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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA)/NATIONAL ENVIRONMENTAL SATELLITE, DATA, AND INFORMATION SERVICE (NESDIS)/
NATIONAL CLIMATE DATA CENTER (NCDC) & NOAA JOINT POLAR SATELLITE SYATEM OFFICE (NJO)

Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation
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(NOAA Working Group Report)

02/27/2013

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

Executive Summary

The Sun is the only significant external source of energy to the Earth system. Thus, total solar irradiance (TSI) has a major impact on Earth’s average temperature. Furthermore, solar radiation is the dominant, direct energy input into terrestrial ecosystems and, consequently, it affects all physical, chemical, and biological processes - many of which impact human health and well-being. Precise and continuous observation of the total solar output is therefore essential for climate change understanding and attribution. Accurate TSI observation is deemed to be obtained from satellites since atmosphere interference can be avoided from the TSI observation above the top of atmosphere (TOA). There are currently about 35-year continuous TSI spacecraft record acquired from several different satellite missions started from 197S. Although the absolute accuracy of this TSI data record has been limited, measurement overlap will eventually allow us to construct high quality long-term TSI climate data record (CDR) through retrospective inter-satellite calibration from future advanced NOAA and NASA Joint Polar Satellite System (JPSS)/Total and Spectral Solar Irradiance Sensor (TSIS) measurement.

Due to the launch failure of NASA/Glory mission satellite in March of 2011, there will be highly likely a gap of at least one year of TSI data record between the measurement from the NASA/Solar Radiation and Climate Experiment (SORCE) Total Irradiance Monitor (TIM) instrument (launched in 2003) and JPSS free-flyer 1 TIM instrument (to be launched in 2016). The opportunity of extending the SORCE mission until the launch of JPSS free-flyer 1 satellite to fully fill the data gap is also vanishing due to evident battery degradation of the SORCE satellite since its operation time (~ 10 years) has greatly exceeded its design lifetime (5 years). Thus, continuous long-term TSI satellite measurement is in jeopardy and NOAA and NASA have the obligation to explore the gap filling mitigation options in order to maintain the continuity and quality of the long-term TSI measurement.

Two simple mitigation options, spanning the gap via the measurement from extant satellite instruments and spanning the gap via an empirical solar model were first investigated through the Phase-A study funded by NOAA climate data record (CDR) Program. Uncertainties in the TSI data record were estimated in the event of a gap in data between the TIM instrument currently on the SORCE mission and that being built for the upcoming JPSS. Three extant satellite TSI instruments (ACRIM3, VIRGO, PREMOS) and the Naval Research Laboratory (NRL) empirical solar model were considered as possible methods of filling a TIM data gap, and uncertainties were provided as a function of gap duration and TIM overlap observational time. Europe Space Agency’s (ESA’s) VIRGO was identified to provide the best means of filling a TIM data gap, with the NRL solar model offering limited capability for short duration gaps; but no gap filling method meets the JPSS TSI CDR requirements, since no other instrument or model has demonstrated the stability or low noise required for SORCE or JPSS TIM instrument.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

Therefore, other gap filling mitigation options need to be sought to meet the TSI CDR requirements.

The TSI Calibration Transfer Experiment (TCTE) mission was proposed to help filling the data gap after an initial feasibility study. NOAA and NASA (who is the instrument procurement contractor for NOAA) accepted the TCTE propose due to its advantage of filling the measurement gap through direct calibration transfer. Moreover, the mission is cost effective since several major components of the TIM instrument are available from the spare parts of previous or current NASA and NOAA TSI missions. The spacecraft and launch vehicle are also available from the current US Air Force (USAF)/Space Test program (STP) Satellite-3 (STPSat-3) mission.

The objective of the TCTE mission is to provide a National Institute of Standards and Technology (NIST) traceable (or absolute) calibration link between current SORCE/TIM instrument and future TSIS/TIM instrument and to provide a bridge for the continuation of the 35 year TSI climate data record. NOAA JPSS Office and NASA JPSS Free Flyer Project in collaboration with the Laboratory of Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder and USAF/Ball Aerospace are responsible for implementing the TCTE mission. The LASP is responsible for building and delivering the TIM instrument and the data processing and production. The TCTE/TIM instrument will satisfy an accuracy requirement of better than 350ppm (or 0.035%; SORCE/TIM requirement) and stability of better than 10 ppm/year (or 83 0.001%; TSIS/TIM requirement). USAF/Ball Aerospace is responsible for integrating the TIM instrument to the STPSat-3 spacecraft, launching the satellite, operating the TIM with the LASP support, and relaying the observational data through its ground system to the LASP for data production. The final TSI data production, archiving, and dissemination will heavily leverage on the data processing, preserving, and distribution systems developed at the LASP and NASA Distributed Active Archive Center (DAAC) at the Goddard Space Flight Center (GSFC) for the SORCE mission to reducecost.

