Campaign : Fall 1997 Shortwave IOP

1997.09.15 - 1997.10.05

Lead Scientist : Graeme Stephens

For data sets, see below.


The Shortwave Radiation IOP, the first in a series of three such IOPs, was devoted to exploring the measurement of broadband and spectral radiation with an array of ground-based ARM and guest instrumentation, including the RCF suite, and with airborne radiometric sensors on all of the IOP aircraft.

Whereas much of the debate on solar radiative transfer has centered on the topic of clouds, there are also a significant number of issues related to clear sky transfer that this IOP hoped to address. Two key aspects of the underlying problem relate to the baseline measurement of solar radiation and the atmospheric composition through which the transfer occurs. Programs like ARESE provided motivation to compare the performance of different instruments both on the ground and in aircraft to assess methodologies for measuring fluxes. Atmospheric composition parameters such as aerosol optical depth, column integrated water vapor and liquid water, and lidar and radar backscatter, when compared with measured radiometric fluxes, will provide an important opportunity to test out transfer calculations. Spectral fluxes will offer insight, in identifying key absorption bands and will allow more rigorous testing of transport calculations.

The main objectives of this IOP were to 1) compare measurements of fluxes from a variety of ARM and guest spectral and broadband radiometers, 2) contrast spectral and broadband fluxes to determine their level of consistency, 3) characterize measurements in terms of other parameters from other sensors, and 4) promote development of a baseline spectral solar transfer model and compare it to measurements.

In order to mitigate time synchronization issues between the various ground-based sensors, the IOP concentrated on three 10-minute periods each day for comparison of shortwave spectra: 11:20-11:30 a.m. Central, 1:20-1:30 p.m. (solar noon), and 3:20-3:30 p.m., rain or shine. Aircraft flights augmented these measurement periods. Scientific coordination meetings were held at the Central Facility each day at 4:00 p.m. to intercompare results from the previous day and make any future plans, if necessary. Jim Barnard of Pacific Northwest National Laboratory (PNNL) made SBDART model output available on a daily basis to the IOP for comparison with observations.

Guest ground-based instrumentation included the NASA/Ames solar spectral flux radiometer (SSFR), Colorado State University scanning spectral polarimeter and visible Michelson interferometer, South Dakota State PGAMS (Portable Ground-based Atmospheric Monitoring System), NOAA hemispheric sky imager, two MICROTOPS ozonometers, University of Denver ASTI, NASA/Ames 6-channel tracking sunphotometer and two MICROTOPS hand-held sunphotometers, NREL absolute cavity radiometers, pyranometers, pyrheliometers, pyrgeometers, UV-A, UV-B, and PAR sensors, NOAA absolute cavity radiometer, pyranometers, and pyrgeometers, ASD shortwave spectrometer, and an O2 A-band spectrometer.

Critical ARM instruments included the suite of instruments on the Radiometer Calibration Facility, GRAMS, RSS, MFRSR, SIRS and SIRS testbed, Cimel sunphotometer, Raman lidar, MWR, MMCR, MPL, TLVC, WSI, and BBSS.

Operations were generally independent of aircraft overflights, but scientifically this IOP will be extremely dependent on the aircraft data collected. As mentioned above, all of the aircraft made some sort of radiometric measurements. And, the aerosol measurements described above, made by the Gulfstream, are of vital importance. Notable other critical aircraft measurements made in support of this IOP included the RAMS (Altus and Twin Otter), scanning spectral polarimeter (Twin Otter), Scanning spectral polarimeter (Altus), Cloud detection lidar (Altus), and MPIR (multispectral pushbroom imaging radiometer - Altus).

Much data analysis and intercomparison will occur before the ARM Science Team Meeting in March 1998. Some discussions have already occurred concerning when to hold the next Shortwave Radiation IOP. It may be desirable to link it with the next Cloud IOP. One scientific mystery hoped to be solved concerns the multi-layer stratus event observed on September 24. The SSFR showed a reappearing hump at the 1.6-micron band, which appeared and disappeared, sometimes in a matter of minutes. There were no visible cloud changes when this was noted. However, the Penn State University cloud radar was able to detect a very thin (100 m thick) layer at about 3-km that alternately appeared and disappeared. More data analysis, and modeling, will be done to further analyze this interesting situation.


Goals: The focus of the Shortwave Radiation IOP is on spectrally resolved and broadband measurements of shortwave solar radiation, especially the diffuse component. Specific issues include:

  • Comparison of fluxes from a variety of CART and guest instruments
  • Contrast of spectral and broadband fluxes to determine level of consistency
  • Characterization of measurements in terms of other parameters from other sensors
  • Development of baseline spectral solar transfer model and compare measurements

Additional Information

Management Structure:

Shortwave Radiation Co-Chief Scientists: Graeme Stephens, Colorado State University

Office phone: (303) 491-8550


Cellular phone: (630) 767-8621

Pager: (405) 699-6726

Warren Wiscombe, NASA/GSFC

Office phone: (301) 286-8449


Instrument Coordination: Bob McCoy, Colorado State University

Office phone: (970) 491-8638


ARM DSIT Representative: Don Slater, Pacific Northwest national Laboratory

Office phone: (509) 372-6049


Data Single Point of Contact:


Principle Investigator: - Robert Calahan, NASA/Goddard

Instrument/System: - Landsat Thematic Mapper

Research Participant: - Guoyong Wen

Principle Investigator: - Joe Michalsky, SUNY Albany

Instrument/System: - MFRSR & RSS

Research Participant: - Mark Beauharnois

Principle Investigator: - Chuck Long, U of Colorado

Instrument/System: - Hemispheric Sky Imager

Research Participant: - Gary Hodges

Principle Investigator: - Graeme Stephens, Colorado State Univ.

Instrument/System: - Scanning Spectral Polarimeter (SSP3)

Research Participant: - PI - Bob McCoy & Co-PI - Renata Rybka

Principle Investigator: - Peter Pilewskie, NASA/AMES Research Center

Instrument/System: - Solar Spectral Flux Radiometer (SSFR)

Research Participants: - Larry Pezzolo & Maura Rabbette

Principle Investigator: - Graeme Stephens & Andrew Heidinger, Colo. State Univ.

Instrument/System: - Visible Michelson Interferometer

Research Participants: - Renata Rybka

Principle Investigator: - John DeLuisi & Gary Hodges, NOAA/ARL/SRRB

Instrument/System: - Eppley Hickey-Frieden Absolute Cavity Radiometer Model AHF

Research Participants: - none

Principle Investigator: - Frank Murcray, University of Denver

Instrument/System: - ASTI

Research Participants: - Arthur Dubdahl & Kevin Murcray

Principle Investigator: - Steve Schiller

Instrument/System: - PGAMS

Research Participants: - none

Campaign Data Sets

IOP ParticipantData Source DescriptionFinal Data
LongHIS Order Data
MurcrayASTI Order Data
PilewskieSSFR Order Data
SchmidSunphotometer Order Data
StoffelCavity Radiometer Order Data