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SGP BORCAL Overview September 2005

SGP BORCAL Overview September 2005. Craig Webb, Ibrahim Reda, & Tom Stoffel U.S. DOE Atmospheric Radiation Measurement (ARM) Program. OUTLINE. Introduction ARM Program Needs Broadband Outdoor Radiometer Calibrations Methodology Radiometer Calibration & Characterization Functionality

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SGP BORCAL Overview September 2005

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  1. SGP BORCAL Overview September 2005 Craig Webb, Ibrahim Reda, & Tom Stoffel U.S. DOE Atmospheric Radiation Measurement (ARM) Program

  2. OUTLINE • Introduction • ARM Program Needs • Broadband Outdoor Radiometer Calibrations • Methodology • Radiometer Calibration & Characterization • Functionality • Quality Assurance of the BORCAL Process • Control Radiometer History • Summary

  3. Improve Global Climate Modeling

  4. Advance Climate Change Research by Providing Accurate Measurements Most ambitious meteorological measurement program since the International Geophysical Year of 1957.

  5. ARM Climate Research Facilities

  6. Oklahoma Alaska ARM Mobile Facility Total of 29 Stations 250+ Radiometers Nauru

  7. In-Situ Cloud Measurements Altus UAV Proteus “Digital” CM-22 & CG-4

  8. Radiometry Working groups Subgroups Shortwave Instantaneous Radiative Flux 3D Rad Tran Longwave / Water Single Column Cloud Parameterization and Modeling 2D/3D Models Cloud Properties Cloud Properties Aerosol Properties Aerosol

  9. Radiometer Calibration FacilityLamont, Oklahoma USA

  10. ARM Radiometer Calibration Facility 100 Pyranometers 30 Pyrheliometers In each of 2 BORCAL Events per Year

  11. ARM Radiometers: Shortwave Calibration Traceability

  12. ARM Radiometers: Longwave Calibration Traceability

  13. BORCAL is the Process Broadband Outdoor Radiometer CALibration Based on component summation…

  14. Component Summation Technique + = Global Reference Reference Diffuse (Shaded Pyranometer) Direct Beam (Cavity Radiometer) * Cos(Z)

  15. But there is NO Reference for Diffuse! Eppley Model PSP & 8-48 Pyranometers

  16. Shade / Unshade Calibration Standard Procedure: Rs = US - S Dir * Cos(Z) where, Rs = Pyranometer Responsivity (uV/Wm-2) US = Unshaded signal (uV) S = Shaded signal (uV) Dir = Direct Normal (Wm-2) Z = Solar Zenith angle Shade / Unshade cycles based on pyranometer time response

  17. Modified Shade / Unshade Calibration 10 Direct Unshade Signal (mV) Shade 0 00:00 35:00 Time (mm:ss)

  18. RCC is the Software Mechanism Radiometer Calibration & Characterization Used to control the BORCAL process with Lab Windows and Access programs…

  19. RCC Schematic

  20. Responsivities • Rs (45-55) Traditional - Pyranometers Mid-latitude USA (following Ed Flowers & Don Nelson/NOAA) • Rs (Composite) Traditional - Pyrheliometers (results depend on amount of data collected) • Rs (9 deg intervals) Discrete Characterization - Improve information available to the user.

  21. Responsivities 4. Rs (45 +/-0.3) Improved trend analyses by more repeatable results 5. Rs (2 deg interval) Improved Characterization • Rs (Z) Polynomial fit to AM & PM responses • Rs (Lat) Single Rs optimized for measurement station location

  22. Information is drawn from the underlying Access data tables Event Configuration Configuration is accomplished through a hierarchical data base selection process for instruments and system parameters. Configuration is summarized in the top-level window

  23. Step 2: The instrument ID located in the RCC system and logging commenced. Step 3: The instrument is shaded for several seconds. The computer operator confirms the telltale drop in instrument voltage. Step 4: The instrument location and cabling is visually verified and compared that in the RCC configuration. Step 5: The instrument is marked as verified. Configuration Verification Configuration verification is conducted by a two-person team. For each instrument, the configuration is verified using a prescribed process of visual inspection and data logging. Step 1: The instrument ID is visually verified and relayed to the computer operator. Verification Path: Visual System Configuration Data Logging

  24. Operator logging GPS or manual time maintenance Real-time error trapping and diagnosis Atmospheric stability monitor Detailed reference irradiance data Real-time graphing of responsivity, irradiance, or voltage Data Acquisition Real-time access to data acquisition and quality control

  25. Responsivity Calculations During the calibration event, responsivity is calculated at 30-second intervals as: RS = Thermopile Voltage / Reference Irradiance Reference Irradiance Diffuse Reference Irradiance Measured by two Eppley 8-48 pyranometers Global Reference Irradiance Calculated from Direct Beam and Diffuse Reference Glo = Dir • Cos(zenith) + Dif Direct Beam Reference Irradiance Measured by the absolute cavity radiometer. Shaded Pyranometers* Pyrheliometers Pyranometers *Experimental