The STPSat-3/TCTE satellite current planned Launch Readiness Date (LRD) is August 2013 and has a nominal 18-month mission design lifetime. NOAA is discussing with the Air Force operating the STPSat-3/TCTE mission as long as possible, hopefully to March 2017. Three-phase observational cadence will be performed for the gap mitigation:1) SORCE-to-TCTE overlap calibration transfer phase (about 50 days or two solar rotations), 2) Periodic TSI measurements phase (TCTE observations between SORCE and TSIS), 3) TCTE-to-TSIS overlap scalibration transfer phase (about 50 days or two solar rotations). Both comprehensive and minimum mission success criteria have been defined.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

In consideration of the TCTE mission and improved data quality from extant satellite TSI instruments, NOAA further funded the Phase-B TSI data gap mitigation study through its CDR program. The best, intermediate, and worst mitigation scenarios have been explored by adding the TCTE in the study. The best scenario is TCTE observation overlaps with both SORCE and TSIS observations, which can maintain the stability of the long-term TSI record on the level of CDR requirements. The worst scenario is TCTE observation doesn’t overlap with either SORCE or TSIS observation. As a result, TCTE mission brings no improvement on the gap filling compared to the case without TCTE mission, The intermediate scenario is TCTE observation overlaps only with SORCE observation and the TCTE-to-TSIS gap will be filled by VIRGO measurement. Even though, in this case, the limit of VIRGO gap filling conceals the advantage brought by the TCTE in the gap filling, TCTE observation does prolong the stability of the TSI record until the end of the TCTE mission, which may allow time to implement alternate measurement approaches.

Through the comprehensive gap mitigation studies and planned TCTE mission funded by NOAA with contributed NASA instruments, the impact of the undesirable TIM data gap, due to the failure of Glory launch, battery degradation of SORCE satellite, and the delay of TSIS launch caused by restructuring the JPSS Program from the NPOESS Program, can be minimized. It will greatly benefit the continuation of 35-years satellite TSI observations as well as preserve its climate quality.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

1. Background

The exchange of radiant energy between the Sun, Earth, and space is fundamental to our climate. The net Earth radiation budget at the top of atmosphere (TOA) is determined by solar radiation absorbed by Earth and thermal infrared radiation emitted back to space. Energy from the Sun establishes the basic structure of the Earth’s surface and atmosphere and defines its external environment. Solar radiation powers the complex and tightly coupled circulation dynamics, chemistry, and interactions among the atmosphere, oceans, ice, and land that maintain the terrestrial environment as humanity’s habitat. Natural variability on a wide range of temporal and spatial scales is ubiquitous in the Earth system, and this constant change combines with anthropogenic influences to define the net system state, in the past, present, and future (see Figure. 1). For this reason a reliable and continuous record of solar irradiance is essential for climate charge understanding and attribution, This is also why a high priority was given to the TOA solar irradiance measurement in the 2007 National Research Council (NRC) Decadal Survey, Earth Science and Applications from Space.

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Figure 1. Schematic diagram of the global mean energy balance of the Earth. Numbers indicate best estimates for the magnitudes of the globally averaged energy balance components together with their uncertainty ranges, representing present day climate conditions at the beginning of the twenty first century. Units Wm-2 (after Wild et al., 2012).

Accurate solar irradiance measurement is generally obtained from the top of atmosphere in order to avoid atmospheric interference. Observations of both total solar

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

irradiance (TSI) (the sum over the entire spectrum of the Sun’s irradiance at all wavelengths incident at TOA) and spectral solar irradiance (SSI) (the Sun’s irradiance incident at TOA for a given wavelength interval) are used to monitor the changes of solar energy arriving the Earth. A solar irradiance monitoring satellite mission generally needs to perform both TSI and SSI measurements with TSI measurement as a minimum requirement. The Total Irradiance Monitor (TIM) instrument is used to measure TSI and the Spectral Irradiance Monitor (SIM) instrument is used to measure SSL There is currently about 35-years uninterrupted TSI data record available due to the result of several overlapping instruments flown on different space missions (see Figure 2). Although the absolute accuracy of this 35-years TSI data record has been limited, continuity of TSI measurements allows successive instruments to be linked to the extant TSI data record and to eventually allow us to construct high quality long-term TSI climate data record (CDR) through retrospective inter-satellite calibration from future advanced TSI instruments.

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Figure 2. The spaceborne TSI data record has been continuous since 1978 (left plot). Offsets due to calibration differences are adjusted by overlap between successive instruments. The composite record (right plot) relies on measurement continuity and instrument stability (after Kopp and Lean, 2011).

To continue the 35-years TSI measurement constructed from previous space solar missions, NASA planned the Glory mission to carry on its TSI/SSI measurement started in 2003 from its SORCE mission to year 2017. Then, the measurements of TSI/SSI from the Total and Spectral Solar Irradiance Sensor (TSIS) of NOAA and NASA Joint Polar Satellite System (JPSS) free-flyer 1 (FF-1) mission (to be launched on 2016) will extend the continuous data record to 2021, which will be further extended beyond 2032 by TSIS measurement onboard JPSS FF-2, -3, and -4 satellites. Due to the launch failure of Glory satellite by using the Taurus XL rocket in March of 2011, there will likely be a data gap between the SORCE TIM measurement and JPSS

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

FF-1 TIM measurement. The mitigation opportunity of extending the SORCE mission until the launch of JPSS FF-1 satellite in 2016 to fully fill the data gap is vanishing due to recent fast battery degradation of SORCE satellite since its operation time 10 years) has greatly exceed the design lifetime (5 years). Restructuring of the JPSS program from NPOESS has resulted in the delay of selecting a spacecraft to accommodate TSIS and exacerbated the gap issue. Thus, a TSI data gap of at least one year (see Figure 3) is expected so that other gap filling mitigation options have to be explored in order to maintain the continuity and quality of the long-term solar irradiance measurement.

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Figure 3. Schematic diagram of TSI data probability of availability.

