Comparison of Airborne Sunphotometer and Near-Coincident In Situ and Remotely Sensed Water Vapor Measurements during INTEX-ITCT 2004

The NASA Ames 14-channel Airborne Tracking Sunphotometer (AATS-14) took measurements from aboard a Jetstream 31 (J31) twin turboprop aircraft during 19 science flights (~53 flight hours) over the Gulf of Maine during the period 12 July to 8 August 2004. The flights were conducted in support of the INTEX-NA (INtercontinental chemical Transport EXperiment-North America) and ITCT (Intercontinental Transport and Chemical Transformation of anthropogenic pollution) field studies. AATS-14 measures the solar direct-beam transmission at 14 discrete wavelengths between 354 and 2138 nm, and provides instantaneous measurements of aerosol optical depth (AOD) at 13 wavelengths and water vapor column content, which is derived from measurements at 940 nm and surrounding wavelengths. AATS-14 measurements obtained during aircraft ascents and descents are differentiated to yield vertical profiles of aerosol extinction and water vapor density. Specific J31 flight patterns were designed to address a variety of science goals and, therefore, included a mixture of vertical profiles (spiral and ramped ascents and descents) and constant altitude horizontal transects at a variety of altitudes. In general, flights were designed to include a near sea surface horizontal transect in a region of minimal cloud cover during or near the time of an Aqua and/or Terra satellite overpass, in addition to a low altitude flyby and vertical profile above the NOAA ship Ronald H. Brown. In this paper, we will compare AATS-14 water vapor profiles with simultaneous measurements obtained with a Vaisala humidity sensor on board the J-31 and with spatially and temporally near-coincident data from radiosondes launched from the Ron Brown. AATS-14 data will also be compared with water vapor retrievals from measurements acquired by remote sensors on Aqua and Terra during near-coincident satellite overflights.