Multi-angle Imaging SpectroRadiometer (MISR) instrument descriptionand experiment overview

The Multi-angle Imaging SpectroRadiometer (MISR) instrument is scheduled for launch aboard the first of the Earth Observing System (EOS) spacecraft, EOS-AM1. MISR will provide global, radiometrically calibrated, georectified, and spatially coregistered imagery at nine discrete viewing angles and four visible/near-infrared spectral bands. Algorithms specifically developed to capitalize on this measurement strategy will be used to retrieve geophysical products for studies of clouds, aerosols, and surface radiation. This paper provides an overview of the as-built instrument characteristics and the application of MISR to remote sensing of the Earth     

MISR photogrammetric data reduction for geophysical retrievals

The theoretical concept, based on modern photogrammetric methods, underlying the design of the Multi-angle Imaging SpectroRadiometer (MISR) science data processing system, responsible for the autonomous and continuous georectification of multiangle imagery, is the subject of this paper. The algorithm partitions effort between the MISR Science Computing Facility and the Earth Observing System (EOS) Distributed Active Archive Center (DAAC) in a way that minimizes the amount of processing required at the latter location to rectify and map project remotely sensed data online, as it comes from the instrument. The algorithm deals with the following issues: (1) removal of the errors introduced by inaccurate navigation and attitude data; (2) removal of the distortions introduced by surface topography; (3) attainment of a balance between limited hardware resources, huge data volume and processing requirements, and autonomous and nonstop aspects of the production system     

Techniques for the retrieval of aerosol properties over land andocean using multiangle imaging

Aerosols are believed to play a direct role in the radiation budget of Earth, but their net radiative effect is not well established, particularly on regional scales. Whether aerosols heat or cool a given location depends on their composition and column amount and on the surface albedo, information that is not routinely available, especially over land. Obtaining global information on aerosol and surface radiative characteristics, over both ocean and land, is a task of the Multi-angle Imaging SpectroRadiometer (MISR), an instrument to be launched in 1998 on the Earth Observing System EOS-AM1 platform. Three algorithms are described that will be implemented to retrieve aerosol properties globally using MISR data. Because of the large volume of data to be processed on a daily basis, these algorithms rely on lookup tables of atmospheric radiative parameters and predetermined aerosol mixture models to expedite the radiative transfer (RT) calculations. Over oceans, the “dark water” algorithm is used, taking full advantage of the nature of the MISR data. Over land, a choice of algorithms is made, depending on the surface types within a scene-dark water bodies, heavily vegetated areas, or high-contrast terrain. The retrieval algorithms are tested on simulated MISR data, computed using realistic aerosol and surface reflectance models. The results indicate that aerosol optical depth can be retrieved with an accuracy of 0.05 or 10%, whichever is greater, and some information can be obtained about the aerosol chemical and physical properties     

Performance of the MISR instrument during its first 20 months in Earth orbit

The Multi-angle Imaging SpectroRadiometer, one of five science instruments aboard NASA's Terra spacecraft, was launched into Earth orbit in December 1999. Acquisition of Earth imagery began in February 2000, and the quality of the data is excellent. Overall, MISR has been performing superbly, though the instrument exhibits several idiosyncrasies, some of which were anticipated prior to launch. Details regarding the in-flight performance of the instrument system are presented.     

An optimization algorithm for separating land surface temperatureand emissivity from multispectral thermal infrared imagery

Land surface temperature (LST) and emissivity are important components of land surface modeling and applications. The only practical means of obtaining LST at spatial and temporal resolutions appropriate for most modeling applications is through remote sensing. While the popular split-window method has been widely used to estimate LST, it requires known emissivity values. Multispectral thermal infrared imagery provides us with an excellent opportunity to estimate both LST and emissivity simultaneously, but the difficulty is that a single multispectral thermal measurement with N bands presents N equations in N+1 unknowns (N spectral emissivities and LST). In this study, we developed a general algorithm that can separate land surface emissivity and LST from any multispectral thermal imagery, such as moderate-resolution imaging spectroradiometer (MODIS) and advanced spaceborne thermal emission and reflection radiometer (ASTER) data. The central idea was to establish empirical constraints, and regularization methods were used to estimate both emissivity and LST through an optimization algorithm. It allows us to incorporate any prior knowledge in a formal way, The numerical experiments showed that this algorithm is very effective (more than 43.4% inversion results differed from the actual LST within 0.5°, 70.2% within 1° and 84% within 1.5°), although improvements are still needed     

Determination of land and ocean reflective, radiative, andbiophysical properties using multiangle imaging