2. Phase-A Gap Mitigation Study

The current SORCE/TIM measurement has demonstrated superior accuracy, noise, and stability to any other TSI instruments on orbit. The upcoming JPSS/TIM has yet more stringent

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

climate driven accuracy requirements that are not met by any other flight instrument Overlapping measurement with JPSS/TIM and retrospective inter-satellite calibration will increase previous TSI measurement quality to a level comparable to that to be achieved from JPSS/TIM measurement. As a result, the constructed long-term TSI CDR through composite wilt meet the CDR accuracy and stability requirements. Since the TSI climate data record currently relies on measurement continuity and instrument stability, a gap in TIM measurement due to the failure of Glory launch and battery degradation of SORCE satellite will jeopardize the continuation of the 35-year TSI data record. Therefore, gap filling mitigation that can meet the TSI CDR requirements has to be explored and implemented.

2.1. TSI Climate Data Record Requirements

The JPSS/TIM measurement requirements are driven by the need to detect any long-term solar variability which is critical for climate studies following the recommendations in the 2006 Achieving Satellite Instrument Calibration for Climate Change (ASIC3) report (Ohring et al., 2007) as well as the NIST publication “Best Practice Guidelines for Pre-Launch Characterization and Calibration of Instruments for Passive Optical Remote Sensing, NISTIR 7637” (Datla et al., 2009). The CDR requirements for JPSS/TIM are summarized in Table 1.

Table 1. CDR Requirements for the JPSS/TIM

Parameter CDR Requirement
Absolute Accuracy 0.01% (100ppm; 0.14Wm-2)
Stability (long-term precision) 0.001%/yr (10 ppm/yr; O.014Wm-2/yr)
Noise (short-term precision) 0.001% (10 ppm; 0.014Wm-2)

      Note: 1ppm ~ 0.0014Wm-2)

Any gap filling approaches should be evaluated to neet the CDR requirements. Based on this guideline, NOAA through its national climatic data center (NCDC)/CDR program funded the Laboratory for Atmospheric and Space Physics (LASP), University of Colorado at Boulder and the Naval Research Laboratory (NRL) to perform a gap mitigation study for TSI CDR, which is named as Phase-A study (see Kopp and Lean, 2011). The mitigation options were investigated through sensitivity studies on gap duration and TIM overlap time by spanning the gap via the measurement from extant satellite instruments or by spanning the gap via NRL empirical solar model. The results of Phase-A study are summarized below.

2.2. Sensitivity Studies on Gap Duration and TIM Overlap Time

Spanning a gap relying on absolute accuracy is limited by the uncertainties of the prior and subsequent instruments. For example, if the SORCE/TIM (with uncertainty of ~360ppm) measurement could be extended to JPSS/TIM era, then it could bridge a gap to ~360 ppm uncertainty independent of the gap duration. Uncertainties from noise and stability for short gap duration are small compared to accuracy limitation. Spanning a gap via either intervening

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

measurements or models relies on the utilized instruments’ or models’ stabilities, which increase uncertainties with gap duration, and on measurement agreement (limited by noise) with the TIMs prior to and after the gap. Longer overlap durations improve knowledge of both stability and agreement, so gap uncertainties decrease with overlap duration. Examples of these effects are shown in Figure 4.

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Figure 4. General effects contributing to uncertainties in spanning a TSI data gap. Stability uncertainties increase with gap duration, limiting accuracy; measurement noise limits the uncertainties at short gap durations. Longer overlap durations with prior (SORCE/TIM) and following (JPSS/TIM) instruments improve knowledge of stability and agreement with intervening gap-filling instrument or model, decreasing uncertainties (after Kopp and Lean, 2011).

2.3. Spanning the Gap Using the Measurement of Extant Satellite Instruments

TM measurement from three extant satellites, ACRIMSat/ACRIM3 (launched in 1999), SoHO/VIRGO (launched in 1996), and PICARD/PREMOS (launched in 2010), were explored by Pls of LASP and NRL to fill the data gap in the phase-A study. In the reality, PREMOS is probably the only instrument that can be used to fill the measurement gap between SORCE/TIM and

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

TSIS/TIM if its operation could be extended to the TSIS era. However, studies of the dependence of filling uncertainty on instrumental absolute accuracy, noise, stability, and the duration of gap and overlap were performed for all three instruments for the comparison purpose. Figure 5 provides an example of a TIM data gap filled by ACRIM3. TIM data prior to the gap are shown in red, with a fainter red curve indicating the “true” TSI values (i.e. in the absence of a gap). Another TIM instrument, offset from the first by one standard deviation (~360 ppm) of the absolute accuracies of both instruments, acquires data (shown in blue) after the 1.5 year gap. ACRIM3 data (green) are used to link the TIM data across this gap. Differences in slope between the TIM instruments and the ACRIM3 during the 1 year overlap periods prior to and after the gap are used to estimate and correct for the ACRIM 3 drifts relative to the TIM s across the gap, when only the ACRIM3 provides any knowledge of solar variability. These slope corrections and the TIM-to-ACRIM3 offsets before and after the gap link the pre- and post-gap TIMs, correcting the TIM data after the gap downward (dark blue). In the example shown, this correction differs from the “true” TSI by 60 ppm, causing an erroneous drift in the TSI climate data record of 40 ppm/yr.

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Figure 5. A simulated 1.5 year gap in TIM data filled by ACRIM3 demonstrates the effects of differences in instrument offsets and slopes leading to a 60 ppm error (after Kopp and Lean, 2011),

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

Actually, TSI variability models can also be constructed for individual extant TSI satellite observations and used for filling the TSI data gap. Since these variability models were developed (through regression) by correlating the TSI satellite observations with solar activity indices (including sunspots darkening and facular brightening) obtained from a variety of ground- and space-based observations of the Sun, the quality of the TSI data generated from these variability models cannot surpass the quality of the corresponding TSI satellite observations. As a result, their gap filling capability can be comparable at most to that of the corresponding satellite observations as indicated in the Phase-A gap mitigation study of Kopp and Lean (2011) so that it will not be further discussed here.

