Spectrographs are used in a variety of applications in the field of remote sensing for radiometric measurements due to the benefits of measurement speed, sensitivity, and portability. However, spectrographs are single grating instruments that are susceptible to systematic errors arising from stray radiation within the instrument. In the application of measurements of ocean color, stray light of the spectrographs has led to significant measurement errors. In this work, a simple method to correct stray-light errors in a spectrograph is described. By measuring a set of monochromatic laser sources that cover the instrument's spectral range, the instrument's stray-light property is characterized and a stray-light correction matrix is derived. The matrix is then used to correct the stray-light error in measured raw signals by a simple matrix multiplication, which is fast enough to be implemented in the spectrograph's firmware or software to perform real-time corrections: an important feature for remote sensing applications. The results of corrections on real instruments demonstrated that the stray-light errors were reduced by one to two orders of magnitude, to a level of approximately 10^-5 for a broadband source measurement, which is a level less than one count of a 15-bit resolution instrument. As a stray-light correction example, the errors in measurement of solar spectral irradiance using a highquality spectrograph optimized for UV measurements are analyzed; the stray-light correction leads to reduction of errors from a 10 % level to a 1 % level in the UV region. This method is expected to contribute to achieving a 0.1 % level of uncertainty required for future remote-sensing applications.

The presence of structures, as observed in real spectral data from earth observing satellites, that are due to the on-board diffusers are discussed. The structures are shown to be caused by the speckles in the entrance slit of the spectrometer, created by the diffusers. A dedicated setup for the study of these spectral features will be presented together with results on different types of diffusers, i.e. surface diffusers and volume diffusers. Finally, methods to reduce the amplitude of the spectral features will be presented. It will be shown that QVD (quasi volume diffuser) and Spectralon (a volume diffuser) are far better in reducing the unwanted spectral features than an aluminum surface diffuser. Overall it can be stated that QVD is the "best" diffuser where the validity of this statement depends on the type of its use.

Many satellite instruments operating in the reflective solar wavelength region between 400 nm and 2500 nm require accurate and precise determination of the Bidirectional Reflectance Distribution Function (BRDF) of on-board diffusers used in their pre-flight and on-orbit calibrations. In this paper we study the characteristics and effects of speckles in the measurement of the BRDF of Spectralon diffusers. Two types of light sources were used in this study: a monochromator based broadband source and a coherent laser source at 632.8 nm. The Spectralon diffuser was measured over a range of incident and scatter angles. The speckle effect is known to be a significant issue in the measurement of Spectralon BRDF using laser sources. In this study, three different speckle pattern minimization techniques are examined. These include moving the Spectralon sample, expanding the incident spot size, and depolarizing the incident laser light. The results were compared with measurements using the incoherent monochromator-based source and the degree to which speckle was reduced is described. Speckle effects are found to be easily minimized using these simple techniques. The experimental data were obtained using the out-of-plane scatterometer located in NASA's Goddard Space Flight Center's Diffuse Calibration Facility (DCaF). The typical measurement uncertainty of reported BRDF measurements is 0.7% (k=1).

We have performed an absolute calibration comparison between the Sun and a NIST-calibrated spectral irradiance standard lamp. The comparison at seven bands ranging from 1.2 to 2.3 μm was made using a highly stable Short Wave IR Transfer Radiometer. The experiment consisted of laboratory and outdoor measurements of an irradiated diffusely reflecting panel. Outdoors, simultaneous atmospheric transmittance measurements were also obtained in order to correct for atmospheric effects. The results were used to compare three absolute exo-atmospheric solar spectral irradiance data sets currently used in various remote sensing applications to a NIST traceable radiometric calibration. The comparison with the limited set of recently produced SORCE-SIM data showed almost no differences at 1.2 and 1.6 μm; however, the comparison with three other data sets showed larger differences.

Pre-flight performance has been characterized on the Medium-sized Aperture Camera (MAC) of the RazakSAT: capable of Earth observation at 2.5 m resolution and 20 km swath width. Topics discussed in this paper include measurements of system modulation transfer function (MTF) and pixel lines-of-sight (LOS); characterization of focal plane assembly (FPA) and signal processing electronics; end-to-end imaging. The MTF was obtained with knife-edge scanning technique, which is also used to align the FPA. For band-to-band registration, relative pixel LOS was measured using theodolite and effective focal length of the telescope was derived from the measurement. For the FPA and signal processing module, dark reference, pixel-to-pixel response variation and response linearity have been quantified. The end-to-end imaging tests were done to check the imaging function before the launch, by scanning a slide target at the focus of the collimator.

Launched in 1982 and 1984 respectively, the Landsat-4 and -5 Thematic Mappers (TM) are the backbone of an extensive archive of moderate resolution Earth imagery. However, these sensors and their data products were not subjected to the type of intensive monitoring that has been part of the Landsat-7 system since its launch in 1999. With Landsat-4's 11 year and Landsat-5's 20+ year data record, there is a need to understand the historical behavior of the instruments in order to verify the scientific integrity of the archive and processed products. Performance indicators of the Landsat-4 and -5 thermal bands have recently been extracted from a processing system database allowing for a more complete study of thermal band characteristics and calibration than was previously possible. The database records responses to the internal calibration system, instrument temperatures and applied gains and offsets for each band for every scene processed through the National Landsat Archive Production System (NLAPS). Analysis of this database has allowed for greater understanding of the calibration and improvement in the processing system. This paper will cover the trends in the Landsat-4 and -5 thermal bands, the effect of the changes seen in the trends, and how these trends affect the use of the thermal data.

The Landsat Thematic Mappers have obtained imagery of the Earth's surface since 1982 with the launch of Landsat 4. However, the absolute calibration of this first instrument, as well as it's cross-calibration to the other two thematic mappers on Landsat 5 and 7, remains in question. The objective for this work was to provide an absolute radiometric calibration of the Landsat 4 instrument. Landsat 4's internal calibrator, while still useful, does not provide an absolute calibration; it does provide a relative calibration of the instrument's responsivity over the lifetime of the mission. The same is true for the Landsat 5 internal calibrator; however, Landsat 5 has been cross-calibrated to Landsat 7's Enhanced Thematic Mapper Plus, which is believed to be absolutely calibrated to within 5%. Therefore, by cross-calibrating Landsat 4 to Landsat 7 through Landsat 5, an absolute calibration for Landsat 4 can be determined. This study provides only the Landsat 4 and 5 cross-calibration models. To determine these models, Landsat 4/Landsat 5 scene pairs were studied. Within each pair, 8 400x400-pixel sub-regions were selected from the image. The exact geo-located sub-region was located from both instruments and an assumption was made that the ground and the atmosphere did not change between image dates. Therefore, any difference between the images may be attributed to the difference in the instruments. Results of this cross-calibration using multiple dates were consistent to within 2%. Once the cross-calibration points were determined, they were used to correct the relative lifetime-calibration model from the internal calibrator, hence producing an absolute lifetime-calibration model.

