Spectral features are introduced by the diffuser that is used during on-board sun calibration. New findings are presented on how to reduce the size of these spectral features. Reduction can be obtained via optical design of the calibration unit, but also in creating a better diffuser. A novel diffuser design will be presented and its performance will be compared to standard diffusers like an Aluminum diffuser, a Spectralon diffuser, and the QVD (Quasi Volume Diffuser). For the in-house spectral features testing setup an improvement of about a factor of eight was obtained for the new diffuser type when compared to QVD. QVD in its turn is already better than an Aluminum diffuser by a factor of ten. Spectralon and QVD are found to be about equally good when measured in terms of spectral features reduction. The novel diffuser is referred to as SanDiff since it is a sandwich of QVD and PTFE material. For the SanDiff also the BSDF was measured and will be presented here.

Measurements of bi-directional reflectance factor for diffuse reflectance from 1100 nm to 2500 nm using extended-range indium gallium arsenide (exInGaAs) detectors in the NIST Spectral Tri-function Automated Reference Reflectometer (STARR) facility are described. The determination of bi-directional reflectance factor with low uncertainties requires the exInGaAs radiometer to be characterized for low-noise performance, linearity and spatial uniformity. The instrument characterizations will be used to establish a total uncertainty budget for the reflectance factor. To independently check the bi-directional reflectance factors, measurements also were made in a separate facility in which the reflectance factor is determined using calibrated spectral irradiance and radiance standards. The total combined uncertainties for the diffuse reflectances range from < 1 % at 1100 nm to 2.5 % at 2500 nm. At NIST, these measurement capabilities will evolve into a calibration service for diffuse spectral reflectance in this wavelength region.

Satellite instruments operating in the reflective solar wavelength region often require accurate and precise determination of the Bidirectional Reflectance Distribution Function (BRDF). Laboratory-based diffusers are used in their pre-flight calibrations and at ground-based support of on-orbit remote sensing instruments. The Diffuser Calibration Lab at NASA's Goddard Space Flight Center is a secondary diffuser calibration standard after NIST for over two decades, providing numerous NASA projects with BRDF data in the UV, Visible and the NIR spectral regions. The Diffuser Calibration Lab works on extending the covered spectral range from 900 nm up to 1.7 microns. The measurements are made using the existing scatterometer by replacing the Si photodiode based receiver with an InGaAs-based one. The BRDF data was recorded at normal incidence and scatter zenith angles from 10 to 60 deg. Tunable coherent light source was used at this setup. Monochromator based broadband light source application is also under development. The results are discussed and compared to empirically generated BRDF data from simple model based on 6 deg directional/hemispherical measurements and experimental data in the 900 - 1100 nm spectral range.

The NASA Goddard Space Flight Center (GSFC) Radiation Calibration Facility (RCF) maintains several large integrating sphere sources covering the visible and near infrared wavelength range. Two critical requirements of an integrating sphere source are short and long-term operational stability and repeatability. Monitoring the source is essential in determining the origin of systemic errors, thus increasing confidence in source performance, and quantifying repeatability. If monitor data falls outside the established parameters, this is an indication that the source requires maintenance or re-calibration against the National Institute of Science and Technology (NIST) irradiance standard. The GSFC RCF has developed a Filter Radiometer Monitoring System (FRMS) to continuously monitor the performance of its integrating sphere calibration sources in the 400-2400nm region. Sphere output change mechanisms include lamp aging, coating (BaSO₄) deterioration, and ambient water vapor level. The FRMS wavelength bands are selected to quantify changes caused by these mechanisms. The FRMS design and operation is presented, as well as data from monitoring three of the RCF's integrating sphere sources.

The Ozone Mapping and Profiler Suite (OMPS) instruments are important tools that will be used to continue ozone measurements begun by instruments such as SBUV/2, TOMS and SOLSE. This paper presents pre-launch radiometric calibration results for the Nadir Profiler and Total Column instruments, which were delivered to the NPOESS Preparatory Project in late 2008. The paper includes a description of a subset of the calibration testing and data analysis including the radiance mode calibration using NIST-calibrated FEL lamps and a large-aperture integrating sphere using the Walker sphere calibration method.

