Early validation of the Multi-angle Imaging SpectroRadiometer (MISR) radiometric scale

The Multi-angle Imaging SpectroRadiometer (MISR) instrument consists of nine cameras, four spectral bands each, and an on-board calibrator (OBC). Experiments using the latter allow camera radiometric coefficients to be updated bimonthly. Data products are thus calibrated to a stable radiometric scale, even in the presence of instrument response changes. The camera, band, and pixel-relative calibrations are accurately determined using the OBC. Conversely, as the OBC itself is subject to response degradation, MISR also conducts annual field vicarious calibration campaigns. The first of these, conducted in June 2000 at a desert site in Nevada, has been used to establish the present absolute radiometric scale. Validation of this radiometric scale, using AirMISR, shows consistency to within 4%. Following these studies, however, it was determined that MISR radiometry is subject to scene-dependent effects due to ghosting that, for the Nevada test sites, reduces the apparent radiance by 3%. Correction for this effect is required in order to avoid radiometric errors over sites that do not exhibit the same background contrast. Additional studies are in progress, with plans to correct for scene-contrast effects in future Level 1B1 processing.     

MISR prelaunch instrument calibration and characterization results

Each of the nine cameras that compose the Multi-angle Imaging SpectroRadiometer (MISR) has been rigorously tested, characterized, and calibrated. Requirements on these tests include a 3% (1σ) radiometric calibration requirement, spectral response function determination of both the in- and out-of-band regions, and distortion mapping. The latter test determines the relative look-angle to the ground corresponding to each focal plane detector element. This is established to within one-tenth of the instantaneous field-of-view. Most of the performance testing was done on the cameras as they completed assembly. This was done to take advantage of the serial delivery of the hardware, minimize the required size of the thermal-vacuum facilities, and allow testing to occur early in the schedule allocated for the hardware build. This proved to be an effective strategy, as each of the test objectives was met. Additional testing as an integrated instrument included verification of the data packetization, camera pointing, and clearances of the fields-of-view. Results of these studies have shown that the MISR cameras are of high quality and will meet the needs of the MISR science community. Highly accurate calibration data are on-hand and available for conversion of camera output to radiances     

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 stereoscopic image matchers: techniques and results

The Multi-angle Imaging SpectroRadiometer (MISR) instrument, launched in December 1999 on the NASA EOS Terra satellite, produces images in the red band at 275-m resolution, over a swath width of 360 km, for the nine camera angles 70.5/spl deg/, 60/spl deg/, 45.6/spl deg/, and 26.1/spl deg/ forward, nadir, and 26.1/spl deg/, 45.6/spl deg/, 60/spl deg/, and 70.5/spl deg/ aft. A set of accurate and fast algorithms was developed for automated stereo matching of cloud features to obtain cloud-top height and motion over the nominal six-year lifetime of the mission. Accuracy and speed requirements necessitated the use of a combination of area-based and feature-based stereo-matchers with only pixel-level acuity. Feature-based techniques are used for cloud motion retrieval with the off-nadir MISR camera views, and the motion is then used to provide a correction to the disparities used to measure cloud-top heights which are derived from the innermost three cameras. Intercomparison with a previously developed "superstereo" matcher shows that the results are very comparable in accuracy with much greater coverage and at ten times the speed. Intercomparison of feature-based and area-based techniques shows that the feature-based techniques are comparable in accuracy at a factor of eight times the speed. An assessment of the accuracy of the area-based matcher for cloud-free scenes demonstrates the accuracy and completeness of the stereo-matcher. This trade-off has resulted in the loss of a reliable quality metric to predict accuracy and a slightly high blunder rate. Examples are shown of the application of the MISR stereo-matchers on several difficult scenes which demonstrate the efficacy of the matching approach.     

