# Presentation: 295203

## ARM Site Atmospheric State Best Estimates for Aqua: 

**ARM Site Atmospheric State Best Estimates for Aqua: **
**Retrieval, Radiance, and Forward Model Validation**
- David Tobin, Wayne Feltz, _Bob Knuteson_, Hank Revercomb
- CIMSS / SSEC / University of Wisconsin-Madison
- Tasks:
- Development and production of ARM Site Best Estimate Products (SGP, TWP, and NSA sites)
- Improved cloud detection/mask
- Improved surface emissivity estimates
- Improved uncertainty estimates
- Improved temporal and large scale gradient estimates for TWP and NSA sites
- Aqua validation studies using ARM site overpass datasets
- AIRS and MODIS clear sky radiance and forward models
- AIRS cloud cleared radiance
- AIRS and MODIS Temperature and Moisture retrievals

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## ARM Site Atmospheric State Best Estimates

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## Presentation Outline: Status and near term plans

-  ARM upper level water vapor accuracy
-  Phase 2 of dedicated sondes
-  North Slope of Alaska site
-  Surface emissivity

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## 

- ARM FIRE Water Vapor Experiment (AFWEX) SGP ARM Site, December 2000
- Established upper level water vapor truth, through deployment of aircraft based reference sensors*.  Upper level agreement of 5% or better found between:
- LASE (aircraft based DIAL, NASA LaRC)*
- DLH (aircraft based in-situ Diode Laser Hygrometer, NASA LaRC)*
- ARM and GSFC Raman Lidars with T-dependent cross section corrections
- Vaisala RS-80 radiosondes with physical corrections
- Confirmed understanding of RS-80 sensor physics and accuracy of Miloshevich corrections.
- ARM Raman Lidar / RS-90 radiosonde comparisons show good agreement to 10km. Ties RS-90s into AFWEX analysis and suggests upper level uncertainty of 5% or less.
- Prescribed (time-lag) corrections for Vaisala RS-90 radiosondes are small; insignificant for interpretation of AIRS observed minus calculated.
- Using AIRS as the transfer standard, evaluation of clear sky spectral residuals shows very good absolute agreement between the ARM and Voemel validation profile sets:  ~0K differences for in-between line channels implies very good agreement below ~10km; ~0.5K differences for on-line channels is suggestive of a ~5% bias (RS-90s drier) above ~12 km.
- At the 2 band center, where the forward model has best absolute accuracy, very good (~0 K) AIRS clear sky residuals are obtained when using the ARM and Voemel validation profiles.
- My current assessment: SGP and TWP absolute water vapor uncertainty
- is ~5% or less below ~12 km; ~2% in the lower troposphere.

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- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## Example AFWEX flight, 5 December 2000

- AFWEX design:
- Aircraft based sensors provide accurate measurements of upper level water for evaluation of radiosonde and ground based Lidar measurements.
- IR satellite-like measurements (S-HIS, NAST-I, -M, FIRSC) to assess radiative impacts.
- Continuous ground based Lidars used to track variability and interpolate in time.
- Clear sky flights flown directly over ARM site at various altitudes with many coincident radiosondes (RS-80s)

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- 10 minute CART Raman Lidar data

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## 

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## 

**AFWEX analysis,**
**previous slide**

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## Summary of Impact of RS-90 Time-lag corrections 

- Summary of Impact of RS-90 Time-lag corrections** **
- (TWP Nighttime) corrections c/o L. Miloshevich, NCAR

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- These corrections are not currently included in the ARM best estimate products provided to the team

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

##  Summary of AIRS Clear Sky Spectral Residuals

-  Summary of AIRS Clear Sky Spectral Residuals
- Mean Obs and Obs-Calc for various validation datasets

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-            legend:**      **
**Voemel**
**ARM SGP Night**
**ARM SGP Day**
**ARM TWP Night**
**ARM TWP Day**
**GSFC SRL**
**ABOVE**

- Cloud contamination in “ABOVE” dataset?

- Early SRL calibration bias?

- Transparent Band Center

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## Comparison of ARM TWP and Voemel Mean Obs-Calcs

- In-between line ARM obs-calcs are in very good agreement with Voemel obs-calcs.  On-line
- ARM obs-calcs are slightly more negative (~0.5K) than Voemel, implying a slight dry bias
- (~5% RH) of ARM RS-90s w/r/t Voemel above ~12 km.

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- Tb difference between ARM TWP and Voemel ensembles

- Good agreement in WV column at Transparent Band Center

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## H2O Continuum Measurements and Models at 2 Band Center 

- H2O Continuum Measurements and Models at 2 Band Center

- The biggest uncertainty w/r/t the forward model for upper level water vapor channels is the knowledge and parameterization of the foreign broadened water vapor continuum component of the absorption (Cf0).  For these channels, the forward model is most certain at the 2 band center, where a convergence of Cf0 measurements and models exists.  (CKDv2.4 is/was known to be in error in this region and has since been fixed.)  The ARM and Voemel ensemble residuals (obs-calcs) are very close to zero for these channels.

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- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## Remaining on-line AIRS observed minus calculated residuals are consistent with :

- previous and on-going atmospheric and laboratory investigations of a super-Lorentzian near-wing water vapor spectral lineshape
- a height dependent water vapor bias (present in both character and magnitude in the ARM SGP, ARM TWP, and Voemel ensembles)
- some combination of a and b.
- 	These residuals were tuned out in latest version of the fast model (using emperical channel optical depth adjustments to the TWP nighttime obs-calcs).  Tracing the cause back to the spectroscopy will require further investigation.

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

##  TWP Nighttime Mean Obs and Obs-Calc

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

## Other near term plans regarding ARM Water Vapor:

- Resolve RS-90 Diurnal issue (Daytime sondes dryer, with an apparent altitude dependence.  Details presented at May 2003 AIRS STM)
- Investigate why RS-90 radiosondes for ABOVE site are significantly too “dry”.[ Probably includes some cloud contaminated scenes that can be removed.]
- Assess and incorporate AWEX findings when appropriate
- Improved characterization of North Slope of Alaska measurements

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>

##  Phase 2 of Aqua dedicated sondes

-  _Phase 2 of Aqua dedicated sondes_
-  Launches recently completed on 19 February
-  Now working to process best estimate files for all three sites
-  _North Slope of Alaska site_
-  Water Vapor characterization experiment recently conducted.  Plan is to incorporate the lessons-learned.
-  MWR water vapor accuracy for low water amounts in question
-  Radiosonde characterization
-  _Surface emissivity_
- Plan is to assess and improve characterization at each site.
-  TWP: currently using Wu/Smith model (not Masuda)
-  SGP: currently using linear combination of pure bare soil and pure 		vegetated spectral emissivities.  Working to refine “vegetation 		weights”.
-  NSA: plan is to follow SGP approach with various pure 			land, water, and ice emissivities.
- Done in collaboration with Knuteson led effort.

- AIRS STM, 30 Mar - 1 Apr 2004, Greenbelt, MD

- <tobin_airs_stm_mar2004.ppt>