Geostationary Imaging Fourier Transform ... - SPIE Digital Library

Invited Paper

Geostationary Imaging Fourier Transform Spectrometer (GIFTS): Science Applications W. L. Smith1,2, H. E. Revercomb2, D. K. Zhou3, G. E. Bingham4, W. F. Feltz2, H. L. Huang2 R. O. Knuteson2, A. M. Larar3, X. Liu3, R. Reisse3, and D. C. Tobin2 1 Hampton University, Hampton Virginia, 23668 2 University of Wisconsin–Madison, Madison, Wisconsin, 53706 3 NASA Langley Research Center, Hampton Virginia, 23681 4 Utah State University, Logan Utah, 84323 ABSTRACT A revolutionary satellite weather forecasting instrument, called the “GIFTS” which stands for the “Geostationary Imaging Fourier Transform Spectrometer”, was recently completed and successfully tested in a space chamber at the Utah State University’s Space Dynamics Laboratory. The GIFTS was originally proposed by the NASA Langley Research Center, the University of Wisconsin, and the Utah State University and selected for flight demonstration as NASA’s New Millennium Program (NMP) Earth Observing-3 (EO-3) mission, which was unfortunately cancelled in 2004. GIFTS is like a digital 3-d movie camera that, when mounted on a geostationary satellite, would provide from space a revolutionary four-dimensional view of the Earth's atmosphere. GIFTS will measure the distribution, change, and movement of atmospheric moisture, temperature, and certain pollutant gases, such as carbon monoxide and ozone. The observation of the convergence of invisible water vapor, and the change of atmospheric temperature, provides meteorologists with the observations needed to predict where, and when, severe thunderstorms, and possibly tornados, would occur, before they are visible on radar or in satellite cloud imagery. The ability of GIFTS to observe the motion of moisture and clouds at different altitudes enables atmospheric winds to be observed over vast, and otherwise data sparse, oceanic regions of the globe. These wind observations would provide the means to greatly improve the forecast of where tropical storms and hurricanes will move and where and when they will come ashore (i.e., their landfall position and time). GIFTS, if flown into geostationary orbit, would provide about 80,000 vertical profiles per minute, each one like a low vertical resolution (1-2km) weather balloon sounding, but with a spacing of 4 km. GIFTS is a revolutionary atmospheric sensing tool. A glimpse of the science measurement capabilities of GIFTS is provided through airborne measurements with the NPOESS Airborne Sounding Testbed – Interferometer (NAST-I). Key Words: Remote Sensing, Radiation, Interferometer, Spectrometer, Satellite

1. INTRODUCTION The GIFTS was selected from a competitive proposal process in 1999 for the NASA New Millennium Program (NMP) Earth Observing - 3 (EO-3) mission to produce and space validate the technology and measurement concept intended to revolutionize severe storm and extended range weather prediction. The NMP EO-3 mission was cancelled in 2004 due to complex partnership challenges and budgetary constraints. In 2005, NASA completed the GIFTS instrument as an Engineering Development Unit (EDU) to mitigate imaging spectrometer risk on future research and operational satellites in geostationary (and other) orbits. During 2006, the GIFTS EDU science measurement capability was demonstrated through a series of thermal vacuum chamber characterization and calibration tests and by obtaining atmospheric and lunar imaging spectral radiance observations. In this paper, a brief overview of the GIFTS measurement concept is presented. The expected GIFTS geostationary satellite measurement capabilities are demonstrated with empirical results achieved using aircraft ultraspectral sounding radiance observations. Science results achieved with the GIFTS Engineering Demonstration Unit (EDU), through ground-based measurements during September 2006, are presented to demonstrate that the advanced GIFTS technologies have been successfully integrated to form the revolutionary atmospheric observation instrument called GIFTS. *[email protected]: phone: 1 757 869-6977: fax 1 757 874-7294

Multispectral, Hyperspectral, and Ultraspectral Remote Sensing Technology, Techniques, and Applications edited by William L. Smith Sr., Allen M. Larar, Tadao Aoki, Ram Rattan, Proc. of SPIE Vol. 6405, 64050E, (2006) 0277-786X/06/$15 · doi: 10.1117/12.696726 Proc. of SPIE Vol. 6405 64050E-1

