1. Reducing the RObotic Lunar Observatory (ROLO) Irradiance Model Uncertainty SI David B. Pollock 1, Thomas C. Stone 2, Hugh H. Kieffer 3, Joe P. Rice 4 1. The University of Alabama in Huntsville, 301 Sparkman Drive, OB 422, Huntsville, AL 35899 2. U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001 3. Celestial Reasonings, 2256 Christmas Tree Lane, Carson City, NV 89703 4. National Institute of Standards and Technology, 100 Bureau Drive, MS 8441, Gaithersburg, MD 20899-8441

2. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 2 Abstract There is a fundamental remote sensing problem, the inability to identify and to correct biases to the level that current sensor technology permits once a sensor becomes operational in-orbit. This paper presents a concept, retrieval and recalibration of a transfer standard, to reduce in the longer term the uncertainty of the flux from the stars, the solar flux and vicarious sources on the earth using the RObotic Lunar Observatory, ROLO, Irradiance Model as the basis for a technology demonstration. The cause of the fundamental remote sensor problem is the uncertainty of the respective fluxes traced to the International System of Units, SI. This includes the sensors relative to the U. S. Global Climate Change Research Program (U.S. GCRP), sensors for NASA, NOAA, TVA, DoD, DOE, HHS, NSF, USDA, DOI and EPA. An effort to solve this fundamental problem began about 7 years ago with the emergence of the problem at a NIST Workshop in the fall of 1997 and stated in NIST GCR 98-748, High Accuracy Space Based Remote Sensing Requirements, March 1998. Since then there has been expanding recognition and discussion of this remote sensing deficiency at National and International conferences and workshops. Remote sensor data shows that remote sensors are on the order of 4 to 5 times more stable than the uncertainty of either the spectral or total radiant flux from the moon, the stars and the sun. The consequence is data uncertainty increases because there are not adequately uncertain calibration sources available to remove the remote sensor biases that arise during operations. The concept presented by this paper when implemented would begin an effective, systematic attack on the larger problem, the stars, the sun and terrestrial, by attacking a most glaring deficiency of the recognized, accepted ROLO Lunar Irradiance model. Although the lunar data is stable to better than 0.1% there is a significant wavelength dependent uncertainty on an absolute scale thought to be on the order of 5 – 15% SI. A bias of up to 6% is found when results are compared to satellite instrument measurements. Reducing this uncertainty SI will begin to eliminate the deficiency of exo-atmospheric radiometric standards specifically for those remote sensors that can use the lunar flux over the 300 to 2300 nm spectral region for calibration.

3. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 3 * Hugh H. Kieffer et al, On-orbit Calibration Over time and Between Spacecraft Using the Moon, SPIE 4881. Abstract Summary There is a fundamental remote sensing problem. –An inability to identify correct biases to the level that current sensor technology permits once a sensor becomes operational in-orbit. –Years for a total solution, stars, sun, moon and vicarious sources. The ROLO lunar data is stable to better than 0.1% * –A significant wavelength dependent uncertainty 5 – 15% SI. –A bias ~ 6% when compared to satellite instrument measurements. A solution element –Demonstrate a concept using ALIR and the RObotic Lunar Observatory, ROLO, Irradiance Model. –An Absolute Lunar Irradiance Radiometer, ALIR, a transfer standard, flown, retrieved, recalibrated multiple times. Uncertainty SI < 2% will begin to eliminate the deficiency of exo- atmospheric radiometric standards, 300 to 2400 nm spectral region.

4. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 4 Topics The problem Working on a solution

5. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 5 Widespread Disagreement (Data/Model -1) %, Average of Data per Instrument.

6. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 6 Operational envelope Critical parameters and functions Relative spectral response, in-, out-of-band. Absolute response Saturation response Dark off-set Non-linearity of response vs temperature Relative response over field of regard Distortion map over field of regard Response vs array, electronics temperature Focus (energy on a pixel) Pixel fill-factor Response to out-of-field-of-view sources Gain normalization Repeated observations Total Uncertainty “Truth” Chambers1 ~ 2% Stars1.5 ~ 2.5% Moon6 ~ 15% Sun0.1 ~ 2% Terrestrial~ 20% A 2 = P 2 + B 2 + (SNR) -2 + “T” 2 B - Taylor, B.N., Kuyatt C. E., Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, NIST Technical Note 1297, 1994

7. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 7 Heuristic SI Traceability* Path Reference sources International System of Units, SI Convention of the Metre Transfer radiometers Remote sensors Orbital, Airborne, Terrestrial Calibration sources Sun, Moon, Stars, Terrestrial National Measurement Institutes * “Property of the result of a measurement … whereby it can be related to stated references… through an unbroken chain of comparisons all having stated uncertainties.” International Vocabulary of Basic and General Terms in Metrology (VIM), Estler, CALCON 2004 Workshop

8. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 8 Current Path Transfer measurements in situ. –A set of measurements of Vega at 0.5556  m.* Data analysis, multiple observers, instruments and sites. *Hayes, Calibration of Fundamental Stellar Quantities, Proc. IAU Symposium No. 111 (1985) Vega Striplamp, hundreds of meters distant Pt or Au point cavity, inside dome, after telescope optics.

9. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 9 Planned Path Polychromatic to span the ROLO range, 0.34 – 2.4  m. –Combined ROLO bands. –Individual, fixed bandpass filters. HACR – (TBD)XR – MIC – ALIR Joint ROLO & ALIR observations. Repeated ground calibrations. Analysis ALIR @ 12 -45 km Moon Stars ROLO & ALIRSDL NIST - SI Units (TBD)XR

10. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 10 Topics The problem Working on a solution for the Lunar Irradiance

11. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 11 Rationale What – Reduce the ROLO Lunar Irradiance Model uncertainty. Why – Remote sensors are being tasked to produce ever more accurate data. How – Iterative calibrations, coupled with comparative measurements in the field and laboratory. Who – Trained, qualified participants. When – Needed now.

12. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 12 ALIR Selectable band pass filters – Calibrated at NIST – Common to ROLO – Located near aperture stop High out-of-field light rejection – Hard field & aperture stops Internal reference source to monitor stability Detectors Entrance pupil Field stop Aperture stop 19 bandpass filters + Blank Near aperture stop FOV = 0.5  F No. = 10

13. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 13 ROLO Bands, 32

14. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 14 ROLO Bands Combined,19

15. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 15 Dynamic Measurement Range Small

16. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 16 S/N, 1 cm Aperture,

17. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 17 Spurious Flux Control Field-of-view edge

18. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 18 Error Budgets Instrumentation Total Uncertainty, 2 ,% NIST0.02 (TBD)XR0.2 SDL1.0 ALIR1.5 ROLO Model (RSS)1.8

19. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 19 Az-El Gimbals Acquisition / Track ALIR ECI Position Data storage and transmission Housekeeping Command &Control Flight System Aircraft Ground station Balloon or

20. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 20 Trained, Qualified Participants SI traceable path –NIST –Space Dynamics Laboratory –USGS Iterative flights –Balloon, National Scientific Balloon Facility –Aircraft, SOFIA Payload & Operations – UAH Data Analysis – USGS, UAH Peer review and critique – NASA GSFC

21. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 21 Activities Stabilization, pointing and position. –Alt-az gimbals w/ 1” pointing, build or borrow. –GPS and lunar ephemeris from vehicle. Balloon, routine –> 25 km w / a 4 x 10 6 ft 3 volume. –70 ft diameter by 110 ft long parachute. –Payload attached to the end of 65 ft cable ladder below the parachute. –Added distance between balloon - payload possible w / a second ladder or a 1000’ reel-down. Aircraft SOFIA. –12.5 – 13.5 km –3+ years away Repeated pre-, post-flight Sensor calibrations. Concurrent observations w / ROLO telescopes in Flagstaff. Data reduction and error analysis –Statistically significant data set –100 s data on 30 successive days or 100 s on 12 selected days / year Ingest archive data

22. CALCON2004 August 26, 2004 Aboslute Lunar Irradiance Radiometer, ALIR 22 Conclusion A relatively small, < 5 cm aperture, well baffled, <10 -11 @ 1 , multi-spectral, 340 – 2,400 nm radiometer, limited dynamic range, <2, is feasible. Setting the ROLO Model scale < 2% is a reasonable task.