# Presentation: 457269

## Perspectives on the development and use of Observing System [Simulation] Experiments 

- Doreen Neil
- Senior Research Scientist
- NASA
- April, 2006

## What’s an OS(S)E?

- Build a “nature” or “truth” model.
- Need 2 to 4 times better resolution than the observing system being tested
- Obtain real observations (or compute synthetic observations)
- Need a forward radiative transfer model
- Need to know the instrument characteristics.
- Need to estimate realistic measurement errors.
- Assimilate the observations.
- Need assimilation capability
- Assess the impact on the resulting forecast.
- Need meaningful diagnostics.

## What’s an OSSE for?

- Evaluate possible future systems:  Framework created to decide between sounder concepts for GOES-R series.  Sounders measure T, H2O, and winds.
- Quantitative decision guidance for design and implementation of space systems: OSSE framework used for NPOESS performance.
- Reduce time lag between measurement capability and data use: OSSEs require model development.
- Demonstrate the benefit of using NASA products in a partner’s DSS (?)
- Decision to be made affects the approach to quantifying the uncertainty.

## What do we need for an OS(S)E?

- Build a “nature” or “truth” model.
- Need two independent, well characterized models of the process being evaluated.
- Need ever-finer resolved process models to evaluate improved instruments.
- Obtain real observations (or compute synthetic observations)
- Need a forward radiative transfer model: calculates what the system on orbit “sees”
- Need to estimate realistic measurement errors.
- Assimilate the observations.
- Need assimilation capability for the model in use.
- Assess the impact on the resulting “truth”.
- Need meaningful diagnostics.

## What do we know about OSSEs for weather forecast observables?

- OSSEs need to be run for longer periods to obtain seasonal variations (one month is not long enough).
- OSSEs need to be run at finer spatial scales(0.5 deg is too coarse for NPOESS).
- OSSEs need better surface information.
- OSSEs require considerable resources.
- Scale of the assigned errors must match scale of the model.
- OSSEs have have not yet discriminated between related measurement systems for physical observables.

## How can we apply OSSEs in other disciplines?

- Weather focus
- Timely forecast
- Severe storms
- Phase change of H2O
- Temperature, H2O, and winds
- Regional domain
- High temporal and spatial resolution

- Air quality focus
- Accurate chemical composition
- Stagnant weather
- Non-linear chemical evolution
- Minimum: O3, CO, NO2, HCHO, SO2 and aerosol
- Regional domain
- High temporal and spatial resolution

## We can evaluate measurement sensitivity

- Measurement of Pollution in the Troposphere (MOPITT) launched in 1999.
- Its primary objective is the measurement of tropospheric carbon monoxide (CO)
- Sensitivities of instrument signals and CO retrieval errors to various instrument parameters, especially the gas cell pressure and temperature variations, instrument radiometric noise, and ancillary data errors (such as atmospheric temperature and water vapor profile errors), are presented and discussed.
- MOPITT CO retrieval error analysis is based on perturbation analysis, to identify the largest sources of error.
- The error analysis results indicate that tropospheric CO distributions can be retrieved with a precision of 10% for most of the troposphere.
- Uses a robust forward model.
*Wang, Jinxue, Gille, John C., Bailey, Paul L., Drummond, James R., Pan, Liwen.  Instrument Sensitivity and Error Analysis for the Remote Sensing of Tropospheric Carbon Monoxide by MOPITT.  Journal of Atmospheric and Oceanic Technology 1999 16: 465-474.*

## We evaluate sampling strategies

- The Tropospheric Emission Spectrometer (TES) on Aura provides measurements of ozone, CO, and other key chemical species in the troposphere.
- In order for TES to meet a design lifetime of 5 years, a global survey strategy with ~50% duty cycle must be identified.
- In this study, simulated concentrations of ozone and CO from the GEOS-CHEM global three-dimensional (3-D) model of troposphere chemistry are used as a time-varying synthetic atmosphere for demonstrating and assessing the capabilities of TES nadir observations.
- Autocorrelation analyses of the model species fields for different time lags identify a significant 1-day correlation and support a 1-day-on/1-day-off observation strategy. The error in the level 3 products relative to the true fields for ozone and CO is <10% in ~70% of cases and <20% in 80–90% of cases.
- Three major sources of error lie in the asynoptic orbital sampling, the retrieval, and the level 3 global interpolation.
*Luo, M., R. Beer, D. J. Jacob, J. A. Logan, and C. D. Rodgers, Simulated observation of tropospheric ozone and CO with the Tropospheric Emission Spectrometer (TES) satellite instrument, J. Geophys. Res., 107(D15), 4270, doi:10.1029/2001JD000804, 2002.*

## First steps toward AQ assimilation

- In partnership with US EPA, we have begun development of assimilation capability in CMAQ

## So how can we do an OSSE for AQ Assessment?

- Need multiple atmospheric chemistry models with fine spatial resolution and good performance (“truth”).
- Some are being tested for field mission planning
- Spatial resolution needs improvement
- Assimilation techniques are just being developed
- Need good instrument models to assign error magnitudes for spectral, spatial, intensity, thermal, and other systematic errors.
- Instrument models are specific to each measurement concept
- Evaluation of existing instruments provides a reality check on error magnitiude.
- Accuracy is the diagnostic, not forecast skill.
- Model development is key.

## Discussion thoughts

- Model development with partners (DSS) takes stable funding and time.
- Relationship with technology program for instrument characterization.
- What is the balance between instrument characterizations and model development for future systems?
- Relationship with science division to support capability to model new observations.