Breakout Summary Report

ARM/ASR User and PI Meeting

Breakout Description

Broadband Radiometers

● Ibrahim Reda – Update on the development of longwave and shortwave reference standards
* In the process of developing new SW(0.3% change) and LW standards (5 W/m^2 clear sky change)
* Too early for an ENG to propagate these new standards to ARM datastream
because the new standards are still a few years out before they go through all
WMO/IRC approvals. However, some steps that can be taken now are to
examine the potential processing needed when a correction is applied. Group discussion recommended saving 1 second raw voltage data for easier and more accurate correction in the future, and this can be initiated by ENG more or less immediately.
● Aron Habte – Status of new pyranometers and stations reconfiguration plan
* Examined IR loss correction methods. Showed the new pyranometers have
much smaller IR loss correction but apparently larger angular sensitivity.

Discussion of Future of SW Spectral measurements

● Yolanda Shea (virtual) – CLARREO update
● Jennifer Comstock – Update on ARM’s spectral radiometer assessment
* Desired move to commercial instrumentation for SW Spectral instrumentation
* Make better use of historical data in archive by making more accessible (more QC and PI retrieval products). Connor notes that Aerodyne has offered use of their TWST retrieval code for generation of SASZe cloud properties.
● Discussion of collaboration potential between ARM and CLARREO
* CLARREO. Unfortunately, audio/visual issues likely associated with severe
weather interfered with the bulk of Yolanda’s CLARREO update. One key point is
that the anticipated launch is shifting; currently not likely to be collecting
scientifically useful data until 2025/2026 by which time hopefully ARM may have
procured a commercial replacement for the spectral instrumentation. What would
be most useful for CLARREO comparisons is hyperspectral hemispheric
irradiance measurements to do spectral radiative closure experiments.

Update on Spectral SW instrumentation

● Kelly Balmes (virtual) – HSR1 test update
* New system has no moving parts. Gives reasonable AOD retrievals, though not
as accurate as MFRSR and CIMEL. Potential solution for ship-based AOD
measurements
● Connor Flynn – SAS instrument update
* compared SASZE to CSPHOT and NFOV2 though some disagreement that
changes depending on the time period. Outlined a potential vicarious radiance
calibration scheme derived from concurrent clear sky radiances, AOD, SSA, and
surface albedo with radiative transfer modeling. Such an approach, if viable,
would be very attractive in that instruments would be calibrated more frequently
as continuously operated rather than annually or less. Additionally it would
represent a common calibration reference for all collocated zenith radiance
instruments that would not rely on choice of lamp calibration or other terrestrial
radiometric source.
* Gary Hodges noted that NFOV2 hasn’t been calibrated between the last few
campaigns because of COVID. It is usually pretty stable, so not too worried, but
we will check after EPCAPE.
* SASZE and TWST have outstanding spectral agreement in tests at SGP for both
clear-sky and cloudy conditions.

Main Discussion

ARM is investing significant resources in upgrading broadband radiometers and investigating the path forward for the future of spectral radiometry as we move into a new era of scientific goals and technological innovation. This session will include reports on new broadband shortwave radiometers purchased by ARM, new technological innovations such as evaluations of new prototype spectral instruments, and a discussion on the scientific needs for upcoming spectral radiometers in the future. With the upcoming launch of the CLARREO satellite and other spectral satellite instrumentation, we anticipate that the combination of surface and Top of Atmosphere SW spectral measurements will allow for a rich new understanding of the radiative effects of clouds, aerosols, and surface properties.

Key Findings

● IR loss correction needs to be updated from that developed for the PSP in QCRAD to match the new instruments. Some IR loss correction still probably useful for new Hukseflux and Kipp & Zonen instruments at SGP, (though they are much improved over the PSPs) but will need to get to agreement on proper methodology and where in the processing it should occur.
● Temperature correction for new pyranometers is a bigger correction than IR loss so needs to be applied to Hukseflux SR20 output.
● Potential collaboration between CLARREO and ARM when CLARREO launches.
● Recommendations from SW Spectral instrument review includes:
* Increase usability of archived measurements through QC and PI algorithms
* Explore commercial options for hyperspectral measurements in future.
● HSR1 gives AOD retrievals with an instrument that has no moving parts. Not a replacement for current filter-based measurements for AOD retrievals in accuracy, but a potential solution for moving platforms.
● TWST instrument has excellent spectral agreement compared to SASZE in SGP tests.

Issues

No major ones identified other than as discussed in other sections.

Needs

● Need to determine IR loss correction methodology
● Recommended to record 1 second raw data from pyranometers and pyrgeometers for better future calibration corrections when reference changes. Additionally, it could be useful for quality control and variability studies.
● Need to provide Christine Chiu and cloud processes group spectral zenith radiance measurements for work with droplet number concentration retrievals. This can be hyperspectral or filter-based, but needs to have a high temporal resolution and some coverage in the infrared. The TWST-EN or another NFOV were suggested as possible solutions.
● Hemispheric SW spectral measurements by early 2026 at SGP to compare with CLARREO TOA measurements.

Decisions

No major ones identified other than as discussed in other sections.

Future Plans

● Continue discussion with Yolanda Shea and CLARREO team about what sites/measurements would be most useful to have ground-based spectral measurements simultaneous with CLARREO. Launch currently planned for 2025/2026.

Action Items

● Continue discussion on IR loss correction methodology to reach consensus on path forward
● Record 1 second raw data from broadband radiometers going forward to prepare for calibration change