Radiation & Climate: Major Projects
Retrieval of tropospheric ozone from simulations of nadir spectral radiances as observed from space.
Retrieved ozone profile for simulated radiances using an ozone profile from sonde observations at Ascension Island (ASC008a, September 12, 1990) reported by Fishman, et al. [1992].
The
global remote sensing of tropospheric ozone profiles is a critical
environmental measurement to be performed by future satellite
experiments. We have applied the method of nonlinear least squares
in conjunction with an efficient and accurate line-by-line radiative
transfer model to directly retrieve vertical profiles of tropospheric
ozone from simulated clear sky, nadir-viewing radiances covering
the entire 9.6 micron ozone band. The simulations have been generated
for the specifications of the tropospheric emission spectrometer
(TES), a Fourier transform spectrometer with 0.032 cm-1 resolution
(half width at half maximum (HWHM), unapodized) being developed
for NASA's Earth Observing System. Profile retrieval errors for
background tropospheric ozone levels are characterized as a function
of measurement noise, spectral resolution, and vertical resolution
based on a linear error analysis and an initial guess profile
with minimal constraint, hence negligible potential profile bias
at all altitudes. The main conclusions of the study are that (1)
for the TES experiment design, ozone profiles are retrievable
to approximately plus or minus 5% (1 sigma) for a vertical resolution
of 5 km in the middle and upper troposphere, (2) the stratospheric
portion of the profile must be retrieved directly from the measured
nadir spectrum, (3) for equal measurement times and considering
the effects of both systematic error and source radiance noise,
an optimal spectral interferometer resolution exists that is close
to the TES resolution (0.032 cm-1, HWHM unapodized), and (4) ozone
boundary layer retrievals are highly dependent on the contrast
between that layer and the surface. The results from an ozone
retrieval utilizing simulated radiances from an atmosphere defined
by a radiosonde observation at Ascension Island are considered
in the context of the solution of the nonlinear problem and the
nonlinear error analysis. The ozone retrieval analyses presented
in this paper are principally concerned with the effects of measurement
error and thus represent the optimal retrieval capability for
the assumed design. However, the availability of the full high-resolution
spectrum will enable the detection and mitigation of the systematic
errors.
References:
Clough, S.A., C.P. Rinsland, & P.D. Brown, Retrieval of tropospheric
ozone from simulations of nadir spectral radiances as observed
from space, J. Geophys. Res, 100, 16579-16593, 1995.
Fishman, J., V.G. Brackett, & K. Fakhruzzaman, Distribution of tropospheric ozone in the tropics from satellite and ozonesonde measurements, J. Atmos. Terr. Phys., 54, 589-597, 1992.
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