Future Earth observation missions developed by the European Space Agency will be either of pre-operational nature ('Earth Watch') or will be focused on specific research topics ('Earth Explorer'). Nine scientific candidates have been selected for the Earth Explorer missions: atmospheric chemistry, atmospheric dynamics, atmospheric profiling. Earth radiation, gravity field and steady-state ocean circulation, land surface processes and interactions, magnetometry, precipitation, topography. For each of these candidates, a space mission has been defined in cooperation with Earth scientists and its implementation has been studied at pre-phase A level. The pre-phase A activities dealt with the preliminary configuration of the space and ground segments, the assessment of the requirements on the spacecraft and the preliminary study of the instruments, including breadboarding of critical technologies. The results of the scientific and technical definition studies have been presented to the scientific community and the merits of the various missions have been independently assessed.

The moderate resolution imaging spectroradiometer (MODIS) is scheduled for launch on the first of the Earth observing systems AM spacecraft in mid 1998. This instrument is designed to study Earth system processes and includes 36 spectral bands for study of oceanographic, atmospheric, and land surface phenomenon. The MODIS instrument has been under design and development for the past 10 years, with completion of the engineering model (EM) in mid 1995, and is now nearing completion of the first spaceflight unit, the protoflight model (PFM). This paper discusses the development of the PFM, by addressing the features and issues of the many subsystems.

The moderate resolution imaging spectroradiometer (MODIS) presents a series of significant and interesting challenges in the area of system integration and test. Hughes has developed several clever and innovative solutions and so is successfully addressing these challenges as it nears completion of the protoflight model. The broad spectral coverage and large number of bands/detectors present unique challenges in areas such as background radiation, data handling, and the need for some highly capable test equipment. The several demanding performance parameters associated with the optical train often require solutions to be found among conflicting requirements. Specialized alignment techniques and tooling were developed to address image rotation caused by the folded optical train. The large field of view and need to test a wide range of system performance parameters on a tight schedule drove a comprehensive floor layout scheme with full rotation capability of the instrument and associated fixturing. The large number of optical surfaces combined with an extremely low scatter requirement led us to develop several initiatives to improve cleanliness.

The impact of non-unit calibration blackbody emissivity on MODIS airborne simulator (MAS) absolute thermal calibration accuracy is investigated. Estimates of blackbody effective emissivity were produced for MAS infrared channels using laboratory observations of a thermally controlled external source in a stable ambient environment. Results are consistent for spectrally close atmospheric window channels. SWIR channels show an effective emissivity of about 0.98; LWIR channels show an effective emissivity of about 0.94. Using non-unit blackbody effective emissivity reduces MAS warm scene brightness temperatures by about 1 degree Celsius and increases cold scene brightness temperatures by more than 5 degrees Celsius as compared to those inferred from assuming a unit emissivity blackbody. To test the MAS non- unit effective emissivity calibration, MAS and high- resolution interferometer sounder (HIS) LWIR data from a January 1995 ER-2 flight over the Gulf of Mexico were compared. Results show that including MAS blackbody effective emissivity decreases LWIR absolute calibration biases between the instruments to less than 0.5 degrees Celsius for all scene temperatures, and removes scene temperature dependence from the bias.

Over the past few years, the MODIS airborne simulator (MAS) has been providing imagery for EOS scientific algorithm development. Primarily flown aboard NASA's ER-2 aircraft, the MAS provides high spatial resolution (50 m at nadir) in 50 spectral channels from 0.55 to 14.2 micrometer, overlapping many MODIS and ASTER channels. This paper focuses on calibration of the short-wave (0.55 - 2.38 micrometer) channels, both radiometric and spectral, and calibration of the integrating sources. Also discussed is the dependence of the short-wave calibration on instrument temperature, showing significant reduction in the thermal sensitivity after recent instrument enhancements and upgrades. The procedures for intercomparison of MAS and AVIRIS (airborne visible/infrared imaging spectrometer) data are also discussed. Some limited comparisons for flights over Alaska (June 1995) are presented, although this analysis is in its initial stages and quantitative results are preliminary.

