# Presentation: 585236

## Applied SI Traceability and CLARREO IIPs

- John Dykema, Fred Best, Marty Mlynczak, Greg Kopp, Tony Mannucci, and Brian Cairns

**Notes:**
Two key aspects of the CLARREO paradigm, as outlined by Hank yesterday, are high accuracy, demonstrated on orbit, and high information content relevant to decadal climate predictions. In the talks that follow, we’ll look at technological developments targeted at achieving the required on-orbit accuracy and obtaining essential information for climate forecast improvement. Jerry Fraser introduced the science of metrology and its relationship to making demonstrably accurate measurements. To realize accurate measurements from the different CLARREO data types-SW, LW, and GPS-RO, we need to apply the principles of metrology in a practical way. 

## Keeling Record: A Climate Success Story

- Dykema et al.: Applied SI Traceability

- October 22, 2008

**Notes:**
The value of a reproducible standard. The left hand side shows the status of terrestrial carbon dioxide measurements in the 1950s, in the era before Keeling began his measurement time series at Mauna Loa. These data, shown as blue points, were assembled by Slocum, who surveyed all available published data, and concluded the most likely scenario was that carbon dioxide was decreasing. He deemed the point circled to be the most definitive measurement, since it represented the average of some 50,0000 measurements. Keelings approach was built around the idea that the measurements needed to be tied to an absolute standard that was absolute, reproducible, and tested by  different physical principles: in this case, optical and manometric methods. The resulting timeseries in red on the right has been one of the most (if not the most) incontrovertible piece of evidence in climate change science. 

## Microwave Refractivity: A Climate Index Derived from the Definition of the Second

- Dykema et al.: Applied SI Traceability

- October 22, 2008

**Notes:**
GPS-RO, as introduced in Stephen’s talk yesterday, provides profiles of the microwave refractivity of the atmosphere based on a timing measurement. Timing measurements are fundamental to modern metrology, with the advantage that the international definition of the second has an uncertainty of only one part in 1015. To reiterate, the key is that a GPS receiver in low earth orbit measures the signal from a GPS transmitter as it is occulted by the atmosphere, while the signal from that transmitter is also viewed by a ground station that receives a timing signal from the atomic clock. This process allows timing errors in the GPS clocks to be removed. Tony Mannucci will discuss performance numbers for the resulting measurement accuracy later in this session. 

## The International System (SI) of Units

- Maintained in the US by NIST:
- Thermodynamic standards
- Optical standards
- Electrical standards
- CLARREO benefits from multiple links to NIST

- Dykema et al.: Applied SI Traceability

- October 22, 2008

**Notes:**
The base units of the SI define a set of measurement units that are based on fundamental properties of matter and reproducible anywhere in the world, at any time. The measurement units of our CLARREO sensors, with the exception of GPS, are derived from combinations of these measurement units. Jerry discussed yesterday the use of absolute detectors as a primary standard for optical radiometry. In the infrared, currently the lowest achievable uncertainties are obtained by blackbody calibrations. Blackbodies provide a radiometric calibration that is related to fundamental properties of matter through temperature standards and Planck’s Law. The accuracy of a blackbody is dependent both on how accurate its emitting temperature is known and its optical properties. So CLARREO can benefit from multiple levels of calibration at NIST, achieving traceability to both optical and thermodynamic scales.

## Systematic Errors in Models and Sensors

- Dykema et al.: Applied SI Traceability

- October 22, 2008

## Realizing CLARREO paradigm: IIP

- Marty Figure: Far IR Information Content

- Greg Figure: SW SI Traceability

- Dykema et al.: Applied SI Traceability

- October 22, 2008

**Notes:**
The IIPs realize key aspects of the CLARREO paradigm. The Wisconsin-Harvard IIP develops hardware to allow the linkage of the IR on-orbit calibration to international standards of temperature through phase change cells. This linkage provides the foundation for testing for the ensemble of systematic errors that determines the combined IR measurement accuracy. The Langley IIP develops new technology for observing the far infrared, obtaining information about water vapor absorption and thin ice clouds that is essential to climate. The LASP IIP develops technology necessary to tie the on-orbit calibration of the SW instrument to absolute standards that are being refined in the observation of TSI.

## Discussion Questions Follow

- Dykema et al.: Applied SI Traceability

- October 22, 2008

## Discussion Questions

- What further technical advances are necessary to make each IIP flight worthy?
- What systematic errors are known for IR, SW and how do we quantify them?
- What are the NIST scales in the IR, SW?
- What has been done in the past for the traceability of blackbodies cavities and what do we propose to do differently for CLARREO?
- What is the progress on the RO Trends project, which seeks to quantify the SI traceability of GPS-RO by independent analyses of the existing measurement time series by different institutions?

- Dykema et al.: Applied SI Traceability

- October 22, 2008

## Discussion Questions (Continued)

- What relevant lessons have been learned from TSI studies?
- What other lessons can be applied from metrology:
- o       Electrical standards: drifts in standard volt discovered through the introduction of quantum electrical standards, a physically independent method
- o       Assembling the updated temperature scale (ITS-90): a well-known experimental result was rejected because it could not justify its experimental error estimate
- o       The World Radiation Reference (WRR) in Davos has discovered a long term drift that it seeks fix by introducing an SI-traceable, technology-based standard to replace the current  standard which was thought to be very stable but now has been shown to drift

- Dykema et al.: Applied SI Traceability

- October 22, 2008

## The CLARREO calibration strategy must ensure:
high accuracy
testing for systematic errors on-orbit
a tie to irrefutable standards

**high accuracy**
**testing for systematic errors on-orbit**
**a tie to irrefutable standards**

**What specific DS requirements must CLARREO address?**** **

- Dykema et al.: Applied SI Traceability

- October 22, 2008

**Notes:**
Specific language in the Decadal Survey places explicit demands on the calibration approach of CLARREO sensors. To understand the motivation behind this language, it’s worth thinking about the scientific process that eventually led to the Montreal protocol. In that case, science continued more or less unimpeded until restrictions on chemicals were considered. Then the critics emerged from all direction. Anticipating a similar phenomenon in an era of carbon taxes or similar measured, the NRC sought to design a calibration strategy to provide strong new evidence on the reliability of key climate measurements.

## Slide 11

- Dykema et al.: Applied SI Traceability

- October 22, 2008

**Notes:**
To sum up, in this session, we’re looking at technological developments to realize the direct on-orbit measurement of sensor accuracy for data types that carry essential information for defining decadal climate and constraining forecasts of decadal climate. The direct on-orbit measurement of sensor accuracy is designed to provide a qualitatively greater degree of evidence to defend a measurement time series than other strategies used to create decadal climate time series. History tells us that once public policy decisions begin to be made based on measurements, the level of critical scrutiny that those meaurements receive will jump at least on order of magnitude. So the IIPs in this session aim to make the experimental tests that we use to test measurement uncertainty in the laboratory available on-orbit.

## Testing Climate Models: An Analogy

- Formal detection and attribution studies such as those in the IPCC-4AR test for systematic errors in climate models arising from chance agreement between model and observations
- This agreement is tested to show that the historical climate simulation has a physically meaningful interpretation by testing that the model response (fingerprint) to different forcings (greenhouse gases, sulfate aerosols, volcanic aerosols, solar variation) is consistent with the observed spatiotemporal pattern in measurements
- This procedure is equivalent to testing individual systematic errors on orbit via their spectral fingerprints

- Dykema et al.: Applied SI Traceability

- October 22, 2008