Airborne measurements of aerosol optical depth and columnar

Airborne measurements of aerosol optical depth and columnar water vapor in support of the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) Experiment, 2001 Jens Redemann 1, B. Schmid 1, J. M. Livingston 2, P. B. Russell 3, J. A. Eilers 3, P. V. Hobbs 4, R. Kahn 5, W. L. Smith Jr. 6, B. N. Holben 7 , C. K. Rutledge 8, M. C. Pitts 6, M. I. Mishchenko 9, B. Cairns 10, J. Chowdhary 10, J. V. Martins 11, A. Plana-Fattori 11, R. C. Levy 7, T. P. Charlock 6 1 Bay Area Environmental Research Institute, CA 2 SRI International, CA, 3 NASA Ames Research Center, CA 4 University of Washington, WA, 5 Jet Propulsion Lab, CA 6 NASA La. RC, VA, 7 NASA GSFC, MD, 8 AS&M, Inc. /NASA La. RC, VA, 9 NASA GISS, NY, 10 Columbia University, NY, 11 UMBC / NASA GSFC, MD; on leave from the University of Sao Paulo, Brazil

Contents 1. AATS-14 aboard the UW CV-580 2. Comparability with other platforms and instruments 3. Comparisons of AATS-14 to AERONET Cimel sunphotometer at COVE: implications for satellite validation 4. Spatial statistics of AOD off the US East Coast 5. MODIS validation over the ocean 6. Summary

AATS-14 aboard the UW CV-580 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 1059. 4 1241. 3 1557. 8 nm 2. Yields: aerosol optical depth + aerosol extinction when A/C flies profiles columnar water vapor + water vapor concentration when A/C flies profiles 3. 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. 4. Weight: 131. 6 lbs

Typical UW CV-580 flight track in CLAMS Chesapeake Lighthouse

Typical AATS-14 measurement day

AERONET vs. AATS-14 at COVE, July 17, 2001

Statistics of AERONET vs. AATS-14 at COVE, July 10 – Aug. 2, 2001 y=1. 035 x+0. 016 y=1. 041 x+0. 002 r 2=0. 995 r 2=0. 993 rmse=0. 04 rmse=0. 021 y=0. 987 x 0. 004 y=0. 957 x 0. 005 r 2=0. 959 r 2=0. 916 rmse=0. 011 rmse=0. 012

Suborbital measurements of AOD spatial vs. temporal variability: Temporal: Long-term Ground-based (e. g. , AERONET) Ship-based sunphotometer Aircraft-based TDDR Aircraft-based AATS Temporal: Short-term Spatial resolution yes (15 min. ) no no yes no ? ? yes 45 sec. ~ 3 -4 km yes 2 sec. ~ 100 -200 m no no possible

CV-580/AATS-14 location, CLAMS July 17, 2001, 16: 00 - 16: 15 UTC

AOD variability on July 17 th, 2001 ΔAOD~30%

AATS-14 vs. AERONET: spatial and temporal variability

AATS-14: spatial variability

Summary of AATS-14 derived AOD spatial variability by flight in CLAMS-2001

MODIS: 6 wavelengths validation over ocean Courtesy of R. Levy, MODIS team

Vertical aerosol structure, July 17, 2001

Vertical water vapor structure, July 17, 2001

Summary 1. Available as of Feb. 23, 2002: Version 1. 0 of all full-column measurements of AATS-14 in CLAMS in 11 ASCII data files (one per CV-580 flight). 2. In CLAMS, AATS-14 measured full column aerosol optical depth spectra and columnar water vapor at exact TERRA overpass time on at least 7 occasions. For five of these opportunities, AOD at 499 nm was at or below 0. 1. 3. During TERRA overpass time on July 17, 2001, AATS-14 measured the highest AOD encountered during the entire experiment (~0. 49 at 499 nm), including a horizontal gradient in AOD of more than 30% over a horizontal distance of ~70 kilometers. 4. Comparisons between airborne AATS-14 in the vicinity of and AERONET Cimel derived AOD’s directly at the Chesapeake Lighthouse show good agreement and complementary results in assessing both spatial and temporal AOD variability. 5. AOD variability during low-level legs of 11 research flights was frequently as high as 50% over distances ≤ 50 km.