A major difficulty in accurately quantifying various of the Earth's geophysical and biophysical features from the multi- spectral reflectance data acquired from space is the lack of extensive and reliable validation measurements from good ground truth. A new, active airborne sensor system, AVIS (airborne vegetation index sensor), addresses that problem. AVIS uses a flash lamp mounted on a NASA helicopter to illuminate the Earth with a 15 by 35 mrad spot. The visible and near-IR backscattered radiation is then received hyperspectrally and can be analyzed. Initially designed for validation of theories on vegetation index determination, AVIS has broad application as a simulator for solar illumination for remote surface analysis. Its primary advantage is the reduction or elimination of atmospheric scattering and solar angle effects, and the removal of shadowing. It also provides repeatability for time analysis over the same sites.

High resolution infrared spectroscopy is a versatile tool that provides measurements of a wide variety of atmospheric constituents. This paper describes the atmospheric emission spectrometer, an infrared Fourier transform spectrometer designed for remote sensing from an aircraft platform.

A look-up table approach is planned for the atmospheric correction of ASTER data in the solar reflective region. As part of the work to develop this atmospheric correction a sensitivity analysis of top-of-the-atmosphere radiances to changes in aerosol properties has been done. The results presented here use a Gauss-Seidel iteration radiative transfer code to examine effects of changes in aerosol parameters on retrieved surface reflectance. For reflectances greater than 0.1, the surface reflectance retrieval is most sensitive to changes in the aerosol complex index of refraction. At low reflectances, the retrieval is most sensitive to the aerosol scattering optical depth and size distribution. The impact of these results in determining a validation method is discussed.

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is a 14 channel high spatial resolution instrument selected for flight on the EOS AM-1 platform. This instrument has a 60 km pointable cross-track swath and five thermal infrared channels between 8 and 12 micrometers with 90 m spatial resolution. Correction for the effect of atmospheric attenuation and emission will be made using a radiative transfer model and atmospheric parameters either from the EOS AM-1 platform instruments MODIS (moderate- resolution imaging spectroradiometer) and MISR (multi-angle imaging spectroradiometer) or temperature and moisture profiles from global numerical assimilation models. The correction accuracy depends strongly on the accuracy of the atmospheric information used. To provide an objective assessment of the validity of the atmospheric correction in situ measurements of water surfaces under a variety of atmospheric conditions will be used to estimate the surface leaving radiance at the scale of an ASTER pixel. The procedure will use an array of continuously recording temperature buoys to establish the bulk water temperature, broadband radiometers to determine the near surface water temperature gradient and radiosonde and sunphotometer measurements and a radiative transfer model to deduce the sky irradiance. These measurements and the spectral emissivity of the water will be combined with the relative system spectral response to provide an estimate of thermal infrared surface leaving radiance for each ASTER thermal channel. An example of this approach using a multichannel thermal aircraft scanner as a stand in for ASTER is described. It is expected this approach will provide estimates of surface radiance accurate, in temperature terms, to better than 1 K.

From spacecraft platforms, the clouds and the Earth's radiant energy system (CERES) scanning thermistor bolometers are designed to measure broadband Earth-reflected solar shortwave (0.3 - 5.0 micrometer) and Earth-emitted long wave (5.0 - greater than 100 micrometer) radiances as well as emitted longwave radiances in the 8 - 12 micrometer water vapor window over geographical footprints as small as 10 kilometers at the nadir. In ground vacuum facilities, the thermistor bolometers and in-flight blackbody and tungsten lamp calibration systems are being calibrated using radiometric sources tied to the international temperature scale of 1990 (ITS'90). Using the in-flight calibration systems, the bolometers will be calibrated periodically before and after spacecraft launch to verify the stability of the bolometers responses and to determine response drifts/shifts if they occur. The in-flight systems calibration analyses along with validation analyses will be used to determine the flight data reduction coefficients (instrument gains and offsets) which will be used to convert the bolometer measurements into calibrated radiances at the top-of-the-atmosphere (approximately 30 km). If a bolometer response shifts or drifts more than 0.5% in the longwave region or more than 1.0% in the shortwave region, and if the validation studies verify the bolometer response change, the flight data reduction coefficients will be corrected. A coastline detection method, using strong contrasting longwave ocean-land scenes, will be used to assess error limits on the geographical locations of the radiances. The detection method was successfully used to assess upper limits (6 km) on the geolocation errors for the Earth radiation budget satellite (ERBS) bolometric measurements of longwave radiances. For CERES, the detection method may be extended to shortwave radiances. In this paper, elements of the CERES instrument level 1 validation plan radiometric strategies are presented as well as the geolocation validation approaches.