VIIRS sensor for National Polar-orbiting Operational Environmental Satellite System (NPOESS) is one of the nation's key civil space programs. The Flight Model 1 is planned to be launched in 2011. VIIRS is designed to measure the radiometric data of Earth's atmosphere, ocean, and land surfaces from visible to infrared wavelengths, and precision pre-flight radiometric calibration is required. A 100 cm Sphere Integrating Source (SIS(100)-1), which was used to calibrate NASA's MODIS sensor, is used to calibrate VIIRS. Cary 14, a spectrophotometer used to calibrate reflectance and transmittance of optical components since LANDSAT missions, is used to transfer the calibration of a NIST-traceable standard lamp to SIS(100)-1 for different lamp levels from visible to short wave infrared wavelengths. In this paper, the method and result of absolute radiometric calibration of SIS(100)-1 are discussed.

The VIIRS instrument has a polarization sensitivity requirement. There is also a requirement that the instrument's polarization sensitivity and associated phase be measured and the uncertainties in the measured results meet requirements. Performing these measurements is conceptually straight forward. However real world complications associated with test equipment and polarization models do arise and are discussed in this paper.

One of the roles of the VIIRS Ocean Science Team (VOST) is to assess the performance of the instrument and scientific processing software that generates ocean color parameters such as normalized water-leaving radiances and chlorophyll. A VIIRS data simulator is being developed to help aid in this work. The simulator will create a sufficient set of simulated Sensor Data Records (SDR) so that the ocean component of the VIIRS processing system can be tested. It will also have the ability to study the impact of instrument artifacts on the derived parameter quality. The simulator will use existing resources available to generate the geolocation information and to transform calibrated radiances to geophysical parameters and visa-versa. In addition, the simulator will be able to introduce land features, cloud fields, and expected VIIRS instrument artifacts. The design of the simulator and its progress will be presented.

Desert test sites such as Railroad Valley (RRV) Nevada, Egypt-1, and Libya-4 are commonly targeted to assess the on-orbit radiometric performance of sensors. Railroad Valley is used for vicarious calibration experiments, where a field-team makes ground measurements to produce accurate estimates of top-of-atmosphere (TOA) radiances. The Sahara desert test sites are not instrumented, but provide a stable target that can be used for sensor cross-comparisons, or for stability monitoring of a single sensor. These sites are of interest to NASA's Atmospheric Carbon Observation from Space (ACOS) and JAXA's Greenhouse Gas Observation SATellite (GOSAT) programs. This study assesses the utility of these three test sites to the ACOS and GOSAT calibration teams. To simulate errors in sensor-measured radiance with pointing errors, simulated data have been created using MODIS Aqua data. MODIS data are further utilized to validate the campaign data acquired from June 22 through July 5, 2009. The first GOSAT vicarious calibration experiment was conducted during this timeframe.

In the framework of the Global Monitoring for Environment and Security (GMES) programme, the European Space Agency (ESA) in partnership with the European Commission (EC) is developing the SENTINEL-2 optical imaging mission devoted to the operational monitoring of land and coastal areas. The Sentinel-2 mission is based on a twin satellites configuration deployed in polar sun-synchronous orbit and is designed to offer a unique combination of systematic global coverage with a wide field of view (290km), a high revisit (5 days at equator with two satellites), a high spatial resolution (10m, 20m and 60 m) and multi-spectral imagery (13 bands in the visible and the short wave infrared spectrum). SENTINEL-2 will ensure data continuity of SPOT and LANDSAT multispectral sensors while accounting for future service evolution. This paper presents the main geometric and radiometric image quality requirements for the mission. The strong multi-spectral and multi-temporal registration requirements constrain the stability of the platform and the ground processing which will automatically refine the geometric physical model through correlation technics. The geolocation of the images will take benefits from a worldwide reference data set made of SENTINEL-2 data strips geolocated through a global space-triangulation. These processing are detailed through the description of the level 1C production which will provide users with ortho-images of Top of Atmosphere reflectances. The huge amount of data (1.4 Tbits per orbit) is also a challenge for the ground processing which will produce at level 1C all the acquired data. Finally we discuss the different geometric (line of sight, focal plane cartography, ...) and radiometric (relative and absolute camera sensitivity) in-flight calibration methods that will take advantage of the on-board sun diffuser and ground targets to answer the severe mission requirements.

In order to meet Earth observation needs of the European Union-ESA Global Monitoring for Environment and Security (GMES) programme, ESA decided to develop the Sentinels as first series of operational satellites. The series of Sentinel-3 satellites will provide global, frequent and near-realtime ocean, ice and land monitoring. It continues Envisat's altimetry, the multispectral, medium-resolution visible and infrared ocean and land-surface observations of ERS, Envisat and Spot, and includes enhancements to meet the operational revisit requirements and to facilitate new products and evolution of services. The first launch is expected in 2013. In this paper the design of the major instruments and their basic performance parameters will be introduced as well as the expected accuracies of the main data products.

