AERONET Quarterly (Jan-June)

Hello everyone,

I apologize for skipping the March issue but rather than report incomplete activities I’ve waited until we have significant information to share. To summarize, the past six months have been fairly important in the development of the program. We have established the GMS link, as of July 9, 1999, we have included Dubovik’s inversion products on our home page, and we have achieved our goal of over 60 instruments operating reliably in the field before the launch of Terra. Additionally the project moved to a new building, is moving forward with a follow-on instrument, added personnel, and continues to monitor the instrument stability. Following are the details.

GMS-At our behest and with the cooperation of NOAA, Vitel Inc. installed a DCS receive site in Hawaii at the NWS Ohau office in May. It became operational in July. We now are receiving data from two sites Chinhae, S. Korea and Mauna Loa (testing phase). Some minor enhancements will be required over the next two weeks to facilitate operations. The addition of this site allows AERONET to transmit from all locations on the planet with the exception of 78 degrees poleward. East and central Asian, Australian western Pacific and Indian Ocean sites may now easily be part of the AERONET program.

International assignments were approved by the CGMS secretariat and a global frequency is expected in the next month. It is hoped this will relieve pressure on the regional platform ID’s issued by EUMETSAT, NOAA and JMA. Currently no new assignments are possible for METEOSAT which is limiting the networks growth in Europe, Africa and West Asia.

Inversion-Since April, Oleg Dubovik has made his new sun-sky radiance inversion available to project staff for internal review. As of July 1 this approach has been available on the AERONET website: http://aeronet.gsfc.nasa.gov/ and to PI’s using the program "demonstrit" the replacement for "demonstrat". In addition to size distribution, the complex index of refraction, SSA and mode effective radius is also available. The sky rad.pak size distribution and phase function retrievals (Nakajima) are also available. These products will remain as level 1 until we figure out how to quality assure them. Further enhancements will continue with the code and any comments regarding Oleg’s inversion should be directed to him. Oleg has submitted a paper to JGR regarding a sensitivity study on his inversion. Upon receipt of reviewers comments, he will post a draft version on the AERONET homepage. A paper on the theory is also in preparation.

Deployments-At last count there were 58 instruments transmitting quality data to us. The AERONET program has six more planned by mid August, AEROCAN has all six instruments operating with a new seventh planned as polar bear bait for Churchill. Photon has 9 of their 20 deployed in Europe and Africa and Simbios has 5 operating two in transit and three waiting for agreements. The DOE program has three operating and all four LTER instruments are functional. Individual investigators have numerous other sites. Other new sites planned include locations in Singapore, S. Korea, Australia, China, Argentina, Morocco and Russia.

Cimel upgrades-Two significant problems persist with the cimel, poor almucantar performance due to cables binding the robot (usually mornings) and excessive exposure of the 340 nm filter between triplet measurements for standard instruments. Cimel is planning a new measurement protocol making half almucantars and parking the filter wheel between filters. The software is expected in July and will be installed in all instruments during their scheduled calibrations at GSFC.

Operational issues-We find that some site managers are not using the daily status reports they receive. To make them more user fiendly, we will only send out the shorter troubleshooting report that state problems. Please look at this and act on it if you can. If you would like the complete status report please contact Ilya Slutsker: ilya@spamer.gsfc.nasa.gov.

We are developing a troubleshooting page on our website with text and pictures.

We’ve checked the cimel for a Y2K bug and it seems no pesticide is necessary. Ilya plans to have analysis complete and bugs fixed on his processing system and homepage by Sept. 30.

We’ve moved to building 33 and everyone appreciates our new facility. The rooftop space for intercomparisons is marginal at best but is adequate during the high sun summer season. We’re in the queue for a rooftop modification, which will probably not be complete until October or November so we may have difficulty with calibration this fall.

Calibration-Calibration has gone relatively smoothly despite the brute force method of swapping instruments. We’ve been able to relax the six-month swapout schedule for a more flexible 9 to 12 months depending on site and performance of an instrument. Our goal remains to have a QA data base with an AOT accuracy ±0.01 in the visible and near-IR bands and ±0.02 in the UV bands. No accuracy has been established for the inversion products or the polarization.