In summary, due to limited absolute accuracy of ACRIM3 (~0.1%) and VIRGO (~0.4%) and extremely high degradation of PREMOS, the phase-A study indicates none of these instruments (and their variability models) can presently fill a potential TIM measurement gap while achieving the CDR stability requirement listed in Table 1.

2.4. Spanning the Gap Using Empirical Solar Models

Proxy-based solar models can estimate TSI in the absence of actual TSI measurements. Such models can then be used to span a TIM data gap. Empirical models utilize information about the primary solar sources of solar irradiance variability to calculate the relative changes that occur when these features are present on the Sun’s disk. The Naval Research Laboratory TSI model, created by Dr. Judith Lean, is constructed from two time series, the sunspot blacking function and the facular brightening function, The model does not allow for long-term changes in the base level of the quiet Sun, but they can track solar variability on the short-term time scales to span a TIM data gap. Uncertainties introduced into the TSI climate data record by the NRL solar model were estimated as a function of gap duration and TIM overlap time.

For a gap of one year the values of the best-case TSI model for the subsequent 365-day averages differ from the “true” TSI (i.e. as measured directly by the TIM) by almost 0.05 Wm-2 (37 ppm), so using the NRL TSI model to span a TIM measurement gap introduces a 37ppm/yr drift uncertainty to the record. For the worst case scenario, the added imprecision can be up to 88 ppm/yr. Further improving empirical model by combing both space and surface measurements was also examined and the conclusion is that proxy models may achieve comparable gap filling capabilities to the alternate extant TSI instruments for the best-case scenario but cannot achieve the CDR stability requirement listed in Table 1.

2.5. Conclusions from the Phase-A Gap Mitigation Study

The ACRIM3, VIRGO, PREMOS (including their variability models), and the NRL empirical solar model were evaluated for noise and stability and for their resulting capabilities in filling a potential gap in TIM measurements between the SORCE and JPSS missions. Uncertainties introduced into the TSI climate data record were estimated as a function of gap duration and TIM overlap time for each, which are summarized in Table 2 for 1.5 year TIM data gap with 1

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

year overlap durations. The VIRGO provides the best method for filling a TIM data gap due to its stability and relatively low noise, both critical for spanning a TIM data gap. Nevertheless, a gap analysis with this instrument indicates the JPSS CDR stability requirement wouId be exceeded by 350%. Solar models are the next best option for spanning a gap of short duration, with ACRIM3 and PREMOS providing the least gap filling capability due to their higher noise and/or lower stabilities. No instrument or model achieves the JPSS TSI CDR requirements in the undesirable event of a TIM data gap. Other gap filling mitigation options need to be sought to meet the TSI CDR requirements.

Table 2. Errors from 1.5 year TIM data gap with 1 year overlap durations.

Instrument ACRIM3 VIRGO PREMOS NRL Model
Error (ppm) 123 53 152 81

3. TCTE Mission

Following the above gap mitigation study, the LASP (who is the TIM and SIM instruments developer for the SORCE, Glory, and TSIS) proposed the concept of Total Solar Irradiance (TSI) Calibration Transfer Experiment (TCTE) to the NOAA/NASA JPSS Office for extending the TSI data record from SORCE to TSIS and mitigating the TSI data gap. The basic concept is to fly a SORCE/TIM-Iike instrument on the US Air Force (USAF) Space Test Program (STP) Satellite 3 (STPSat-3) which is already underway and planned August 2013 launch. The objective of the mission is to provide a National Institute of Standards and Technology (NIST) traceable (or absolute) calibration link between current SORCE/TIM instrument and future TSIS/TIM instrument and to provide a bridge for the continuation of the 35 year TSI climate data record.

The initial feasibility study performed by the SORCE science team found out that the TCTE/TIM instrument payload can be quickly built in cost effective by using some spare or extant parts, For examples, a spare ground-based SORCE/TIM witness sensor is available from the LASP, which was originally developed alongside the SORCE/TIM flight unit and has been used for inter-comparisons at NIST and at the 2010 International Pyrheliometer Comparison (IPC-XI); TSIS/TIM instrument Generic Channel Interface (GCI) flight electronics are also available; a spare Fine Sun Sensor (FSS) that was residual after completion of the Glory TIM instrument delivery can also be used. Ball Aerospace who is responsible for the integration and launch of STPSat-3 satellite confirmed TCTE compatibility and the launch manifest opportunity for STPSat-3 mission was also approved by USAF.

NOAA together with NASA (served as the instrument procurement contractor for NOAA) accepted the TCTE proposal for the TIM calibration transfer and TSI data gap filling mitigation in

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

consideration of its merits compared to the other mitigation options discussed in the above Section 2. The TCTE mission is being implemented through the NOAA/NASA JPSS Program in collaboration with LASP, USAF, and Ball Aerospace. An overview of the TCTE mission is provided below.

3.1. TCTE/TIM Instrument

The LASP is responsible for building and delivering the TCTE/TIM instrument, which is shown schematically in Figure 6. The JPSS/Free-Flyer Project will provide a mass model of TCTE and any required technical support. The TCTE/TIM instrument will satisfy an accuracy requirement of better than 350ppm (0.035%; SORCE/TIM requirement) and stability of better than 10 ppm/year (0.001%; TSIS/TIM requirement) in order to transfer TSI data record from SORCE to TSIS. The instrument has been delivered on September 2012 in order to meet the STPSat-3 launch schedule.