2. GIFTS MEASUREMENT OBJECTIVE The measurement objective of GIFTS is to obtain high spatial and temporal resolution temperature, moisture, and wind profiles needed to revolutionize the prediction of localized severe weather, reduce tropical cyclone path and landfall forecasts errors, and improve initialization (and therefore forecast products) of global numerical weather prediction (NWP) models. The global NWP benefit from GIFTS winds is of particular interest over oceanic regions where there is a void of wind profile data. (The polar orbiting satellites currently provide temperature and moisture profiles over the oceans of the world, but not winds.) The wind profiling technique involves retrieving temperature and water vapor profiles from the radiance spectra observed for each footprint of the instrument at multiple time steps for the same area of the Earth. The result is high vertical resolution (approximately 1-2 km) temperature and water vapor mixing ratio profiles obtained using rapid profile retrieval algorithms (Zhou, et al. 2002; Smith, et al. 2004). For GIFTS, the profiles are obtained on a 4-km grid and then converted to relative humidity profiles. Images of the horizontal distribution of relative humidity for atmospheric levels, vertically separated by approximately 2 km, are constructed for each spatial scan. The sampling period ranges from minutes to an hour, depending upon the spectral resolution and the area coverage selected for the measurement. Successive images of clouds and the relative humidity structure for each atmospheric level are then animated to reveal the motion of small-scale thermodynamic features of the atmosphere1,2. Automated correlation feature tracking programs3,4 are then used to compute the speed and direction of movement of these small scale features, providing a measure of the wind velocity distribution at each atmospheric level. The net result is a dense grid of temperature, moisture, and wind profiles, which can be used for atmospheric analyses and operational weather prediction. The wind profiles observed with GIFTS over oceanic regions are particularly important for improving predictions of path and landfall position and time for tropical storms and hurricanes. This improvement is because these storms are steered by the deep layer mean wind flow in the cloudless environment surrounding the storm, which is not yet routinely observed over the oceans. Increasing the reliability of hurricane landfall position and time results in a more focused response for human evacuation and material preparation, thereby providing a significant reduction in the loss of lives as well as a large cost savings from the decreased warning area that must prepare for the devastating impacts of these storms. Aside from the ability to produce wind profiles for NWP and hurricane track forecast improvements, the GIFTS high vertical and temporal resolution soundings over land areas enable revolutionary improvements in severe thunderstorm and tornado forecasts. This improvement is because GIFTS enables rapid (approximately minutes to hourly, depending on sampling mode) detection of areas of decreasing atmospheric stability caused by solar heating and moisture convergence in the lowest levels of the atmosphere. As a consequence, the locations where intense convective storms develop are observable from the temperature and moisture fields long before clouds and precipitation occur and the storms can be seen in satellite cloud imagery or on radar. It is estimated that GIFTS can identify the location where severe convective storms will develop as much as an hour before they occur, thereby providing significant warning time to decrease death, injury, and property loss due to these storms. With GIFTS, the ultraspectral resolution infrared measurements now being made from polar orbiting satellites (i.e., Aqua AIRS and the METOP IASI instruments) are obtained at high temporal resolution (e.g., minutes to hourly) for fixed locations. Time sequences of the spatial fields of various greenhouse and pollutant gases (e.g., carbon dioxide, water vapor, carbon monoxide, and ozone), retrievable from GIFTS measured Earth radiance spectra, provide an observation of the transport of these trace gases. The observation of the transport of tropospheric carbon monoxide and ozone can be used for air quality forecasts. Simultaneous observation of the transport of water vapor and carbon dioxide is important for understanding the Earth’s water and carbon cycles, critical for predicting climate variability. Cloud radiative, microphysical, and geometrical properties are observed with GIFTS. The GIFTS sensitivity to these cloud parameters is key to being able to retrieve meteorological profiles under cloudy conditions, both down to the top of an opaque overcast cloud and below a thin cirrus and/or a broken cloud layer. The cloud properties are a by-product of the atmospheric sounding retrieval process5,6. The temporal sampling of these cloud properties during the formation and dissipation stage of various atmospheric processes (e.g., convective storm, El Nino, etc.) is useful for improving our understanding of cloud radiation feedback mechanisms in the life cycle of weather and climate systems.

