Results will focus on cirrus events which occurred during the ARM FIRE
Water Vapor Experiment (AFWEX 2000) and Texas 2002 (TX2002) field campaigns over the Southern Great Plains Cloud and Radiation Testbed site (Oklahoma, USA) on 8 December 2000 and 29 November 2002, respectively. Aircraft measurements were taken from the NPOESS Airborne Sounder Testbed-Interferometer (NAST-I) during AFWEX 2000 and the Scanning-High resolution Infrared Sounder (S-HIS) during TX2002. Surface measurements were acquired by the Atmospheric Emitted
Radiance Interferometer (AERI), located at the Central Facility. A
second AERI, operating in rapid-scan mode within the University of
Wisconsin mobile AERIbago, was available during the Texas 2002 case.
Spectral absorption optical depths were retrieved using the high spectral resolution infrared measurements combined with lidar measured cloud boundaries. The spectral variation in each optical depth measurement were used to infer cloud particle effective radius from a database of hexagonal column extinction calculations. Results will compare cloud optical properties from simultaneous below- and above-cloud measurements.
This study presents a new technique for the separation of land surface infrared emissivity and surface skin temperature using high spectral resolution infrared observations. High spectral resolution observations of upwelling radiance at 20 km altitude were obtained by the Scanning High-resolution Interferometer Sounder (S-HIS) aboard the NASA ER-2 aircraft during the TX-2001 experiment. These aircraft observations are used in conjunction with complementary ground-based observations of downwelling radiance at the surface to estimate the surface skin temperature and absolute emissivity for a region in north central Oklahoma, USA. Coincident MODIS Airborne Simulator (MAS) observations are used to quantify the land surface variability within the S-HIS scene in the vicinity of the DOE ARM Southern Great Plain central facility. Ground truth data is presented from a ground based Scanning Atmospheric Emitted Radiance Interferometer. This remote sensing technique has application to satellite based observations from the NASA AIRS, the NPOESS CrIS, the EUMETSAT IASI, and the NASA GIFTS instruments.
Ground-based Atmospheric Emitted Radiance Interferometer (AERI) and
Raman Lidar measurements are used to infer cirrus cloud absorption optical depth and effective particle size. Our methodology will be discussed, and results shown for a number of contrasting cloud cases. The high spectral resolution AERI measurements allow inversion of the infrared radiative transfer equation between gaseous absorption lines (e.g., regions of minimal atmospheric emission), referred to as microwindows, to derive the cloud infrared absorption optical depth. Spectral variation in the cloud optical depth yields information on particle size and shape. A best fit of absorption optical depth to the measured absorption optical depth in each microwindow is used to determine the effective radius of particles within the cloud. Results will also be compared to simultaneous upwelling aircraft measurements.
This paper evaluates the performance of two techniques currently under development for use in the future validation of AIRS surface emissivity measurements over the Southern Great Plains Atmospheric Radiation Measurement site in Oklahoma, USA. The first technique involves a simultaneous retrieval of atmospheric temperature and water vapor, sruface skin temperature, and surface emissivity using a statistical approach; the second, a relative retrieval of the relative surface emissivity from spectral radiance observations between gaseous absorption lines. High spectral resolution upwelling radiance measurements from the aircraft-based NPOESS Atmospheric Sounder Testbed-Interferometer (NAST-I) obtained during the ARM/FIRE Water Vapor Experiment 2000 and Chesapeake Lighthouse and Aircraft Measurements for Satellites 2001 were used to compare each method. Surface truth was provided by ground-based Atmospheric Emitted Radiance Interferometer measurements.
The ARM-FIRE Water Vapor Experiment (AFWEX) was conducted during November-December 2000 at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART). A cirrus event which occurred on 7-8 December was analyzed using ground- and aircraft-based measurements. The ground-based Atmospheric Emitted Radiance Interferometer (AERI) and NPOESS Airborne Sounder Testbed-Interferometer (NAST-I) are high spectral resolution interferometers which measure downwelling and upwelling infrared radiation, respectively. Analysis between water vapor absorption lines within the 8 to 12 μm atmospheric window allow inversion of the radiative transfer equation to derive the cirrus cloud optical depth. These data will be compared to ground-based Raman lidar (GSFC and ARM) measurements of cirrus optical depth. The NAST-I measurements were conducted from the Proteus aircraft.
High spectral resolution Fourier transform spectrometry has been used to derive cirrus cloud optical properties. Data from both ground- and aircraft-based observations, combined with lidar and radiosonde measurements, will be shown from various field campaigns to demonstrate our approach. Ground-based results are from the Atmospheric Emitted Radiance Interferometer, based at the Atmospheric Radiation Measurement program Cloud and Radiation Testbed. Aircraft measurements are from the Scanning High-resolution Interferometer Sounder acquired during the SAFARI-2000 mission in South Africa. It is anticipated that long-term cirrus measurements on a seasonal scale will produce a cloud climatology based on synoptic conditions which can be parameterized on a global scale for use in GCMs.
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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