In the stratosphere, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) has observed the
presence of aerosol plumes associated with the eruptions several volcanoes including Montserrat (May 2006), Chaiten
(May 2008), and Kasatochi (August 2008). While the dense ash plumes from these eruptions dissipate relatively quickly,
CALIPSO continued to detect an enhanced aerosol layer from the Montserrat eruption from the initial observations in
June 2006 well into 2008. Solar occultation missions were uniquely capable of monitoring stratospheric aerosol.
However, since the end of long-lived instruments like the Stratospheric Aerosol and Gas Experiment (SAGE II), there
has been no clear space-based successor instrument. A number of active instruments, some employing new techniques,
are being evaluated as candidate sources of stratospheric aerosol data. Herein, we examine suitability of the CALIPSO
532-nm aerosol backscatter coefficient measurements.
When the first observations of a tropospheric trace gas were obtained in the 1980s, carbon monoxide enhancements from
tropical biomass burning dominated the observed features. In 2005, an active remote-sensing system to provide detailed
information on the vertical distribution of aerosols and clouds was launched, and again, one of the most imposing
features observed was the presence of emissions from tropical biomass burning. This paper presents a brief overview of
space-borne observations of the distribution of trace gases and aerosols and how tropical biomass burning, primarily in
the Southern Hemisphere, has provided an initially surprising picture of the distribution of these species and how they
have evolved from prevailing transport patterns in that hemisphere. We also show how interpretation of these
observations has improved significantly as a result of the improved capability of trajectory modeling in recent years and
how information from this capability has provided additional insight into previous measurements form satellites.
The Wide Field Camera (WFC) is one of three instruments in the CALIPSO science payload, with the other two being
the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) and the Infrared Imaging Radiometer (IIR). The
WFC is a narrow-band, push-broom imager that provides continuous high-spatial-resolution imagery during the daylight
segments of the orbit over a swath centered on the CALIOP footprint. The instantaneous field of view of each WFC
pixel is approximately 125 m × 125 m when projected on the Earth's surface from an orbit altitude of 705 km. The
spectral band of the WFC, with a center wavelength of 645 nm and a FWHM bandwidth of 50 nm, is designed to match
the Aqua MODIS instrument's channel 1. The primary WFC Level 1 products are radiance and reflectance registered to
an Earth-based grid centered on the CALIOP ground track. "First light" WFC images were acquired on 18 May 2006
and routine data acquisition began in early June 2006. An initial science assessment of the WFC on-orbit performance
was conducted based on analysis of the first twelve months of flight data. Comparisons of the WFC measurements with
the well-calibrated Aqua MODIS channel 1 data were performed to evaluate the on-orbit radiometric performance of the
WFC. Overall agreement is excellent, especially over bright deep convective clouds where the WFC measurements
agree to within a few percent of MODIS. This paper provides a summary of our overall assessment of the on-orbit
radiometric performance of the WFC.
The Stratospheric Aerosol and Gas Experiment III/Meteor Instrument was launched from Baikonur, Kazakhstan on December 10, 2001. After initial commissioning phase activities, it began routine solar occultation measurements by March 2002. During the first year of operation, additional measurement capabilities such as lunar occultation and limb scattering were successfully implemented with the SAGE III instrument. This paper will present a summary of the various data sets gathered from the SAGE III instrument during the first year of operation. Measurements of ozone, aerosol, and nitrogen dioxide from solar occultation, lunar occultation, and limb scattering techniques will be presented and discussed.
This paper presents a comparison of the three forward model computational schemes, namely, Emissivity Growth Approximation (EGA), Curtis-Godson Approximation (CGA), and line-by-line (LBL) approach developed for SAGE III water vapor retrieval. For all three schemes, we have incorporated the most recent laboratory measurements of spectral line parameters to avoid the bias which is known to exist in HITRAN-96 database. Discussions are focused on the strength and weakness of each scheme with respect to accuracy and computational efficiency. The computer time for the LBL has been reduced significantly. The advantage of the LBL is manifest when the dependence of EGA and CGA on a huge pre-calculated lookup table and the breakdown of assumptions for these two schemes at lower altitudes are taken into account.
The Stratospheric Aerosol and Gas Experiment (SAGE) III is the fourth generation of solar occultation satellite instruments designed by NASA to measure vertical profiles of aerosol extinction and the molecular densities of gaseous species in the atmosphere. With an expanded spectral range compared with its predecessors, SAGE III has the capability to retrieve profiles of atmospheric temperature and pressure utilizing multi-spectral measurements of the oxygen A-band absorption feature near 762 nm. As part of NASA's Earth Science Enterprise, Earth Observing System, the first of two SAGE III instruments was successfully launched onboard the Meteor-3M satellite in December 2001. Given the inherent insensitivity of solar occultation experiments to long-term instrument degradation and the expected lifetime of the instruments (6+ years), the SAGE III instruments should provide a long-term record of self-calibrated, high vertical resolution temperature and pressure measurements. These measurements will be valuable for monitoring temperature trends in the stratosphere and mesosphere and for comparison studies with other temperature data sets.