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Figure 6. Schematic diagram of TCTE instrument.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

3.2. Satellite Launch, Flight Configuration, and Observing Sequence

Ball Aerospace as the contractor of USAF STPSat-3 mission is responsible for the integration of spacecraft and the lunch of the STPSat-3 satellite. The satellite is scheduled being launched on August 3, 2013 from Wallops Flight Facility, VA using Minotaur-1 rocket. The target orbit altitude is ~500 km with an inclination angle of 40.5° (or 48.2°). The normal mission operational time is 12 months with an 18-months goal after one month commissioning period. A Memorandum of Agreement (MOA, 2012 April) has been developed between NASA and USAF for the integration, launch, and flight of TCTE on P10-1 (STPSat-3) satellite. Figure 7 shows the flight configuration of the satellite. Solar-viewing TCTE instrument shares observational time with other four original STPSat-3 Earth-viewing instruments. Spacecraft is oriented and solar panel is rotated to track the sun so that TIM can point to the sun for ≥ 40 minutes for each measurement while the other 4 instruments will stay as non-producing mode during the solar viewing. TCTE science observation requires every solar observation being bracketed by periods of dark sky measurements for on-board calibration. Dark sky measurement is defined as no Sun or Earth limb within ±20° of TIM boresight (moon intrusion is permitted). Thus, the observing sequence includes pre-solar dark sky measurement (at least 20 minutes), solar observation (at least 40 minutes), and post-dark sky measurements (at least 40 minutes). Dark sky-Sun or Sun-dark sky pointing transition will be achieved in 100 seconds to guarantee the best observation results.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

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Figure 7. STPSat-3 flight configuration.

3.3. TCTE Success Criteria

Since TCTE mission is not intended to directly achieve the measurement requirements of Table 1, but to reduce the severity of a long-duration measurement gap between the SORCE and TSIS TIMs. So specific TCTE mission success criteria have been defined and are described below.

3.3.1. Comprehensive Success Criteria

Comprehensive success requires an overlap of 6 months with both SORCE and TSIS. During the overlap periods a measurement should be acquired at least every 2 days while weekly measurements should be acquired during the intervening period without overlap. The TCTE must meet its stability requirement of 10 ppm/yr and its accuracy requirement of 350 ppm. The stability requirement helps to maintain the TSI record from SORCE forward with needed long-term solar trend detection capability, while the accuracy requirement reduces the offsets between the SORCE and TSIS TIMS should overlap not be achieved.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

3.3.2. Minimum Success Criteria

Two scenarios need to be considered for minimum success. The first scenario is assuming only overlap with SORCE is achieved. Then, minimum success criterion is two months of overlap with one measurement every 2 days while weekly measurements should be acquired for at least 1-year intervening period. In this way, the data record acquired is sufficient to improve the filling data record provided by other methods discussed in the above Section 2. The second scenario is no overlap with SORCE. Then, the minimum success criterion is 3-years duration of one measurement per day. This will provide a gap filling on either side of TCTE with an uncertainty lower than any other gap filling mitigation methods discussed in Section 2. In both scenarios, the TCTE must meet its stability requirement of 10 ppm/yr.

3.4. 3-Phases Observational Cadence

To meet the objective of TIM calibration transfer and TSI data gap filling mitigation, the following 3-phases observational cadence will be performed. Both threshold and objective time sampling criteria are defined so that a successful gap mitigation mission can be achieved at least on the threshold level.

1)  SORCE-to-TCTE overlap calibration transfer phase: Overlap observations need to span at least two solar rotations (~50 days). Measurement of once per day is the objective and once of every other day is the threshold.

2)  Periodic TSI measurements phase: TCTE observations between SORCE and TSIS. Measurement of once per day is the objective and once of every week is the threshold.

3)  TCTE-to-TSIS overlap calibration transfer phase: Overlap observations need to span at least two solar rotations (~50 days). Measurement of once per day is the objective and once of every other day is the threshold.

3.5. Data Processing, Archive, and Dissemination

The raw data record (RDR) (or Level-0 data) from the TCTE/TIM observation will be transferred to the LASP through the USAF STPSat-3 ground system to producing sensor data record (SDR) (or Level-1 data), Climate Data Record (CDR) (or Level-2), and daily averaged CDR

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

(or level-3 data). Only level-3 data will be released to pubic for the comparison to other TSI instruments and models. Lower level data are not intended for broad dissemination. This is because, due to anticipated temperature excursions and limited observing time, interpretation of lower level data requires instrument insight and will be improved with ongoing on-orbit calibration measurements (i.e. darks) throughout the mission. Security is another reason since STPSat-3 is a classified mission (see Section 3.6). To reduce the mission cost, TCTE data production, preservation, and dissemination will heavily leverage on the data processing, archiving, and distribution systems developed at the LASP and NASA Distributed Active Archive Center (DAAC) at the Goddard Space Flight Center (GSFC) from the SORCE mission.

3.6. Limits and Risk

One limit of the TCTE observation is caused by the time sharing measurements with the other four Earth-viewing instruments. Measurements of the four original STPSat-3 instruments have a high priority so that TCTE measurement time and sampling numbers will be greatly reduced comparing to normal TIM measurement of SORCE or TSIS. This precludes the low noise measurements needed to fully meet the CDR requirements (see Table 1). Thus, the TCTE mission is defined as a TSI calibration transfer mission rather than a standard TSI observation mission. More calibration/validation (cal/val) efforts and quality control procedures need to be involved in TCTE data processing compared to that of SORCE and TSIS. Both comprehensive and minimum mission success criteria are defined so that a successful gap mitigation mission can be achieved at least on the minimum success level.

