Breakout Summary Report
ARM/ASR User and PI Meeting
2 - 6 May 2016
4 May 2016
1:30 PM - 3:30 PM
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Chuck Long, with support from BBRad Group members.
Breakout Description
The BBRad Focus Group Charter statement reads: "Instrument and Measurement Focus Group for Broadband Radiometric Measurements will address issues related to producing accurate, reliable, and continuous broadband radiation measurements for scientific use." The breakout gives opportunity for status updates, discussions, and identification of related issues.Main Discussion
The group during this session discussed several areas, including updates from the NREL broadband Instrument Mentors on LW BORCAL instrument calibrations and radiometer ventilation issues progress. Other topic areas included ventilator and heater design standardization for cold-climate upwelling radiation measurement instruments, a proposal for an international absolute IR instrument comparison and analysis campaign for the fall of 2017 at the SGP Central Facility, an update on substantial progress on BBRad related VAPs, the procedure for updating calibration information in the raw data files when an instrument is changed, and estimating broadband from the MFRSR data for the QCRAD VAP. The session ended with a presentation on the design of the newly formulated “ShipRad” AMF shipboard radiometer system for obtaining broadband downwelling radiation measurements corrected for tilt from horizontal currently being built.Key Findings
Key Findings (recommendations and action items at end of each numbered section).1) The LW BORCAL is now operational at SGP and the first round was accomplished this past calibration season, with 81 Eppley PIRs successfully calibrated, producing coefficients for the 3-coefficient LW formulation that ARM uses. Results indicate a 95% calibration accuracy of about 2 Wm-2. 8 PIRs failed the calibrations, mostly because of a discovered bad channel on the BORCAL systems data loggers.
2) Related to the LW BORCALs is the question of reprocessing of historical pyrgeometer data that has been recommended and facilities reprocessing order prioritized previously (see 2015 STM BBRad report). Given only this first LW BORCAL has been accomplished, and with a few failures, it is deemed prudent to wait until each PIR has had at least one more BORCAL so that the coefficients can be compared for stability. Thus it is recommended that at least one more BORCAL be performed on each PIR before reprocessing is started to test the actual stability and veracity of the calibration coefficients of each.
3) The NREL Broadband Instrument Mentors reported that all sites have now been converted to 12V DC fans for the ventilators. Analysis shows that one benefit of the switch to DC fans is a significant decrease in the magnitude of IR loss from the pyranometers. There was a proposal by the NREL Mentors to hold off on adding 5” ventilation holes in the tracker plates under the ventilators until they complete a “currently available commercial instrument” assessment. The idea was that if the ARM Program was to switch to Kipp & Zonen instruments, their ventilators' air inlets hang out away from the tracker mounting plate and the holes would not be needed. However, it was pointed out that a conversion to K&Z would cost the program a considerable investment and in the current fiscal environment is not likely, certainly not anywhere in the near future. Thus it was recommended that the tracker plate modification to add 3 ventilation holes proceed, since the holes would not interfere with any possible eventual future conversion to K&Z ventilators.
4) A discussion ensued pertaining to standardization of the radiometer systems across ARM, in essence combining the SKYRAD and GROUNDRAD systems into one system similar to the SIRS configuration. One consideration is that the SKYRAD systems have two PIR pyrgeometers for redundancy in the LW measurements, while the SIRS do not. It is estimated it will cost about $155K to upgrade the current SIRS systems to have redundancy in the LW measurements similar to having redundancy in the SW (direct plus diffuse SW compared to global SW) and upwelling LW (GndRad PIR compared to downfacing IRT) of all systems. On the other hand, degrading the current redundant SKYRAD systems will cost about ($12K). While the question of how often the redundant PIRs actually caught “bad” episodes arose, a statement that “we have never had a PIR problem in the SIRS systems” was questioned, particularly wondering how one would know if a subtle issue occurred without a redundant measure to compare with? (An example of this was presented at the 2016 IRS Conference where renowned surface radiation operator John Augustine showed a subtle issue with a SURFRAD PIR that went undetected for 7 months even with daily QC scrutiny superior to ARM’s student-trained methods.) It was decided that an analysis of the TWP and NSA SkyRad data might shed some light on the frequency of problem occurrence. Any recommendation by the BBRad Group will be held until a future discussion.
5) Joe Michalsky gave a presentation proposing a campaign to be held at the ARM SGP site in the fall of 2017 for comparing two newly developed “absolute IR instruments” to the original Absolute Sky-scanning radiometer (ASR) on which the current World Infrared Standard Group (WISG) is based. Recent brief comparisons at Davos, Switzerland suggest that the two new designs agree well, but are offset from the WISG by about 4 Wm-2. The SGP affords a rich observational environment with typically frequently occurring (and needed) clear skies and a range of column water vapor amounts in the fall. The BBRad Group enthusiastically supports this campaign, and members will assist in the planning and proposal process led by Dr Michalsky.
6) A presentation and discussion pertaining to ventilation of downward-facing radiometers in the cold climate sites and AMF deployments, needed to mitigate frost and riming, occurred. The SGP and TWP sites have never employed ventilation for the upwelling measurements, whereas the NSA group and two of the AMFs have each independently experimented with designs. It was decided that it would be good to standardize a design for ARM systems. To facilitate choosing a design, it is proposed that an IOP be conducted at the Barrow NSA site to study ventilator and heating configurations, similar in nature to the previous NSA Pyranometer IR Loss Study (2006) and Evaluation of Heated Ventilators in the Arctic campaigns. Task leads Mike Ritsche and Fred Helsel are charged with soliciting help to organize and propose a campaign.