Breakout Summary Report

ARM/ASR User and PI Meeting

13 - 17 March 2017

Session Title: Broadband Radiometric Instrument Focus Group
Session Date: 16 March 2017
Session Time: 10:45 AM - 12:45 PM
Number of Attendees: 25
Summary Authors: Chuck Long

Breakout Description

The Instrument and Measurement Focus Group for Broadband Radiometric Measurements is charged to address issues related to producing accurate, reliable, and continuous broadband radiation measurements for scientific use for the ARM Facility.

Main Discussion

The 2017 ARM/ASR Joint User Facility and Principal Investigator Meeting session addressed some ongoing issues, heard reports on current and upcoming campaigns relevant to the group charter, and discussed expanding the group to include ARM spectral radiometric measurements along with broadband. The session agenda was as follows:

Instrument Issues:

Status update on Ventilation issues progress (Mike Ritsche) [10 min]
Any progress on downward facing radiometer ventilation design? (Mike Ritsche) [2 min]
ShipRad/PRP progress (Chuck Long) [5 min]
Status update on IR calibrations progress (Mike Dooraghi) [10 min]
Discussion: [20 min]
- Are we ready to recommend reprocessing of historical LW data yet?
- Ventilator issues?
- Single Radiometer Configuration
- Etc.

Group Charge and Focus:
- Expanding the group to include spectral radiometers (Connor Flynn) [5 min]
Discussion [20 min]

Related Campaigns:

Allison McComiskey [10 min]
- Fall 2017 Absolute IR Instrument Campaign

Chuck Long: [15 min]
- Ongoing IR Loss Methodologies Study
- Collaboration with 2017-18 Cold Climate mitigation campaign

General Discussion

Key Findings

Three campaigns of interest to ARM radiometry were described during the breakout.

Allison McComiskey reported on a campaign that is scheduled for fall at the ARM SGP site where two independent designs of what are purportedly absolute hemispheric infrared radiometers will be compared to available infrared data such as integrated AERI and LBLRTM model LW as well as pyrgeometers traceable to the World Infrared Standard Group. The WMO - Commission for Instruments and Methods of Observations (CIMO) Task Team on Radiation References will send representatives to review the design, operations, and performance of these new radiometers in the framework of establishing a world absolute infrared reference.

Chuck Long reported on a collaborative effort between NOAA GMD and NREL to study the effectiveness of various permutations of correction methodologies for IR loss from pyranometers. Several months of data are being collected from several makes and models of pyranometers commonly in use, and operated both ventilated with 12V DC fans and not in ventilators. Preliminary results were reported on a poster at the ARM/ASR meeting, with the significant result that the VAP methodology developed for ARM, back when the ventilators used 120V AC fans that have since been shown to exacerbate IR loss, still works well now that all ARM ventilators have been switched to 12V DC fans that produce significantly less IR loss.

Chuck Long also reported on the De-Icing Comparison Experiment (D-ICE) scheduled to be held starting this coming fall at the NOAA Barrow facility under the auspices of the BSRN Cold Climate Issues Working Group chaired by Chris Cox of NOAA PSD. The campaign is a "bake off' of manufacturer and other organizations' various ventilation schemes to test which ideas and designs might perform better to mitigate frost/snow/riming that adversely affect cold-climate observations. So far, about 22 radiometers and 9 different ventilator designs are signed up to participate. The campaign analyses will make use of the nearby ARM Barrow site atmospheric state and other relevant observations. It is asked and recommended that ARM actively participate at a minimum by installing cameras to capture images every 10 minutes of the ARM operational broadband radiometers in their ventilators at both Barrow and Oliktok during the year of the campaign.

