Exploiting the inherent redundancy in hyperspectral observations, Principle Component Analysis (PCA) is a simple yet very powerful tool not only for noise filtering and lossy compression, but also for the characterization of sensor noise and other variable artifacts using Earth scene data. Our approach for dependent set PCA of radiance spectra from the Atmospheric Infrared Sounder (AIRS) on NASA Aqua is presented. Aspects of the analyses include 1) estimation of NEDT and comparisons to values derived from on-board blackbodies, 2) estimation of the signal dependence of NEDN, 3) estimation of the spectrally correlated component of NEDT, 4) investigation of non-Gaussian noise behavior, and 5) inspection of individual PCs. The results are generally consistent with results obtained pre-launch and on-orbit using blackbody and space view data. Specific findings include: 1) PCA estimates of AIRS spectrally random and spectrally correlated NEDN compare well with estimates computed from blackbody and space views, 2) the signal dependence of AIRS NEDN is accurately parameterized in terms of scene radiance, 3) examination of the reconstruction error allows non-Gaussian phenomenon such as popping to be characterized, and 4) inspection of the PCs and filtered spectra is a powerful technique for diagnosing variable artifacts in hyperspectral data.
Exploiting the redundancy in high spectral resolution observations, dependent set Principle Component Analysis (PCA)
is a simple yet very powerful tool not only for noise filtering and lossy compression, but also for the characterization of
sensor noise and other variable artifacts using Earth scene data. Our approach for dependent set PCA of AIRS Earth
scene data is presented. Aspects of the analyses include 1) estimation of NEDT using PCA and comparisons to values
derived from on-board blackbodies, 2) estimation of the scene dependence of NEDN, 3) estimation of the spectrally
correlated component of NEDT and comparison to pre-launch analyses using blackbody views, 4) investigation of non-
Gaussian noise behavior, and 5) inspection of individual PCs. The results of the PCA analyses are generally consistent
with results obtained pre-launch and on-orbit using blackbody and/or space view data. Specific findings include: 1)
PCA estimates of AIRS spectrally random and spectrally correlated NEDN compare well with estimates computed from
on-board blackbody and space views, 2) the signal dependence of AIRS NEDN is accurately parameterized in terms of
the scene radiance, 3) examination of the reconstruction error allows non-Gaussian phenomenon such as popping to be
characterized, and 4) inspection of the PCs and individual PC filtered radiance spectra is a powerful technique for
diagnosing low level artifacts in hyperspectral data.
The international experiment EAQUATE (European AQUA Thermodynamic Experiment) was held in September 2004 in Italy and in the United Kingdom. The Italian phase, performed in the period 6-10 September 2004, was mainly devoted to assessment and validation of performances of new IR hyperspectral sensors and benefits from data and results of measurements of AQUA and in particular of AIRS. It is also connected with the preparatory actions of MetOp mission with particular attention to calibration and validation of IASI products (as water vapour and temperature profiles), characterization of semitransparent clouds and study of radiative balance, demonstrating the role of ground-based and airborne systems in validation operations.
The Italian phase of the campaign was carried out within a cooperation between NASA Langley Research Center, University of Wisconsin, the Istituto di Metodologie per l'Analisi Ambientale (CNR-IMAA), the Mediterranean Agency for Remote Sensing (MARS) and the Universities of Basilicata, Bologna and Napoli. It involved the participation of the Scaled Composites Proteus aircraft (with NAST thermal infrared interferometer and microwave radiometer, the Scanning HIS infrared interferometer, the FIRSC far-IR interferometer), an Earth Observing System-Direct Readout Station and several ground based instruments: four lidar systems, a microwave radiometer, two infrared spectrometers, and a ceilometer. Radiosonde launches for measurements of PTU and wind velocity and direction were also performed as ancillary observations. Four flights were successfully completed with two different AQUA overpasses. The aircraft flew over the Napoli, Potenza and Tito Scalo ground stations several times allowing the collection of coincident aircraft and in- situ observations.