Proc. of SPIE Vol. 6405 64050E-2

3. ULTRASPECTRAL SOUNDER CHARACTERISTICS Figure 1 illustrates the spectral coverage of the major ultraspectral sounders already developed for flight on polar and geostationary satellites. The AIRS (Chahine et. al., 2006) is a large focal plane detector array grating spectrometer that utilizes a separate detector element for each spectral channel. The IASI (Blumstein et. al., 2004), the CrIS (Glumb and Pedina, 2002), and the GIFTS (Smith et. al., 2000) are Fourier Transform Spectrometers (FTS). The spectral resolution of the AIRS is a constant relative resolution ( / = 1200), whereas the spectral resolutions for the IASI, CrIS, and GIFTS are a fixed absolute spectral resolution, being 0.25 cm-1, 0.625 cm-1, and 0.57 cm-1,unapodized, respectively. Currently, the CrIS data spectral resolution is planned to be reduced, on board the spacecraft, to 1.25 cm-1 and 2.50 cm-1 for its midwave and shortwave spectral bands, respectively, as a means to reduce the downlink data rate; although, there is strong scientific pressure to bring the data down at its full spectral resolution for all three spectral bands in order to realize the full potential of CrIS measurements. The FTS is a preferred instrumental approach to atmospheric sounding, since it uses the same detector element for observing most, if not all, of the radiances forming a spectrum, thereby optimizing the spectral continuity of the radiance measurements. The spectral precision of the radiance measurements is the single most important measurement quality required for the retrieval of small vertical scale sounding features from radiance spectra. Small vertical structure features are extracted through a de-convolution of the spectrum of radiance, in which each spectral radiance possesses very low vertical resolving power (8-15 km). Very high spectral relative accuracy is thus required to reveal the small vertical structure (1-2 km) atmospheric features contained in the small spectral variations of radiance that they produce. Since an FTS uses the same detector element to observe a large part of the radiance spectrum, spectrally varying calibration and co-registration errors are minimized with this instrument approach to ultraspectral sounding.

Figure 1: Spectral coverage of IASI, AIRS, CrIS, and GIFTS hyperspectral sounding instruments. The broad spectral channels of the current GOES filter wheel sounding instrument are shown for comparison.

4. GIFTS SCIENCE APPLICATIONS Radiance Measurements: GIFTS views areas of the Earth with a linear dimension in excess of 500 km, anywhere on the visible disk at collection rates between 0.125 and 11.0 seconds, depending on the data application (i.e., imaging, or sounding). GIFTS uses two co-aligned infrared detector arrays to cover spectral bands 685 to 1130 cm-1 and 1650 to 2250 cm-1 (Figure 2). The Michelson interferometer enables a wide range of spectral resolutions (Table 1). The GIFTS spectral characteristics are sufficient for achieving all scientific measurement objectives, including the sounding spatial and temporal resolution and accuracy desired for future operational geostationary satellite sounding instruments. The Michelson interferometer (FTS) approach for geostationary satellite applications allows spectral resolution to be easily


traded for higher area coverage or higher temporal resolution. Table 1 shows the area coverage, measurement frequency, spectral resolution, and geophysical measurement for example modes of operation for GIFTS. Quasi-continuous imagery of localized areas and minute-interval imagery of large-scale areas can be achieved. Full disk sounding coverage can be obtained every 7 minutes at contemporary NOAA operational satellite sounder spectral resolutions (e.g., 18 cm-1). High vertical resolution sounding and atmospheric chemistry measurements with GIFTS require 0.6 cm-1 spectral resolution and a longer stare time, thereby reducing the area coverage and/or the sounding refresh rate relative to the imagery mode of operation.

