Polar stratospheric clouds (PSCs) are known to play key roles in the springtime chemical depletion of ozone at high latitudes. PSC particles provide sites for heterogeneous chemical reactions that transform stable chlorine and bromine reservoir species into highly reactive ozone-destructive forms. Furthermore, large nitric acid trihydrate (NAT) PSC particles can irreversibly redistribute odd nitrogen through gravitational sedimentation, which prolongs the ozone depletion process by slowing the reformation of the stable chlorine reservoirs. Spaceborne observations from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite are providing a rich new dataset for studying PSCs. CALIOP began data collection in mid-June 2006 and has since acquired, on average, over 300,000 backscatter profiles daily at latitudes between 55° and 82° in both hemispheres. PSCs are detected in the CALIOP backscatter profiles as enhancements above the background aerosol in either 532-nm scattering ratio (the ratio of total-to-molecular backscatter) or 532-nm perpendicular-polarized backscatter. CALIOP PSCs are separated into composition classes based on the ensemble 532- nm scattering ratio and 532-nm particulate depolarization ratio (which is sensitive to the presence of non-spherical, i.e. NAT and ice particles). In this paper, we provide an overview of the CALIOP PSC measurements and then examine the vertical and spatial distribution of PSCs in the Arctic and Antarctic on vortex-wide scales for entire PSC seasons over the more than eight-year data record.
Aerosols and clouds play important roles in Earth's climate system but uncertainties over their interactions and their
effects on the Earth energy budget limit our understanding of the climate system and our ability to model it. The
CALIPSO satellite was developed to provide new capabilities to observe aerosol and cloud from space and to reduce
these uncertainties. CALIPSO carries the first polarization-sensitive lidar to fly in space, which has now provided a
four-year record of global aerosol and cloud profiles. This paper briefly summarizes the status of the CALIPSO mission,
describes some of the results from CALIPSO, and presents highlights of recent improvements in data products.
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.
Long-term measurements of the global distributions of clouds, trace gases, and surface reflectance are needed for
the study and monitoring of global change and air quality. The Geostationary Imaging Fabry-Perot Spectrometer
(GIFS) instrument is an example of a next-generation satellite remote sensing concept. GIFS is designed
to be deployed on a geostationary satellite, where it can make continuous hemispheric imaging observations of
cloud properties (including cloud top pressure, optical depth, and fraction), trace gas concentrations, such as tropospheric
and boundary layer CO, and surface reflectance and pressure. These measurements can be made with
spatial resolution, accuracy, and revisit time suitable for monitoring applications. It uses an innovative tunable
imaging triple-etalon Fabry-Perot interferometer to obtain very high-resolution line-resolved spectral images of
backscattered solar radiation, which contains cloud and trace gas information. An airborne GIFS prototype and
the measurement technique have been successfully demonstrated in a recent field campaign onboard the NASA
P3B based at Wallops Island, Virginia. In this paper, we present the preliminary GIFS instrument design and
use GIFS prototype measurements to demonstrate the instrument functionality and measurement capabilities.
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.
Recent assessments of global climate change conclude that the radiative effect of aerosols is one of the largest uncertainties in our ability to predict future climate change. A myriad of new sensors and satellite missions are being designed to address this major question confronting credible prediction of climate change. The NASA Langley Airborne A-Band Spectrometer (LAABS) is a recently developed aircraft instrument that provides high spectral resolution (~0.03 nm) radiance measurements of reflected sunlight over the oxygen A-band spectral region centered near 765 nm. High resolution O2 A-band spectrometry of reflected sunlight is a promising new approach for remote sensing of aerosol and cloud optical properties. While the LAABS instrument provides valuable data on a stand-alone basis, greater scientific return may be realized by combining the A-band spectra with coincident lidar measurements that supply additional information on the vertical distribution of the aerosol. In particular, an instrument suite that combines LAABS with the new airborne High Spectral Resolution Lidar (HSRL) has the potential to provide a comprehensive suite of aerosol and cloud optical property measurements never before achieved. In this paper, we investigate the combined use of LAABS and HSRL measurements to infer aerosol single scatter albedo. We explore the information content of the O2 A-band reflectance spectra and, in particular, the advantages offered by high resolution A-band spectrometers such as LAABS. The approach for combined LAABS/HSRL retrievals is described and results from simulation studies are presented to illustrate their potential for retrieval of single scatter albedo.
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.
Recent theoretical studies have demonstrated the potential of spaceborne high spectral resolution O2 A-band spectrometers for retrieval of aerosol and cloud optical properties. High spectral resolution is the key to these retrievals because it permits a separation of the surface and atmospheric scattering components of the reflectance measurements. Although promising, this new approach poses numerous technical challenges related to instrument design, characterization, and calibration that have not been fully addressed by previous conceptual studies. To experimentally assess the capabilities of this promising new remote sensing application, the NASA Langley Research Center has developed the Langley Airborne A-Band Spectrometer (LAABS). This instrument will serve as a unique test bed to evaluate the impact of realistic instrument performance on A-band retrieval capabilities. After full characterization of the instrument through laboratory testing, a detailed forward model of the instrument's radiance measurements will be developed. The instrument model will be validated against actual measured spectra obtained from ground-based operations of the instrument. Airborne A-band spectra obtained during initial test flights of this instrument during the CLAMS field campaign in July 2001 will be analyzed to assess aerosol retrieval capability.
12 Atmospheric remote sensing with the O2 A-band has a relatively long history, but most of these studies were attempting to estimate surface pressure or cloud-top pressure. Recent conceptual studies have demonstrated the potential of spaceborne high spectral resolution O2 A- band spectrometers for retrieval of aerosol and cloud optical properties. The physical rationale of this new approach is that information on the scattering properties of the atmosphere is embedded in the detailed line structure of the O2 A-band reflected radiance spectrum. The key to extracting this information is to measure the radiance spectrum at very high spectral resolution. Instrument performance requirement studies indicate that, in addition to high spectral resolution, the successful retrieval of aerosol and cloud properties from A-band radiance spectra will also require high radiometric accuracy, instrument stability, and high signal-to-noise measurements. To experimentally assess the capabilities of this promising new remote sensing application, the NASA Langley Research Center is developing an airborne high spectral resolution A-band spectrometer. The spectrometer uses a plane holographic grating with a folded Littrow geometry to achieve high spectral resolution (0.5 cm-1 and low stray light in a compact package. This instrument will be flown in a series of field campaigns beginning in 2001 to evaluate the overall feasibility of this new technique. Results from these campaigns should be particularly valuable for future spaceborne applications of A-band spectrometers for aerosol and cloud retrievals.
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.