KEYWORDS: Equipment, Space operations, Space weather, Optical fabrication, Data processing, Calibration, Atmospheric sciences, Earth atmosphere, Atmospheric modeling, Air temperature
NASA’s Atmospheric Waves Experiment (AWE) mission is a Heliophysics Small Explorers Mission of Opportunity designed to investigate how terrestrial weather affects space weather, via small-scale atmospheric gravity waves (GWs) produced in Earth’s atmosphere. Following its launch to the International Space Station (ISS) in November 2023, AWE began a 2-year mission to explore the global distribution of AGWs, study the processes controlling their propagation throughout the upper atmosphere, and quantify their impacts on the ionosphere–thermosphere–mesosphere (ITM) system. The AWE science instrument is an ISS–compatible version of the Advanced Mesospheric Temperature Mapper (AMTM)—a wide field-of-view Shortwave Infrared (SWIR) imager that quantifies gravity wave-induced temperature disturbances in the hydroxyl (OH) airglow layer, which lies near the mesopause at ~87 km altitude. The AMTM’s four identical telescopes make continuous nighttime observations of the P1(2) and P1(4) emission lines of the OH (3,1) band, as well as the atmospheric background simultaneously, from which the OH layer temperature is derived. AWE images are collected once per second, co-added, and processed into temperature swaths using correction algorithms derived from ground calibration test results. Global coverage of the GWs in the OH layer is achieved about every four days, which will enable regional and seasonal studies, as well as characterization of AGW ‘hot spots.’ This paper will present an overview of the AWE mission, including science objectives, measurement technique, instrument design and development, prelaunch performance and environmental testing, data processing, and a brief look at on-orbit science results.
The NASA New Millennium Program (NMP) Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS)
instrument was designed to demonstrate new and emerging technologies and provide immense improvements in satellite
based remote sensing of the atmosphere from a geostationary orbit [1]. Combining a Fourier Transform Spectrometer
(FTS) and Large Area Focal Plane Arrays, GIFTS measures incident infrared radiance with an extraordinary
combination of spectral, temporal, and spatial resolution and coverage. Thermal vacuum testing of the GIFTS
Engineering Development Unit (EDU) was performed at the Space Dynamics Laboratory and completed in May 2006
[2,3].
The GIFTS noise performance measured during EDU thermal vacuum testing indicates that threshold performance has
been realized, and that goal performance (or better) has been achieved over much of both the Longwave Infrared
(LWIR) and Short/Midwave Infrared (SMWIR) detector bands.
An organizational structure for the division of the noise sources and effects for the GIFTS instrument is presented. To
comprehensively characterize and predict the effects of measurement noise on expected instrument performance, the
noise sources are categorically divided and a method of combining the independent effects is defined. Within this
architecture, the total noise is principally decomposed into spectrally correlated noise and random (spectrally
uncorrelated) noise. The characterization of the spectrally correlated noise sources specified within the structure is
presented in detail.
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) represents a revolutionary step in satellite
based remote sensing of atmospheric parameters. Using the combination of a Fourier Transform Spectrometer and
Large Area Focal Plane Arrays, GIFTS measures incident infrared radiance with an unprecedented combination of
spectral, temporal, and spatial resolution and coverage. In its regional sounding mode, it measures the infrared
spectrum every 11 seconds at a spectral resolution of ~0.6 cm-1 in two spectral bands (14.6 to 8.8 μm, 6.0 to 4.4 μm)
using two 128 × 128 detector arrays. From a geosynchronous orbit, the instrument will have the capability of taking
successive measurements of such data to scan desired regions of the globe, from which thermal and gaseous
concentration profiles, cloud properties, wind field profiles, and other derived products can be retrieved.
Thermal vacuum testing of the GIFTS Engineering Development Unit (EDU) was performed at the Space Dynamics
Laboratory in Logan Utah and completed in September 2006. With a focus on spectral characterization of the sensor,
analyses of selected thermal vacuum tests are presented here.