Knowledge of the directional and hemispherical reflectance properties of natural surfaces, such as soils and vegetation canopies, is essential for classification studies and canopy model inversion. The Multi-angle Imaging SpectroRadiometer (MISR), an instrument to be launched in 1998 onboard the EOS-AM1 platform, will make global observations of the Earth's surface at 1.1-km spatial resolution, with the objective of determining the atmospherically corrected reflectance properties of most of the land surface and the tropical ocean. The algorithms to retrieve surface directional reflectances, albedos, and selected biophysical parameters using MISR data are described. Since part of the MISR data analyses includes an aerosol retrieval, it is assumed that the optical properties of the atmosphere (i.e. aerosol characteristics) have been determined well enough to accurately model the radiative transfer process. The core surface retrieval algorithms are tested on simulated MISR data, computed using realistic surface reflectance and aerosol models, and the sensitivity of the retrieved directional and hemispherical reflectances to aerosol type and column amount is illustrated. Included is a summary list of the MISR surface products     

Surface roughness characterizations of sea ice and ice sheets: case studies with MISR data

This work is an examination of potential uses of multiangular remote sensing imagery for mapping and characterizing sea ice and ice sheet surfaces based on surface roughness properties. We use data from the Multi-angle Imaging SpectroRadiometer (MISR) to demonstrate that ice sheet and sea ice surfaces have characteristic angular signatures and that these angular signatures may be used in much the same way as spectral signatures are used in multispectral classification. Three case studies are examined: sea ice in the Beaufort Sea off the north coast of Alaska, the Jakobshavn Glacier on the western edge of the Greenland ice sheet, and a region in Antarctica south of McMurdo station containing glaciers and blue-ice areas. The MISR sea ice image appears to delineate different first-year ice types and, to some extent, the transition from first-year to multiyear ice. The MISR image shows good agreement with sea ice types that are evident in concurrent synthetic aperture radar (SAR) imagery and ice analysis charts from the National Ice Center. Over the Jakobshavn Glacier, surface roughness data from airborne laser altimeter transects correlate well with MISR-derived estimates of surface roughness. In Antarctica, ablation-related blue-ice areas, which are difficult to distinguish from bare ice exposed by crevasses, are easily detected using multiangular data.     

Uniqueness of multiangular measurements. II. Joint retrieval of vegetation structure and photosynthetic activity from MISR

For pt.I see ibid., vol.40, no.7, p.1560-73 (2002). The Multi-angle Imaging SpectroRadiometer (MISR) instrument on board the Terra platform offers the capability of acquiring reflectance data on any Earth target in four spectral bands, from nine different directions, in at most seven minutes, at a spatial resolution adequate for the monitoring of the status of terrestrial surfaces. This paper describes the implementation of a physical and mathematical approach to design a simple two-dimensional algorithm dedicated to the interpretation of data collected by this instrument. One dimension fully exploits the spectral information in the blue, red and near-infrared bands while the other dimension capitalizes on the multiangular capability of MISR to assess the anisotropic behavior of terrestrial surfaces with respect to solar radiation. The spectral information is derived following an approach proposed for single angle instruments, such as the MEdium Resolution Imaging Spectrometer (MERIS), the Global Imager (GLI), the Sea-viewing Wide Field-of-view Sensor (SeaWIFS) and VEGETATION. The access to simultaneous multiangular observations from MISR allows extending this approach. This strategy delivers an estimate of the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), which pertains to vegetation photosynthetic activity and is a measure of the presence and density of vegetation.     

Cloud fraction and cloud shadow property retrievals fromcoregistered TIMS and AVIRIS imagery: the use of cloud morphology forregistration

The Thermal Infrared Multispectral Scanner (TIMS) and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) were operated simultaneously from the ER2 aircraft during a March 1990 test over the Rio Bravo region, Belize. Coregistration of the imagery obtained by these two instruments is necessary to utilize the data effectively. A technique for registering the TIMS imagery to AVIRIS imagery is presented. It takes advantage of the morphology of the fair weather cumulus (FWC) clouds present in the imagery for estimating inter-sensor distortions. It relies on an iterative process in which skew, nearest neighbor sampling, and cross-correlation (1D and 2D) are applied. Comparison between the AVIRIS three-band ratio (3BR) imagery and the coregistered TIMS imagery shows that TIMS is superior in detecting thin cloud and cloud edge pixels, especially over shadowed background. Although the seven scenes analyzed in the study were obtained within the same one-hour time period and over the same geographical region, the optimum temperature threshold for cloud detection, with respect to the background temperature, varies significantly from 2.1 to 3.3°C. These values agree with the AVIRIS 3BR cloud fraction equivalent temperature thresholds to within 0.5°C. When applying a cloud shadow mask from the AVIRIS near infrared imagery to the coregistered TIMS background imagery, a 1°C temperature differential is found between the shadowed and nonshadowed background. This significant radiative cooling by Fair Weather Cumulus cloud shadows could introduce errors in surface emissivity retrievals by other Earth Observing System (EOS) investigators     

