Retrieval of ozone column content from airborne Sun photometer measurements during SOLVE II: Comparison with coincident satellite and aircraft measurements

1
Retrieval of ozone column content from airborne
Sun photometer measurements during SOLVE II
Comparison with coincident satellite and aircraft
measurements J. Livingston1, B. Schmid2, P.
Russell3, J. Eilers3, R. Kolyer3, J. Redemann2,
S. Ramirez2, J-H. Yee4, C. Trepte5, L. Thomason5,
M. Pitts5, M. Avery5,C. Randall6, J. Lumpe7, R.
Bevilacqua8, M. Bittner9, T. Erbertseder9, R.
McPeters10, R. Shetter11, J. Kerr12, K.
Lamb13 1SRI International, Menlo Park, CA USA
2Bay Area Environmental Research Institute,
Sonoma, CA USA 3NASA Ames Research Center,
Moffett Field, CA USA 4Applied Physics
Laboratory, Johns Hopkins University, Laurel, MD
USA 5NASA Langley Research Center, Hampton, VA
USA 6Laboratory for Atmospheric and Space
Physics, University of Colorado, Boulder, CO USA
7Computational Physics, Inc., Springfield, VA USA
8Naval Research Laboratory, Washington, DC USA
9DLR (German Aerospace Center), Oberpfaffenhofen,
Wessling, Germany 10NASA Goddard Space Flight
Center, Greenbelt, MD USA 11National Center for
Atmospheric Research, Boulder, CO USA
12Environment Canada, Cobble Hill, BC Canada
13International Ozone Services, Inc., Toronto, ON
Canada
ATMOSPHERIC ATTENUATION
ABSTRACT
RETRIEVAL METHODOLOGY
During the 2003 SAGE (Stratospheric Aerosol and
Gas Experiment) III Ozone Loss and Validation
Experiment (SOLVE) II, the fourteen-channel NASA
Ames Airborne Tracking Sunphotometer (AATS-14)
was mounted on the NASA DC-8 aircraft and
measured spectra of total and aerosol optical
depth (TOD and AOD) during the sunlit portions of
eight science flights. Values of ozone column
content above the aircraft have been derived from
the AATS-14 measurements by using a weighted
least squares method that exploits the
differential ozone absorption in the seven
AATS-14 channels located within the Chappuis
band. We compare AATS-14 columnar ozone
retrievals with temporally and spatially
near-coincident measurements acquired by the SAGE
III and the Polar Ozone and Aerosol Measurement
(POAM) III satellite sensors. We also compare
AATS-14 ozone retrievals during selected DC-8
horizontal transects with total column ozone data
acquired by the Total Ozone Mapping Spectrometer
(TOMS) and the Global Ozone Monitoring Experiment
(GOME) satellite sensors. To enable these
comparisons, the amount of ozone in the column
below the aircraft is estimated either by
assuming a climatological model or by combining
SAGE and/or POAM data with high resolution
in-situ ozone measurements acquired during the
aircraft vertical profile at the start or end of
each flight. We also compare AATS-14 ozone
retrievals with values derived from coincident
measurements by two other DC-8 based solar
occultation instruments GAMS (the NASA Langley
Gas and Aerosol Monitoring System) and DIAS (the
NCAR Direct Beam Solar Irradiance
Spectroradiometer).
This graph shows the optical thickness (from
MODTRAN) due to Rayleigh and aerosol scattering
and gas absorption along a horizontal path from
10 km altitude to space for the AATS-14 spectral
range.
MAUNA LOA CALIBRATION COMPARISONS
We apply the method of King and Byrne 1976 to
retrieve columnar ozone from AATS-14 spectral
optical depth measurements. This approach
assumes that the spectral variation in aerosol
optical depth (AOD) can be described by a
quadratic fitting function in log-log space. The
amount of ozone is varied until the optimum least
squares fit is found between the resultant AOD
spectrum and that calculated using the fitting
function.
AATS-14 exoatmospheric detector voltages, Vo,
were calculated using the Langley plot technique
for sunrise measurements acquired at Mauna Loa
Observatory (MLO) before and after SOLVE II.
These plots show the effect of uncertainty in Vo
on retrieved ozone by comparing coincident
measurements by Dobson and Brewer spectrometers
with AATS-14 ozone retrievals that use either the
actual Vo values calculated from the Langley
analysis for the particular day or the mean Vo
values from the November and March calibration
data.
