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

Reducing the RObotic Lunar Observatory (ROLO) Irradiance

Model Uncertainty SI David B. Pollock1, Thomas C. Stone2, Hugh H. Kieffer3, Joe P. Rice4

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 860013. Celestial Reasonings, 2256 Christmas Tree Lane, Carson City, NV 897034. National Institute of Standards and Technology, 100 Bureau Drive, MS 8441,

Gaithersburg, MD 20899-8441

CALCON2004 August 26, 2004

Aboslute Lunar Irradiance Radiometer, ALIR 2

AbstractThere 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.



* 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.



Topics

• The problem

• Working on a solution



Widespread Disagreement

(Data/Model -1) %, Average of Data per Instrument.



• 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”

Chambers 1 ~ 2%

Stars 1.5 ~ 2.5%

Moon 6 ~ 15%

Sun 0.1 ~ 2%

Terrestrial ~ 20%

A2 = P2 + B2 + (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



Heuristic SI Traceability* Path

Reference sources

International System of Units, SIConvention of the Metre

Transfer radiometers

Remote sensors Orbital, Airborne, Terrestrial

Calibration sourcesSun, 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 ofcomparisons all having stated uncertainties.” International Vocabulary of Basic and General Terms in Metrology (VIM), Estler, CALCON 2004 Workshop



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, hundredsof meters distant

Pt or Au point cavity,inside dome, aftertelescope optics.



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



Topics

• The problem

• Working on a solution for the Lunar Irradiance



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.



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 pupilField stop

Aperture stop

19 bandpass filters + BlankNear aperture stop

FOV = 0.5F No. = 10



ROLO Bands, 32Lunar Spectral Irradiance, 2° / 15°

0.0

10.0

20.0

30.0

40.0

50.0

60.0

300 800 1300 1800 2300 2800

Wavelength, nm

Spectral Irradiance, nW/cm^2-nm

2°

15°



ROLO Bands Combined,19Combined Bands Spectral Irradiance

0

10

20

30

40

50

60

300 800 1300 1800 2300 2800

Band center, nm

Specral Irradiance, nW/cm

2- nm



Dynamic Measurement Range Small

Lunar flux dynamic range, 2° - 15°

1.00

1.50

2.00

300 600 900 1200 1500 1800 2100 2400

Wavelength, nm

Ratio



S/N, 1 cm Aperture, Selected - Combined ROLO Bands

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

300 600 900 1200 1500 1800 2100 2400

Wavelength, nm

1.0E-01

1.0E+00

1.0E+01

Si Phototdiode

PV HgCdTe

Comb. Bands Irr.



Spurious Flux Control

1.E-20

1.E-17

1.E-14

1.E-11

1.E-08

1.E-05

1.E-02

Off-axis angle, deg

Total

Scatter

Diffraction

Field-of-view edge



Error Budgets

Instrumentation Total Uncertainty, 2,%

NIST 0.02

(TBD)XR 0.2

SDL 1.0

ALIR 1.5

ROLO Model (RSS) 1.8



Az-El Gimbals

Acquisition / Track

ALIR

ECI Position Data storage and transmission

Housekeeping

Command &Control

Flight System

Aircraft

Ground station

Balloon or



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



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 106 ft3 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



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.

Documents

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