We have observed rapid degradation of the 670 and 340 filters on some instruments. This is apparent in the real time data but can usually be compensated after the post field calibration. If they are out of spec after the post field calibration, those channels will not be raised to the level 2 data base. The same applies to data that for one reason or another have been compromised in the field by such things as obstructions in the collimator, high or variable dark current values etc.

Reference instrument stability:

 

 

Below are the % changes in Vo calibration coefficients for Cimel #101 from MLO Langleys made Feb. 1999 to May 1999 (~2.5 months):

Vo % change: ((Feb-May)/Feb))*100

1020: -0.36%

870: -0.27%

675: 0.26%

440: 0.92%

500: 0.70%

380: 0.39%

340: -0.13%

940: 1.01%

Negative denotes higher Vo in May. Most channels showed insignificant changes in Vo (similar in magnitude to Vo uncertainty as defined by MLO repeatability). The Vo coefficient of variation of daily Vo values at MLO for the 940 filter was ~3.0%, compared to coefficient of variation for the 7 aerosol channels of ~0.25-0.65%.

 

Below are the % changes in Vo calibration coefficients for Cimel #37 from MLO Langleys made March 1999 to June 1999, ~3 months):

Vo % change: ((Mar-Jun)/Mar))*100

1020: 0.83%

870: 0.52%

675: 0.78%

440: 0.62%

500: 0.89%

380: 0.79%

340: 8.33%

940: -0.55%

Negative denotes higher Vo in June. Most channels showed very small changes in Vo (<1%; similar in magnitude to Vo uncertainty as defined by MLO repeatability). The exception is the 340 nm filter which exhibited very rapid degradation (~8%) within a 3 month period. The direction of change is notable also, since prior 340 nm filter degradation resulted in higher Vo values while the degradation noted here for Mar-Jun 99 shows a sharp decrease in 340 nm Vo value. We changed the 340 nm filter, after collecting some data with the original filter at GSFC.

The Vo coefficient of variation of daily Vo values at MLO for the 940 filter was ~2.5%, compared to coefficient of variation for the 7 aerosol channels of ~0.20-1.07%.

Personnel-Mikhail Sorokin joined the staff in May and will head the development of a prototype follow-on instrument primarily with extended spectral capability. Anne Vermeulen has also joined the staff in support of Oleg’s inversion effort which she will emphasize inversions from polarization measurements.

We continue to participate in field campaigns including INDOEX, EOPACE, LBA, CONVEX, AHDSFM and a variety of EOS validation efforts scheduled for this year and next.

Research-The research staff has managed excellent work despite operational obligations. Norm O’Neill has extended his visiting scientist position for another year and has bolstered our research capability. Additionally the philosophy of the AERONET program has greatly facilitated our research collaborations as well as opened up possibilities for others. I think the federated network has been a success for development of the public domain data-base and the subsequent research opportunities.

Concerns-

Maintenance: We try to keep a small inventory of parts and supplies. As needed we will replace/repair components but we will ask the owner of the equipment to purchase a replacement part for us (Large maintenance jobs will go to the manufacturer but so far that has been rare.

Network size: Our staff size has reached it’s funding limit and we’re happily overworked. Expansion of the network is largely due to greater non NASA participation and increased efficency of the Goddard operation.

Participation: The Canadian network’s 7 working instruments is operating very successfully after a somewhat difficult 3 year ramp up. CCRS has notified AEROCAN that it’s funding will likely not be renewed next fiscal year. Please contact Norm O’Neill for more details.

There are many institutes and Universities with highly qualified personnel in developing and economically ailing countries where we would like to have AERONET sites. I encourage those who can to develop collaborations in those countries. This is a political/scientific issue that I view as an opportunity for our administrators and politicians to make an impact.

Anyone wishing to be added or removed from the distribution list please contact Laura East: least@pop900.gsfc.nasa.gov

Brent Holben