Another limitation is related to the data transfer from classified STPSat-3 system to the civil LASP data production and distribution systems. All telemetered data from the STPSat-3 spacecraft are initially classified. USAF currently lacks any means of declassifying the TCTE data in a timely fashion. While intended for public release eventually, these data will likely remain classified until well after launch, precluding broad community assessments of the data quality and approval of operations scenarios initially. The TCTE TIM science and operation teams are acquiring security clearances to assess instrument state of health and acquisition of intended data for the planned initial mode of operation. How to transfer the data from STPSat-3 system to LASP data production and distribution systems after initial model of operation still needs to be worked out between NOAA/NASA JPSS Office and USAF STP program.

Since STPSat-3 mission was designed for 12 months with an 18-month goal limited by spacecraft bus, it poses a risk that the TCTE may not be able to overlap with the TSIS/TIM planned for launch no earlier than mid-2016. Thus, TCTE can postpone a pre-TSIS TSI

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

measurement gap but highly likely cannot prevent this gap completely. Thus, new gap filling mitigation by combing the TCTE with extant TSI measurements or solar models should be explored, which is the task of phase-B gap mitigation study to be presented below in Section 4. This is another reason that both comprehensive and minimum mission success criteria were defined for the TCTE (see Section 3.3) so that success of the TCTE mission can be achieved at least on the minimum success level.

4. Phase-B Gap Mitigation Study

Phase-A gap mitigation study introduced in the above Section 2 was performed prior to planning for the TCTE mission. The calibration of PICARD/PREMOS launched in June 2010 has also been gradually improved after its launch and has achieved good agreement with the absolute calibration value of the SORCE/TIM. However, the PICARD is intended to be decommissioned in January 2013 so that it will likely not provide continued TSI measurements beyond those of the SORCE. The ACRIM3 data processing has also been updated to correct a previous thermal artifact causing high noise. In consideration of these new scenarios, NOAA believed it is necessary to perform a new round of (named Phase-B) gap mitigation study by including these new scenarios. NOAA/NCDC CDR program funded the same Pls of Phase-A study at the LASP and NRL to further carry out the Phase-B tasks. They repeated the previous gap mitigation studies in a more completed way by including the TCTE mission and improved data of extant instruments and adding a new San Fernando Observatory (SFO) empirical solar model.

First, the Phase-B study (Kopp and Lean, 2013) carefully evaluated the performance of the TSI instruments and solar models used in the study by using up-to-date information and the results are summarized in Table 3 (or Table 5 of Kopp and Lean, 2013), 480

Table 3. Instrument and Model Performance Estimates.

Instrument/Model Accuracy (ppm) Stability (ppm/yr) Noise (ppm)
ACRIMSat/ACRIM3 1000 71 34
SoHO/VIRGO 2500 29 28
PICARD/PREMOS 300 79 <52
SORCE/TIM 350 10 4
Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
TCTE/TIM 350 10 50*
TSIS/TIM 100 10 10
NRL Model N/A 48 38
SFO Model N/A 88 19

*This is effective noise which is much larger than the instrument noise (< 10 ppm) due to sparse orbital sampling of TCTE mission at the times of high solar activity (see Section 3.6).

Then, in-depth studies were performed for a variety of gap mitigation scenarios by combing the instruments and models listed in Table 3. The major results are summarized below.

4.1. SORCE-to-TSIS Gap without TCTE

This is the baseline scenario which had been studied in the Phase-A. The conclusion from the Phase-A study is still valid: The VIRGO provides the best method for filling a TIM data gap due to its stability and relatively low noise. The net uncertainty induced in the TSI record over the 4-year period between the present (early 2013) and the TSIS launch (end of 2016) is 97 ppm (24 ppm/yr), mainly due to the 3-year TIM measurement gap from late 2013 to late 2016 spanned by VIRGO having 1-year overlaps with both SORCE and TSIS; Solar models are the next best option for spanning the gap, which may induce a net uncertainty of 154 ppm; ACRIM3 and PREMOS provide the least gap filling capability due to their higher noise and/or lower stabilities. No instrument or model achieves the JPSS TSI CDR requirements in the undesirable event of a TIM data gap..

4.2. No TCTE Overlaps with Either SORCE or TSIS

If SORCE/TIM we re fail imminently and STPSat-3/TCTE achieves its 1-year measurement requirement, there will be a 6-month gap between the SORCE and TCTE TIMs followed by 1-year stable TCTE measurements and then a 2.5-year gap between TCTE and TSIS TIMs. In this case, VIRGO measurement again provides the best gap filling result, assuming it remains operational to provide 1 year of overlap after the TSIS launch. The weekly TCTE observing cadence slightly increases the noise connecting the TCTE record to that of VIRGO. Spanning

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

both the SORCE-to-TCTE and the TCTE-to-TSIS gaps with VIRGO induces a net uncertainty to the TSI record of 98 ppm (24 ppm/yr), with 15 ppm attributable to the SORCE-to-TCTE gap, 10 ppm to the TCTE stability during one year of operation, and 73 ppm to the 2.5-year TCTE-to-TSIS gap. Thus, the TCTE brings no improvement on the gap filling compared to the above baseline (no TCTE mission) case.

