B.Schmid, J.M.Livingston, P.B.Russell, P.A.Durkee, P.Formenti, and M.O.Andreae, Ground-based lidar measurements of aerosols during ACE-2: instrument description, results, and comparisons with other ground-based and airborne measurements, Tellus, 2000 (accepted).

Yamasoe, M.A., Y.J. Kaufman, O. Dubovik, L.A. Remer, B.N. Holben and P. Artaxo, "Retrieval of the real part of the refractive index of aerosols from sun/sky radiometers during SCAR-B", J. Geophys. Res., 103, 31893-31902, 1998.