Home > solar > NIST and TSI ” unknown systematic bias”

NIST and TSI ” unknown systematic bias”


Image from PDF on NASA/NIST TSI Workshop July 18-20, 2005,
R. C. Willson click image or link

The brief presentation linked above shows some of the story, more follows…

The range of absolute total solar irradiance (TSI) values measured by different exo-atmospheric radiometers is currently about 5 W/m2, which is about 0.35 % (3500 × 10–6, Fig. 1) of the exo-atmospheric absolute TSI value at a distance of 1 astronomical unit (AU) from the Sun. This difference is greater than the individual standard uncertainties reported for most of these instruments, and greater than the 0.02 % per decade value typically stated as required to understand solar vs. anthropogenic forcing in climate change. The discrepancy between different instruments during the
same time indicates the presence of unknown systematic bias.

Sources of Differences in On-Orbital Total Solar Irradiance Measurements
and Description of a Proposed Laboratory Intercomparison.
Journal of Research of the National Institute of Standards and Technology
Volume 113, Number 4, July-Aughust 2008
J. J. Butler, National Aeronautics and Space Administration
B. C. Johnson, J. P. Rice, and E. L. Shirley
National Institute of Standards and Technology

paper here, PDF

This paper seems to originate 2005 so it is old but nevertheless this is a telling admission, the USA equivalent of the UK NPL admitting things are a travesty, all that effort and it’s wrong.

Perhaps the meaning is not entirely clear.

We know the various satellite based instruments for measuring TSI disagree, this well known plot shows it


NIST are stating there should not be the differences and they do not know why they exist. I assume this is because NIST were involved with the metrology of several (or all) of these instruments. (metrology is the name for the field, science of measurement if you like, ought to be a metrologist as well as a statistician in all science teams)


Oops. This is from the SORCE December 2006 newsletter where there is more information about ground based testing of the TIM instrument retained as a reference (other is flying). Still no dice, the compare just shows error.

This does reveal some thinking.

The bridging problem

I go on about bridging quite often to do with meteorological instruments. This is where any significant change of equipment or conditions makes it necessary to run the old and new together for an extended period, only then can the old be decommissioned. Expensive but how it is and violated all the time.

The newsletter mentions this using different language but also mentions an intent of producing absolute instruments which are so superb they can be just dropped in. Sorry, I don’t care how good, good practice is just that. As it stands the results are way off, figures of the same order (same decade ) which is not even accuracy of the same order. And then an order better still is necessary. Even at that I am sceptical the instrument measures the entire solar output nor have they mentioned the electronics or signal processing.

Finally on this “Until good absolute accuracy is achieved, the long-term TSI record relies on data continuity via mission overlap [the bridging except not sufficient]; and the short-term future for continued measurements is bright, with the SORCE/TIM, VIRGO, and ACRIM 3 funded to last until the launch of the Glory/TIM and the PICARD’s TSI instruments in 2008.”


An Orbital Sciences Taurus XL rocket blasts off from Vandenberg Air Force Base, Calif., Friday carrying NASA’s Glory environmental research satellite. The spacecraft was lost when the rocket’s protective nose cone fairing failed to separate.
(Credit: Orbital Sciences Corp.)

The Glory spacecraft failed to reach orbit after liftoff aboard a Taurus XL rocket on March 4 at 5:09 a.m. EST from Vandenberg Air Force Base in southern California.

$424m according to cnet

The 1,200-pound solar-powered Glory spacecraft, also built by Orbital Sciences, was designed to precisely measure how much solar energy enters and leaves Earth’s atmosphere and how small particles called aerosols, both manmade and natural, affect the global environment.

Nothing serious. Backup satellites are normal.

The cause of the failure?

The summary report provides an overview of the mishap investigation board’s findings. The board’s complete report is not available for public release because it contains information restricted by U.S. International Traffic in Arms Regulations and information proprietary to the companies involved.

Summary report, they don’t know what caused it. Or at least in public.

While the T9 MIB was able to identify the proximate cause and two possible intermediate causes for the T9 mishap, they were unable to identify the root cause for this failure. As a matter of explanation, an intermediate cause is between the proximate cause and the root cause in the causal chain. The root cause is the factor or set of factors that contributes to, or creates the proximate cause. Typically multiple root causes contribute to an undesired outcome.

The T9 MIB was unable to determine a root cause for the mishap mainly due to limited flight telemetry and the inability to recover the payload fairing hardware for analysis that would have enabled the determination of a definitive intermediate cause or causes.


Undesired outcome, hmm…  how to spend $500m excavating a hole in the Pacific, plus heaven knows how much collateral expenditure.



Slide from presentation (PDF)

SORCE was supposed to live for 5 years, but the failure of GLORY pushed things, with battery cell failure starting to cause real trouble.


Due for launch mid-2013

The TCTE instrument, largely built alongside the original SORCE/TIM, provides a means of quickly readying a replacement instrument for a flight on the Air Force’s existing STPSat-3 mission for a mid-2013 launch.


Cobbled together out of scrap? Let’s hope this time it works.

Here is a barely legible poster discussing how the dataset transfer might be done

Poster as PDF. (2.4MB)

I’m struck by how little progress has been made over 100+ years of trying to determine solar intensity.


Categories: solar

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