The Geostationary Ocean Colour Imager (GOCI) is a visible band ocean colour instrument onboard the Communication, Ocean, and Meteorological Satellite (COMS) scheduled to be in operation from early 2010. The instrument is designed to monitor ocean water environments around the Korean peninsula in high spatial and temporal resolutions. We report a new imaging and radiometric performance prediction model specifically designed for GOCI. The model incorporates the Sun as light source, about 4000km x 4000km section of the Earth surrounding the Korean peninsula and the GOCI optical system into a single ray tracing environment in real scale. Specially, the target Earth section is constructed using high resolution coastal line data, and consists of land and ocean surfaces with reflectivity data representing their constituents including vegetation and chlorophyll concentration. The GOCI instrument in the IRT model is constructed as an optical system with realistic surface characteristics including wave front error, reflectivity, absorption, transmission and scattering properties. We then used Monte Carlo based ray tracing computation along the whole optical path starting from the Sun to the final detector plane, for simultaneous imaging and radiometric performance verification for a fixed solar zenith angle. This was then followed by simulation of red-tide evolution detection and their radiance estimation, in accordance with the in-orbit operation sequence. The simulation results prove that the GOCI flight model is capable of detecting both image and radiance originated from the key ocean phenomena including red tide. The model details and computational process are discussed with implications to other earth observation instruments.

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002. Early in the mission, the AIRS instrument demonstrated its value to the weather forecasting community with better than 6 hours of improvement on the 5 day forecast. Now with over six years of consistent and stable data from AIRS, scientists are able to examine processes governing weather and climate and look at seasonal and interannual trends from the AIRS data with high statistical confidence. Naturally, long-term climate trends require a longer data set, but indications are that the Aqua spacecraft and the AIRS instrument should last beyond 2016. This paper briefly describes the AIRS products, reviews past science and weather accomplishments from AIRS data product users and highlights recent findings in these areas.

It is widely accepted that the knowledge of the frequencies of the spectral response functions (SRF) of the channels of hyperspectral sounders at the 10 parts per million (ppm) of frequency level is adequate for the retrieval of temperature and moisture profiles and data assimilation for weather forecasting. However, SI traceability and knowledge at the 1 ppm level and better are required to separate artifacts in the knowledge of the SRF due to orbital and seasonal instrument effects from diurnal and seasonal effects due to climate change. We use examples from AIRS to discuss a spectral calibration that uses the SI traceable upwelling radiance spectra to achieve an absolute accuracy of 0.5 ppm.

Clouds and the Earth's Radiant Energy System (CERES) instruments were designed to measure the reflected shortwave and emitted longwave radiances of the Earth's radiation budget and to investigate the cloud interactions with global radiances for the long-term monitoring of Earth's climate. The three scanning thermistor bolometers measure the broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to >100 micrometer) and 8 - 12 micrometer water vapor window regions. Four CERES instruments (Flight Models1 through 4) are flying aboard EOS Terra and Aqua platforms with two instruments aboard each spacecraft. The post launch calibration of CERES sensors are carried out using the internal calibration module (ICM) comprising of blackbody sources and quartz-halogen tungsten lamp, and a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The ICM calibration results are instrumental in understanding the shift in CERES sensors' gains after launch from the pre-launch determined values. Several validation studies are also conducted with the CERES measurements to monitor the behavior of the sensors in various spectral regions. In addition to the broadband response changes derived from the on-board blackbody and the tungsten lamp, the shortwave and the total sensors show further drop in responsivity in the UV spectral region that were brought to light through validation studies. Further analyses were performed to correct for these response changes at all spectral regions. This paper reports the sensor response changes that were determined with the on-board calibration sources and the investigation of the additional factors that influence the performance of the CERES sensors in orbit.

The Clouds and the Earth's Radiant Energy System (CERES) spacecraft scanning thermistor bolometers were used to measure earth-reflected solar and earth-emitted longwave radiances, at satellite altitude. The bolometers measured the earth radiances in the broadband shortwave solar (0.3 - 5.0 micrometers) and total (0.3->100 micrometers) spectral bands as well as in the (8 - 12 micrometers) water vapor window spectral band over geographical footprints as small as 10 kilometers at nadir. In May 2002, the fourth and fifth sets of CERES bolometers were launched aboard the Aqua spacecraft. Ground vacuum calibrations defined the initial count conversion coefficients that were used to convert the bolometer output voltages into filtered earth radiances. The mirror attenuator mosaic (MAM), a solar diffuser plate, was built into the CERES instrument package calibration system in order to define in-orbit shifts or drifts in the sensor responses. The shortwave and total sensors are calibrated using the solar radiances reflected from the MAM's. Each MAM consists of baffle-solar diffuser plate systems, which guide incoming solar radiances into the instrument fields-of-view of the shortwave and total wave sensor units. The MAM diffuser reflecting type surface consists of an array of spherical aluminum mirror segments, which are separated by a Merck Black A absorbing surface, overcoated with silicon dioxide. Temperature sensors are located in each MAM plate and baffle. The CERES MAM wass designed to yield calibration precisions approaching .5 percent for the total and shortwave detectors. In this paper, the MAM solar calibration procedures are presented along with on-orbit results. Comparisons are also made between the Aqua,Terra and the Tropical Rainfall Measurement Mission (TRMM) CERES MAM solar calibrations.