Detector responses to the Internal Calibrator (IC) pulses in the Landsat-4 Thematic Mapper (TM) have been observed to follow an oscillatory behavior. This phenomenon is present only in the Short Wave Infrared (SWIR) bands and has been observed throughout the lifetime of the instrument, which was launched in July 1982 and imaged the Earth's surface until late 1993. These periodic changes in amplitude, which can be as large as 7.5 percent, are known as outgassing effects and are believed to be due to optical interference caused by a gradual buildup of an ice-like material on the window of the cryogenically cooled dewar containing the SWIR detectors. Similar outgassing effects in the Landsat-5 TM have been characterized using an optical thin-film model that relates detector behavior to the ice film growth rate, which was found to gradually decrease with time. A similar approach, which takes into consideration the different operational history of the instrument, has been applied in this study to three closely sampled data sets acquired throughout the lifetime of the Landsat-4 TM. Although Landsat-4 and Landsat-5 Thematic Mappers are essentially identical instruments, data generated from analyses of outgassing effects indicate subtle, but important, differences between the two. The estimated lifetime model could improve radiometric accuracy by as much as five percent.

The ability to detect and quantify changes in the Earth's environment depends on satellites sensors that can provide calibrated, consistent measurements of Earth's surface features through time. A critical step in this process is to put image data from subsequent generations of sensors onto a common radiometric scale. To evaluate Landsat-5 (L5) Thematic Mapper's (TM) utility in this role, image pairs from the L5 TM and Landsat-7 (L7) Enhanced Thematic Mapper Plus (ETM+) sensors were compared. This approach involves comparison of surface observations based on image statistics from large common areas observed eight days apart by the two sensors. The results indicate a significant improvement in the consistency of L5 TM data with respect to L7 ETM+ data, achieved using a revised Look-Up-Table (LUT) procedure as opposed to the historical Internal Calibrator (IC) procedure previously used in the L5 TM product generation system. The average percent difference in reflectance estimates obtained from the L5 TM agree with those from the L7 ETM+ in the Visible and Near Infrared (VNIR) bands to within four percent and in the Short Wave Infrared (SWIR) bands to within six percent.

Recent results of the vicarious calibration of the Landsat-7 ETM+ sensor are presented based on the reflectance-based vicarious method using results from a smaller test site in close proximity to the University of Arizona. The typical, larger test site is brighter and more spatially uniform then the smaller site. However, the location of the small test site allows for more frequent data collections and a more complete understanding of the calibration coefficients of the sensor as a function of time. The Remote Sensing Group previously reported results based on data collected from the smaller test site on seven dates. Here we report calibration values for additional dates as well as a comparison of the calibration values for the large and smaller test sites over recent years. The most recent data shows the calibration values using the smaller sites continue to agree within 3% of the large test sites in all bands.

Ground-reference techniques for the Enhanced Thematic Mapper Plus (ETM+) on Landsat 7 are described. The reflectance-based approach for vicarious calibration has been applied by the Remote Sensing Group of the Optical Sciences Center to 59 sets of ground-based data collected at large uniform test sites imaged by Landsat-7 ETM+. The results of this work coupled with the apparent stability of the ETM+ sensor shows that a one-sigma precision less than 3% is currently being achieved. Band-by-band analysis of the precision gives insight into the effects of atmospheric correction and surface reflectance uncertainties giving an understanding of the error sources in this approach. Variations in results are not seen between test sites and atmospheric effects are not the primary cause of day-to-day variability. These results are discussed with an emphasis on the current state of vicarious calibration accuracies/precision as well as areas for improvement and future accuracy expectations.

Since shortly after launch the radiometric performance of band 6 of the ETM+ instrument on Landsat 7 has been evaluated using vicarious calibration techniques for both land and water targets. This evaluation indicates the radiometric performance of band 6 has been both highly stable and accurate. Over a range corresponding to a factor of two in radiance (5 to 55 C in kinetic temperature terms) the difference between the in-situ derived radiance and the image derived radiance is on average 0.5% or less. Water targets are the easiest to use but are limited to the temperature range from 0 to about 32 C. Land targets can reach 55 C or more but are far less spatially homogeneous than water targets with respect to both local surface temperature and spectral emissivity. The techniques used and the results are described.

Since May 31, 2003, when the scan line corrector (SLC) on the Landsat-7 ETM+ failed, the primary foci of Landsat-7 ETM+ analyses have been on understanding and attempting to fix the problem and later on developing composited products to mitigate the problem. In the meantime, the Image Assessment System personnel and vicarious calibration teams have continued to monitor the radiometric performance of the ETM+ reflective bands. The SLC failure produced no measurable change in the radiometric calibration of the ETM+ bands. No trends in the calibration are definitively present over the mission lifetime, and, if present, are less than 0.5% per year. Detector 12 in Band 7 dropped about 0.5% in response relative to the rest of the detectors in the band in May 2004 and recovered back to within 0.1% of its initial relative gain in October 2004.

An atmospheric correction tool has been developed on a public access web site for the thermal band of the Landsat-5 and Landsat-7 sensors. The Atmospheric Correction Parameter Calculator uses the National Centers for Environmental Prediction (NCEP) modeled atmospheric global profiles interpolated to a particular date, time and location as input. Using MODTRAN radiative transfer code and a suite of integration algorithms, the site-specific atmospheric transmission, and upwelling and downwelling radiances are derived. These calculated parameters can be applied to single band thermal imagery from Landsat-5 Thematic Mapper (TM) or Landsat-7 Enhanced Thematic Mapper Plus (ETM+) to infer an at-surface kinetic temperature for every pixel in the scene. The derivation of the correction parameters is similar to the methods used by the independent Landsat calibration validation teams at NASA/Jet Propulsion Laboratory and at Rochester Institute of Technology. This paper presents a validation of the Atmospheric Correction Parameter Calculator by comparing the top-of-atmosphere temperatures predicted by the two teams to those predicted by the Calculator. Initial comparisons between the predicted temperatures showed a systematic error of greater then 1.5K in the Calculator results. Modifications to the software have reduced the bias to less then 0.5 ± 0.8K. Though not expected to perform quite as well globally, the tool provides a single integrated method of calculating atmospheric transmission and upwelling and downwelling radiances that have historically been difficult to derive. Even with the uncertainties in the NCEP model, it is expected that the Calculator should predict atmospheric parameters that allow apparent surface temperatures to be derived within ±2K globally, where the surface emissivity is known and the atmosphere is relatively clear. The Calculator is available at http://atmcorr.gsfc.nasa.gov.

The EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) mission has been recently selected as the 6^th ESA's Earth Explorer Mission. The mission objective is to determine, in a radiatively consistent manner, the global distribution of vertical profiles of cloud and aerosol field characteristics. A major innovation of the EarthCARE mission is to include both active and passive instruments on a single platform, which allows for a complete 3-D spatial and temporal picture of the radiative flux field at the top of the atmosphere and the Earth's surface to be developed. While the active instruments provide vertical cloud profiles, the passive instruments (mainly the multi-spectral imager) provide supplementary horizontal data to allow for the extrapolation of the 3-D cloud and aerosol characteristics. The EarthCARE payload is composed of four instruments: an Atmospheric backscatter Lidar, a Cloud Profiling Radar, a Multi-Spectral Imager and a Broad Band Radiometer. The mission baseline is a sun-synchronous orbit with an altitude around 450 km. The EarthCARE mission is a cooperative mission with Japan (JAXA and NiCT), which will provide the Cloud Profiling Radar. ESA will provide the ground segment and the rest of the space segment including the lidar, the imager and the broadband radiometer. The launch is planned for 2012.

We are presenting new experimental data on atmospheric carbon dioxide and oxygen column absorption collected with a passive instrument developed at Goddard Space Flight Center called FPICC (Fabry-Perot Interferometer for Column CO₂). The data were recorded on board of NASA's DC-8 flight laboratory during the PAVE experiment (Polar Aura Validation Experiment), January 2005. The precise alignment of the transmission peaks of the Fabry-Perot etalon to the CO₂ absorption lines is achieved through altering the refractive index of the material (fused silica) using its temperature dependence. The experimental data presented showed excellent agreement with our theoretical expectations. They are recorded at different gas pressures and temperatures and also at various weather conditions. The goal of the experiment is to demonstrate that variations of the column density of the CO₂ can be detected using this passive instrument and the target precision is <0.3%. Some of the major advantages of the optical setup are its compactness, high sensitivity, high signal-to-noise ratio, and stability.

Large 2-D focal plane arrays (FPAs) can be used for multispectral imaging by sequentially viewing a scene through multiple discrete narrow-band filters on a continuously rotating filter wheel. The constant angular velocity of the wheel minimizes momentum disturbances, jitter and power consumption and maximizes reliability, but the optical beam straddles two adjacent filters during each transition between them. The duty cycle of the imager can be maximized by separating these narrow band filters into two equal groups: long-wavelength and short-wavelength. The narrow-band filters can then be mounted contiguous to one another on a ring of the filter wheel, alternating between long and short wavelength filters. The optical beam transmitted by the filter wheel can then be divided into a long-wavelength beam and a short-wavelength beam by a dichroic beamsplitter that transmits the output of one group of filters and reflects the output of the other group. Each beam can then be transmitted through an additional broadband spectral filter and can be imaged on a separate FPA. When the optical beam straddles two narrow-band filters on the wheel, the dichroic beamsplitter and the broadband filters prevent out-of-band radiation from reaching either FPA, allowing FPA to integrate a spectrally-pure 2D image (although the flux will decrease and the diffraction will increase as the beam is vignetted.) When the incident beam passes through a long-wavelength filter on the wheel, the short wavelength FPA can be read our without requiring a shutter, and vice versa.

This paper reports on a novel approach to atmospheric cloud segmentation from a space based multi-spectral pushbroom satellite system. The satellite collects 15 spectral bands ranging from visible, 0.45 um, to long wave infa-red (IR), 10.7um. The images are radiometrically calibrated and have ground sample distances (GSD) of 5 meters for visible to very near IR bands and a GSD of 20 meters for near IR to long wave IR. The algorithm consists of a hybrid-classification system in the sense that supervised and unsupervised networks are used in conjunction. For performance evaluation, a series of numerical comparisons to human derived cloud borders were performed. A set of 33 scenes were selected to represent various climate zones with different land cover from around the world. The algorithm consisted of the following. Band separation was performed to find the band combinations which form significant separation between cloud and background classes. The potential bands are fed into a K-Means clustering algorithm in order to identify areas in the image which have similar centroids. Each cluster is then compared to the cloud and background prototypes using the Jeffries-Matusita distance. A minimum distance is found and each unknown cluster is assigned to their appropriate prototype. A classification rate of 88% was found when using one short wave IR band and one mid-wave IR band. Past investigators have reported segmentation accuracies ranging from 67% to 80%, many of which require human intervention. A sensitivity of 75% and specificity of 90% were reported as well.

NOAA is planning to include a hyperspectral Coastal Waters imaging capability (HES-CW) as part of the Hyperspectral Environment Suite (HES) on the next generation Geostationary Operational Environmental Satellite (GOES-R) to be launched in 2012. The key advantage of a geostationary imager is frequency of revisit. Coastal waters are highly dynamic. Tides, diurnal winds, river runoff, upwelling and storm winds drive currents from one to several knots. Three hour or better sampling is required to resolve these features, and to track red tides, oil spills or other features of concern for coastal environmental management. The HES-CW will image the U.S. coastal waters once every three hours, with a goal of hourly. Additionally, HES-CW can be cued using the Advanced Baseline Imager (ABI) to image when the area is cloud free, rather than at fixed times set by the orbit for traditional polar orbiting ocean color imagers like SeaWiFS and MODIS. To prepare for HES-CW NOAA has formed the Coastal Ocean Applications and Science Team (COAST). COAST goals are to assure that ocean applications and science requirements are met and to help NOAA prepare for the immediate use of the data when HES-CW is launched. I will describe the HES-CW requirements, current status and the activities of the COAST team.

The Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is a new concept for a microwave sounder, intended to be deployed on NOAA's next generation of geostationary weather satellites, GOES-R. A ground based prototype has been developed at the Jet Propulsion Laboratory, under NASA Instrument Incubator Program sponsorship, and is currently undergoing tests and performance characterization. The initial space version of GeoSTAR will have performance characteristics equal to those of the AMSU system currently operating on polar orbiting environmental satellites, but subsequent versions will significantly outperform AMSU. In addition to all-weather temperature and humidity soundings, GeoSTAR will also provide continuous rain mapping, tropospheric wind profiling and real time storm tracking. In particular, with the aperture synthesis approach used by GeoSTAR it is possible to achieve very high spatial resolutions without having to deploy the impractically large parabolic reflector antenna that is required with the conventional approach. GeoSTAR therefore offers both a feasible way of getting a microwave sounder in GEO as well as a clear upgrade path to meet future requirements. GeoSTAR offers a number of other advantages relative to real-aperture systems as well, such as 2D spatial coverage without mechanical scanning, system robustness and fault tolerance, operational flexibility, high quality beam formation, and open ended performance expandability. The technology and system design required for GeoSTAR are rapidly maturing, and it is expected that a space demonstration mission can be developed before the first GOES-R launch. GeoSTAR will be ready for operational deployment 2-3 years after that.

Stars are regularly observed in the visible channels of the GOES Imagers for real-time navigation operations. However, we have been also using star observations off-line to deduce the rate of degradation of the responsivity of the visible channels. We estimate degradation rates from the time series of the intensities of the Imagers' output signals, available in the GOES Orbit and Attitude Tracking System (OATS). We begin by showing our latest results in monitoring the responsivities of the visible channels on GOES-8, GOES-10 and GOES-12. Unfortunately, the OATS computes the intensities of the star signals with approximations suitable for navigation, not for estimating accurate signal strengths, and thus we had to develop objective criteria for screening out unsuitable data. With several layers of screening, our most recent trending method yields smoother time series of star signals, but the time series are supported by a smaller pool of stars. With the goal of simplifying the task of data selection and to retrieve stars that have been rejected in the screening, we tested a technique that accessed the raw star measurements before they were processed by the OATS. We developed formulations that produced star signals in a manner more suitable for monitoring the conditions of the visible channels. We present specifics of this process together with sample results. We discuss improvements in the quality of the time series that allow for more reliable inferences on the characteristics of the visible channels.

Lacking onboard calibration devices, the GOES Imager visible channel must be vicariously calibrated on orbit. Several methods have been explored. In this study, the method using a well-calibrated radiometer (MODIS) as an external reference for calibration was expanded and improved. This method is complementary to other techniques in that, in addition to long term trending, it also provides absolute calibration shortly after launch. Care must be taken, though, to account for the lack of simultaneity of the measurements by the two sensors and the differences in the sensors' spectral response functions.

Although the visible channel of the Imagers carried by NOAA's operational Geostationary Operational Environmental Satellites (GOES) has no onboard calibration device, the decrease in the responsivity of this channel over time must be known if we are to make the data in this channel useful for detecting trends in the signals from the Earth. Therefore, some external method is required to provide this information. In this paper, we examine an external technique for monitoring responsivity changes based on empirical distribution functions (EDFs) of observations of the Earth's full disk. A time series of instrument outputs (in digital counts) at fixed levels at the tops of the EDFs is produced. A nonlinear least squares technique is then employed to adjust the time series for solar and seasonal effects and to fit it with an exponential, whose argument provides the rate of degradation of the responsivity. This technique assumes that the probabilistic structure of the signal from the earth does not change over time. The resulting time series and estimated responsivity degradation rates for the visible channels of GOES-8 and -10 Imagers will be presented. These results are similar to those obtained earlier with a star-based technique, thus increasing our confidence in the results of both techniques. The EDF technique and the star-based technique are synergistic, as they use very different approaches and data sets. Also, the star based technique works at the low end of the Imager's output signal range, whereas the EDF technique works at the high end.

Solar-band imagery from geostationary meteorological satellites has been utilized in a number of important applications in Earth Science that require radiometric calibration. Because these satellite systems typically lack on-board calibrators, various techniques have been employed to establish "ground truth", including observations of stable ground sites and oceans, and cross-calibrating with coincident observations made by instruments with on-board calibration systems. The Moon appears regularly in the margins and corners of full-disk operational images of the Earth acquired by meteorological instruments with a rectangular field of regard, typically several times each month, which provides an excellent opportunity for radiometric calibration. The USGS RObotic Lunar Observatory (ROLO) project has developed the capability for on-orbit calibration using the Moon via a model for lunar spectral irradiance that accommodates the geometries of illumination and viewing by a spacecraft. The ROLO model has been used to determine on-orbit response characteristics for several NASA EOS instruments in low Earth orbit. Relative response trending with precision approaching 0.1% per year has been achieved for SeaWiFS as a result of the long time-series of lunar observations collected by that instrument. The method has a demonstrated capability for cross-calibration of different instruments that have viewed the Moon. The Moon appears skewed in high-resolution meteorological images, primarily due to satellite orbital motion during acquisition; however, the geometric correction for this is straightforward. By integrating the lunar disk image to an equivalent irradiance, and using knowledge of the sensor's spectral response, a calibration can be developed through comparison against the ROLO lunar model. The inherent stability of the lunar surface means that lunar calibration can be applied to observations made at any time, including retroactively. Archived geostationary imager data that contains the Moon can be used to develop response histories for these instruments, regardless of their current operational status.

The Moderate Resolution Imaging Spectroradiometer (MODIS) was designed with a set of on-board calibrators (OBCs) that include a solar diffuser (SD), a solar diffuser stability monitor (SDSM), a blackbody (BB), and a spectro-radiometric calibration assembly (SRCA). The SD and SDSM, used for calibration of the reflective solar bands (RSB), are normally operated on a bi-weekly basis (weekly during the first year of the mission). The BB is primarily used for calibration of the thermal emissive bands (TEB) on a scan-by-scan basis. The sensor's spatial and spectral stability is monitored bi-monthly and quarterly respectively by the SRCA. The MODIS characterization support team (MCST) at NASA/GSFC is responsible for scheduling and implementing the calibration and characterization activities, performing calibration data analyses, and monitoring instrument on-orbit performance (short-term and long-term). This paper provides a description on how each of the OBCs is operated and a summary of the activities that support instrument calibration and characterization and data product quality. Using the EOS Terra MODIS (launched in December 1999) as an example, this paper illustrates and evaluates the OBCs' design capabilities and summarizes their overall on-orbit performance. Several papers included in these proceedings focus on individual on-board calibrators.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the five Earth-observing instruments onboard the NASA EOS Terra spacecraft launched in December 1999. It makes frequent global observations over a broad spectral range (0.41 to 14.4μ) and at three spatial resolutions (0.25km, 0.5km, and 1km at nadir). The MODIS was designed with a set of on-board calibrators (OBCs) that include a solar diffuser (SD), a blackbody (BB), and spectro-radiometric calibration assembly (SRCA). One SRCA function is to provide on-orbit spectral characterization of the MODIS reflective solar bands (RSB) with wavelengths from 0.41 to 2.2μ. This paper provides an overview of the MODIS SRCA on-orbit spectral characterization approach and summarizes the results derived from five years of Terra MODIS on-orbit observations. In general, the on-orbit characterization of the Terra MODIS RSB relative spectral responses (RSR) has been satisfactory. The measured center wavelength (CW) shifts are less than 0.6nm for the 412nm spectral band, 0.5nm for the 443nm band, and 0.4nm for the remaining reflective solar bands (short-wave infrared bands excluded). The bandwidth (BW) changes are typically less than 1nm. Excluding the differences between pre-launch and initial on-orbit results, the CW shifts and BW changes are very stable. For a given band, the detector-to-detector spectral characterization differences are typically less than 0.2nm.