4.3. TCTE Overlaps with SORCE only

If SORCE lasts to provide a minimum of 2 months of overlap with TCTE, during which time TCTE acquires its minimum of one orbit of measurements every two days, the continuity of the TSI record in the near future can be greatly improved. This is because the SORCE/TIM’s low measurement noise allows nearly cotemporaneous high cadence data comparisons between SORCE and the TCTE’s orbital measurements so that offset uncertainties due to the TCTE’s subsampling of solar variability can be reduced and the connection of the two data records can be improved. If VIRGO measurement is still chosen to fill the TCTE-to-TSIS gap of 2.5 years, the net uncertainty induced in the TSI record is 88 ppm (22 ppm/yr), with 5 ppm from the 6-month SORCE-to-TCTE period, 10 ppm for the TCTE’s 1-year duration of measurements, and 73 ppm for the 2.5-year TCTE-to-TSIS gap. Similar to the case of Section 4.2, TCTE-to-TSIS gap filled by VIRGO measurement limits the gap filling capability for the current case. However, TCTE measurement does prolong the stability of the TSI record until the end of the TCTE mission, which may allow time to implement alternate measurement approaches.

4.4. TCTE Overlaps with Both SORCE and TSIS

If SORCE can last to provide 2-months overlap with the TCTE and the TCTE can last 4 years (despite the 18-months lifetime designing goal of STPSat-3 satellite) to provide 2-months overlap with the subsequent TSIS/TIM, expected uncertainties induced in the TSI record over these four years from the three stable and overlapping instruments are 40 ppm (10 ppm/yr), with 5 ppm from the 6-month SORCE-to-TCTE period, and 35 ppm for the following continuous TCTE operations. For this most ideal scenario, the stability of the TSI record can be maintained on the level of CDR requirement.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

5. Summary

In order to find a better solution for filling the TSI measurement gap created from the failure of Glory mission between SORCE and TSIS missions and maintain the continuity of long-term TSI CDR, NOAA through its JPSS and CDR programs funded the LASP of University of Colorado at Boulder and the NRL to study possible gap filling mitigation options in the two phases (A and B). In phase-A, two simple mitigation options, spanning the gap via the measurement from extant satellite instruments and spanning the gap via NRL empirical solar model were first investigated through the studies on gap duration, TIM measurement overlap time, and meeting the CDR requirements. The results indicate these simple gap filling options cannot achieve the JPSS TSI CDR requirements in the undesirable event of a TIM data gap.

Then, TSI Calibration Transfer Experiment (TCTE) mission was proposed to help filling the data gap after an initial feasibility study. NOAA and NASA (who is the instrument procurement contractor for NOAA) accepted the TCTE propose due to its advantage on filling the TSI measurement gap and maintaining the continuation of long-term TSI CDR. Moreover, the mission is cost effective due to the usage of spare instrument parts from previous or current NASA and NOAA TSI missions. The spacecraft and launch vehicle are also available from the current USAF STPSat-3 mission.

The objective of the TCTE mission is to provide an absolute calibration link between current SORCE/TIM instrument and future TSIS/TIM instrument and to provide a bridge for the continuation of the 35 year TSI climate data record. NOAA JPSS Program and NASA JPSS Free Flyer Project in collaboration with the LASP and USAF/Ball Aerospace are responsible for implementing the TCTE mission. The LASP is responsible for building and delivering the TIM instrument and the data processing and production. The TCTE/TIM instrument will satisfy an accuracy requirement of better than 350ppm in (or 0.035%; SORCE/TIM requirement) and stability of better than 10 ppm/year (or 0.001%; TSIS/TEM requirement). USAF/Ball Aerospace is responsible for integrating the TIM instrument to the STPSat-3 spacecraft, launching the satellite, operating the TIM with the LASP support, and relaying the observational data through its ground system to the LASP data production system. The final data production, archiving, and dissemination will heavily leverage on the data processing, preserving, and distribution systems developed at the LASP and NASA/GSFC DAAC for the NASA/SORCE mission to reduce cost.

The STPSat-3/TCTE satellite current planned Launch Readiness Date (LRD) is August 2013 and has a nominal 18-month mission design lifetime. NOAA is discussing with the Air Force operating the STPSat-3/TCTE mission as long as possible, hopefully to March 2017. Three-phase observational cadence will be performed for the gap mitigation: 1) SORCE-to-TCTE overlap calibration transfer phase (about 50 days or two solar rotates), 2) Periodic TSI

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

measurements phase (TCTE observations between SORCE and TSIS), 3) TCTE-to-TSIS overlap calibration transfer phase (about 50 days or two solar rotates). Both comprehensive and minimum mission success criteria have been defined.

In consideration of the TCTE mission and improved data quality from extant satellite TSI instruments, NOAA further funded the Phase-B TSI data gap mitigation study. The best, intermediate, and worst mitigation scenarios have been explored by adding TCTE in the study. The best scenario is SORCE measurement can last to provide 2-months overlap with the TCTE measurement and the TCTE measurement can last 4 years to provide 2-months overlap with the subsequent TSIS/TIM measurement. Then, the stability of the long-term TSI record can be maintained on the level of CDR requirements. The worst scenario is TCTE measurement doesn’t overlap with either SORCE or TSIS measurement, as a result, TCTE measurement brings no improvement on the gap filling compared to the case without the TCTE mission, which had been studied in Phase-A. The intermediate scenario is TCTE measurement overlaps only with SORCE measurement and TCTE-to-TSIS gap will be filled by VIRGO measurement. Even though, in this case, the limit of VIRGO gap filling conceals the advantage brought by the TCTE in gap filling, the TCTE does prolong the stability of the TSI record until the end of the TCTE mission, which may allow time to implement alternate measurement approaches.

Through above comprehensive gap mitigation studies and planned TCTE mission, NOAA and NASA will be able to minimize the impact of the undesirable TIM data gap due to the failure of Glory launch, battery degradation of SORCE satellite, and the delay of TSIS launch caused by restructuring the JPSS program from the NPOESS. It will greatly benefit the continuation of 35-years satellite TSI observations as well as preserve its climate quality.