Long-term climate data records often consist of observations made by multiple sensors. It is, therefore, extremely important to have instrument overlap, to be able to track instrument stability, to quantify measurement uncertainties, and to establish an absolute measurement scale traceable to the International System of Units (SI). The Moderate Resolution Imaging Spectroradiometer (MODIS) is a key instrument for both the Terra and Aqua missions, which were launched in December 1999 and May 2002, respectively. It has 20 reflective solar bands (RSB) with wavelengths from 0.41 to 2.2μm and observes the Earth at three nadir spatial resolutions: 0.25km, 0.5km, and 1km. MODIS RSB on-orbit calibration is reflectance based with reference to the bi-directional reflectance factor (BRF) of its on-board solar diffuser (SD). The SD BRF characterization was made pre-launch by the instrument vendor using reference samples traceable directly to the National Institute of Standards and Technology (NIST). On-orbit SD reflectance degradation is tracked by an on-board solar diffuser stability monitor (SDSM). This paper provides details of this calibration chain, from pre-launch to on-orbit operation, and associated uncertainty assessments. Using MODIS as an example, this paper also discusses challenges and key design requirements for future missions developed for accurate climate studies.

Data from the two MODIS instruments have been accurately geolocated (Earth located) to enable retrieval of global geophysical parameters. The authors describe the approach used to geolocate with sub-pixel accuracy over nine years of data from MODIS on NASA's EOS Terra spacecraft and seven years of data from MODIS on the Aqua spacecraft. The approach uses a geometric model of the MODIS instruments, accurate navigation (orbit and attitude) data and an accurate Earth terrain model to compute the location of each MODIS pixel. The error analysis approach automatically matches MODIS imagery with a global set of over 1,000 ground control points from the finer-resolution Landsat satellite to measure static biases and trends in the MODIS geometric model parameters. Both within orbit and yearly thermally induced cyclic variations in the pointing have been found as well as a general long-term trend.

MODIS collects data in 36 spectral bands, including 20 reflective solar bands (RSB) and 16 thermal emissive bands (TEB). The TEB on-orbit calibration is performed on a scan-by-scan basis using a quadratic algorithm that relates the detector response with the calibration radiance from the sensor on-board blackbody (BB). The calibration radiance is accurately determined each scan from the BB temperature measured using a set of 12 thermistors. The BB thermistors were calibrated pre-launch with traceability to the NIST temperature standard. Unlike many heritage sensors, the MODIS BB can be operated at a constant temperature or with the temperature continuously varying between instrument ambient (about 270K) and 315K. In this paper, we provide an overview of both Terra and Aqua MODIS on-board BB operations, functions, and on-orbit performance. We also examine the impact of key calibration parameters, such as BB emissivity and temperature (stability and gradient) determined from its thermistors, on the TEB calibration and Level 1 (L1B) data product uncertainty.

Scanning radiometers on earth-orbiting satellites are used to measure the chlorophyll content of the oceans via analysis of the water-leaving radiances. These radiances are very sensitive to the atmospheric correction process, which in turn is polarization dependent. The image created by a scanning radiometer is usually composed of successive scans by two mirror sides and one or several detectors. The Moderate Resolution Imaging Spectroradiometer (MODIS) has 10 detectors for each ocean color band. If the polarization sensitivities are different among detectors and this is not taken account of in the atmospheric correction process, striping will occur in different parts of the images. MODIS polarization parameters were derived using ground truth data from another earth-orbiting sensor (Sea-viewing Wide Field-of-view Sensor, SeaWiFS), allowing a comparison of the on-orbit characterization and the prelaunch characterization. This paper presents these comparisons for the MODIS instruments on the Aqua and Terra satellites. The detector dependency is clearly different in the prelaunch characterization. This paper also describes the detector dependency of the vicarious corrections to the radiometric calibration coefficients. During the first four years of each mission, the only correction needed to minimize striping in the ocean color products is a constant offset, there is indication of a temporal trend or a view angle dependency for these offsets. The offsets are similar for both instruments, but larger in Terra.