The Moderate Resolution Imaging Spectroradiometer (MODIS) reflective solar bands (RSB) cover wavelengths from 0.41 to 2.2μm. They are calibrated on-orbit by a solar diffuser (SD) panel, made of space-grade Spectralon. During each SD calibration a solar diffuser stability monitor (SDSM) is operated concurrently to track the changes of the SD bidirectional reflectance factor (BRF). The SDSM views alternately the sunlight (Sun View) through a fixed transmission screen and the sunlight diffusely reflected from the SD panel (SD view). A design error in the SDSM system, not discovered until post-launch, has caused significant ripples in the SDSM Sun view responses. Consequently an alternative normalization approach has been developed to remove the ripples in the SDSM Sun view responses and their impacts on the SD degradation analysis. This approach has been successfully used in the SDSM measurements on-orbit. In order to reduce the direct solar exposure onto the SD panel, the MODIS instrument was designed with a SD door that is normally commanded to an "open" position during SD/SDSM observations and to a "closed" position when the calibration is completed. For Terra MODIS launched in December 1999, an SD door related anomaly occurred in May 2003 that led to a decision to set the SD door permanently at the open position. This operational configuration has resulted in extra time of direct solar illumination on the SD plate and therefore a much faster SD degradation rate. In this paper we provide a brief description of the MODIS RSB calibration algorithm and the on-board SD and SDSM system used for the calibration. We examine the Terra MODIS SD degradation rate and its spectral dependency. The results from five years of SDSM observations are summarized in this paper and used to evaluate the SD on-orbit performance and its impact on the MODIS RSB calibration uncertainty. Prior to the SD door anomaly, the SD annual degradation rate was approximately 3% at 0.41μm, 2% at 0.47μm, and 1% at 0.53μm. After the SD door anomaly, the SD annual degradation rate has increased to 10% at 0.41μm, 7% at 0.47μm, and 4.5% at 0.53μm.

Twenty of the 36 MODIS spectral bands are reflective solar bands (RSB). They are calibrated on-orbit by an onboard solar diffuser (SD). For the high-gain ocean color bands (8-16), an attenuating solar diffuser screen (SDS) is used in front of the SD panel to avoid detector saturation caused by direct solar illumination of the SD. The use of the SDS, a metal plate with uniformly distributed pinholes, introduces an additional factor to the radiometric calibration uncertainty. Since a system level characterization of the SDS transmission versus SD viewing geometry was not performed pre-launch, the vignetting function (VF) for both Terra and Aqua MODIS had to be characterized on-orbit. The VF can be derived either from SD observations made with and without the SDS in place during specially planned spacecraft yaw maneuvers or by using routine SD calibration pairs (with and without the SDS) accumulated over a long period in order to cover all possible viewing geometries. In this paper we present details of the methods used to characterize the MODIS SDS VFs and examine the results derived from both spacecraft yaw maneuvers and long-term SD calibration pairs. The VF results obtained for Terra and Aqua MODIS are discussed and compared. In addition, an estimate of the calibration uncertainties introduced by the SDS is provided.

The Moderate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands covering wavelengths from 0.41 to 14.4_m. It is a cross-track scanning radiometer that uses a two-sided paddle-wheel scan mirror to make observations over a wide field-of-view (FOV). Each scan of 1.478 seconds, it produces a swath of 10km along-track (at nadir) by 2330km along-scan. Bands 1-19 and 26 are the reflective solar bands (RSB) and bands 20-25 and 27-36 are the thermal emissive bands (TEB). There are a total of 160 detectors (10 detectors per band) for the thermal emissive bands that are calibrated on-orbit by a blackbody (BB) on a scan-by-scan basis. The spectral radiance of each individual TEB detector is calculated every scan from the BB source temperature. The temperature of the BB is measured by a set of 12 thermistors. On-orbit performance of the BB, such as its temperature stability and uncertainty, directly impacts the TEB calibration and data product quality. Excluding a few spacecraft and instrument related anomalies or safe hold events, the Terra MODIS (launched in December 1999) BB has operated continuously on-orbit for more than five years. Using its on-orbit calibration data, this paper examines the Terra MODIS BB performance and its impact on the TEB calibration uncertainty. The results show that the Terra MODIS BB has been performing extremely well in terms of its reliability and stability. Under the same operating configuration, the average BB temperature drift per year (long-term stability) is less than 0.005K. The scan-to-scan temperature variation (short-term stability) is within ±0.03K. Also illustrated in this paper are examples of the TEB detectors' responses to the on-board BB and the detectors' noise characterization results at different BB temperatures.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Earth Observing System (EOS) Aqua platform uses biweekly solar diffuser measurements for the radiometric calibration of the ocean color bands. The solar angle relative to the spacecraft changes throughout the year. This document describes correlations in the solar diffuser measurements of the ocean color bands to the sun yaw angle. The functional form of the correlations depends on the position of the respective band and detector on the focal plane. The proposed corrections often exceed 0.5% (peak-to-peak). The most likely source of the correlations is the radiometric characterization of the solar diffuser screen. These results show the importance of a complete prelaunch characterization for spaceborne sensors regarding the radiometric calibration.

The Ocean Biology Processing Group (OBPG) at NASA's Goddard Space Flight Center is responsible for the processing and validation of oceanic optical property retrievals from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS). A major goal of this activity is the production of a continuous ocean color time-series spanning the mission life of these sensors from September 1997 to the present time. This paper presents an overview of the calibration and validation strategy employed to optimize and verify sensor performance for retrieval of upwelling radiances just above the sea surface. Substantial focus is given to the comparison of results over the common mission lifespan of SeaWiFS and the MODIS flying on the Aqua platform, covering the period from July 2002 through December 2004. It will be shown that, through consistent application of calibration and processing methodologies, a continuous ocean color time-series can be produced from two different spaceborne sensors.