Preliminary results of a sensitivity analysis of the post- launch calibration of the visible (channel 1; approximately equals 0.58 - 0.68 micrometer) and near-infrared (channel 2; approximately equals 0.72 - 1.1 micrometer) channels of the advanced very high resolution radiometer using the southeastern part of the Libyan desert (21 - 23 degrees N; 28 - 29 degrees E) as a radiometrically stable calibration target are presented. It is observed that small but finite changes in the Lambertian surface albedo, and in the contributions of gaseous and particulate scattering and absorption to the upward radiation at the top of the atmosphere lead to changes in the relative degradation rates of comparable magnitude.

To gain insight in the dynamics and the long-term behavior of constituents (e.g., ozone, CFCs) of the Earth atmosphere, satellite-based instruments allowing global monitoring provide unsurpassed information. In order to study atmospheric trends over a very long period of time, these instruments generally have to be calibrated normalized to the sun very accurately. Furthermore, the accuracy has to be maintained during the lifetime of the instruments. This contribution addresses the issue of radiometric calibration of earth-observation instruments, both on ground and in flight. Some of the related issues will be illustrated by focusing on two specific instruments (to be) calibrated at TPD: the global ozone monitoring experiment (GOME), which was launched on ERS-2 in April 1995, and the scanning imaging absorption spectrometer for atmospheric cartography (SCIAMACHY), to be launched on Envisat around the turn of the century. We distinguish between sun-normalized calibration and absolute radiometric calibration. In both cases instrument sensitivity to polarization is a complicating factor. Other factors to be dealt with are, e.g., the etalon effect and the influence of humidity during on-ground calibration. These all require a sophisticated calibration approach and well-adapted radiometric calibration equipment. After on-ground calibration the instruments are susceptible to possible changes or degradation. Therefore, GOME and SCIAMACHY both contain a well-calibrated on-board diffuser providing an accurate reflectance standard. However, this diffuser itself is degrading with time due to contamination and radiation effects. An in-flight monitoring concept is therefore mandatory. The addressed calibration aspects are elucidated using the example of SCIAMACHY.

Clouds and the Earth's radiation energy system (CERES), a key experiment in the Earth observing system (EOS), is designed to measure the reflected shortwave and the emitted longwave radiances from Earth and its atmosphere. The CERES instrument consists of a scanning thermistor bolometer package with built in flight calibration systems. The first CERES instrument is scheduled for launch in 1997 aboard the joint National Aeronautics and Space Administration (NASA) and Japanese National Space Development Agency (NASDA) tropical rainfall measuring mission (TRMM) spacecraft. The laboratory calibrations of the instrument were conducted in the TRW vacuum facilities which are equipped with blackbodies, a cryogenically cooled transfer active-cavity radiometer, shortwave reference source, solar simulator and a constant radiance reference source. This paper describes the calibration facility and the calibration procedures for the CERES instrument.

The multi-angle imaging spectroradiometer (MISR) will be reporting band-weighted spectral radiances for its level 1B1 radiometric product. Although the out-of-band is a small percentage of the in-band response, the entire range from 365 to 1100 nm can potentially contribute to the reported radiance. For certain geophysical parameter retrieval algorithms, therefore, it is desirable to remove the out-of- band contribution. This will be done for select level 2 products. In order to provide such a correction, some estimation must be made of the out-of-band scene spectral properties, so that this signal might be removed. For MISR this can be done by making use of information from all four bands (nominally 443, 555, 670, and 865 nm). This paper evaluates the effectiveness of a four point, piecewise- linear, approximation to the surface reflectance. This representation is derived from the four MISR bands. To evaluate this approach, data from the airborne visible/infrared imaging spectrometer (AVIRIS) is utilized. This sensor measures the total upwelling radiance from 400 to 2450 nm in the electromagnetic spectrum through 224 channels at 10-nm intervals. This study shows that, for MISR, there can be as large as a 5% difference in the total band-weighted spectral radiance, as compared to the desired in-band weighted spectral radiance. The MISR retrieved four point surface profile is sufficient to provide out-of-band correction to within 1% accuracy.