Staggered arrays is the common rule for high resolution earth observing systems, particularly for panchromatic/multispectral acquisition: the linear arrays are shifted in the telescope focal plane along the satellite velocity direction, which means registration performances sensitivity to both terrain elevation and high frequency platform perturbances. This paper aims to show how this sensitivity may be transformed from a drawback to an asset, allowing to retrieve high frequency attitude perturbances ranging above the gyros cutoff frequency or refine the viewing directions, compute digital elevation model and apply superresolution technique with direct applications within the framework of SPOT5, Quickbird and Pleiades-HR satellites.

Ball Aerospace and Technologies Corporation in Boulder, Colorado, has developed a heliostat facility that will be used to determine the preflight radiometric calibration of Earth-observing sensors that operate in the solar-reflective regime. While automatically tracking the Sun, the heliostat directs the solar beam inside a thermal vacuum chamber, where the sensor under test resides. The main advantage to using the Sun as the illumination source for preflight radiometric calibration is because it will also be the source of illumination when the sensor is in flight. This minimizes errors in the pre- and post-launch calibration due to spectral mismatches. It also allows the instrument under test to operate at irradiance values similar to those on orbit. The Remote Sensing Group at the University of Arizona measured the transmittance of the heliostat facility using three methods, the first of which is a relative measurement made using a hyperspectral portable spectroradiometer and well-calibrated reference panel. The second method is also a relative measurement, and uses a 12-channel automated solar radiometer. The final method is an absolute measurement using a hyperspectral spectroradiometer and reference panel combination, where the spectroradiometer is calibrated on site using a solar-radiation-based calibration.

The Airborne Compact Atmospheric Mapper (ACAM) was designed and built at the NASA Goddard Space Flight Center (GSFC) as part of an effort to provide cost-effective remote sensing observations of tropospheric and boundary layer pollutants and visible imagery for cloud and surface information. ACAM has participated in three campaigns to date aboard NASA's Earth Science Project Office (ESPO) WB-57 aircraft. This paper provides an overview of the instrument design and summarizes its ability to determine the minimal measurable slant-column concentration of nitrogen dioxide (NO₂) as well as exploring the calibration stability of commercially available miniature spectrometers.

Monitoring the responsivities of the visible channel of the Imagers on operational GOES satellites is a continuing effort at NOAA. To estimate the rate of degradation of the responsivity, we have been analyzing the time series of star signals measured by the Imagers for attitude and orbit determination. In this report, we begin by showing our latest results of monitoring of the responsivities of the visible channels of GOES-8, GOES-9, GOES-10, GOES-11, GOES-12, and GOES-13. One complicating factor in the analysis has been the presence in the time series of an annual cycle that modulates the gradual long-term degradation whose rate we are trying to infer. We describe a method we are developing to reduce the influence of the annual cycle on the analysis. The method enables us to include in the analysis the star observations near local midnight, which had been excluded in the past to prevent loss of accuracy in the derived long-term degradation rate. With a fuller set of data, we can subdivide the data within each year into 48 bins and estimate the degradation separately in each bin, thereby reducing the influence of the annual cycle on the derived degradation rates. One indication that the method is valid is that the degradation rates estimated in all the bins are consistent.

Landsat-7 ETM+, launched in April 1999, and Landsat-5 TM, launched in 1984, both have a single thermal band. Both instruments' thermal band calibrations have been updated: ETM+ in 2001 for a pre-launch calibration error and TM in 2007 for data acquired since the current era of vicarious calibration has been in place (1999). This year, the vicarious calibration teams have made regular collects of very hot targets, and have been able to make use of archived buoy data to extend the TM calibration back in time. The new data has made it clear that both instruments require slight adjustments in their thermal calibration coefficients. These new coefficients will be generated and put into the operational processing system to remove the calibration errors. The JPL vicarious calibration team has long operated automated buoys on Lake Tahoe for the purpose of vicarious calibration. This year, the Salton Sea station came on line. Salton Sea, located in southern California, gets far hotter than Lake Tahoe. Vicarious calibration results of the Salton Sea for both instruments added to the understanding of a small gain error that the Tahoe data had suggested. With the Salton Sea data, an ETM+ gain error became statistically significant. Though it causes errors as large as 1.2K at high temperatures (35C), at more usual earth temperatures (4-20C) the calibration error is within the noise of the calibration methodology (+/-0.6K). With an ETM+ calibration update, the RMSE will be +/-0.6K for all temperatures. The RIT vicarious calibration team mined the archive of the NOAA National Data Buoy Center for sites on the Great Lakes and in the Atlantic Ocean where buoy data was regularly available between 1984 and 2007 and there were radiosonde data within close proximity to allow for atmospheric correction. Four Landsat scenes were chosen and the study made use of almost 200 separate acquisitions of these scenes. The technique was first tested with Landsat-7 data, and was shown to be as reliable as the standard RIT vicarious calibration methods. The TM calibration was largely unmonitored for most if it's lifetime. The buoy results suggest a lifetime error in gain and a change in the offset after 1997. The 2007 TM calibration update accounted for much of the offset error but was only implemented for data acquired after 1999. With the additional buoy data, the calibration will be corrected for the earlier time period and the result will be a consistent calibration to within +/-0.6K for the lifetime of the TM.