The Moderate Resolution Imaging Spectroradiometer (MODIS), a key instrument for the NASA EOS mission, is currently operating on-board the Terra and Aqua spacecrafts. MODIS has 36 bands covering a spectral range from 0.41 to 14.4μm. It is a cross track scanning radiometer which samples over scan angles from -55° to +55° resulting a 2330km cross track by 10km along track swath each scan. The nadir spatial resolutions are 250m (2 bands), 500m (5 bands) and 1000m (29 bands). This study uses observations from simultaneous nadir overpasses (SNO) to conduct an inter-comparison of the Aqua and Terra MODIS. The GLobal Imager (GLI) onboard the Advanced Earth Observing Satellite-II (ADEOS_II, launched December 14, 2002) is used as a transfer reference since it has many bands which are spectrally similar to MODIS bands. The inter-comparison was performed on one visible band at 0.41μm, one near-IR band at 0.86μm, and six bands from the middle to longwave infrared between 3.7 and 12.3μm over a period from April to October 2003 when the GLI was operating normally. The results show that the Aqua and Terra MODIS agree to within 2% in radiance in the visible and near-IR bands. For the thermal bands, the differences in brightness temperature are less than 0.35K in the atmospheric window region between 11 and 12μm. Higher uncertainties in the other thermal bands are likely due to spectral differences between MODIS and GLI.

Launched on 15 July 2004 aboard the EOS AURA satellite, the Ozone Monitoring Instrument (OMI) is intended as the successor to the Total Ozone Mapping Spectrometer (TOMS). OMI's improved horizontal spatial resolution and extended wavelength range (264-504nm) will provide total column ozone, surface reflectance, aerosol index, and ultraviolet (UV) surface flux as well as ozone profiles and tropospheric column ozone, trace gases, and cloud fraction and height. We present results from a variety of calibration techniques that have been developed over the years to assess the calibration accuracy of backscatter UV sensors. Among these are comparisons of OMI solar measurements with external solar reference spectra and radiances measured over Antarctica and Greenland. OMI UV measured irradiances show wavelength dependencies and spectral features on order of 5% when compared to external solar spectra while all channels exhibit a nearly wavelength independent 1% seasonal goniometric error. No instrument throughput degradation has been identified beyond this level and has been confirmed through ice radiance comparisons. A 3% OMI radiance cross-track swath dependence is seen when comparing radiances over ice fields to radiative transfer results. Reflectances derived at low latitudes show the same cross-track swath dependence with an additional 5% offset.

This paper reviews the calibration techniques used for 19 years of SPOT satellite exploitation: - from the decision to fly a calibration system (involving a lamp and a sun sensor) on SPOT1 to its suppression on SPOT5 and to the emphasis placed on the development of calibration methods over natural targets like oceans or deserts. Oceans provide low reflectance targets for short wavelengths calibration over the atmospheric molecular scattering, while deserts (warm over North Africa and Middle East, cold over Antarctica) provide stable references for sensors cross-calibration and temporal monitoring. - from vicarious calibration campaigns performed by scientific teams over test sites like White Sands (USA) or La Crau (France) to an autonomous ground based station. An automatic radiometer continuously characterizes the reflectance and the atmosphere of the French test site and thanks to its original calibration procedure provides the top of atmosphere radiance needed for in-flight calibration. The results provided by these different methods are discussed. We show that the on-board calibration unit used to monitor with time SPOT1, 2, 3 and 4 cameras sensitivity is loosing sensitivity, justifying the overall calibration update that was proposed to users in October 2004 for all SPOT since their beginning of life.

The Atmospheric Infrared Sounder (AIRS), a hyperspectral infrared sounder, was launched onboard NASA's Aqua spacecraft on May 4, 2002 into sun-synchronous polar Earth orbit for a mission expected to last 7 years. By monitoring calibration data from views of deep space and two on-board calibrators, we have identified a number of effects attributed to in-orbit radiation. Transient effects include 1. steps in the output level of individual channels, attributed to injection of charge into a large capacitor in the read-out electronics integrated circuit (ROIC); and 2. spikes in the calibration data and, by inference, in the scene data, attributed to the passage of ionizing radiation through the active region of the HgCdTe detectors. On-board signal processing corrects for most of the spike effects, and ground processing smoothes the hot and cold calibration data and provides a system of flags to alert the user in cases where the calculated radiances are still suspect. Persistent effects include 1. extremely rare degradations of channels due to large charge injection events; and 2. slow increases in noise levels for a small number of channels, attributed to bias shifts due to the slow accumulation of radiation dose in the ROIC input cells for some channels. In addition to these detector effects, two operational anomalies have been attributed to the high radiation levels in the South Atlantic Anomaly (SAA), one an unplanned cooler shut-down, the second an unplanned stopping of the scan mirror. This paper presents statistics on the frequency and location of these radiation events, and provides a description of the mechanisms by which such events are identified and accounted for. It should be emphasized that the vast majority of the 2378 AIRS infrared channels, and the instrument as a whole, have shown excellent stability and operability throughout the mission.

Cloud's and the Earth's Radiant Energy System (CERES) is an investigation into the role of clouds and radiation in the Earth's climate system. Four CERES scanning thermistor bolometer instruments are currently in orbit. Flight model 1 (FM1) and 2 (FM2) are aboard the Earth Observing System (EOS) Terra satellite and FM3 and FM4 are aboard the EOS Aqua satellite. Each CERES instrument measures in three broadband radiometric regions: the shortwave (SW 0.3-5μm), total (0.3- > 100μm), and window (8-12μm). It has been found that both CERES instruments on the Terra platform imply that the SW flux scattered from the Earth had dropped by up to 2% from 2000 to 2004. No climatological explanation for this drop could be found, suggesting the cause was a drift in both the Terra instruments. However, the onboard calibration lamps for the SW channels do not show a change in gain of this magnitude. Experience from other satellite missions has shown that optics in the orbital environment can become contaminated, severely reducing their transmission of ultra-violet (UV) radiation. Since the calibration lamps emit little radiance in the UV spectral region it was suggested that contaminates could be responsible for an undetectable 'spectral darkening' of the CERES SW channel optics and hence the apparent drop in SW flux. Further evidence for this was found by looking at the comparison between simultaneous measurements made by FM1 and FM2. The proposed mechanisms for contaminant build up would not apply to a CERES instrument operating in the normal cross track scan mode. Indeed it was found from the comparison between CERES instruments on Terra that the response of the instrument operating in rotating azimuth plane (RAPS) mode consistently dropped relative to the other cross track instrument. Since at all times one of the instruments operates in cross track mode, where it is not subject to spectral darkening, it allowed that unit to be used as a calibration standard from which the darkening of the other RAPS instrument can be measured. A table of adjustment coefficients to compensate for this spectral darkening are therefore derived in this paper. These figures are designed to be multiplied by SW fluxes or radiances produced in the climate community using Edition 2 CERES data. SW CERES measurements that have been revised using these coeffcients are therefore to be referred to as ERBE-like Edition2_Rev1 or SSF Edition2B_Rev1 data in future literature. Current work to fully characterize the effect of spectral darkening on the instrument spectral response before the release of Edition 3 data is also described.