Figure 2. The science measurement objectives for various spectral regions observed within the 2 GIFTS spectral bands with spectral features of key atmospheric species and surface properties. Table 1. Example GIFTS operating modes showing geophysical measurement objective, spectral resolution, area coverage, and measurement frequency to meet GIFTS Science objectives. MODE

SPECTRAL RESOLUTION1

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Regional Imaging 36 cm-1 6,000 Global Sounding 18 cm-1 10,000 Global Wind Tracking 1.2 cm-1 10,000 Regional Sounding and Chemistry 0.6 cm-1 6,000 High SNR4 0.6 cm-1 1,000 1 Spatial resolution is 4 km. 2 Linear dimension (km) 3 Minutes; assumes a constant data rate associated with a Michelson mirror scan velocity of 0.17cm/sec telescope pointing step time 4 Provides radiometric precision better than 0.1 K

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Temperature, Moisture, and Wind Profiles: Ultraspectral resolution IR radiance measurements are used to determine temperature and moisture profiles with high vertical resolution10,11,12. The rapid repeat times of GIFTS measurements


enable the production of wind profiles and record the time rate of change of thermodynamic features in the turbulent atmosphere leading to formation of severe storms, including tornadoes and hurricanes9. Wind profile estimates can be diagnosed through direct real-time assimilation of GIFTS radiance measurements, or the retrieved temperature and water vapor profile data, in a mesoscale numerical model13,14. Alternatively, vertical profiles of wind velocity can be estimated by tracking the horizontal displacement of features in retrieved water vapor profiles. Such a feature-tracking approach that employs imager and sounder radiance fields is now used operationally and has been shown to provide improved weather forecasts on both regional and global scales15,16,17. However, the current GOES application only provides water vapor tracked winds derived from three broad water vapor channels18,3, which limits the vertical resolution and accuracy of the wind product. More complete vertical profiles of wind velocity are needed to realize the full potential of satellite measurements to improve both regional scale intense weather forecasts and global scale synoptic weather predictions2,19. Temperature: The Temperature Profile Objective for GIFTS is to provide high resolution, vertical (1 km to 2 km) and horizontal (4 km by 4 km), temperature profiles with 1 K accuracy. Figure 3 displays the high vertical resolution temperature sounding capability expected for GIFTS, as demonstrated with the NAST-I ultraspectral resolution passive infrared remote sounder flying aboard the NASA ER-2 aircraft20,5 The measurement was made near Hawaii along a 150 km flight track over an upper level thermal discontinuity, shown by the dropsonde data to be within a narrow vertical layer near 10 km. As can be seen by the color coded vertical-latitude cross-sections of the NAST-I and dropsonde temperature data, the soundings from the NAST-I resolve both the vertical and horizontal variability of atmospheric temperature, although with somewhat reduced vertical resolution than the point measuring dropsonde. A comparison of the vertical profile plots shown on the left hand side of Figure 3, shows that the GIFTS-like ultraspectral sounder can resolve vertical temperature profile features with relatively high resolution within the surface boundary layer as well as within the free-troposphere. NASTI MEAN

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Figure 3. An illustration of the spatial variation of atmospheric temperature features resolved by NAST-I with a spatial resolution similar to the GIFTS. The dashed line denotes the altitude of the NOAA G-IV aircraft used to provide dropsondes beneath the NASA ER-2 aircraft, which was carrying the NAST-I instrument.

Water Vapor: The Water Vapor Profile Objective for GIFTS is to obtain high resolution, vertical (2 km) and horizontal (4 km by 4 km), tropospheric water vapor profiles with a 15 percent accuracy. Fine scale spatial features of the water vapor distribution are displayed by moist and dry layers, of 1 to 2 km atmospheric depth, clearly resolved in the NAST-I soundings shown in Figure 4. The vertical resolving power of GIFTS should be similar to that shown here for the NASTI airborne demonstrator. Figure 4 shows the capability of GIFTS to altitude-resolve small-scale horizontal features of the moisture field enables the vertical profile of wind velocity to be determined.