This paper presents a summary of the performance of the Landsat Operational Land Imager (OLI) spectral filters. An overview of OLI is presented along with background on filter performance and manufacture. Performance results versus requirements are presented for all key performance metrics.

The ability to achieve continuous monitoring of the global water supply from satellite imagery is an ongoing effort in the remote sensing community. Historically, sensors such as SeaWiFs and MODIS have been used over the open ocean and along coastal regions to determine the constituents in the water body. Due to their poor spatial resolution, these satellites are ineffective in monitoring many inland and near shore, case 2 waters whose constituents can have large spatial variability. Alternatively, current Landsat instruments have adequate spatial resolution but lack the radiometric fidelity necessary to perform constituent retrieval. In this paper, a new sensor being developed by NASA is introduced that is potentially both spectrally and spatially sufficient for the monitoring of case 2 waters. This study presents the relevant sensor design parameters and initial results of an experiment to determine what impact the improved features of the Landsat Data Continuity Mission's (LDCM) Operational Land Imager (OLI) will have on water resource assessment. Specifically, we investigate how the addition of a deep blue band, 12-bit quantization, and improved signal-to-noise ratios affect our ability to retrieve water constituents. Preliminary results of a simulated case study indicate that the LDCM instrument introduces retrieval errors of less than 6% for three constituents while its predecessor, the Enhanced Thematic Mapper Plus (ETM+), introduces errors of over 20%. This suggests that LDCM's OLI instrument exhibits the potential to be a useful tool for the continuous monitoring of coastal and inland water resources. To actually achieve the potential demonstrated in this study, ongoing work focuses on atmospherically compensating simulated OLI data.

Observations of the Moon provide one technique for the cross calibration of Earth remote sensing instruments. Monthly lunar observations are major components of the on-orbit calibration strategies of the SeaWiFS and MODIS instruments. SeaWiFS has collected more than 132 low phase angle and 59 high phase angle lunar observations over 12 years, while Terra MODIS has collected more than 82 scheduled and 297 unscheduled lunar observations over 9 years and Aqua MODIS has collected more than 61 scheduled and 171 unscheduled lunar observations over 7 years. The NASA Ocean Biology Processing Group's Calibration and Validation Team (OBPG CVT) and the NASA MODIS Characterization Support Team (MCST) use the U.S. Geological Survey's RObotic Lunar Observatory (ROLO) photometric model of the Moon to compare these time series of lunar observations. In addition, the Moon was observed simultaneously by SeaWiFS and Terra MODIS on 14 April 2003 as part of the Earth Observing System (EOS) Lunar Calibration Experiment, allowing a direct comparison of one set of lunar measurements. The OBPG CVT and MCST use residuals of the lunar observations from the ROLO model to cross calibrate SeaWiFS and the two MODIS instruments. The cross calibration results show that Terra MODIS and Aqua MODIS agree, band-to-band, at the 1-3% level, while SeaWiFS and either MODIS instrument agree at the 3-8% level. The main implication of these cross-calibration results is that the operations concepts for upcoming remote sensing instruments should be designed to maximize the number of lunar observations over the mission time frame, while minimizing the phase angle range of the observations.