It is important to maintain measurements of Earth Radiation Budget parameters from orbit. Such measurements require broadband radiance detectors such as bolometers or thermopiles that rely on the conversion of radiant energy into heat. This heat conversion/conduction results in a thermal detector typically having an exponential time lag of a few milliseconds. However, it is found that there is often a far slower 'slow mode transient' response of around 300ms because the detector mounting material tends to rise in temperature as heat flows out of the detector to its surroundings. Hence this can cause the detector response to a constant input of radiance to continue increasing by a further 1%, for up to half a second after initial exposure. Using analysis of the heat flow out from a bolometer and through its mounting, the Laplace domain impulse response of the detector is derived that includes both first and second time constant effects. Transformation to the Z domain then allows design of a numerical filter to remove the second time constant effect while retaining that of the first time constant. Restoration of the ideal detector response is shown to be advantageous when applied to the output of thermistor bolometers onboard the Cloud's and the Earth's Radiant Energy System (CERES). It also allows more complete characterization of the response of such detectors using general calibration data. The design and use of such a filter is therefore highly applicable to any scanning bolometer or thermopile instrument with spurious slow mode effects.

A comparison of S-HIS instrument performance on various airborne platforms, and during ground characterization is presented. Specific emphasis is placed on instrument improvements, 1998 to present day, and the engineering lessons learned. Also discussed is the ability to accurately validate high spectral resolution IR radiance measurements from space using comparisons with aircraft spectrometer observations. Aircraft comparisons of this type provide a mechanism for periodically verifying expected absolute calibration of spacecraft instruments with instrumentation for which the calibration can be carefully maintained on the ground. This capability is especially valuable for achieving the long-term consistency and accuracy of climate observations, including those from the NASA EOS spacecrafts (Terra, Aqua, Aura).

The Moon has served as a reference for several satellite instruments including SeaWiFS and MODIS, both of which provide design innovations for NPP VIIRS. However, as yet, the Moon is not a formal part of the calibration baseline for NPP VIIRS. In particular, the lunar measurements by the MODIS instruments require on-orbit maneuvers (spacecraft rolls of up to 20 degrees) to maintain a constant lunar phase angle. Here, we use a simulated set of NPP VIIRS lunar measurements to demonstrate the quality of the Moon as a reference for long-term measurements by VIIRS. With nine lunar comparisons (1 year of VIIRS measurements), it is possible to detect linear changes over time in the calibration of the VIIRS reflective solar bands at the 0.1% per year level or better. In addition, the surface of the Moon does not change over periods of a million years or more. As a result, the Moon can act as a cross-calibration reference for NPP VIIRS and the Terra MODIS instrument that precedes it, even with a time gap between the operation of the two sensors. The quality of this cross-comparison reference is estimated to be significantly better than 1%. However, to accomplish both of these functions, NPP VIIRS must make measurements at the same lunar phase angle as Terra MODIS, that is, at 55 degrees after full phase. This requires periodic spacecraft maneuvers.

The Remote Sensing Group at the University of Arizona has successfully used various vicarious calibration methods for the absolute radiometric calibration of over 14 separate sensors since 2000. The results of this work implies that the absolute radiometric accuracy of the reflectance-based approach has absolute uncertainties of less than 3% in the visible and near infrared. The precision of the method also appears to have similar uncertainties. This work better quantifies these uncertainties through sensitivity analysis of typical inputs for the Ivanpah and Railroad Valley test sites and comparisons of results from the ALI, ASTER, and ETM+ sensors. The number of data sets collected for these sensors also allows for attempts to determine trends in the radiometric calibration of these sensors. The current work examines the difficulties in trending of reflectance-based results due to temporal sampling issues, site-to-site variability, and accuracy of the method. The results indicate that monthly results over a one-year period at the current accuracy levels may not be sufficient for determining trends in radiometric calibration even though the method provides an accurate absolute radiometric calibration.

The Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) sensor on the Terra spacecraft has been providing remote sensing data for the past five years. ASTER has three separate sensor sections including a sensor with six bands in the shortwave infrared section of the spectrum. The radiometric calibration of the SWIR sensor has been updated from preflight values based on the on-board calibration sources. The SWIR sensor shows evidence of crosstalk between SWIR bands which is probably optical in origin. The crosstalk was present during preflight calibration and is present in all data collected in-flight including calibration data. The effects of crosstalk can be partially removed by applying a crosstalk correction program. This correction changes the calibration of the system. In this paper we apply a vicarious calibration to crosstalk corrected ASTER imagery over high reflectance desert test sites using a reflectance based method. The updated calibration provides for better retrieval of spectral reflectance or radiance of ground targets in ASTER SWIR imagery.

The Remote Sensing Group (RSG) at the University of Arizona is currently developing inexpensive, unmanned radiometers based on light-emitting diodes (LEDs). This work describes these radiometers, which are now used as part of the extensive vicarious calibration research that has been conducted since the mid-1980s and presently includes such sensors as MODIS, ASTER, AVHRR, Landsat-7 ETM+, Ikonos, and Quickbird. RSG performs a typical vicarious calibration with on-site personnel measuring atmospheric and surface conditions at a test site during actual sensor overpass. A radiative-transfer code is used to calculate a top-of-atmosphere radiance, which is then compared to that reported by the sensor under test. Data collection can be limited by poor weather conditions, and in addition, it is generally difficult to collect data during every sensor overpass due to the large travel distances to the test sites. The LED radiometers are being developed as a solution to the temporal sampling limitations seen in the past. They are used in a nadir-viewing configuration to measure the surface reflectance in three spectral bands, while the atmospheric conditions are measured using a Cimel sun photometer. The data from these two instruments are used to produce a top-of-atmosphere radiance during overpass when no personnel are present. Results of laboratory calibration measurements of the radiometers are described, and include the spectral responsivity, temperature dependence of the spectral responsivity, and calibration coefficient. Finally, the top-of-atmosphere radiances produced by the unmanned vicarious instrumentation are compared to those reported by Aqua MODIS for three days in March 2005.