Winds: The Wind Profiling Objective for GIFTS is to obtain high resolution, vertical (2 km) and horizontal (50 km), cloud and water vapor tracer tropospheric wind profiles with a 4 m/s accuracy. NASA ER-2 NAST-I data have also been used to simulate a time sequence of GIFTS water vapor fields to test the wind-profiling concept. Shown in Figure 5 is a comparison between the wind velocity profile obtained by tracking horizontal water vapor features and that observed with an airborne Doppler Lidar over a small region (shown by the red oval) off the California coast. The water vapor and cloud tracer winds were produced from three consecutive frames of NAST-I retrieved water vapor humidity imagery

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using the UW-NOAA automatic wind tracking program, which operationally produces wind vector estimates from GOES radiance imagery2,19. The Doppler Wind Lidar (DWL) observation was made from a Twin Otter aircraft (G. D. Emmitt, personal communications) beneath the NAST-I. As can be seen, there is excellent agreement in the wind direction and reasonable agreement in the wind speed for these two independent measures of the velocity profile. The comparison is limited to the lower troposphere due to limitations in the signal to noise of the Doppler lidar above 3 km altitude. It is noted that the accuracy of the NAST-I, and the GIFTS, derived wind profiles is expected to increase with increasing altitude throughout the troposphere. The wind velocity errors are expected to be superior (less than 4 m/s) to those associated with current geostationary satellite single level operational cloud and water vapor radiance tracer results (approximately 6 m/s). The revolutionary aspect of GIFTS is that it provides access to the vertical dimension of the wind field with more accurate altitude assignment. Cloud Radiative Properties and Soundings with Cloud: Simultaneous retrieval of cloud height and cloud radiative/microphysical properties are required for accurate single field of view retrievals of atmospheric soundings in all cloud conditions. A time sequence of spatially coherent derived product images is used for wind profile determinations and for nowcasting severe weather. Accurate determination of cloud and moisture feature altitude is essential for deriving accurate wind vector profiles. The GIFTS algorithm concept for retrieving cloud parameters simultaneously with temperature and moisture profiles under cloudy conditions has been demonstrated with NAST-I measurements20,21,6. The employment of this novel algorithm is made possible by the cloud information signatures available in infrared radiance spectra. Accurate soundings down to cloud top level, and beneath semi-transparent and/or broken cloud can be obtained on a single field of view basis. This capability greatly increases the density of sounding data for constructing the imagery used for tracking retrieved water vapor features and clouds. The algorithm has been applied to NAST-I data and validated by the Cloud Physics Lidar (CPL) and dropsondes. The retrieval results of cloud and thermodynamic parameters are shown in Figure 6. Panel (a) is a plot of retrieved cloud top height compared with the CPL observed heights for the 2 highest cloud layers (L1 and L2). Panel (b) is a plot of retrieved visible cloud optical thickness (COT) compared with the CPL measurements. Panel (c) is a plot of the retrieved cloud particle size. Panels (d) and (e) are plots of the retrieved temperature and relative humidity vertical cross sections, respectively. The “white” regions of the color-coded atmospheric profile cross-sections indicate the lack of sensitivity due to the existence of an opaque cloud (defined as having a visible optical thickness greater than unity). The black vertical bars in panel (d) indicate dropsonde locations. As shown in Figure 6, accuracies similar to those achieved in totally cloud-free conditions can be achieved down to cloud top level. The accuracy of the profile retrieved below the cloud top level is dependent upon the optical thickness and fractional coverage of the clouds.


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Figure 6. Cloud properties captured by ultraspectral NAST-I measurements will also be obtainable by GIFTS. The horizontal consistency of the cross-section indicates that accuracies close to those achieved in totally cloud-free conditions are achieved down to 6 cloud top level (after Zhou et. al ).

