A necessary condition for accumulating fundamental climate data records is the use of observation instruments whose stability and accuracy are sufficiently high for climate monitoring purposes; the number of instruments and their distribution in space should be sufficient for measurements with no spatial or temporal gaps. The continuous acquirement of data over time intervals of several decades can only be possible under the condition of simultaneous application of instruments produced by different manufacturers and installed on different platforms belonging to one or several countries.The design of standard sources for pre-flight calibrations and in-flight monitoring of instruments has to meet the most stringent requirements for the accuracy of absolute radiometric measurements and stability of all instruments. This means that the radiometric scales should be stable, accurate, and uniform.Current technologies cannot ensure the high requirements for stability and compatibility of radiometric scales: 0.1% per decade within the 0.3 - 3 mu m band and 0.01 K per decade within the 3 - 25 mu m band.It is suggested that this task can be aided through the use of the pure metals or eutectic alloy phase transition phenomenon that always occur at the same temperature. Such devices can be used for pre-flight calibrations and for on-board monitoring of the stability of radiometric instruments. Results of previous studies of blackbody models that incorporate phase transition phenomenon are quite promising. A study of the phase transition of some materials in small cells was conducted for future application in onboard monitoring devices and its results are positive and allow us to begin preparations for similar experiments in space.

The geosynchronous-imaging Fourier transform spectrometer (GIFTS) engineering demonstration unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. It measures the infrared spectrum in two spectral bands (14.6 to 8.8 microns, 6.0 to 4.4 microns) using two 128 x 128 detector arrays with a spectral resolution of 0.57 cm(exp -1) with a scan duration of approximately 11 seconds. 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 atmospheric status, cloud parameters, wind field profiles, and other derived products can be retrieved. The GIFTS EDU provides a flexible and accurate testbed for the new challenges of the emerging hyperspectral era. The EDU ground-based measurement experiment, held in Logan, Utah during September 2006, demonstrated its extensive capabilities and potential for geosynchronous and other applications (e.g., Earth observing environmental measurements). This paper addresses the experiment objectives and overall performance of the sensor system with a focus on the GIFTS EDU imaging capability and proof of the GIFTS measurement concept.

The GIFTS EDU noise performance measured during thermal vacuum testing indicates that the required noise performance has been realized, and that goal performance has been achieved over much of both the Infrared detector bands.

For the most part, satellite observations of climate are not presently sufficiently accurate to establish a climate record that is indisputable and hence capable of determining whether and at what rate the climate is changing. Furthermore, they are insufficient for establishing a baseline for testing long‐term trend predictions of climate models. Satellite observations do provide a clear picture of the relatively large signals associated with interannual climate variations such as El Niño‐Southern Oscillation (ENSO), and they have also been used to diagnose gross inadequacies of climate models, such as their cloud generation schemes. However, satellite contributions to measuring long‐term change have been limited and, at times, controversial, as in the case of differing atmospheric temperature trends derived from the U.S. National Oceanic and Atmospheric Administration's (NOAA) microwave radiometers.

Spectral radiance validation of the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) engineering design unit has been performed using zenith sky viewing comparisons with an Atmospheric Emitted Radiance Interferometer (AERI). Good agreement is demonstrated.

Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Engineering Demonstration Unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. The EDU groundbased measurement experiment was held in Logan, Utah during September 2006 to demonstrate its extensive capabilities for geosynchronous and other applications.

The geosynchronous-imaging Fourier transform spectrometer (GIFTS) engineering demonstration unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. It measures the infrared spectrum in two spectral bands (14.6 to 8.8 mum, 6.0 to 4.4 mum) using two 128times128 detector arrays with a spectral resolution of 0.57 cm -1 with a scan duration of ~11 seconds. 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 atmospheric status, cloud parameters, wind field profiles, and other derived products can be retrieved. The GIFTS EDU provides a flexible and accurate testbed for the new challenges of the emerging hyperspectral era. The EDU ground-based measurement experiment, held in Logan, Utah during September 2006, demonstrated its extensive capabilities and potential for geosynchronous and other applications (e.g., earth observing environmental measurements). This paper addresses the experiment objectives and overall performance of the sensor system with a focus on the GIFTS EDU imaging capability and proof of the GIFTS measurement concept.

The performance of modem IR instruments is becoming so good that meeting science requirements requires an accurate instrument model be used throughout the design and development process. The huge cost overruns on recent major programs are indicative that the design and cost models being used to predict performance have lagged behind anticipated performance. Tuning these models to accurately reflect the true performance of target instruments requires a modeling process that has been developed over several instruments and validated by careful calibration. The process of developing a series of Engineering Development Models is often used on longer duration programs to achieve this end. The accuracy of the models and their components has to be validated by a carefully planned calibration process, preferably considered in the instrument design. However, a good model does not satisfy all the requirements to bring acquisition programs under control. Careful detail in the specification process and a similar, validated model on the government side will also be required. This paper discusses the model development process and calibration approaches used to verify and update the models of several new instruments, including Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) and Far Infrared Spectroscopy of the Troposphere (FIRST).