MODIS is one of the key instruments for the NASA's EOS mission, currently operated on both Terra and Aqua spacecraft making continuous and complementary observations in 36 spectral bands from 0.4 to 14.2 micrometers. Among them are long-wave infrared (LWIR) bands (11-14.2 micrometers) with Photoconductive (PC) HgCdTe detectors. The Terra MODIS pre-launch thermal vacuum calibration and characterization have shown clear evidence of an optical leak presented by the 11 micron band (band 31) into other PC bands (bands 32-36). A correction algorithm has been designed and implemented in the MODIS Level 1B (L1B) code using coefficients determined from the lunar observations made in year 2000. In this work we evaluate the optical leak correction coefficients derived from Terra MODIS lunar observations from January 2001 to December 2004. Our method assumes that in the absence of an optical leak the detector's signal would decay away from its peak response to the moon as an inverse power series function of the frame offset number. The least Chi-squared minimization method is used to calculate the parameters in the fitting function. Analysis results from the lunar and Earth view observations show that the Terra MODIS PC optical leak has been effectively removed. The Level 1B algorithm has been shown to be stable.

The Moderate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands that are distributed, according to their wavelengths, on four focal plane assemblies (FPAs): visible (VIS), near infrared (NIR), short- and mid-wave infrared (SMIR), and long-wave infrared (LWIR). One of the MODIS on-board calibrators, the spectro-radiometric calibration assembly (SRCA), is used to track the sensor's on-orbit spatial characterization. It is also capable of performing instrument radiometric stability monitoring and spectral characterization (measurements of the center wavelengths and bandwidths). This paper focuses on the SRCA's spatial characterization function and presents the results (on-orbit performance) derived from the observations made by the Terra MODIS since its launch in December 1999. The SRCA spectral characterization results of Terra MODIS over the same five-year period are covered in another paper in these proceedings (Xiong et. al.). The MODIS on-orbit spatial characterization discussed in this paper includes measurements of the detector-to-detector registration (DDR) in the along-scan direction, the band-to-band registration (BBR) in both along-scan and along track directions, and the focal plane-to-focal plane registration (FFR) in both directions. These measurements are typically performed bi-monthly. The results will show that the overall along-scan BBR performance of the Terra MODIS has been satisfactory (less than 0.16km), meeting the specification of 0.20km. Except for a few bands of slightly over 0.20km, the along-track BBR values are also within the specification.

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) instrument is a hyperspectral sounder slated to undergo thermal vacuum testing within a year. The University of Wisconsin - Madison is authoring a software suite to answer the requirement of testing the conversion of raw interferogram images into calibrated high-resolution spectra. The software consists of algorithm components that assemble into a processing pipeline as well as a testing harness utilizing a lightweight scripting language. The processing requirements for an imaging FTS are considerable, and necessitate an understanding of maximum achievable accuracy as well as exploration of tradeoffs in the interest of processing efficiency. We present an overview of the design of this testing software.

The National Environmental Satellite, Data, and Information Service (NESDIS) of the National Oceanic and Atmospheric Administration (NOAA) recently implemented enhancements to its operational calibration processing to mitigate the effects of two performance anomalies affecting the Imagers and Sounders aboard the current Geostationary Operational Environmental Satellites (GOES). This paper describes the anomalies, our algorithm enhancements to mitigate their effects, and results. In the first anomaly, the values of the computed calibration slopes in the infrared channels of the Imagers exhibit erroneous spikes during the six hours surrounding satellite midnight, causing observations of scene temperatures to be too low. We believe the spikes are the result of radiation from the solar-heated scan-cavity that reaches the detectors during the Imagers' calibration cycles. In November 2003, NOAA/NESDIS implemented a statistical algorithm that provides more realistic slopes around midnight. The second anomaly is "banding" in frames of observations by the Sounders' infrared channels. This also occurs during the six hours centered on satellite midnight. We believe the source of this anomaly is rapid changes in the temperatures of Sounder fore-optics components. They cause large and rapid changes in calibration offsets, which are not accounted for properly by the Sounder calibration updates, which only occur once every two minutes. In October 2004, NOAA/NESDIS implemented a remedial algorithm that removes the banding by interpolating the offsets to 1.1s intervals.

The Microwave Limb Sounder (MLS) instrument, launched in July of 2004 on NASA's EOS Aura satellite, has been in its nominal science operating mode since August 2004. The objective of EOS MLS is to obtain measurements of atmospheric composition, temperature and pressure through observations of millimeter- and submillimeter-wavelength thermal emission as the instrument field-of-view is scanned through the atmospheric limb. The MLS instrument has completed activation, in-orbit calibrations have been performed leading to adjustments to radiometric calibration (Level 1) algorithms, a software upgrade was implemented for more robust operation of the laser local oscillator, and engineering performance trends have been established. This paper discusses the current status of the MLS instrument which now continuously provides data to produce global maps of targeted chemical species as well as temperature, cloud ice, and gravity wave activity. Performance trends are assessed with respect to characterization during initial on-orbit activation of the instrument, and with data from ground test verification prior to launch.

The Microwave Limb Sounder instrument was launched aboard NASA's EOS AURA satellite in July, 2004. The overall scientific objectives for MLS are to measure temperature, pressure, and several important chemical species in the upper troposphere and stratosphere relevant to ozone processes and climate change. MLS consists of a suite of radiometers designed to operate from 118 GHz to 2.5 THz, with two antennas (one for 2.5 THz, the other for the lower frequencies) that scan vertically through the atmospheric limb, and spectrometers with spectral resolution of 6 MHz at spectral line centers. This paper describes the on-orbit commissioning the MLS instrument which includes activation and engineering functional verifications and calibrations.

Lockheed Martin is developing an innovative and adaptable optical telescope comprised of an array of nine identical afocal sub-telescopes. Inherent in the array design is the ability to perform high-resolution broadband imaging, Fizeau Fourier transform spectroscopy (FTS) imaging, and single exposure multi-spectral and polarimetric imaging. Additionally, the sensor suite's modular design integrates multiple science packages for active and passive sensing from 0.4 to 14 microns. We describe the opto-mechanical design of our concept, the Multiple Instrument Distributed Aperture Sensor (MIDAS), and a selection of passive and active remote sensing missions it fulfills.