Decisions

The discussions on ventilation issues and progress toward a Single Radiometer Configuration (SRC) resulted in several decisions. First, it was decided to add a second pyrgeometer to the SGP systems for measurement redundancy, and switch to a 3-radiometer tracker mounting plate to facilitate adding the 5-inch ventilation hole below each Eppley ventilator that had been previously decided. It was additionally decided to remove all of the ventilator fan screens, since these were installed by the manufacturer simply because "they came with the fans" (Tom Kirk, Eppley). Victor Cassella (Kipp & Zonen) also provided some remarks regarding filter use on their ventilators. There has never been any study as to their effectiveness or any necessity whatsoever that they are needed or useful, but plenty of evidence that the screens can sometimes cause detrimental issues. The NOAA SURFRAD, Integrated Solar Irradiance Study, and GMD Baseline Observatories networks do not use the fan screens, and have not noted any significant detrimental issues in operating that way, given yearly cleaning of the fan blades, and replacement of the fans themselves on a three-year cycle. However, it was noted that the screens do help prevent "critters" like geckos from getting into the ventilators where they might be prevalent, perhaps for tropical AMF deployments. And ARM site operators at SGP and OLI have provided input that screens have been useful when large amounts of insects and airborne plant matter have been present. Switching to fan models that include fan speed indicators was also discussed, with the idea of adding extra variables to the output files to log fan speeds as a diagnostic for fan health. This was deemed desirable, and also that perhaps it would be a good idea to include a couple of "blank" variables in the upcoming massive reprocessing required by the SRC effort so that in the future some additionally desired measurements could be added to the systems that would use these extra variable spaces and thus then not require another mass reprocessing.

As part of the reporting on progress with ARM LW pyrgeometer calibrations, it was decided to wait at least another year for another round of LW BORCALs before any recommendation on whether and when to recommend reprocessing all previous ARM LW data to the new 3-coefficient formulation with new coefficients. The reasoning is so that there are at least 2 BORCALs for each ARM pyrgeometer to confirm expected calibration stability.

The relevant discussion led to agreement of those present to propose expanding the group to include ARM spectral radiometric measurements along with broadband. Unfortunately the discussion on ventilation and configuration issues at the start of the breakout took longer than anticipated, and several of the spectral radiation folks had to leave the meeting before this group expansion discussion could occur. It was recommended that a message be sent out to the ARM community announcing the idea and asking anyone interested to reply. Then the response will be used toward activities for organizing a group proposal to be submitted to Jim Mather for consideration, with an eventual inaugural workshop to be hosted by NOAA GMD in Boulder, given acceptance of the proposal. It is noted that, similar to the current BBRad group, this expanded group would be an ARM Instrument Focus Group, not an ASR science group.

Future Plans

We still need to decide for SRC if the SKYRAD/GNDRAD configuration will be combined into a system similar to the SIRS configuration. Or whether to separate the SIRS data into SKYRAD and GNDRAD files in the system data logger to make the SIRS system similar to those. There are concerns with long cabling runs or perhaps a data logger on the towers to connect for long distances over to the central data logger required for the current NSA sites layout and likely for AMF deployments as well. So essentially converting SIRS to two separate SKYRAD and GNDRAD files requires no additional equipment, only a logging program and ingest changes (though the ingests for SKYRAD and GNDRAD already exist; we just need to apply them at SGP instead of the current SIRS ingest).

Announce the possible formation of an expanded (including both broadband and spectral observations) ARM Radiometric Instrument Focus Group. Organize a discussion and formation workshop hosted at NOAA GMD in Boulder.

Continue and pursue the discussion for adding variable spaces for ventilator fan speed data along with several extra variable spaces in the SRC output files so that any future instrument additions would not necessitate another massive reprocessing effort.

Action Items

Discussion and decision on whether to convert SIRS to SKYRAD/GNDRAD or vice versa for the SRC will be facilitated by ARM BB Instrument Mentors.

ARM BB Instrument Mentors will conduct a study to see if there is any discernible effect of using or not using ventilator fan screens during BORCALs.

ARM BB Instrument Mentors will also contact the sites' various operations folks as the fan screens are removed and ask them to report if problems or other notable conditions are observed in operating the ventilators without screens. This is of particular interest for frost/snow/riming conditions.

Chuck Long will draft and send out an email to the relevant ARM/ASR email list to notify the community of the plans to propose an ARM Radiometric Instrument Focus Group, and ask any who are interested to reply. He will then compile a listing of responders and work toward a proposal for forming a Radiometric Instrument Focus Group. Should the proposal be accepted, Chuck will work with Allison McComiskey to organize an inaugural workshop for discussion, planning, and group charge formation.

Chuck Long will follow up with Fred Helsel and Mark Ivey on installing cameras to capture images every 10 minutes of the ARM operational broadband radiometers in their ventilators at both Barrow and Oliktok during the year of the D-ICE campaign. Plus he will follow-up with ARM BB Instrument Mentors if they have any desire to field alternative ventilation ideas at the ARM or NOAA Barrow site.