# Presentation: 657656

## Comparison of airborne sunphotometer and satellite sensor retrievals of aerosol optical depth during MILAGRO/INTEX-B

- J. Redemann(1,3),** **J. Livingston(2,3), P. Russell(3), R. Johnson(3),
- Q. Zhang(1),  L. Remer(4), R. Kahn(5), O. Torres(6), B. Veihelmann(7),
- P. Veefkind(7), A. Smirnov(6), B. Holben(4)
- (1) Bay Area Environmental Research Institute (BAERI), Sonoma, CA, USA
- (2) SRI International, Menlo Park, CA, USA
- (3) NASA Ames Research Center, Moffett Field, CA, USA
- (4) NASA Goddard Space Flight Center, Greenbelt, MD, USA
- (5) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
- (6) University of Maryland, Baltimore County (UMBC)/NASA Goddard, Greenbelt, MD, USA
- (7) Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands
- http://geo.arc.nasa.gov/sgg/INTEX-B/index.html
- email: jredemann@mail.arc.nasa.gov

## Outline

- Jetstream 31 (J31) instrument payload and flight overview
- Airborne, satellite, and ground-based AOD comparisons
- AATS-14 (Ames Airborne Tracking Sunphotometer) & MODIS AOD spectra over water (Gulf of Mexico) for all coincidences during MILAGRO
- AATS-14, OMI (UV and MW retrievals), & MODIS over water (2 cases)
- 	  -10 March (Aqua, Aura)
- 	  -17 March (Aqua, Aura)
- AATS-14, OMI, & AERONET over Mexico City (1 case)
- 	  -19 March (Aura)
- AATS-14, MODIS, & MISR over water (1 case)
- 	  -10 March (Terra)
- Summary/Conclusions

## Jetstream 31 in MILAGRO/INTEX-B: Instrument Locations

**Jetstream 31 in MILAGRO/INTEX-B: Instrument Locations**

| RSP | Total & linearly polarized reflectance | 412-2250 nm, 9  |
| --- | --- | --- |
| SSFR | Upwelling & downwelling spectral hemispheric irradiance | 300-2200 nm, many 
~8-12 nm resolution |
| CAR | Spectral & angular distribution of scattered light from clouds, aerosols, land and water surfaces; imagery of clouds & surface | 340-2130 nm |

## NASA Ames Airborne Tracking Sunphotometer: AATS-14

- 1.	Measures direct solar beam transmission:
- 	 353.5    380.0     449.0      499.4     525.0
-      605.7    675.1     778.4      864.5     939.7
-     1019.1   1241.3   1557.8    2139.0 nm
- Yields:
- 	aerosol optical depth + aerosol extinction when A/C flies profiles
- 	columnar water vapor (ozone) + water vapor (ozone) concentration when A/C flies profiles
- Size:
- 	Telescope dome 8" OD  (hemisphere) atop 5" H pedestal.  (Total H:  9" above A/C skin), Inside A/C: 12" D x 18" H cylinder.
- Weight:
- 	131.6 lbs

## J31 flight tracks: 13 flights out of Veracruz, Mexico

**J31 flight tracks: 13 flights out of Veracruz, Mexico**

**9 flights over water**

**4 flights over land**

- Mexico

- Gulf of Mexico

## J31 flight patterns:Coordinated satellite, in-situ and radiative missions 

**J31 flight patterns:****Coordinated satellite, in-situ and radiative missions**

## J-31 Research Flight 06, 10 March 2006

- Note: MODIS RGB images, with MODIS AOD maps overlaid for every J-31 flight available at: http://geo.arc.nasa.gov/sgg/INTEX-B/            Acknowledgements appreciated.

**J31 flight track**

## Slide 8

## AOD Comparisons, MODIS vs AATS

**92% of points **
**fall within **
**band**

**MODIS uncertainty band**

**100% of points **
**fall within **
**band**

**Satellite (MODIS) AOD**

**Sunphotometer (AATS-14) AOD**

- Agreement at MODIS SWIR wavelengths is better than expected, because the number of points falling within the uncertainty band exceeds 66%, which is the expected fraction if the MODIS uncertainty (±0.03 ±0.05AOD) is ±1.

**AOD Comparisons, MODIS vs AATS**
- Gulf of Mexico, INTEX-B/MILAGRO, 2006

**37 cells**

**18 cells**

**MODIS-Terra (March 5, 10, 12)**

**MODIS-Aqua (March 10, 17)**

**MODIS wavelengths**

## The A-Train is a set of satellites that fly in sequence

**The A-Train is a set of satellites that fly in sequence**

**Many J31 flights included legs or profiles under the A-Train or other satellites**

## AOD Comparisons, OMI - MODIS - AATS

- INTEX-B/MILAGRO, 2006

- MODIS

## AOD Comparisons, OMI - MODIS - AATS

- INTEX-B/MILAGRO, 10 March 2006

- J31 low altitude transect 19:40-20:01 UT

## 10 March 2006 (over water)

- 10 March 2006 *(over water)*

*Case 1*

**J31/AATS measurements**

- AOD extrema along transect

## 10 March 2006 (over water)

- 10 March 2006 *(over water)*

*Case 1*

- OMI MW & UV AOD retrievals significantly exceed MODIS and AATS values.

## 17 March 2006 (over water)

- 17 March 2006 *(over water)*

- Aqua overpass: 20.07 UT

*Case** 2*

- Aura overpass: 20.32 UT

- Large OMI AODs may be due to cloud contamination.

## 10 March 2006 (over water)

- Does the good agreement between MODIS and AATS AOD warrant “vicarious validation” of OMI with MODIS?

- 10 March 2006 *(over water)*

- 17 March 2006 *(over water)*

## Slide 17

## Slide 18

## Larger OMI MW AOD retrievals over land likely due to incorrect surface albedo assumption.

- highest quality

- AATS AOD:   high variability, flat  depend.

## Overestimate of sunphotometer AODs by OMI UV algorithm may also be due to incorrect assumption of surface reflectivity.

## J31 flight track

**J31 flight track**

## Slide 22

## Slide 23

## AOD Comparisons, MISR - MODIS - AATS

- Gulf of Mexico, INTEX-B/MILAGRO, 10 March 2006

## Summary/Conclusions

- AATS-14 MILAGRO/INTEX-B data set is very mature and the latest version is archived; future changes will likely affect only singular data points at high altitude; would require fine-combing by hand.
- Validation of MODIS (-Terra & -Aqua) AOD well underway: major finding is exceptionally good agreement with AATS and appreciable AOD at SWIR.
- For AATS/OMI coincidences, archived OMI near-UV AODs and preliminary OMI MW AODs exceed AATS AODs, but these cases need to be examined in more detail.  Differences may be due to cloud contamination over water or to the surface albedo assumed by the OMI retrieval algorithms over land.  *Analysis of coincident measurements by other J31 sensors (SSFR, RSP, and CAR) should provide additional information on surface spectral albedo and BRDF.*
- AATS, MODIS, and MISR over-water AOD spectra have been compared for a Terra overpass: near IR AODs agree within uncertainties in all 3 MISR grid cells; in the visible, MISR AODs agree with AATS and MODIS values in 2 of 3 co-located MISR cells.
- Collaboration between AATS and other J-31 sensors is in its initial phase.