Geoscience Reference
In-Depth Information
1 Introduction
Tropospheric ozone is a main component of the summer smog. The investigation of
tropospheric ozone based on satellite measurements has been performed for a long
time to improve the understanding of its sources, sinks and transport processes
(Thompson 2001 ). The Limb-Nadir matching (LNM) technique is one of the
residual methods to retrieve tropospheric ozone by subtracting the stratospheric
ozone column (usually retrieved from limb or occultation measurements) from the
total ozone column (obtained from nadir observations). This technique has previ-
ously been used for over 20 years by combining measurements from two different
instruments (e.g., Fishman et al. 1990 , 1999 ; Thompson and Hudson 1999 ; Ziemke
et al. 1998 , 2006 , 2011 ; Schoeberl et al. 2007 ). Altering limb and nadir viewing
geometries within 7 min, the passive imaging spectrometer SCIAMACHY (Bur-
rows et al. 1995 ; Bovensmann et al. 1999 ) provides an opportunity to apply the
LNM technique to collect information about both total and stratospheric ozone for
the same volume of air from the same instrument. A SCIAMACHY tropospheric
ozone database covering about 10 years (August 2002
April 2012) has been
-
generated by Ebojie et al. ( 2014 ).
As 90 % of ozone is located in the stratosphere, the usage of the LNM technique
requires very high accuracy of the input limb, nadir, and tropopause height data.
Our previous studies revealed that the current SCIAMACHY LNM retrieval
overestimates tropospheric ozone in northern high latitudes by 12
28 DU. In
addition to the need of LNM tropospheric ozone retrieval, an accurate stratospheric
ozone data base is also a requirement for stratospheric ozone trends study as well as
the establishment of a long-term essential climate variable (ecv) data record.
This work suggests a method to improve the results of SCIAMACHY limb
ozone retrieval in the lower stratosphere at high northern latitudes and provides a
-
cation results are presented in
terms of stratospheric ozone columns (integrated limb pro
first veri
cation of the obtained results. The veri
les) as they are the direct
input to the LNM technique. Section 2 introduces the limb measurements and
methodology of the limb partial column comparisons. Algorithm basics and limi-
tations of the current limb retrieval are described in Sect. 3 . Algorithm improve-
ments and
first veri
cation results for the upcoming SCIAMACHY limb retrieval
(V3.0)
follow in Sect. 4 . Section 5 summarizes our principal
results and
conclusions.
2 Limb Measurements and Comparison Methodology
The SCIAMACHY instrument operated from August 2002 to April 2012 on board
the European satellite Envisat (Bovensmann et al. 1999 ). SCIAMACHY was
designed to measure radiances in 8 channels covering a wide spectral range from
214 to 2,384 nm with a moderate spectral resolution of 0.21
1.56 nm depending on
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