MODIS has 20 reflective solar bands (RSB), covering the VIS, NIR, and SWIR spectral regions. They are calibrated on-orbit using a solar diffuser (SD) panel, made of space-grade Spectralon. The SD bi-directional reflectance factor (BRF) was characterized pre-launch by the instrument vendor with reference to the NIST reflectance standard. Its on-orbit degradation is tracked by an on-board solar diffuser stability monitor (SDSM). The SeaWiFS on-orbit calibration strategy uses monthly lunar observations to monitor the long-term radiometric stability of the instrument and applies daily observations of its solar diffuser (an aluminum plate coated with YB71 paint) to track the short-term changes in the instrument response. This paper provides an overview of MODIS and SeaWiFS SD observations, applications, and approaches used to track their on-orbit degradations. Results from both sensors are presented with emphasis on the spectral dependence and temporal trends of the SD degradation. Lessons and challenges from the use of SD for sensor on-orbit calibration are also discussed.

The Remote Sensing Group (RSG) at the University of Arizona has a long history of using ground-based test sites for the calibration of airborne and satellite based sensors. Often, ground-truth measurements at these tests sites are not always successful due to weather and funding availability. Therefore, RSG has also employed automated ground instrument approaches and cross-calibration methods to verify the radiometric calibration of a sensor. The goal in the cross-calibration method is to transfer the calibration of a well-known sensor to that of a different sensor. This work studies the feasibility of determining the radiometric calibration of a hyperspectral imager using multispectral imagery. The work relies on the Moderate Resolution Imaging Spectroradiometer (MODIS) as a reference for the hyperspectral sensor Hyperion. Test sites used for comparisons are Railroad Valley in Nevada and a portion of the Libyan Desert in North Africa. Hyperion bands are compared to MODIS by band averaging Hyperion's high spectral resolution data with the relative spectral response of MODIS. The results compare cross-calibration scenarios that differ in image acquisition coincidence, test site used for the calibration, and reference sensor. Cross-calibration results are presented that show agreement between the use of coincident and non-coincident image pairs within 2% in most bands as well as similar agreement between results that employ the different MODIS sensors as a reference.

Earth observation technologies can be widely used in such domains as territorial planning and management, urban development, precision agriculture, intelligent transportation. As a member of the Inter-governmental Earth Observation Consultative Organization, China's earth observation system is an indispensable component of globe earth observation systems. The development of China's earth observation satellites can contribute to globe earth observation system. The general situation and performance parameters of China's main running satellites for earth observation like meteorological satellites, resource satellites, marine satellites, environment and disaster reduction satellites, and Beijing-1 small satellite are illustrated. The applications of China's earth observation satellites are analyzed according to various domains such as nature disaster early warning and monitoring, marine monitoring, geographic surveying. The construction of China's earth observation system is a key element of globe spatial information technology infrastructure. Its development and improvement certainly strengthen science and technology support level of human observing ability and earth system science enormously. It provides the important technology support to global environmental change research, specially the influence of humanities factor to global change.

Active and passive microwave sensor are very important for atmospheric and surface parameters monitoring. In past decades, microwave sensors like SSM/I, AMSR-E and PR have got great achievements in measuring global temperature profile and Precipitation, as well as surface parameters like soil moisture and snow water equivalent. FY3 series satellite is the new generation meteorological satellites of China. Its main objective is to provide data needed for meteorological application. There are 2 microwave sounders and 1 microwave imager onboard the FY3 satellite, provide the air temperature, humidity and surface parameters information under all weather conditions. we plan to develop our own active microwave sensor In FY3-02 series satellites, which is planed to be launched in 2012. In FY3-02 series, the active microwave sensor, together with other two sensors, are to be setting in a low altitude orbit satellite, together with other two mid-altitude satellites, consists the whole FY3-02 series meteorological satellite constellation. The main target of the active microwave sensor is to monitor the precipitation and disaster weather in global scale.

The remote sensing measurement of the land surface temperature from satellites provides an overview of this magnitude on a continuous and regular basis. The study of its evolution in time and space is a critical factor in many scientific fields such as weather forecasting, detection of forest fires, climate change, and so on. The main problem of making this measurement from satellite data is the need to correct the effects of the atmosphere and the surface emissivity. The aim was to define an enhanced vegetation cover method to calculate and generate, automatically, maps of land surface emissivity from images of the AATSR (Advanced Along Track Scanning Radiometer) onboard the Envisat satellite. For the production of these emissivity maps, the geometric model purposed is based on [6]. Its validation was made by comparing the obtained results and the values measured in previous field campaigns [2] carried out in the area of rice fields of Valencia, Spain.