The improved TOMS instruments, flight models 3, 4, and 5, are to be flown aboard Earth probe (EP), Japanese ADEOS, and Russian Meteor-3M satellites, respectively. TOMS obtains the total column amount of the atmospheric ozone from measurements of the extra-terrestrial solar spectral irradiance and the backscattered earth spectral radiance at six ultraviolet wavelengths between 308.6 nm and 360 nm. The added scientific goal of new generation instruments is to monitor the trend of the global burden of the atmospheric ozone, which requires an accuracy of 1% in the calibration for the ratio of the radiance to the irradiance measurements. The emphasis of the prelaunch-calibration approaches was to maximize the accuracy in the ratio of the calibration for the two measurement modes and to minimize possibility of the systematic errors. The source geometry was maintained as close as possible in the calibration setup for the two measurement modes so that the uncertainty associated with the source could be canceled out in the ratio of the two calibrations. Also, multiple calibration techniques and radiometric sources have been used to check consistency of the calibration. The FM-3 calibration results show a three sigma standard errors of the mean for the ratio calibration that range from 0.28% to 0.63% in descending order of the wavelength.

The multi-angle imaging spectro-radiometer (MISR) instrument, which is scheduled to fly on the EOS AM1 platform, contains nine refractive cameras (four different lens designs) at preselected view angles which image in the push broom mode. Each focal plane contains four charge coupled device (CCD) line arrays consisting of 1504 active pixels; each array is preceded by one of the MISR spectral filters. In order to facilitate registration of the data generated by the 36 arrays during the initial phase of the mission, the crosstrack pointing angle of each pixel in each array was measured in the laboratory at the camera subsystem level. These measurements were particularly challenging because the pixels had to be calibrated under flight conditions (in a vacuum over the temperature range 0 to 10 degrees Celsius) to an accuracy of 1/8 pixel or 2.6 micrometer. Given the first order properties of the various lenses, this requirement implies that the distortion had to be calibrated to better than 10 arcsec. This paper will discusses the hardware and software techniques utilized to accomplish this stringent calibration.

As a part of the Earth observing system (EOS) cross- calibration activities before the first flight (denoted AM- 1), a radiometric measurement comparison was held in February 1995 at the NEC Corporation in Yokohama, Japan, Researchers from the National Institute of Standards and Technology (NIST), the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC), the University of Arizona Optical Sciences Center, and the National Research Laboratory of Metrology (NRLM) used their portable radiometers to measure the spectral radiance of the advanced spaceborne thermal emission and reflection radiometer (ASTER) visible/near-infrared (VNIR) integrating sphere at three radiance levels. The levels each correspond to 83% of the maximum radiance that is expected to be measured using the three VNIR bands of the EOS ASTER instrument, which are centered at 0.56 micrometer, 0.66 micrometer, and 0.81 micrometer. These bands are referred to as bands 1, 2, and 3. The average of the measurements of the four radiometers was between 1% and approximately 1.5% higher for all three bands when compared to the NEC calibration of the sphere. A comparison of the measurements from the participating radiometers resulted in good agreement. These results are encouraging and will be followed by extension to other EOS AM-1 instrument calibration sources.

Multiple photon scatterings inside an integrating sphere can result in significant path lengths compared with line-of- sight sources. In strong water vapor absorption channels, such as those on MODIS and the MODIS airborne simulator, these internal path lengths can result in a significant reduction in sphere output radiance. Path length probability distributions for photons exiting a sphere are determined using Monte Carlo calculations. Approximate analytic expressions are also derived. Results are used to determine the effect of water vapor absorption on integrating sphere sensor calibrations in several pertinent channels.

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is designed to provide a high-resolution map of the Earth in both visible, near-infrared, and thermal spectral regions of the electromagnetic spectrum. The ASTER science team has developed standard data product algorithms to permit the estimation of surface radiances and reflectance values, to calculate surface temperatures both over water and land, to provide a color enhanced product with a high degree of surface discriminability, in addition to other functions. The ASTER product generation system (PGS) team is implementing these requirements within the constraints of the EOSDIS system, using a rapid development methodology that emphasizes open lines of communication in a team approach using concurrent engineering techniques. The PGS development environment was structured both to conform to the changing needs of the EOSDIS system and to incorporate experimentation with and modification of the science algorithms as the software was being developed and tested. This challenging environment required a focus on novel methods of requirements tracking, software interface uniformity, toolkit transparency, and platform independence. This approach required a high degree of interoperability of the software development environment, a well as a flexible and highly integrated configuration management and testing approach. In addition in order to validate the PGS software in the operational environment of the EOSDIS, a remote integration testing approach was adopted to provide a rapid convergence of the final integrated system. This paper describes the critical elements in the development and integration of the ASTER PGS system.