The sounding of the atmosphere using broadband emission radiometry (SABER) instrument is a 10-channel infrared (1.27-16.9 mu m) radiometer launched on the TIMED (Thermosphere, Ionosphere, Mesosphere Energetics, and Dynamics) satellite in December 2001 from Vandenburg Air Force Base. SABER measures earthlimb emissions and characterizes infrared radiation, allowing calculation of atmospheric temperature and composition (ozone, water vapor, and carbon dioxide), as well as solar and chemical heating rates and infrared cooling rates. Although SABER focuses on the unexplored 60-180km region, it makes measurements covering the 10-350kin altitude region. Ground calibration testing was completed in September 1999. Subsequent data analyses and report generation were completed in June, 2000. This paper provides a brief overview of instrument design, calibration planning, ground calibration testing, and results. Also included is an assessment of nearly five years of post launch validation and calibration maintenance. Using SABER as an example, conclusions are given regarding the benefit of a detailed calibration approach and how it enhances the quality of science data and mission success.

The state-of-the-art electro-optical sensors being designed for today's space-based environmental applications require a complete characterization and thorough calibration. This is especially true for sensors designed to assess global climate change, which require very small uncertainties. This paper describes a system-level approach that addresses each phase of calibration, from planning to on-orbit operations. This approach encourages early planning and continuity of effort throughout the lifetime of the project (pre- and post-flight) to promote an optimum calibration approach that will minimize uncertainty for the intended application. This paper also discusses considerations for component level characterization, ground calibration and standards, in-flight calibration sources and trending, and in-flight validation assessment.

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.

A linear mathematical error model for the assessment of validation activity of atmospheric retrievals is presented. The purpose of the validation activity is to assess the actual performance of the remote sensing validated system while in orbit by comparing its measurements to some relevant-validating-data. sets.The validating system samples volumes of the atmosphere at times and locations that are different from the ones when and where the validated system makes its own observations. The location of the validating system can be either stationary, e.g. a ground ARM site, or movable, e.g. an aircraft or some other satellites. The true states may be correlated or not. The sampled volumes differ from each other by their location, timing, and size. The validated and validating systems have different vertical resolution and grid, absolute accuracy, and noise level. All the above factors cause apparent differences between the data to be compared.The validation assessment model makes the comparison accurate by allowing for the differences. The model can be used for assessment and interpretation of the validation results when the above mentioned sources of discrepancies are significant, as well as for evaluation of a particular validating data source.

This paper describes ground calibration of a 10-channel infrared (1.27-17 mum wavelength) radiometer instrument known as sounding of the atmosphere using broadband emission radiometry (SABER). SABER is one of four experiments that will fly on the thermosphere, ionosphere, mesosphere, energetics and dynamics (TIMED) mission to be launched in 2001. SABER will be used to measure atmospheric infrared emissions from the earthlimb. Ground calibration testing was completed in September 1999. Subsequent data analyses and report generation was completed in June 2000. This paper provides an overview of the instrument design, calibration approach, calibration equation and radiometric model. It also describes the SABER ground calibration facility, survey of calibration results and calibration radiance uncertainty.

A 10-channel infrared (1.25-17.24 µm wavelength) radiometer known as SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) is one of four experiments that will fly on the TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics) mission that was successfully launched on 7 December 2001. Theoretical models of the relative spectral response (RSR) for each SABER channel were developed during the design and build of the instrument. The RSR calculations were then refined using a component level technique where theoretical predictions of filter transmittance were replaced with measurements from filter witness samples. During SABER ground calibration, full system measurements of RSR were performed using a Michelson step-scan interferometer to present an interferometrically modulated infrared source to the instrument with the resultant interferogram recorded by the instrument detectors. Fourier transform of this interferogram and correction of the resulting spectrum for the spectral output of the interferometer and the transmittance of any intervening optics provide a measurement of the system level RSR. We compare the full system level measurements with the theoretical and component level RSR predictions for both in-band and out-of-band spectral regions. Our results show that the system level method for determining RSR provides the clearest picture of the instrument's spectral properties.

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is one of four experiments that will fly on the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission to be launched in May 2000. The primary science goal of SABER is to achieve major advances in understanding the structure, energetics, chemistry, and dynamics, in the atmospheric region extending from 60 km to 180 km altitude. This will be accomplished using the space flight proven experiment approach of spectral broadband limb emission radiometry. SABER will scan the horizon in 10 selected bands ranging from 1.27 micrometer to 17 micrometer wavelength. The observed vertical horizon emission profiles will be processed on the ground to provide vertical profiles with 2 km altitude resolution, of temperature, O3, H2O, and CO2; volume emission rates due to O2(1(Delta) ), OH((upsilon) equals 3,4,5), OH((upsilon) equals 7,8,9), and NO; key atmospheric cooling rates, solar heating rates, chemical heating rates, airglow losses; geostrophic winds, atomic oxygen and atomic hydrogen. Measurements will be made both night and day over the latitude range from the southern to northern polar regions. The SABER instrument uses an on-axis Cassegrain design with a clam shell reimager. Preliminary test and calibration results show excellent radiometric performance.