The NASA New Millennium Program's Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) instrument
was designed to provide enormous advances in water vapor, wind, temperature, and trace gas profiling from
geostationary orbit. The top-level instrument calibration requirement is to measure brightness temperature to better than
1 K (3 sigma) over a broad range of atmospheric brightness temperatures, with a reproducibility of ±0.2 K. For the onboard
calibration approach used by GIFTS that employs two internal blackbody sources (290 K and 255 K) plus a space
view sequenced at regular programmable intervals, this instrument level requirement places tight requirements on the
blackbody temperature uncertainty (0.1 K) and emissivity uncertainty (0.001). The blackbody references are cavities
that follow the UW Atmospheric Emitted Radiance Interferometer (AERI) design, scaled to the GIFTS beam size. The
engineering model blackbody system was completed and fully calibrated at the University of Wisconsin and delivered
for integration into the GIFTS Engineering Development Unit (EDU) at the Utah State Space Dynamics Laboratory.
This paper presents a detailed description of the methodology used to establish the required temperature and emissivity
performance, with emphasis on the traceability to NIST standards. In addition, blackbody temperature data are presented
from the GIFTS EDU thermal vacuum tests that indicate excellent temperature stability. The delivered on-board
blackbody calibration system exceeds performance goals - the cavity spectral emissivity is better than 0.998 with an
absolute uncertainty of less than 0.001, and the absolute blackbody temperature uncertainty is better than 0.06 K.
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS), developed for the NASA New Millennium
Program (NMP) Earth Observing-3 (EO-3) mission, has recently completed a series of uplooking atmospheric
measurements. The GIFTS development demonstrates a series of new sensor and data processing technologies that can
significantly expand geostationary meteorological observational capability. The resulting increase in forecasting
accuracy and atmospheric model development utilizing this hyperspectral data is demonstrated by the uplooking data.
The GIFTS sensor is an imaging FTS with programmable spectral resolution and spatial scene selection, allowing
spectral resolution and area coverage to be traded in near-real time. Due to funding limitations, the GIFTS sensor module
was completed as an engineering demonstration unit that can be upgraded to flight quality. This paper reviews the
GIFTS system design considerations and the technology utilized to enable a nearly two order performance increase over
the existing GOES sounder and shows its capability. While not designed as an operational sensor, GIFTS EDU provides
a flexible and accurate testbed for the new products the hyperspectral era will bring. Efforts to find funding to upgrade
and demonstrate this amazing sensor in space are continuing.
KEYWORDS: Staring arrays, Sensors, Calibration, Digital signal processing, Fourier transforms, Mirrors, Long wavelength infrared, Infrared radiation, Spectroscopy, Black bodies
The NASA Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) has been completed as an Engineering
Demonstration Unit (EDU) and has recently finished thermal vacuum testing and calibration. The GIFTS EDU was
designed to demonstrate new and emerging sensor and data processing technologies with the goal of making
revolutionary improvements in meteorological observational capability and forecasting accuracy. The GIFTS EDU
includes a cooled (150 K), imaging FTS designed to provide the radiometric accuracy and atmospheric sounding
precision required to meet the next generation GOES sounder requirements. This paper discusses a GIFTS sensor
response model and its validation during thermal vacuum testing and calibration.
The GIFTS sensor response model presented here is a component-based simulation written in IDL with the model
component characteristics updated as actual hardware has become available. We discuss our calibration approach,
calibration hardware used, and preliminary system performance, including NESR, spectral radiance responsivity, and
instrument line shape. A comparison of the model predictions and hardware performance provides useful insight into
the fidelity of the design approach.
We discuss the relationship between instrument footprint size, field-of-regard sample density, and cloud clearing technique on measured top of the atmosphere radiance error under partly cloudy conditions. The cloud clearing technique (N*) uses the linear relationship between observed radiance and the amount of cloud in a field-of-view. We extrapolate radiance observed for two adjacent fields-of-view possessing differing cloud amounts to the cloud free value (i.e., zero cloud). Options include techniques to compensate for “black” or “gray” clouds, where a single channel N* may not provide adequate spectral correction. Spectrally dependent error statistics are developed from partly cloudy samples of varying footprint size and sample patterns. Data were collected by the NPOESS (National Polar-orbiting Operational Environmental Satellite System) Aircraft Sounding Testbed-Interferometer (NAST-I) flying on the NASA Proteus or ER-2 high altitude research aircraft, and include tropical, temporal and arctic flight sections. Analysis shows that larger sounder footprints contain more cloud contamination and higher cloud clearing errors; these errors can be significantly reduced by techniques that utilize high-spectral and -spatial resolution coincidently collected radiance measurements from sensors like MODIS. Data also indicates that full area sampling results in smaller cloud clearing errors than small footprint sampling on a wider spaced grid.
