CLARREO Requirements Traceability Matrices Bruce Wielicki CLARREO Mission Study Team Meeting NASA Langley Research Center April 30, 2008
Why a Requirements Traceability Matrix? • A common tool to relate science requirements to mission requirements for: – – – – Instrument characteristics • • • Field of View Size Scanning Swath Spectral response, coverage Accuracy, noise Design Lifetime Spacecraft Orbits • • • Diurnal sampling (orbit inclination) Coordination of multiple platforms and instruments (e. g. A-train) Altitude (sun synch vs geo) Pointing control and knowledge Design Lifetime Multiple Missions/Overlap? Used to trade off costs versus science benefits Used to support why some requirements are "critical", others "important" Used to move from "seat of the pants" to more rigorous requirements Due Diligence in getting the best science for limited resources Helps communicate mission objectives/design to broader science community 2
How do we develop a Traceability Matrix? • The Langley CLARREO team took the existing CLARREO definition: – – – NRC Decadal Survey CLARREO description CLARREO July 2007 Workshop Reports and Presentations Inputs from Workshop participants on mission definition study concepts • Solar Requirements very different from Infrared Requirements: Split them • Also provided two separate views of Science Requirements & Mission Studies • – – Not an easy one to one mapping between the two perspectives Science requirements are the ultimate driver of priorities Mission studies are the organizational driver of actual research to be done We need to keep track of both science and mission study perspectives • • • cloud feedback as a science requirement feeds into a range of requirements climate model OSSE results feed into a range of requirements any given organization (La. RC, Harvard, UW, LASP, GFDL, etc) feed into a range of requirements As a result, the first draft of the Requirements Traceability Matrix, is 4 charts – – Science LW (longwave or infrared) Study LW Science SW Science LW 3
Study Integration - LW Traceability Matrix Science Driver Contributing X Critical X Science Study Instrument Incubator (IIPs) 4
LW Traceability Matrix: Science Drivers 5
LW Traceability Matrix: Mission Study Results 6
Study Integration - SW Traceability Matrix Science Driver Contributing X Critical X Science Study U. S. LASP IIP U. K. NPL study 7
SW Traceability Matrix: Science Drivers 8
SW Traceability Matrix: Mission Study Results 9
How do we develop this Matrix? • We discuss and develop an agreed upon structure and elements of the Traceability Matrices at the friday working group meetings (solar and infrared) – – – Overall structure of the draft matrices: ok or needs changes? Gaps: are science or study elements missing? Redundancies: what should be compressed or eliminated? Clarifications: wording, methods of showing low/medium/high impact on requirements. Schedule: when can we reach the following milestones • • alpha requirements (rough, partial, prior to fall 08 CLARREO open workshop) beta requirements (close enough to pass Mission Concept Review, prior to summer 09 open workshop) final requirements (end of phase A: expect 6 to 12 months after MCR, depends on progress Plan our mission studies results and their delivery/discussion/use to meet the schedule for the requirements matrix development. CLARREO Open Workshops: Fall 2008, Late Summer 2009 – – – Allow open science community review of our alpha and beta requirements, the science logic and mission study results that led us to those requirements. Focuses CLARREO mission study team on a coordinated result with outside peer review Help communicate CLARREO science, benefits, rationale to the climate community Each CLARREO requirement should have a summary document that describes the rationale, results, and cost/benefit that led to the requirement Need to also engage the international community in this activity (e. g. TRUTHS). Final requirements will be a combination of mission study team consensus, outside community review, NASA HQ cost/benefit decisions 10
Climate OSSEs • Major new tool for analysis of climate observation requirements • Climate Modeling Simulation Approaches • Observation + Radiative Transfer Theory Simulation Approaches • Improved approaches to relate observations to key IPCC uncertainties like climate sensitivity • Example answer to “Call of the Quest” 11