COMPARISONS WITH SAGE III AND POAM III
24 Jan 2003
column O3 DU
(d)
(e)
Plots (a) and (b) show the variation in AOD and
columnar ozone, respectively, measured by AATS-14
during the 24 Jan 2003 flight. AATS-14 and GAMS
retrievals of ozone number density along the line
of sight (LOS) are plotted in (c), and agree to
within an rms difference of 4.4. In (d) and
(e), the spatio-temporal variation in AATS-14
columnar ozone along the DC-8 flight track is
shown for data acquired at flight altitudes of
9.9 km (10.6-10.9 UT and 11.8-12.2 UT) and 8.74
km (11.0-11.7 UT), respectively. Values are
consistent with the integrated 10.98 UT SAGE III
retrieval (color coded dot).
AATS-14 columnar ozone retrievals have been
compared with temporally and spatially
near-coincident SAGE III and POAM III
measurements of ozone number density during four
satellite solar occultation events each. The rms
difference between AATS-14 retrievals and
integrated SAGE III values is 19 DU (6), and the
rms difference between corresponding AATS-14 and
POAM III retrievals is 10 DU (3).
COMPARISONS WITH TOMS and GOME
21 Jan 2003
19-20 Dec 2002
AATS-14 retrievals are shown for the DC-8
southbound and northbound flight segments before
(blue southbound, black northbound) and after
(yellow for both directions) adding an estimate
of the amount of ozone below aircraft altitude.
DIAS ozone retrievals (green) obtained during the
northbound transect agree with AATS-14 values to
within a few DU except at the northern and
southern DIAS data boundaries. Adjusted AATS-14
values reflect a latitudinal gradient similar to
that indicated by corresponding TOMS and GOME
total column retrievals interpolated to the DC-8
flight track (southbound cyan, northbound
gray), but exceed the satellite data, which
exhibit significant temporal variation, at most
latitudes.
6 Feb 2003
GOME composite 12UT
Edwards AFB
AATS-14 retrievals are presented for data
acquired during the DC-8 return flight from
Sweden to California. Data are shown for the
latitudinal transect (blue) from 49N to 35N at
12.4 km altitude and for the final descent (red)
from 12.4 km to 1.1 km into Edwards Air Force
Base. The yellow band displays the range of
values that results after adding estimates of the
amount of ozone below aircraft altitude. AATS-14
retrievals agree well with corresponding TOMS and
GOME measurements (cyan) both in shape and in
magnitude.
COMPARISON WITH IN-SITU DATA DURING DC-8 DESCENT
ON 6 FEB 2003
AATS-14 columnar ozone retrievals for data
acquired during the DC-8 descent into Edwards Air
Force Base are compared with coincident
measurements from FASTOZ, the NASA Langley
in-situ fast response ozone sensor on board the
DC-8. FASTOZ measurements of ozone concentration
(b) have been normalized to the AATS-14 columnar
ozone at 12.4 km altitude and vertically
integrated for comparison to AATS-14 retrievals
in (a). Differentiation of a cubic spline fit to
AATS-14 columnar ozone retrievals (a) yields
ozone concentrations that are compared to FASTOZ
data in (b). Not suprisingly, the second order
AATS-14 product is unable to reproduce the fine
structure seen by FASTOZ. In (c) and (d),
corresponding AATS-14 columnar water vapor
retrievals are shown to agree well with
coincident DC-8 based water vapor density
measurements from the NASA Langley Diode Laser
Hygrometer (DLH) and with nearby radiosonde data
acquired 1.5 hr earlier.
AATS-14 columnar ozone retrievals are shown for
an extended longitudinal transect during the 21
Jan 2003 DC-8 flight. Coincident AATS-14 and DIAS
measurements agree to within an rms difference of
4.7 (20 DU). After the AATS-14 retrievals are
increased by the amount of ozone estimated to lie
in the column below aircraft altitude, values are
consistent with corresponding TOMS and GOME total
column ozone retrievals. The rms difference
between AATS retrievals and GOME retrievals
interpolated to DC-8 locations is 3.3 (12 DU).
REFERENCE
King, M. D., and D. M. Byrne, A method for
inferring total ozone content from the spectral
variation of total optical depth obtained with a
solar radiometer, J. Atmos. Sci., 33, 2242-2251,
1976.