Data compression on future space-based imaging interferometers can be used to reduce high telemetry costs, provided the performance is acceptable. This paper investigates lossy data compression of imaging interferometer datacubes using a wavelet transform-based compression algorithm, the Set Partitioning in Hierarchical Trees (SPIHT) image compression algorithm. Compression is performed on individual frames of the interferogram datacubes. Simulated datacubes from the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) are modified to produce new complex GIFTS datacubes used to perform the experiments. Separate programs are written for the encoder and decoder in C++. The encoder and decoder are simulated to the bit-level, meaning they simulate the exact bit streams that would be generated by hardware implementations. All compression ratios reported are based on the actual file size of the encoded data. The simulations indicate very high performance of the algorithm in the interferogram domain, with average errors of less than one least significant bit (LSB) for the GIFTS long-wave band and just over one LSB for the GIFTS short/mid-wave band at compression ratios as high as 13.7:1 and 15.4:1, respectively. At the same compression ratios, errors in the spectral radiance domain are comparable to the simulated instrument noise and RMS temperature profile retrieval errors of less than 1 K are achieved using a University of Wisconsin-Madison prototype retrieval algorithm.
We provide an evaluation of cloud clearing error and sensor footprint size in high spectral resolution sounding instrumentation. Input data are actual atmospheric spectra collected by the NPOESS Aircraft Sounding Testbed - Interferometer (NAST-I) [see Cousins and Smith (1998), and Smith et. al., (1999, 2001)]. NAST-I data is averaged to create sensor configurations of varying field of view size and array number. The cloud-clearing techniques, based on the N* approach (Smith, 1968, Chahine, 1977, and McMillin and Dean, 1982), use the linear relation between observed radiance and cloud amount to extrapolate the radiance observed for two adjacent fields of view possessing differing cloud amounts to the cloud free value. The option of including MODerate resolution Imaging Spectroradiometer (MODIS) style data was also investigated. With the MODIS filter, the assumption of cloud emissivity homogeneity is not needed because of the MODIS high spatial resolution spectral channels in which the clear air radiance can be defined for a scene. This relaxation of the need for cloud optical property homogeneity enables a higher yield of valid clear column radiance estimates. We show that the use of MODIS-like multi-spectral imagery data in the cloud clearing of high spectral resolution sounder data will minimize the dependence of the sounding retrieval accuracy and yield on instrument field-of-view size. The errors of the multi-spectral MODIS cloud-cleared spectral radiance are generally a factor of two lower than those errors associated with the use of a single window channel for the cloud clearing of radiance spectra.
A geostationary Imaging Fourier Transform Spectrometer (GIFTS) has been selected for the NASA New Millennium Program (NMP) Earth Observing-3 (EO-3) mission. Our paper will discuss one of the key GIFTS NMP mission is designed to demonstrate new and emerging sensor and data processing technologies with the goal of making revolutionary improvements in meteorological observational capability and forecasting accuracy. The GIFTS payload is a versatile imaging FTS with programmable spectral resolution and spatial scene selection that allows radiometric accuracy and atmospheric sounding precision to be traded in near real time for area coverage. The GIFTS sensor combines high sensitivity with a massively parallel spatial data collection scheme to allow high spatial resolution measurement of the Earth's atmosphere and rapid broad area coverage. An objective of the GIFTS mission is to demonstrate the advantages of high spatial resolution on temperature and water vapor retrieval by allowing sampling in broken cloud regions. This small gsd, may require extremely good pointing control. This paper discusses the analysis of this requirement.
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