Trace Gas Concentrations: The GIFTS capability to observe trace gas concentrations, together with the water vapor winds, is important for monitoring the global transport of pollutant gases resulting from biomass burning and industrial sources. GIFTS water vapor and trace gas motion sensing provide the capability to observe chemical pollutant episode evolution and transport. The use of ultraspectral sounding capability to detect and track pollutant CO, impacting air quality, has been demonstrated with AIRS data (McMillan, et al. 2005; McMillan, et al. 2006). Ozone profiles are currently retrieved from AIRS radiances with a precision of 10 percent (Chris Barnet, NOAA/NESDIS, personal communication). GIFTS measurements determine the time varying spatial distribution of tropospheric O3 with a 3 to 11 km vertical resolution and free troposphere CO with a 3 to 8 km vertical resolution (Figure 7), the vertical resolution being dependent on the temperature structure of the atmosphere and the surface air temperature/surface skin temperature contrast.

5. GIFTS ENGINEERING DEMONSTRATION UNIT (EDU) SCIENCE RESULTS The GIFTS EDU has been characterized and calibrated in a series of thermal vacuum tests performed at the Utah State University Space Dynamics Laboratory (USU-SDL) during the fall of 2005 and spring of 2006. The results demonstrate that the instrument, as designed and fabricated, meets the demanding radiometric and spectral measurement requirements for the intended science measurement applications of this new imaging Fourier transform spectrometer. Subsequent up-looking observations have also validated this conclusion by viewing an atmospheric source with spectral line characteristics similar to those to be viewed from space. Radiometric sensitivity and detector operability of the current GIFTS EDU indicates the retrieval accuracy from the EDU is equivalent to the current AIRS performance and is much better than the current operational GOES performance. The current GIFTS EDU noise level has been utilized in


the retrieval simulation to derive the temperature and water vapor retrieval accuracy. The RMS temperature retrieval error is about 1 K and the RMS water vapor retrieval error is about 15 percent; that is equivalent to the current AIRS sounding performance. 45 40 35 30 E

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Sky-view measurements were obtained by configuring the GIFTS EDU to look outside to view real world targets. One of the key tests was to view the zenith sky through a large 45-degree mirror, located outside the building, for radiance validation. Viewed from below, the atmospheric spectral line structure is very similar to that seen when viewing downward from space. The configuration is shown in Figure 8 (left panel). The GIFTS EDU is located inside the thermal vacuum test chamber, viewing out horizontally through the chamber ZnSe window to the mirror. The high emissivity reference blackbody used for EDU calibration testing was used to calibrate the full system, including the chamber window. Measurements of the atmospheric state were also made to provide the basis for calculating the expected radiance spectrum. These measurements include radiosonde, ceilometers, and surface based temperature, water vapor, and wind. As a radiance reference, an Atmospheric Emitted Radiance Interferometer (AERI) 22,23 was located very close to the GIFTS chamber window with a view to zenith through the same 45-degree mirror (AERI and GIFTS each viewed about 1.5º off zenith). The AERI provides just one 32 mrad view to zenith, while the GIFTS provides 16,384 pixels, each with a 0.11 mrad Instantaneous Field Of View (IFOV). The AERI provides a well-known reference with a calibration accuracy of better than 1 percent of ambient radiance (3-sigma). AERI instruments were developed by the University of Wisconsin – Space Science and Engineering Center (UW-SSEC) for the Department of Energy (DoE) Atmospheric Radiation Measurement (ARM) Program and have been providing data to the ARM science community for over a decade. An example of the comparison of GIFTS EDU calibrated radiance spectra to AERI radiance spectra is shown in Figure 8 (right panel). (The higher spectral resolution AERI data were reduced to the GIFTS-EDU spectral resolution and repositioned to the GIFTS EDU spectral scale in order to achieve such comparisons.) In Figure 8, the GIFTS observed near-zenith radiance spectrum (red) is compared to the near-zenith AERI radiance spectrum (black) as observed simultaneously on 6 September 2006. The spectra observed with the two instruments are nearly identical. This comparison is for just one of the 16,384 GIFTS pixels, and the GIFTS calibrated radiance did not include a correction for detector/digital readout nonlinearity. The spectra have been interpolated to show the detailed line shapes, a process that can be performed rigorously given the Nyquist sampling inherent in FTS observations. These comparisons, although


