Observing System Simulation Experiments

1
Observing System Simulation Experiments

• Lars Peter Riishojgaard
• Global Modeling and Assimilation Office
• and
• Joint Center for Satellite Data Assimilation

2
Role of a National OSSE Capability

• Impact assessment of future missions
• Decadal Survey and other science and/or
  technology demonstration missions (NASA)
• Future operational systems (NOAA)
• Objective way of establishing scientifically
  sound and technically feasible user requirements
  for observing systems
• Tool for assessing performance impact of
  engineering decisions made throughout the
  development phases of a space program or system
• Preparation/early learning tool for assimilation
  users

3
OSSEs

• Observing System Simulation Experiments
• Typically aimed at assessing the impact of a
  hypothetical data type on a forecast system
• Not straightforward EVERYTHING must be simulated
• Simulated atmosphere (nature run)
• Simulated reference observations (corresponding
  to existing observations)
• Simulate perturbation observations
• (object of study)
• gt Costly in terms of computing and manpower

4
Data assimilation
Nature (atmospheric state)
Assessment
End products
Sensors
Observations (RAOB, TOVS, GEO, surface, aircraft,
etc.)
Short range product
Analysis
Forecast model
Initial conditions
5
OSE, conceptual model
Nature (atmospheric state)
Assessment
End products
Sensors
Reference observations (RAOB, TOVS, GEO,
surface, aircraft, etc.)
Short range product
Analysis
Forecast model
Candidate observations (e.g. AIRS)
Initial conditions
6
OSSE, conceptual model
Nature run (output from high resolution, high
quality climate model)
Assessment
End products
Simulator
Reference observations (RAOB, TOVS, GEO,
surface, aircraft, etc.)
Forecast products
Analysis
Forecast model
Candidate observations (e.g. GEO MW)
Initial conditions
7
OSSE QAWhy cant you just use real
atmospheric situations and real data instead of
having to simulate everything?

• The goal of the OSSE is to test whether a given
  non-existing type of data could improve on the
  initial conditions and hence prediction
  capabilities how would we do that?
• You just simulate these new observations and add
  them to the assimilation
• We simulate them based on what?
• Based on the actual atmospheric state!
• Unfortunately that would be impossible. The
  actual atmospheric state is by definition
  unknown we only have an imperfect estimate based
  on the actual observations. There is no way of
  knowing how additional data would have changed
  that had they existed.

8
Why a NASA-NOAA OSSE capability?

• OSSEs are expensive
• Nature run, entire reference observing system,
  additional observations must be simulated
• Calibration experiments, perturbation experiments
  must be assessed according to standard
  operational practice and using operational
  metrics and tools
• OSSE-based decisions have many stakeholders
• Decisions on major space systems have important
  scientific, technical, financial and political
  ramifications
• Community ownership and oversight of OSSE
  capability is important for maintaining
  credibility
• Independent but related data assimilation systems
  allows us to test robustness of answers

9
Why a NASA/NOAA OSSE Capability? (II)

• Both agencies have a need for an OSSE-based
  impact assessment capability
• Both agencies have resources and expertise to
  contribute
• NOAA
• Operational data assimilation/prediction systems
• Operational satellite data processing
• NASA
• Data assimilation RD
• Space system RD development
• Ultimate Research to Operations tool
• Systematic and bojective way of applying
  research tool and results to the design of future
  operational systems