Multi-angle Imaging SpectroRadiometer (MISR) on-board calibrator (OBC) in-flight performance studies

The Multi-angle Imaging SpectroRadiometer (MISR) consists of nine cameras pointing from nadir to an extreme of 70.5/spl deg/ in the view angle. It is a pushbroom imager with four spectral bands per camera. Instrument specifications call for each camera to be calibrated to an absolute uncertainty of 3% and to within 1% relative to the other cameras. To accomplish this, the MISR instrument utilizes an on-board calibrator (OBC) to provide updates to the instrument gain coefficients on a bimonthly basis (i.e. once every two months). Spectralon diffuse panels are used in the OBC to provide a uniform target for the nine MISR cameras to view. The radiometric scale of the OBC is established through the use of photodiodes. The stability of the MISR OBC system and its in-flight calibration are discussed.     

The high resolution imaging spectrometer (HIRIS) for Eos

The high resolution imaging spectrometer (HIRIS) designed for the Earth Observing System (Eos) is designed to acquire images in 192 spectral bands simultaneously in the 0.4-2.5-μm wavelength region. HIRIS is a targeting rather than a continuous acquisition instrument and obtains high-spatial- and spectral-resolution images in a 30-km swath with a 30-m ground instantaneous field of view (GIFOV) in vertical viewing. Pointing will allow image acquisition at -30° to +60° along-track and ±24° cross-track. The raw data rate of the instrument is 512 Mbs. The high spectral resolution will make it possible to identify many surficial materials such as rocks, soils, and suspended matter in water directly. HIRIS also offers the possibility of studying biochemical processes in vegetation canopies     

Improving MODIS surface BRDF/Albedo retrieval with MISR multiangle observations

We explore a synergistic approach to use the complementary angular samplings from the Multi-angle Imaging SpectroRadiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) to improve MODIS surface bidirectional reflectance distribution function (BRDF) and albedo retrieval. Preliminary case studies show that MODIS and MISR surface bidirectional reflectance factors (BRFs) are generally comparable in the green, red, and near infrared. An information index is introduced to characterize the information content of directional samplings, and it is found that MISR angular observations can bring additional information to the MODIS retrieval, especially when the MISR observations are close to the principal plane. We use the BRDF parameters derived from the MISR surface BRFs as a priori information and derive a posteriori estimates of surface BRDF parameters with the MODIS observations. Results show that adding MISR angular samplings can reduce the relative BRF prediction error by up to 10% in the red and green, compared to the retrievals from MODIS-only observations which are close to the cross-principal plane.     

利用MODIS和MISR资料对APEC会议期间气溶胶时空分布特征的分析

利用卫星遥感的MODIS和MISR数据,对比分析了2014年亚太经合组织（APEC）会议期间（11月3日~12日）及其前后一个月的气溶胶时空分布特征。分析发现APEC会议期间的气溶胶光学厚度（aerosol optical depth, AOD）相比APEC会议前期,在京津冀地区有明显减小,MODIS（MISR）数据显示在京津冀地区AOD减小了38.7%（36.4%）,在北京地区减小更多,减小了64.6%（39.9%）。Angstrom指数在京津冀地区的廊坊、保定、衡水等大部分城市,APEC会议期间的Angstrom指数相对前期较小,说明其在APEC会议期间气溶胶粒子的有效半径相对较大。APEC会议期间的细模态气溶胶光学厚度相比APEC会议前期也有所减小,且在北京地区细模态气溶胶光学厚度的下降幅度要大于粗模态气溶胶的下降幅度。     

Use of stereo-matching to coregister multiangle data from MISR

The pattern-matching algorithms originally developed for Multi-angle Imaging SpectroRadiometer (MISR) (flying on the Earth Observing System (EOS) Terra platform) cloud retrieval have also proven useful in independently providing quality assurance of the coregistration of multiangle measurements with the nadir view. Two new techniques developed to test the coregistration are described in this paper along with results of the misregistration detection on both historical and current data. No ground-control points are strictly necessary for these calculations-just simultaneous clear-sky land imagery for three cameras and knowledge of the terrain altitude. The difficulty of registration increases with the obliquity of the view angle, so our emphasis is on coregistering to the nadir view. This paper also provides proxy validation of the stereo-matching algorithms for clear-sky land scenes.     

