Aerosol optical depth measurements by airborne sun photometer in SOLVE II: Comparisons to SAGE III, POAM III and airborne spectrometer measurements
Résumé
For 6 DC-8 flights, 19 January-2 February 2003, AATS and DIAS results for LOS aerosol OT at ?=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 ?>440nm, because of signal depletion for shorter ? on the satellite full-limb LOS. For the 4 AATS-SAGE and 4 AATS-POAM near-coincidences conducted 19-31 January 2003, AATS-satellite AOD differences were ?0.0041 for all ?>440nm. RMS differences were ?0.0022 for SAGE-AATS and ?0.0026 for POAM-AATS. RMS relative differences in AOD ([SAGE-AATS]/AATS) were ?33% for ?<~755nm, but grew to 59% for 1020nm and 66% at 1545nm. For ?>~755nm, AATS-POAM differences were less than AATS-SAGE differences, and RMS relative differences in AOD ([AATS-POAM]/AATS) were ?31% for all ? between 440 and 1020nm. Unexplained differences that remain are associated with transmission differences, rather than differences in gas subtraction or conversion from LOS to vertical quantities. The very small stratospheric AOD values that occurred during SOLVE II added to the challenge of the comparisons, but do not explain all the differences.