Comparison of Airborne Sunphotometer and NearCoincident In Situ and Remotely Sensed Water Vapor Meas

1
Comparison of Airborne Sunphotometer and
Near-Coincident In Situ and Remotely Sensed Water
Vapor Measurements during INTEX-ITCT 2004 J.
Livingston1, B. Schmid2, J. Redemann2, P.
Russell3, S. Ramirez2, J. Eilers3, W. Gore3, S.
Howard2, J. Pommier2, T. Bates4, P. Quinn4, D. A.
Chu5, Bo-Cai Gao6, E. Fetzer7, W. McMillan8, S.
Wetzel Seeman9, E. Borbas9 1SRI International,
Menlo Park, CA USA, 2Bay Area Environmental
Research Institute, Sonoma, CA USA, 3NASA Ames
Research Center, Moffett Field, CA USA, 4NOAA
PMEL, Seattle, WA USA, 5NOAA Goddard Space Flight
Center, Greenbelt, MD USA, 6Naval Research
Laboratory, Washington, DC USA, 7Jet Propulsion
Laboratory, California Institute of Technology,
Pasadena, CA USA, 8University of Maryland
Baltimore County, Baltimore, MD USA, 9University
of Wisconsin Madison, CIMSS, Madison, WI USA
AATS-14, J31 Vaisala, and MODIS Retrieval
Comparisons
AIRS Retrieval Comparisons
Abstract
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 12 July 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 compare
AATS-14 water vapor profiles with simultaneous
measurements obtained with a Vaisala humidity
sensor on board the J31 and with spatially and
temporally near-coincident data from radiosondes
launched from the Ron Brown. AATS-14 water vapor
retrievals are also compared with retrievals from
measurements acquired by the Moderate Resolution
Imaging Spectroradiometer (MODIS) on Aqua and
Terra and by AIRS (Atmospheric Infrared Sounder)
on Aqua during near-coincident satellite
overflights.
21 July
29 July
Aqua MODIS overpass time
08 Aug
AATS-14 retrievals and J31 Vaisala measurements
are overplotted with temporally and spatially
near-coincident water vapor density retrievals
from the Atmospheric Infrared Sounder (AIRS)
during three Aqua overflights. Left J31 flight
tracks color-coded according to aircraft
altitude location of AIRS grid centers (colored
upward-pointing triangles) where water vapor
profiles have been retrieved at standard
atmosphere pressure surfaces. Right overlays of
AIRS water vapor density profile retrievals
(colored upward-pointing triangles connected by
dashed lines for ease in viewing) at the
locations shown in the adjacent map and
corresponding water vapor density retrievals from
AATS-14 and J31 Vaisala measurements during the
J31 ascent or descent nearest in time and space
to the AIRS retrievals.
02 Aug
Airborne, balloonsonde, and satellite water vapor
retrievals are presented for four MODIS
overflights. Left frames temporal plots of J31
altitude and AATS-14 retrievals of columnar water
vapor (CWV, g/cm2 or precipitable cm) above
aircraft altitude. Middle left frames profiles
of CWV and water vapor density derived from
measurements made by AATS-14, J31 Vaisala
humidity sensor, and Vaisala balloonsonde
launched from NOAA Ship Ronald H. Brown. Middle
right frames color-coded maps of MODIS infrared
full column water vapor retrievals, complete J31
flight track overlay (dashed line), and
corresponding color-coded AATS-14 CWV above
aircraft altitude for J31 flight altitudes at or
below 100 m ASL. Right frames scatterplots of
MODIS-vs.-AATS CWV and MODIS-minus-AATS CWV
differences vs. AATS CWV no estimate of the
amount of water vapor in the layer between the
sea surface and the J31 has been added to the
AATS retrievals.
AATS-14 and J31 Vaisala Retrieval Comparisons
during J31 Vertical Profiles
Detailed comparisons (top three multi-frame
plots) of AATS-14 retrievals of columnar water
vapor or water vapor density and coincident J31
Vaisala humidity sensor measurements are shown
for 33 separate J31 vertical profiles. Results
for all 33 cases are summarized in
AATS-vs.-Vaisala scatterplots (Bottom left) the
amount of water vapor in the layer between the
lowest and highest aircraft altitudes for a
particular profile, (Bottom middle) water vapor
density at all altitudes, and (Bottom right)
water vapor density at altitudes below 3 km.
Funding for this research has been provided by
the NOAA Atmospheric Chemistry and Climate
Program, the NASA Tropospheric Chemistry Program,
the NASA Radiation Sciences Program, and the NASA
Earth Observing System Inter-Disciplinary
Sciences (EOS-IDS) Program.