The moderate resolution imaging spectroradiometer (MODIS) instrument will view the Earth in 36 spectral bands ranging from 0.4 to 1.4 micrometers with spatial resolution from 250 to 1,000 meters. Its first flight will be onboard the EOS- AM1 spacecraft scheduled for launch in mid '98 into a near- polar 10:30 AM descending sun-synchronous orbit. In this orbit MODIS will provide global coverage every two days. Science instrument data will be brought to Goddard Space Flight Center for conversion from raw counts to TOA radiances supplemented with geolocation, view angle, and sun angle information. The MODIS science team consists of twenty six members, divided into four discipline groups: atmosphere, land, ocean, and calibration. The MODIS science team is developing algorithms to routinely produce the following standard data products: cloud mask, aerosol concentration and optical properties, cloud properties, vegetation and land-surface cover (including surface reflectance, vegetation indices, land cover type, FPAR/LAI, and net productivity), snow and sea-ice cover and reflectance, land and ocean surface temperature, ocean color, chlorophyll-a concentration and chlorophyll florescence. This paper gives an overview of these products, and identifies information resources associated with the MODIS standard data products.

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is designed to provide a high resolution map of the Earth in both visible, near-infrared, and thermal spectral regions of the electromagnetic spectrum. The ASTER science team has developed several standard data product algorithms, but the most complex and computing-intensive of these is the estimation of surface radiance and reflectance values, which is done by modeling and correcting for the effects of the atmosphere. The algorithm for atmospheric correction in the visible bands sensed by ASTER calls fur the use of a very large atmospheric correction look up table (ACLUT). The ACLUT contains coefficients which describe atmospheric effects on ASTER data under various conditions. The parameters used to characterize the atmosphere and its effects on radiation in the ASTER bands include aerosol and molecular optical depth, aerosol size distribution, single scattering albedo, and solar, nadir view, and azimuth angles. The ACLUT coefficients are produced by thousands of runs of a radiative transfer code (RTC) program produced by Phil Slater and Kurt Thome of U. of A. The final version of ACLUT is expected to be in the neighborhood of 10 gigabytes. The RDBMS Sybase is used to manage the process of generating the ACLUT as well as to host the table and service queries on it. Queries on the table are made using ASTER band number and seven floating-point values as keys. The floating-point keys do not necessarily exactly match key values in the database, so the query involves a hierarchical closest-fit search. All aspects of table implementation are described.

The primary objective of the Earth Resources Observation System (EROS) Data Center (EDC) Distributed Active Archive Center (DAAC) for land processes data is to promote the interdisciplinary study and understanding of the integrated Earth system by providing remotely sensed and related ancillary data for the study, characterization, and monitoring of natural and anthropogenic conditions and processes existing and operating at or near the land surface. Generating, distributing, and preserving data and products from the National Aeronautics and Space Administration's (NASA) earth observing system (EOS) are primary functions of the DAAC. To that end, the EDC DAAC is using existing data sets in developing capabilities to efficiently and effectively ingest, process, manage, distribute, and archive for future generations land-related data collected by EOS sensors. Capabilities also are being developed to help users search for and acquire data and products, as well as to support their scientific application of those data and products. EDC DAAC programs and capability development activities address DAAC-defined science support requirements that relate to a broad spectrum of services and capabilities needed by science users.

The EOSDIS Product Survey was designed to understand the need for, and use of, data products that will become available through EOSDIS in the years 1998 - 2000. This information is needed by the EOSDIS Core System (ECS) performance modelers and system developers for determining adequate processing-, storage-, and network-size specifications to accommodate the expected user-pull load. The survey was tailored to science users. A message inviting potential EOSDIS users to complete the survey was e-mailed in late spring of 1995. The survey was administered electronically via the World Wide Web (WWW) and responses were received from 595 potential users. Quantitative results and analyses are presented on the user demographics, product levels, time-space research requirements and relative product access frequencies. The results indicate that the pull of a product is related to the dynamic nature of the phenomena studied, which, in turn, is closely related to the temporal resolution of the product.