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A Moon Tracking Event (MTE) was conducted on 11 September 2006. The major objective was to obtain high quality images of th t e moon th t roughout GIFTS EDU spectr t al channels at th t e highest spectr t al resolution of 0 57 cm-1, while t e th

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lunar images obtained with GIFTS visible and two infrared IR detector arrays. The measurements occurred at 5:50 am MST in North Logan, Utah. The radiance spectra observed by detector elements viewing the warm lunar surface (e.g., the red spectrum) are similar in spectral character to those that are obtained by GIFTS viewing the Earth from orbit. The radiance spectra observed by detector elements viewing the cold space background (e.g., the blue spectrum) are inverted relative to those observed by GIFTS viewing a warm surface background (i.e., the red spectrum). In spectral regions where the atmosphere is a very strong absorber/emitter, one sees little difference between the lunar and cold space background views. Although the main purpose of this experiment was to demonstrate the GIFTS imaging spectrometer


concept, the GIFTS high spatial and temporal resolution images of the moon provide significant scientific information for understanding lunar surface properties and using the moon as calibration source for future space missions. Finally, an Atmospheric Variability Experiment (AVE) was held on September 13, 2006 to illustrate the ability of GIFTS to resolve the diurnal temperature changes in the atmospheric boundary layer, which take place due to nocturnal infrared cooling and daytime solar heating of the Earth’s surface. A ten hour sequence of GIFTS upward viewing data were obtained along with simultaneous AERI measurements and radiosonde observations, from two hours before sunrise into the early afternoon. The GIFTS and AERI measurements were obtained every 10 minutes, and the radiosonde measurements every 1.5 hours, during the ten-hour observation period. Temperature retrievals were performed using the AERI methodology24. The results shown in figure 10 reveal very close agreement between the three independent observations, all three illustrating the low level inversion during the night-time hours (12-15 GMT) eroding rapidly after sunrise during the morning hours (15-18 GMT) and becoming a strong lapse rate condition during the early afternoon hours (18-22 GMT). Absolute differences between the GIFTS temperature profiles and the AERI and Radiosonde profiles are not considered to be significant since the GIFTS radiance calibration did not include a correction for detector/readout system non-linearity.

Figure 10. GIFTS, AERI, and Radiosonde temperature vertical cross-sections obtained during the GIFTS AVE measurement experiment on September 13, 2006.


6.

SUMMARY AND CONCLUSIONS

The GIFTS technology and science should lead to better forecasts that can reduce loss of life and property from severe weather events and improve the quality of life through improved extended range environmental predictions. Improved forecasts will reduce expenditures for storm preparedness, energy resource allocation, and fuel costs for air transport. The GIFTS new technologies (e.g., large area format Infrared focal plane arrays and high speed detector readout electronics, mini-pulse tube cooler, lightweight carbon composite optics, long lifetime precision laser, etc) have been integrated to produce an Engineering Demonstration Unit (EDU) of the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS). Space chamber tests and preliminary analyses of atmospheric science data validate the GIFTS design and capability to provide the desired science data from a space-borne system. It is being proposed to modify the GIFTS EDU, as required to space qualify the instrument and validate the measurement objectives through a space mission. Acknowledgment: NASA and NOAA supported the GIFTS EDU development and testing. The authors acknowledge the support of the Integrated Program Office (IPO) for the NPOESS for obtaining the NAST-I data needed to validate GIFTS measurement concepts and for supporting the preparation and presentation of this manuscript.

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Velden, C. S., C. M. Hayden, S. J. Nieman, W. P. Menzel, S. Wanzong, and J. S. Goerss (1997), UpperTropospheric Winds Derived From Geostationary Satellite Water Vapor Observations, Bull. Am. Meteorol. Soc., 78, 173–195.

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Nieman, S., W. Menzel, C. Hayden, D. Gray, S. Wanzong, C. Velden, and J. Daniels, 1997: Fully Automated Cloud-Drift Winds in NESDIS Operations. Bull. Amer. Meteor. Soc., 78, 1121-1133.

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