The MODIS reflective solar bands (RSB) include both the low-gain and high-gain spectral bands depending on their specific applications. MODIS RSBs are calibrated on-orbit by an on-board solar diffuser. In order to avoid detector response saturation when calibrating the high-gain bands, an optional attenuation screen, made of a metal plate with pinhole arrays, is placed in front of the SD panel. Since no pre-launch system-level characterization was made for the SD screen (SDS) vignetting function (VF), a series of spacecraft (Terra and Aqua) yaw maneuvers were carried out to perform on-orbit characterization of the VF. Assuming that the low-gain bands and the high-gain bands have the same VF, the current VF was derived from yaw observations using the MODIS low-gain bands through taking the ratio of their SD responses with and without the SDS in place. In this study, we attempt to characterize the SDS VF directly using detector responses of individual high-gain bands with the SDS in place only. The corresponding SD responses without the SDS, not available from measurements due to saturation, are calculated using detector gains, the SD bi-directional reflectance factor (BRF), and the view geometry that matches the yaw observations with the SDS in place. Results and discussions are focused on the band dependent and detector dependent features of the SDS VF, and their potential impact on the RSB calibration.

MODIS reflective solar bands (RSB) are calibrated on-orbit using a solar diffuser (SD) with its degradation tracked by an on-board solar diffuser stability monitor (SDSM). The SDSM has 9 detectors with wavelengths from 0.41 to 0.94μm. It is operated during each scheduled SD calibration event, making alternate observations of the Sun and the SD. Due to a design defect in the SDSM there are significant ripples in the Sun view responses. Because of this, an alternative approach was developed by normalizing SDSM detector responses to detector 9 at 0.94μm. It has been very effective since the responses of all SDSM detectors have the same ripples and SD degradation at detector 9 wavelength is extremely small. After many years of on-orbit operations, the accumulated degradation at detector 9 can have some impact on the RSB calibration quality. As a result, a new approach is developed and implemented to characterize the SD degradation directly. This approach reduces the ripples via a look-up table (LUT) constructed with data carefully selected from the existing SDSM observations made in a short period. In this paper, we provide an overview of different approaches applied over the years by the MODIS Characterization Support Team (MCST) to track the on-board SD degradation. Results of both Terra and Aqua MODIS SD degradation derived from different approaches are presented and evaluated. Lessons learned from MODIS SD on-orbit operation and recent improvements for the RSB calibration are also discussed.

The MODIS instrument is currently operated onboard NASA's Terra and Aqua spacecrafts, launched in December 1999 and May 2002, respectively. MODIS has 36 spectral bands, among which 20 are the Reflective Solar Bands (RSB), covering a spectral range from 0.41 to 2.2 microns. The RSB are calibrated on-orbit using an onboard Solar Diffuser (SD), together with lunar observations and measurements from an onboard Spectroradiometric Calibration Assembly (SRCA). MODIS views the Earth's surface and the onboard calibrators via a two-sided scan mirror. Previous analysis of on-orbit observations from the SD, Moon, and SRCA has revealed that the Response Versus Scan angle (RVS) of the scan mirror is time, Angle of Incidence (AOI), and wavelength (band) dependent. Consequently, algorithms have been developed to track the on-orbit RVS change. In addition to the SD, Moon, and SRCA observations, the Earth View (EV) measurements at different AOI are trended and used to derive the time-dependent RVS look-up tables (LUT) for the RSB calibration in the Level 1B (L1B). On-orbit RVS algorithms were first applied to MODIS Version 4 and have, since then, been revised several times for both Terra and Aqua MODIS in order to adequately track on-orbit changes. In this paper, we present MODIS RSB RVS algorithm development history, focusing on the recent improvements for the upcoming Version 6. Results show that the RVS change is larger at shorter wavelengths and is different for the two mirror sides. For both Terra and Aqua MODIS, the degradation is also detector dependent for a few visible spectral bands.

The SIMBIOS (Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies) Program was conceived as a result of a NASA management review of the agency's strategy for monitoring the bio-optical properties of the global ocean through space-based ocean color remote sensing. SIMBIOS Radiometric Intercomparisons (SIMRICs) were carried out in 2001 and 2002. The purpose of the SIMRICs was to ensure a common radiometric scale among the calibration facilities that are engaged in calibrating in-situ radiometers used for ocean color related research and to document the calibration procedures and protocols. The SeaWiFS Transfer Radiometer (SXR-II) measured the calibration radiances at six wavelengths from 411nm to 777nm in the participating laboratories. The measured radiances were compared with the radiances expected by the laboratories. NIST calibrations of the SXR-II were obtained in December 2000, December 2001 and January 2003. Two independent light sources (SQMs, SeaWiFS Quality Monitors) were used to monitor changes in the SXR-II responsivity between the NIST calibrations and after, with monthly measurements until the end of 2003, and less frequent measurements thereafter. This paper discusses the calibration and trending history of the SXR-II from December 2000 to June 2008.