In the present work we show the potential of multiangular hyperspectral PROBA-CHRIS data to estimate aerosol optical properties over dense dark vegetation. Data acquired over San Rossore test site (Pisa, Italy) have been used together with simultaneous ground measurements. Additionally, spectral measurement over the canopy have been performed to describe the directional behavior of a Pinus pinaster canopy. Determination of aerosol properties from optical remote sensing images over land is an under-determined problem, and some assumptions have to be made on both the aerosol and the surface being imaged. Radiance measured on multiple directions add extra information that help in reducing retrieval ambiguity. Nevertheless, multiangular observations don't allow to ignore directional spectral properties of vegetation canopies. Since surface reflectivity is the parameter we wish to determine with remote sensing after atmospheric correction, at least the shape of the bi-directional reflectance factor has to be assumed. We have adopted a Rahman BRF, and have estimated its geometrical parameters from ground spectral measurements. The inversion of measured radiance to obtain aerosol optical properties has been performed, allowing simultaneous retrieval of aerosol model and optical thickness together with the vegetation reflectivity parameter of the Rahman model.
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) is the first hyper-spectral remote sounding system to be orbited aboard a geosynchronous satellite. The GIFTS is designed to obtain revolutionary observations of the four dimensional atmospheric temperature, moisture, and wind structure as well as the distribution of the atmospheric trace gases, CO and O3. Although GIFTS will not be orbited until 2006-2008, a glimpse at the its measurement capabilities has been obtained by analyzing data from the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Airborne Sounder Test-bed- Interferometer (NAST-I) and Aqua satellite Atmospheric Infrared Sounder (AIRS). In this paper we review the GIFTS experiment and empirically assess measurement expectations based on meteorological profiles retrieved from the NAST aircraft and Aqua satellite AIRS spectral radiances.
Development in the mid 80s of the High-resolution Interferometer Sounder (HIS) for the high altitude NASA ER2 aircraft demonstrated the capability for advanced atmospheric temperature and water vapor sounding and set the stage for new satellite instruments that are now becoming a reality [AIRS (2002), CrIS (2006), IASI (2006), GIFTS (2005/6)]. Follow-on developments at the University of Wisconsin-Madison that employ interferometry for a wide range of Earth observations include the ground-based Atmospheric Emitted Radiance Interferometer (AERI) and the Scanning HIS aircraft instrument (S-HIS). The AERI was developed for the US DOE Atmospheric Radiation Measurement (ARM) Program, primarily to provide highly accurate radiance spectra for improving radiative transfer models. The continuously operating AERI soon demonstrated valuable new capabilities for sensing the rapidly changing state of the boundary layer and properties of the surface and clouds. The S-HIS is a smaller version of the original HIS that uses cross-track scanning to enhance spatial coverage. S-HIS and its close cousin, the NPOESS Airborne Sounder Testbed (NAST) operated by NASA Langley, are being used for satellite instrument validation and for atmospheric research. The calibration and noise performance of these and future satellite instruments is key to optimizing their remote sensing products. Recently developed techniques for improving effective radiometric performance by removing noise in post-processing is a primary subject of this paper.
Current and future advanced atmospheric profile sounding and imaging instruments are evolving to enable global or hemispherical hyperspectral resolution measurements from space. The NASA/Navy/NOAA Geosynchronous Imaging FTS (GIFTS) for EO-3, NOAA Hyperspectral Environmental Sounder (HES) for GOES-R, and the currently operational Atmospheric Infrared Sounder (AIRS) on the NASA's Aqua Spacecraft will collect infrared high-spectral resolution/hyperspectral radiance spectra for remote sensing of the atmosphere, clouds, land, and ocean surfaces. These semi-continuous infrared high spectral- resolution/hyperspectral radiances will provide unprecedented information in the infrared region that is highly sensitive to absorption and emission of clouds. For sounding the atmospheric profiles one must perform cloud clearing or model the radiative effects of cloud explicitly if sounding is desired under cloud-contaminated conditions. We will describe the approach for modeling cloud attenuation in a fast-parameterized forward model that treats clouds as an additional absorber. Together with the usual clear forward model spectroscopic inputs, cloud altitude, effective particle size and shape and its ice or liquid water content are required input variables. Based on this efficient cloudy radiative transfer model, the simulation of the spatial and temporal coherent radiance images in three dimensions becomes possible. We will further explain how these 3-D GIFTS radiance cubes are used as test bed for a variety of trade studies.