Climate Sensitivity Uncertainty The Climate Feedback System Uncertainty in Feedback Defines Climate Sensitivity Uncertainty The skewed tail of high climate sensitivity is inevitable in a feedback system Reducing uncertainty in predictions of T is critical for public policy since changes in global surface temperature drive changes in sea level and precipitation IPCC Mean Sensitivity 2 Feedback Factor, f IPCC Climate Feedback Uncertainty T for 2 x CO 2 (o. C) Current Climate Uncertainty 0. 26 Total Feedback Factor, f Current measured feedback uncertainties result in large uncertainties in predicted T (Roe and Baker, 2007). To = the Earth’s temperature as a simple blackbody Cloud W. Vapor Lapse Rate Surface Albedo The uncertainty in climate feedback is driven by these three components. The feedback for the climate system is f = 0. 62 ± 0. 26 (2 ) 12
CERES/CLARREO Requirements Based on Reducing Feedback Uncertainty: Cloud Feedback Example T for 2 x CO 2 (o. C) Reducing Climate Uncertainty Requires a More Accurate Measurement of Feedback CLARREO Reduces Climate Uncertainty 0. 09 Feedback Factor, f The high accuracy measurements from CLARREO can constrain predictions of T through improved estimates of the feedback. The accuracy requirement is driven by the goal for climate uncertainty reducton. Decadal Trend Observation Requirement Total Cloud W. Vapor Lapse Rate Surface Albedo These feedback uncertainty goals define the CLARREO observation requirements Cloud Feedback Uncertainty Goal Defines the Observation Requirement The uncertainty goal for feedback factor f sets the observation goal for Net Cloud Radiative Forcing (CRF) at 1. 2 Wm-2/K IPCC models predict a 0. 2 K / decade warming in the next few decades independent of sensitivity. (because the warming is controlled by the slow ocean response time) Therefore, the Net CRF observation goal is: (1. 2 Wm-2/K) * (0. 2 K/decade) = 0. 24 Wm-2/decade 13
CERES/CLARREO Requirements for Cloud Feedback CERES/CLARREO Calibration Requirement For Measuring Cloud Feedback CERES/CLARREO Sampling Requirement The Net CRF observation goal sets the decadal calibration goal: Net CRF = SW CRF + LW CRF = Clear minus All-Sky TOA Flux Shortwave (SW): 0. 24/50 = 0. 5% (2 ) Longwave (LW): 0. 24/30 = 0. 8% (2 ) This requirement is four times more accurate than the current SW broadband channel absolute accuracy: Requires overlap for current observations (no gap) and/or Requires CLARREO for future observations (gap OK) The Quest Has Just Begun A new era of climate Observing System Simulation Experiments (OSSEs), a new era of calibration. • A new methodology for linking climate model uncertainties to observation requirements has been highlighted. • The current large uncertainties in climate feedbacks are not inevitable, nor is large uncertainty in climate sensitivity. CLARREO will likely play a key role. • The example of cloud feedback linked to Net CRF does NOT eliminate the need to separately determine aerosol indirect effect. This remains the largest radiative forcing uncertainty and must be subtracted from the observed decadal change in SW CRF. The Net CRF observation goal also sets the sampling requirements • 20+ year record for trend to exceed natural variability • Full swath sampling for low observation sampling noise • 20 km FOV or smaller to separate clear and cloud scenes Solution: CLARREO required to calibrate broadband observations to needed absolute accuracy. CERES provides sampling of the Net CRF decadal change. Additional Climate Feedbacks: Similar climate model and data sampling analyses could be performed for other climate feedbacks • water vapor/lapse rate feedback will require latitude profile and height profile requirements for temperature and humidity. Can be extended to spectral fingerprinting. • surface albedo (e. g. snow/ice) will require latitude dependent requirements • other feedbacks could also be considered in this framework. • climateprediction. net perturbed physics modeling provides an ideal framework to explore the relationships. 14
CLARREO Requirements Traceability Matrix: Summary The CLARREO Mission Study Team Goal Make the CLARREO Requirements So Clear, So Compelling that they are inescapable. 15
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