  26. BORCAL Results Normal Incident Pyrheliometer (NIP)

  27. ± 4% ± 0.9% for 1º bin BORCAL Results Pyranometer Rs (45º) 8.10 µV/Wm-2 ± 4%

  28. Calibration Results Calibration Conditions Calibration Certificates Traceability and Certification

  29. Composite Responsivity Calibration History Responsivity Function Latitude-Optimized Responsivity 9-Degree Responsivities Suggested Methods of Applying Results 45-55 Degree Responsivity

  30. Instrument Responsivity Responsivity (RS) is Calculated from the 30-second Individual Instrument Responsivities Pyrheliometer Responsivity Mean of all 30-second RS at 45°±0.3° Shaded Pyranometer Responsivity* Mean of all 30-second RS Pyranometer Responsivity Mean of all 30-second RS at 45°±0.3° *Experimental

  31. Additional Pyranometer Characterizations Responsivity Function: RS(z) Polynomial in cos(z), fitted to all available 2-degree responsivities 2-degree Bins Mean of all 30-second RS ±0.3° at 2° zenith angle increments 45-55 Degree Mean of responsivities calculated from RS(z) between 45° - 55° 9-degree Bins Mean of responsivities calculated from RS(z) over 9° wide intervals Composite Cosine weighted from z = 0° to 90° of RS(z) Latitude Optimized Latitude limited, calculated from RS(z) and latitude

  32. Sources of Calibration Uncertainty ~ 0.4% WRR Transfer of Direct Beam Irradiance Data Logger ~ 0.12% ~ 0.06% Zenith Angle Calculations (< 75°) ~ 0.25% - 2.5% Diffuse Sky Irradiance (w.r.t. reference global) Base Uncertainty for each data point as Root Sum Square of Sources of Uncertainty (with respect to reference irradiance) Pyrheliometers ~ 0.5% Pyranometers ~ 0.8% – 3.0% Excludes zenith angle and diffuse irradiance uncertainties Includes zenith angle and diffuse irradiance uncertainties

  33. Pyranometer Calibration Uncertainty Calculated from 30-second data points Terms Uavg = Mean of base uncertainties (%) Ustd = Standard deviation, base uncertainties RSmax = Highest responsivity (all data) RSmin = Lowest responsivity (all data) RS = Mean responsivity @ 45° Intermediate Calculations Urad = [ Uavg2 + (2 • Ustd )2 ]1/2 E+ = 100 • (RSmax – RS) / RS E– = 100 • (RS – RSmin) / RS ±Uncertainties (%) U95+ = +(Urad + E+) U95– = –(Urad + E–)

  34. Pyrheliometer Calibration Uncertainty Calculated from 30-second data points Terms Uavg = Mean of base uncertainties (%) Ustd = Standard deviation, base uncertainties RSmax = Highest responsivity (all data) RSmin = Lowest responsivity (all data) RS = Mean responsivity (all data) Intermediate Calculations Range = 100 • (RSmax –RSmin) / RS Uncertainty (%) U95 = [ Uavg2+ (2 • Ustd) 2 + (Range/2) 2 ]1/2

  35. Database Maintenance Tools Data Editing Forms Data Access • System • Data Tables • Instrument Inventory • Customer • Calibration Results • System Configuration • Calibration Facility • Data Acquisition Data Plotting Tools Calibration Results

  36. Data Exporting and Distribution Responsivity Data Export for Transferring Calibration Results Custom Exports with Selectable Parameters and Output Format Dedicated Export Format (AIM Database, Calibration Stickers)

  37. ARM Instrument Management (AIM) System

  38. Confirming the Process 11-year History of Control NIP Calibrations 8.70 2.0% Rs (uV/Wm-2) 8.40 2005 1995 BORCAL Event

  39. Confirming the Process 11-year History: Control PSP Calibrations (Set 1) 9.10 5.0% Rs (uV/Wm-2) 7.60 2005 1995 BORCAL Event

  40. Confirming the Process 11-year History: Control PSP Calibrations (Set 2) 8.90 5.6% Rs (uV/Wm-2) 7.80 2005 1995 BORCAL Event

  41. Summary • The Atmospheric Radiation Measurement (ARM) Program needs accurate broadband irradiance data from three climatic regions. • NREL has developed RCC software to semi-automate the BORCAL process for hundreds of shortwave radiometer calibrations each year. • The AIM Database contains BORCAL and deployment information for all ARM radiometers (http://www.nrel.gov/aim) • Control Radiometer calibration history shows long-term performance of BORCAL process and radiometer responsivities.

  42. Thanks!Questionsfor Craig or Reda?More information available fromhttp://www.arm.gov

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