This paper presents an overview of the SAGE III water vapor retrieval algorithm. Results of simulated retrieval are shown to demonstrate the advantages of the non-linear optimization algorithm in reducing the influence of the contributions due to interfering species. Diagnostic analyses of the retrieval are conducted to examine the characteristics of the matrices of contribution functions and the averaging kernels. The results indicate that high vertical resolution profiles of water vapor can be retrieved form the SAGE III measurements and the total random errors are less than 10% for altitudes below 42 km.
This study shows that the temperature information in the upper stratosphere can be derived from the SAGE II 385-nm observations. The preliminary results indicate that the zonal mean temperature increases with altitude below 50 km and decreases above 50 km. At 50 km, a regional maximum of 263 K is located in the tropics, and a minimum of 261 K occurs in the subtropics in both hemispheres. The derived long-term temperature changes from 1985 to 1997 reveal a statistically significant negative trend of -2 to -2.5 K/decade in the tropical upper stratosphere and about -2 K/decade in the subtropics near the stratopause. At latitudes poleward of 50 degrees, the results show a statistically significant positive trend of about 1 K/decade in the upper stratosphere. The preliminary results also show large annual temperature oscillations in the extratropics with a maximum amplitude of approximately 8 K located at about 44 km near 50 degrees in both hemispheres during local summer. In addition, the semiannual oscillation is found to be a maximum in the tropics with a peak amplitude of approximately 3.3 K located at about 42 km during the equinox.
KEYWORDS: Oxygen, Temperature metrology, Aerosols, Absorption, Error analysis, Signal to noise ratio, Solar radiation, Remote sensing, Ozone, Satellites
The Stratospheric Aerosol and Gas Experiment (SAGE) III will make multi-spectral measurements of the oxygen A-band absorption feature near 762 nm that can be used to retrieve profiles of temperature and pressure. The retrieval algorithm is based on a global fitting technique that uses a non-linear least squares procedure to simultaneously fit measured absorptivities from all spectral channels and slant paths. The feasibility of this approach is demonstrated through a series of simulated retrievals using synthetic measurements with realistic noise. An assessment of the expected uncertainties associated with the retrieved temperature and pressure data products is also provided.
The SAGE III is the fourth generation of solar occultation instruments designed to measure aerosols and trace gas species in the stratosphere and upper troposphere. It will be launched aboard a Meteor-3M platform in the summer of 1999 and the International Space Station Alpha in 2001. SAGE III preserves the robust characteristics of the SAGE series, including self-calibration and high vertical resolution, and adds new capabilities including a lunar occultation mode. This paper will describe the SAGE III instrument and outline its potential contribution to global change research.
The SAGE Ill and ILAS instruments are scheduled to be launched in 1998 and 1996,
respectively. These instruments will provide unique information regarding the composition and
size distribution of poiar stratosphere clouds. SAGE ffi, scheduled for a METEOR 3M launch,
will provide aerosol extinction measurements at 7 wavelengths in the visible and near-infrared
(385, 450, 525, 750, 940, 1020, and 1550 nm) from which the aerosol size distribution may be
inferred. ILAS, which will be launched aboard ADEOS, will provide continuous spectral
coverage between 6 and 12 tim. Extinction by aerosol at these wavelengths is strongly dependent
on the composition of the aerosol. The combination of measurements from these instruments
should provide substantially improved understanding of the microphysical character of PSCs and,
ultimately, into ozone depletion.
The Stratospheric Aerosol and Gas Experiment (SAGE III) is the fourth generation of solar occultation instruments designed to measure aerosols and trace gas species in the stratosphere and upper troposphere. It is scheduled to be launched aboard a Meteor-3M platform in the summer of 1998 and the International Space Station Alpha in 2001. SAGE III preserves the robust characteristics of the SAGE series, including self-calibration and high vertical resolution, and adds new capabilities including a lunar occultation mode. This paper describes the SAGE III instrument and outlines its potential contribution to global change research.
The Stratospheric Aerosol and Gas Experiment (SAGE) II solar occultation instrument has been making measurements on stratospheric aerosols and gases continually since October 1984. Observations from the SAGE II instrument provide a valuable long-term data set for study of the aerosol in the stratosphere and aerosol and cloud in the upper troposphere. The period of observation covers the decay phase of material injected by the El Chichon volcanic eruption in 1982, the years 1988 - 1990 when stratospheric aerosol levels approached background levels, and the period after the eruption of Mount Pinatubo in 1991. The Mount Pinatubo eruption caused the largest perturbation in stratospheric aerosol loading in this century, with effects on stratospheric dynamics and chemistry. The SAGE II data sequence shows the global dispersion of aerosols following the Mount Pinatubo eruption, as well as the changes occurring in stratospheric aerosol mass and surface area. The downward transfer of stratospheric aerosols into the upper troposphere following the earlier eruption of El Chichon is clearly visible. Estimates have been made of the amount of volcanic material lying in the upper troposphere and the way in which this varies with latitude and season.
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