Meeting the goals for EOSDIS to acquire, manage, and distribute large volumes of remote sensing data can be accomplished by leveraging the capabilities of advanced technologies. In this paper we first introduce the EOSDIS architecture and the concepts of sponsored research prototypes and technology transfer. We discuss the motivations and roles that collaboration, emergence, and changing technology play in the process of adapting technology to the challenges of developing the EOSDIS core system (ECS). Further discussions include the implementation of a testbed which has been established for ECS technology transfer. The ECS technology transfer testbed (ET3) demonstrates NASA's strategy for risk mitigation where near- term and long-term objectives can be met by appropriately exploiting emerging technology research. The technology transfer process we describe defines the mechanisms necessary to evaluate, assess, and integrate research results into the full system engineering and development life cycle for EOSDIS.

In the course of global change studies, a scientist would often like to efficiently store, retrieve, analyze and interpret selected data sets from a large collection of scientific information scattered across heterogeneous computational environments, Earth observing system data repositories, and to share the gleaned information with other scientific communities. To facilitate the above activities, we have developed OASIS, a flexible, extensible, and seamless environment for scientific data analysis, knowledge discovery, visualization, and collaboration.

During the last decade, we have seen an explosive growth in our ability to collect and generate data. When implemented, NASA's Earth observing system data information system (EOSDIS) will receive about 50 gigabytes of remotely sensed image data per hour. This will generate an urgent need for new techniques and tools that can automatically and intelligently assist in transforming this abundance of data into useful knowledge. Some emerging technologies that address these challenges include data mining and knowledge discovery in databases (KDD). The most basic data mining application is a content-based search (examples include finding images of particular meteorological phenomena or identifying data that have been previously mined or interpreted). In order that these technologies be effectively exploited for EOSDIS development, a better understanding of data mining and the requirements for using this technology is necessary. The authors are currently undertaking a project exploring the requirements and options of content-based search and data mining for use on EOSDIS. The scope of the project is to develop a prototype with which to investigate user interface concepts, requirements, and designs relevant for EOSDIS core system (ECS) subsystem utilizing these techniques. The goal is to identify a generic handling of these functions. This prototype will help identify opportunities which the earth science community and EOSDIS can use to meet the challenges of collecting, searching, retrieving, and interacting with abundant data resources in highly productive ways.

Improved methods for calibrating and characterizing the CCD array based off-nadir tiltable advanced solid-state array spectroradiometer (ASAS) were developed and applied. Sensor characteristics such as radiometric sensitivity, polarization sensitivity, signal-to-noise-ratio, temperature sensitivity, spectral bandpass, spectral distortion, spatial distortion, and spatial resolution were measured. Radiometric sensitivity, array temperature sensitivity, and signal-to-noise were measured using a barium sulfate coated integrating hemisphere whose output calibration is traceable to NIST. Polarization sensitivity was measured for 48 of 62 spectral bands across all 512 spatial pixels. Spectral bandpass and spectral distortion were measured using a 0.5 meter doublepass monochromator. Spatial resolution (given as the modulation-transfer-function -- MTF) and distortion were measured using a combination of monochromatic collimated light to directly measure the point-spread-function (PSF) and the edge spread function (ESF) derived from actual image data. The MTF obtained using the two techniques are compared. Potential improvements to the test setups and methods are described.

The primary objective for the MOPITT algorithm test radiometer (MATR) is to support the pre-launch testing of data retrieval algorithms for the MOPITT satellite instrument. Particular areas of concern in the retrieval are the effects of variable ground reflectance, the operation of the PMR, the accuracy of the CH₄ spectral data in the HITRAN data base, and the calculated interference from water vapor. The review panel for the MOPITT algorithm theoretical basis document strongly encouraged a ground-air field effort to obtain measurements of the real atmosphere with prototype instruments. The plans for MATR include three detection channels. Channel one will use a length modulator cell (LMC) followed by a detector system with a spectral bandpass near 2.3 micrometer. This LMC will be filled with CO (or alternatively with CH₄) to make total column measurements that are strongly weighted near the surface. Channel two will use the same length modulator cell (LMC) as channel one, but it will use a detector system with a spectral bandpass near 4.6 micrometer. This channel will be sensitive to CO primarily in the free troposphere. Channel three will use a pressure modulator cell (PMC) followed by a detector system with a spectral bandpass also near 4.6 micrometer. This channel will be sensitive to CO primarily in the upper troposphere and lower stratosphere. A first round of laboratory, ground-based atmospheric, and airborne measurements have been completed to date using the 2.3 micrometer CH₄ channel. The current status of MATR will be presented, along with results obtained to date.