Mapping visual field with positron emission tomography bymathematical modeling of the retinotopic organization in the calcarinecortex

We developed an objective and quantitative method of mapping the human visual field with positron emission tomography (PET) and magnetic resonance imaging (MRI). The regional cerebral blood flow (rCBF) images were acquired with H₂¹⁵O-PET under visual fixation as well as under visual stimulation with flickering diodes arranged along the ring at 0°, 3°, 7°, 14°, 21°, or 29° from the fixation point. After coregistration of PET and MR images, we extracted the surface of the calcarine cortex from the MR images and unfolded it to a two-dimensional (2-D) elliptic plane, on which the activated PET images were superimposed. Then we transformed the unfolded calcarine cortex into the visual field coordinates using the complex logarithmic function proposed by Schwartz. A large individual variation was observed in the retinotopical organization as well as in the morphology of the calcarine cortex. The formula was valid only within 15° from the center of the visual field. The constant parameter in the formula was estimated to be 1.5. The cortical linear magnification factor was 12.1, 2.8, and 1.6 at 0, 5, and 10°, respectively. The areas of the central 10° and 40° in the visual field correspond to 50% and 81% of the calcarine surface, respectively     

Vicarious calibration experiment in support of the Multi-angle Imaging SpectroRadiometer

On June 11, 2000, the first vicarious calibration experiment in support of the Multi-angle Imaging SpectroRadiometer (MISR) was conducted. The purpose of this experiment was to acquire in situ measurements of surface and atmospheric conditions over a bright, uniform area. These data were then used to compute top-of-atmosphere (TOA) radiances, which were correlated with the camera digital number output, to determine the in-flight radiometric response of the on-orbit sensor. The Lunar Lake Playa, Nevada, was the primary target instrumented by the Jet Propulsion Laboratory for this experiment. The airborne MISR simulator (AirMISR) on board a NASA ER-2 acquired simultaneous observations over Lunar Lake. The in situ estimations of top-of-atmosphere radiances and AirMISR measurements at a 20-km altitude were in good agreement with each other and differed by 9% from MISR measurements. The difference has been corrected by adjusting the gain coefficients used in MISR standard product generation. Data acquired simultaneously by other sensors, such as Landsat, the Terra Moderate-Resolution Imaging SpectroRadiometer (MODIS), and the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS), were used to validate this correction. Because of this experiment, MISR radiances are 9% higher than the values based on the on-board calibration. Semiannual field campaigns are planned for the future in order to detect any systematic trends in sensor calibration.     

New methods to infer snow albedo from the MISR instrument with applications to the Greenland ice sheet

Snow-covered surfaces have a very high surface albedo, thereby allowing little energy to be absorbed by the snowpack. As the snowpack ages and/or begins to melt, the snow albedo decreases and more solar energy is absorbed by the snowpack. Therefore, accurate estimation of snow albedo is essential for monitoring the state of the cryosphere. This paper examines the retrieval of snow albedo using data from the Multi-angle Imaging SpectroRadiometer (MISR) instrument over the Greenland ice sheet. Two different methods are developed and examined to derive the snow albedo: one based on the spectral information from MISR and one utilizing the angular information from the MISR instrument. The latter method is based on a statistical relationship between in situ albedo measurements and the MISR red channel reflectance at all MISR viewing angles and is found to give good agreement with the ground-based measurements. Good agreement is also found using the spectral information, although the method is more sensitive to instrument calibration, snow bidirectional reflectance distribution function models, and narrowband-to-broadband relationships. In general, using either method retrieves snow surface albedo values that are within about 6% of that measured at the stations in Greenland.     

Wind direction over the ocean determined by an airborne, imaging,polarimetric radiometer system

The speed and direction of winds over the ocean can be determined by polarimetric radiometers. This has been established by theoretical work and demonstrated experimentally using airborne radiometers carrying out circle flights and thus measuring the full 360° azimuthal response from the sea surface. An airborne experiment, with the aim of measuring wind direction over the ocean using an imaging polarimetric radiometer, is described. A polarimetric radiometer system of the correlation type, measuring all four Stokes brightness parameters, is used. Imaging is achieved using a 1-m aperture conically scanning antenna. The polarimetric azimuthal signature of the ocean is known from modeling and circle flight experiments. Combining the signature with the measured brightness data from just a single flight track enables the wind direction to be determined on a pixel-by-pixel basis in the radiometer imagery