6. References

Datla, R. U., et al., 2009: Best Practice Guidelines for Pre-Launch Characterization and Calibration of Instruments for Passive Optical Remote Sensing. NISTIR 7637 Available at: http://calvalportal.ceos.org/cvp/c/document_library/get_file?uuid=2b4007bf-7a47-4fc9-a63e-b5313b4ab2c9&groupld=10136.

Kopp, G., and J, Lean, 2011: Uncertainties Spanning Potential SORCE/TIM and TSIS/TIM Gap (Study A), Project report to the NOAA/NCDC CDR Program, 15pp. Available upon request from NOAA/NCDC CDR Program.

Kopp, G., and J, Lean, 2013: The Solar Climate Data Record: Scientific Assessment of Strategies to Mitigate an Impending Gap in Total Solar Irradiance Observations between the NASA SORCE and NOAA TSIS Missions (Study B), Project report to the NOAA/NCDC CDR Program, 27pp. Available upon request from NOAA/NCDC CDR Program.

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

Memoraidum of Agreement between DoD STP, USAF SMSC/SDTD, and NASA for the integration, launch, and flight of TCTE on P10-1 (STPSat-3) Mission, 2012. Available upon request from NOAA/NCDC CDR Program.

NRC, 2007: Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. Available at: http://www.nap.edu/catalog.php?record_id=11820

 

Ohring, G., et al., 2007: Achieving Satellite Instrument Calibration for Climate Change (ASIC3), Workshop report. Available at: http://www.star.nesdis.rioaagov/star/documents/ASIC3-071218-webversfinal.pdf.

 

Wild, M. et al., 2012: The Global Energy Balance from a Surface Perspective, Springer-Verlag Berlin Heidelberg, DOI: 10.1007/s00382-012-1569-8.

7. Acronyms

ACRIM3: Active Cavity Radiometer Irradiance Monitor 3
ACRIMSat: Active Cavity Radiometer Irradiance Monitor Satellite
ASIC3: Achieving Satellite Instrument Calibration for Climate Change
CDR: Climate Data Record
DAAC: Distributed Active Archive Center
DoD: Department of Defense
ESA: European Space Agency
FF: Free Flyer
FSS: Fine Sun Sensor
GCI: Generic Channel Interface
GSFC: Goddard Space Flight Center
IPC: International Pyrheliometer Comparison
JPSS: Joint Polar Satellite System
LASP: Laboratory of Atmospheric and Spacs Physics
LRD: Launch Readiness Date
Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
MOA: Memorandum of Agreement
NAS: National Academy of Science
NASA: National Aeronautics and Space Administration
NCDC: National Climate Data Center
NESDIS: National Environmental Satellite, Data, and Information Service
NIST: National Institute of Standards and Technology
NISTIR: NIST Interagency Report
NJO: NOAA JPSS Office
NOAA: National Oceanic and Atmospheric Administration
NPOESS: National Polar-orbiting Operational Environmental Satellite System
NPP: NPOESS Preparatory Project
NRC: National Research Council
NRL: Naval Research Laboratory
PI: Principal Investigator
PICARD: Last name of the 17th century French astronomer Jean Picard
PREMOS: PREcision Monitor Sensor
RDR: Raw Data Record
SDR: Sensor Data Record
SFO: Sar Fernando Observatory
SIM: Spectral Irradiance Monitor
SoHO: Solar and Heliospheric Observatory
SDTD: Space Development and Test Directorate
SORCE: Solar Radiation and Climate Experiment
SMSC: Space and Missile Systems Center
Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
SSI: spectral solar irradiance
STP: Space Test Program
STPSat-3: STP Satellite 3
TCTE: TSI Calibration Transfer Experiment
TIM: Total Irradiance Monitor
TOA: Top of Atmosphere
TSI: Total Solar Irradiance
TSIS: Total and Spectral Solar Irradiance Sensor
USAF: US Air Force
VIRGO: Virtual Geosatellite

8. NOAA Working Group

Drs. Xuepeng (Tom) Zhao and Jeff Privette (NESDIS/NCDC)

Drs. Mitch Goldberg and Stephen Walters (NOAA/JPSS)

9. External Review Panel

An ad-hoc external review committee will be organized by the National Research Council (NRC) of National Academy of Science (NAS).

Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"B--NOAA Working Group Report." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Solar irradiance is a vital source of energy input for the Earth's climate system and its variability has the potential to mitigate or exacerbate a human-created climate. Maintaining an unbroken record of Total Solar Irradiance (TSI) is critical in resolving ongoing debates regarding the potential role of solar variability in influencing Earth's climate. Space-borne instruments have acquired TSI data since 1978. Currently, the best calibrated and lowest noise source of TSI measurements is the Total Irradiance Monitor (TIM) onboard NASA's Solar Radiation and Climate Experiment (SORCE). These TIM-era data are of higher quality than the older data in the full record. Thus, the TSI climate data record (CDR) has two components. There is the shorter, but more accurate record of the TIM era and the full (33+ year) space-based TSI measurement record. Both are important and require preservation.

Review of NOAA Working Group Report on Maintaining the Continuation of Long-Term Satellite Total Irradiance Observations evaluates NOAA's plan for mitigating the loss of total solar irradiance measurements from space, given the likelihood of losing this capacity from instruments currently on the SORCE satellite in coming years and the short term/experimental nature of the currently identified method of filling the data gap. This report evaluates NOAA's plan for mitigating the gap in total solar irradiance data.

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