In this study we compare different approaches to retrieve Cloud Top Height (CTH), Cloud Effective Emissivity (CEE), and the Cloud Particle Size (CPS) from aircraft high-spectral resolution infrared measurements. Two independent methods are used to infer CTH. One approach is based on a high spectral resolution version of the CO2 Slicing algorithm characterized by a statistically based selection of the optimal channel pairs. Another approach the Minimum Local Emissivity Variance algorithm (MLEV) takes advantage of high-resolution observations in the 8-12 micron region to simultaneously derive CTH and CEE. Once CTH has been retrieved a third method, based on the comparison between simulated and observed radiances, is used to infer CPS and CEE. Simulated radiances are computed for 18 microwindows between 8.5 and 12 microns. The cirrus scattering calculations are based on three-dimensional randomly oriented ice columns assuming six different particle size distributions. Multiple scattering calculations are performed for 26 different cloud optical thicknesses (COT) between 0 and 20. The simulated radiances are then compared to the observed radiances to infer COT and CPS for each spectral measurement. We applied these approaches to High-resolution Interferometer Sounder (HIS), National Polar-Orbiting Operational Environmental Satellite System Airborne Sounder Testbed-Interferometer (NAST-I) and Scanning-HIS (S-HIS) data. The preliminary results, consistent between the different algorithms, suggest that the high spectral resolution measurements improve the accuracy of the cloud property retrievals.
KEYWORDS: Clouds, Device simulation, Fourier transforms, Data processing, Data compression, Computer simulations, Sensors, Instrument modeling, Black bodies, Imaging systems
GIFTS, a forerunner of next generation geostationary satellite weather observing systems, will be built to fly on the NASA EO-3 geostationary orbit mission in 2004 to demonstrate the use of large area detector arrays and readouts. Timely high spatial resolution images and quantitative soundings of clouds, water vapor, temperature, and pollutants of the atmosphere for weather prediction and air quality monitoring will be achieved. GIFTS is novel in terms of providing many scientific returns that traditionally can only be achieved by separate advanced imaging and sounding systems. GIFTS' ability to obtain half- hourly high vertical density wind over the full earth disk is revolutionary. However, these new technologies bring forth many challenges for data transmission, archiving, and geophysical data processing. In this paper, we will focus on the aspect of data volume and downlink issues by conducting a GIFTS data compression experiment. We will discuss the scenario of using principal component analysis as a foundation for atmospheric data retrieval and compression of uncalibrated and un-normalized interferograms. The effects of compression on the degradation of the signal and noise reduction in interferogram and spectral domains will be highlighted. A simulation system developed to model the GIFTS instrument measurements is described in detail.
The National Polar-orbiting Operational Satellite System (NPOESS) Aircraft Sounder Testbed-Interferometer (NAST-I) is one of two airborne infrared sounder systems currently being used to evaluate future spaceborne advanced sounder designs. The NAST-I instrument is a cross-track scanning Fourier Transform Spectrometer (FTS) that measures the upwelling radiation in the infrared spectrum between 645 - 2700 cm-1 (15.5 - 3.7 micrometer) at a high-spectral resolution of 0.25 cm-1. Each observation has a spatial resolution of 2.6 km from NASA's ER-2 high-altitude aircraft, which operates 20 km above the surface. Measurements from this instrument in its first year of operation have not only contributed to risk reduction studies for future IR sounders but have also provided valuable datasets from three different climate regimes. The spatial coverage, 40 km swath width, has facilitated evaluation of non-linear retrieval algorithms using high-spectral resolution information content and provided a means for further validation of infrared radiative transfer models. The capabilities of the NAST-I instrument have already been tested under varied field conditions such as tropical, mid-latitude summer, and mid- latitude winter regimes. Preliminary results from these field experiments have demonstrated favorable sounding capability under such conditions, including intensive tropical cyclone environments (Hurricane Bonnie, August 1998 and Hurricane Georges, September 1998). In addition, repeated observations over the same geographic location near Andros Island in the Bahamas have provided additional information on the temporal change and spatial distribution of water vapor responding to complex mesoscale and large-scale dynamic processes. The framework for future spaceborne IR sounders will be well established by current and future observations made by the NAST-I instrument with its capability to remotely sense atmospheric state variables and cloud radiative properties.
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