Scheduled for launch in October 2011, the NPOESS Preparatory Project (NPP) mission includes the Ozone Mapping and
Profiler Suite (OMPS) which is composed of two Nadir looking sensors and an Earth-limb viewing sensor. This paper is
concerned with the OMPS limb sensor, the primary product of which is an ozone vertical profile with a 1.5 km vertical
resolution, a vertical range of cloud top to 60 km and an along-track spacing of 125 km. Secondary products include
stratospheric aerosol vertical distribution, cloud top height and NO<sub>2</sub> vertical profiles. The paper describes the OMPS
mission (sensor specifications, orbital characteristics, timeline), reviews the heritage in space-based ozone
measurements, illustrates the limb sensor expected performance (accuracy and precision), describes the planned product
validation effort (comparison with ground and space instruments) and defines the data release procedure (content, format
and release schedule).
The performance of the OMPS/LP retrieval algorithm is assessed by conducting a series of numerical experiments and
evaluating the quality of the primary (ozone profile) and secondary products (aerosol profiles, NO2, cloud height, surface
reflectance) as well as height registration under a set of realistic atmospheric conditions selected randomly. The study
considers a number of orbits corresponding to Winter/Summer solstice and Spring/Autumn Equinox. It is shown that the
quality of the OMPS/LP retrieval products (accuracy, precision, vertical resolution, height registration) varies along the
orbit, as the single scattering angle transitions from backscatter to forward scatter and zenith angles vary from sunrise to
sunset. Instrument effects (straylight, gain consolidation, instrument noise) are also investigated. It is shown that ozone
profiles can be retrieved with an accuracy of 5% or better from the tropopause up to 50 km, a precision of about 3-5%
from 18 to 50 km, and a vertical resolution of 1.5-2 km. Stratospheric aerosol extinction profile can be retrieved with an
accuracy/precision of about 30%. The scene-based tangent height registration algorithm is shown to yield height
information with an RMS error of 250-300m.
An alternative algorithm is being developed to retrieve ozone vertical distribution information from the OMPS/LP sensor
which will be manifested on the upcoming NPOESS Preparatory Project (NPP) platform in late 2011. In contrast to most
limb sensors retrieval methods, the proposed algorithm will forgo the spherical symmetry assumption for the
atmospheric structure, and will attempt to simultaneously retrieve the ozone distribution in both the vertical and the
along-track directions. The paper describes the two-dimensional forward model as well as the methods which have been
developed to simultaneously retrieve a whole orbit of data. Sample retrieval results are shown to illustrate the technique.
An alternative algorithm is being analyzed to retrieve ozone and aerosol vertical distribution information from the
OMPS/LP sensor which will be manifested on the upcoming NPOESS Preparatory Project (NPP) platform in early 2011.
The algorithm relies on the optimal estimation method to infer ozone density and aerosol extinction directly from the
radiance measurements made by the ensemble of CCD array pixels. The fundamentals of the technique are reviewed and
the advantages of the method with respect to the mainstream retrieval algorithm are discussed. Sample results are given
to illustrate the performance of the new method.
Three candidate algorithms for the retrieval of ozone profile for the NPP OMPS Limb Profiler are described. The first
one relies on the well established Doublet/Triplet method coupled with Optimal Estimation. The second one performs
spectral fitting and uses Multiple Linear Regression. The last one is a direct application of the Optimal Estimation
method on the actual CCD array measurements. The fundamentals of each technique are reviewed and their
advantages/disadvantages are discussed. Sample results are given to illustrate the performance of each method.
Solar occultation observations made by the SAGE family of space instruments have provided a record of global
stratospheric and upper tropospheric aerosols that extends over 25 years. Since the demise of SAGE II and SAGE III
however, there are presently no space instruments devoted to continuing this aerosol data set. The paper aims to
demonstrate that aerosol extinction profiles, together with a moment of the size distribution, can be accurately retrieved
from Limb Scatter measurements. The methodology is described, and retrieval examples are presented using data from a
Limb Scatter instrument, namely SAGE III. The retrieved extinction profiles are compared with SAGE II and SAGE III
occultation aerosol products for a series of wavelengths. It is shown that the relative retrieval accuracy is good (less than
5%), with a relative precision on the order of 25%. Once operational, it is planned to apply the retrieval method to the
data collected by the two still-operating Limb Scatter instruments (namely OSIRIS and SCIAMACHY) in order to
extend the aerosol data record into the present time. In the future, the OMPS Limb Profiler instrument, which is presently
manifested on NPP with a launch date of September 2009, will be used for additional stratospheric aerosol research.
Ozone profiles retrieved from SAGE III limb scatter measurements are compared with correlative measurements made by two occultation instruments (SAGE II, SAGE III), a limb scatter instrument (OSIRIS) and a series of ozonesondes, in order to ascertain the accuracy and precision of the SAGE III instrument in limb scatter mode. The measurement accuracy is found to be 5-10% from the tropopause to about 45km whereas precision is found to be less than 10% from 20 to 38km. The main source of error is height registration uncertainty, which is found to be Gaussian with a standard deviation of about 400m.
The ability of SAGE III to retrieve ozone, NO<sub>2</sub> and aerosol vertical distribution within Earth atmosphere from limb scatter measurements is being investigated. The sunlight scattered by atmospheric gases and particulates (aerosol, clouds) and the Earth's surface is measured and spectrally dispersed by SAGE III spectrometer. Ozone density vertical profiles are retrieved from 10 km (or cloud top) to 50 km at a resolution of about 1 km and a precision of less than 10 % using Chappuis and Huggins ozone absorption bands. NO<sub>2</sub> vertical density profiles are retrieved from 15 to 40 km at a resolution of about 2 km and a precision of 20% using the NO<sub>2</sub> absorption features in the 430-450 nm spectral range. Aerosol extinction vertical profiles (from 15 to 30 km) are retrieved using a series of non absorbing channels. Retrieved products are compared with available correlative data (ozone sondes, SAGE III in occultation, OSIRIS).
The Ozone Mapping Profiler Suite will produce ozone profiles using the limb scatter technique. While this technique has been used in the 1980s for mesospheric retrievals with data from the Solar Mesospheric Explorer, its use for the stratosphere and upper troposphere is relatively recent. To increase the scientific experience with this method, the Limb Ozone Retrieval Experiment LORE was flown on-board STS107 in 2003. A significant amount of data from
thirteen orbits was down-linked during the mission and exists for analysis. LORE was an imaging filter radiometer, consisting of a linear diode array, five interference filters (plus a blank for dark current) and a simple telescope with color correcting optics. The wavelengths for the channels were 322, 350, 602, 675 & 1000 nm and can be viewed as a minimum set of measurements needed for ozone profiling from 50 km to 10 km. The temporal sampling of the channels, along with the shuttle orbital and attitude (e.g. pitch) motions present a challenge in retrieving precise ozone profiles. Presented are the retrieval algorithms for determination of the channel's altitude scale, cloud top height and aerosol extinction. Also shown are a sub-set of flight data and the corresponding retrieved ozone profiles.
The limb scattering radiances measured by SAGE III are analyzed. After accounting for instrument issues, ozone and nitrogen dioxide vertical density profiles are retrieved from the data and compared with results from other instruments. These initial results are very promising and show the potential of SAGE III to operate in this mode.
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.
12 Atmospheric remote sensing with the O<SUB>2</SUB> 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 O<SUB>2</SUB> 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 O<SUB>2</SUB> 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<SUP>-1</SUP> 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.