Aerosol optical depth measurements by airborne sun photometer in SOLVE II: Comparisons to SAGE III, POAM III and airborne spectrometer measurements

For 6 DC-8 flights, 19 January-2 February 2003, AATS and DIAS results for LOS aerosol OT atλ=400nm agree to ≤12%of the AATS value. Mean and root-mean-square (RMS) differences,(DIAS-AATS)/AATS, are -2.3% and 7.7%, respectively.For DC-8 altitudes, AATS-satellite comparisons are possible only for λ>440nm, because ofsignal depletion for shorter λ on the satellite full-limb LOS. For the 4 AATS-SAGE and4 AATS-POAM near-coincidences conducted 19-31 January 2003, AATS-satellite AODdifferences were ≤0.0041 for all λ>440nm. RMS differences were ≤0.0022 for SAGE-AATSand ≤0.0026 for POAM-AATS. RMS relative differences in AOD ([SAGE-AATS]/AATS) were≤33% for λ<~755nm, but grew to 59% for 1020nm and 66% at 1545nm. For λ>~755nm,AATS-POAM differences were less than AATS-SAGE differences, and RMS relativedifferences in AOD ([AATS-POAM]/AATS) were ≤31% for all λ between 440 and 1020nm.Unexplained differences that remain are associated with transmission differences, rather thandifferences in gas subtraction or conversion from LOS to vertical quantities. The very smallstratospheric AOD values that occurred during SOLVE II added to the challenge of thecomparisons, but do not explain all the differences. 展开▼