MISR in-flight camera geometric model calibration and georectification performance

In order to facilitate a unique georectification approach implemented for Multi-angle Imaging SpectroRadiometer (MISR) data, specific calibration datasets need to be derived during flight. In the case of the spaceborne MISR instrument, with its unique configuration of nine fixed pushbroom cameras, continuous and autonomous coregistration and geolocation of image data are required prior to the application of scientific retrieval algorithms. In-flight-generated calibration datasets are required to (a) assure accuracy, (b) reduce processing load, and (c) support autonomous aspects of the processing algorithm. This paper describes the in-flight geometric calibration approach with the focus on the first year of activities and the georectification performance achieved.     

MISR: A multiangle imaging spectroradiometer for geophysical andclimatological research from Eos

The scientific objectives, instrument concept, and data plan for the multiangle imaging spectroradiometer (MISR), an experiment proposed for the Eos (Earth Observing System) mission, are described. MISR is a pushbroom imaging system designed to obtain continuous imagery of the sunlit Earth at four different view angles (25.8°, 45.6°, 60.0°, and 72.5° relative to the vertical at the Earth's surface), in both the forward and aftward directions relative to nadir, using eight separate cameras. Observations will be acquired in four spectral bands, centered at 440, 550, 670, and 860 nm. Data analysis algorithms will be applied to MISR imagery to retrieve the optical, geometric, and radiative properties of complex, three-dimensional scenes, such as aerosol-laden atmospheres above a heterogeneously reflecting surface, nonstratified cloud systems, and vegetation canopies. The MISR investigation will address a number of scientific questions concerning the climatic and ecological consequences of many natural and anthropogenic processes, and will furnish the aerosol information necessary     

The Frequent Image Frames Enhanced Digital Orthorectified Mapping (FIFEDOM) Camera for Acquiring Multiangular Reflectance From the Land Surface

The Frequent Image Frames Enhanced Digital Orthorectified Mapping (FIFEDOM) camera was designed to provide a cost-effective remote-sensing method for accurate acquisition of forest information, such as spatial distributions of individual tree species and tree structures for forest monitoring and management. Compared with existing regular digital cameras, the FIFEDOM camera has several unique features as follows: (1) it can collect data not only in the visible bands (550 and 670 nm) but also in the near-infrared band (800 nm); (2) it has a frame rate of up to 3 frames/s with a frame size of 3500 times 2300; and (3) it has a wide angular field view with 150deg along track and 78.8deg across track. Its high frame rate and wide angular field view allow it to obtain a sequence of images that oversample ground target areas. The multiangle database and bidirectional reflectance signatures of forest canopies can be generated from the oversampled image data, which can be used to identify forest species and estimate tree structures. In addition, the multiframe highly overlapped FIFEDOM data can also be used to generate a very dense, high-quality, and reliable digital surface model. Effective methods for radiometric and geometric calibration of the FIFEDOM camera were developed in this paper. A data-acquisition campaign was carried out in 2004 over the Algoma boreal forest, Ontario, Canada. The FIFEDOM data were validated using the data acquired by the Compact Airborne Spectrographic Imager instrument, which was flown together with the FIFEDOM camera.     

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.     

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.     

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.     

Aerial video surveillance and exploitation

There is growing interest in performing aerial surveillance using video cameras. Compared to traditional framing cameras, video cameras provide the capability to observe ongoing activity within a scene and to automatically control the camera to track the activity. However, the high data rates and relatively small field of view of video cameras present new technical challenges that must be overcome before such cameras can be widely used. In this paper, we present a framework and details of the key components for real-time, automatic exploitation of aerial video for surveillance applications. The framework involves separating an aerial video into the natural components corresponding to the scene. Three major components of the scene are the static background geometry, moving objects, and appearance of the static and dynamic components of the scene. In order to delineate videos into these scene components, we have developed real time, image-processing techniques for 2-D/3-D frame-to-frame alignment, change detection, camera control, and tracking of independently moving objects in cluttered scenes. The geo-location of video and tracked objects is estimated by registration of the video to controlled reference imagery, elevation maps, and site models. Finally static, dynamic and reprojected mosaics may be constructed for compression, enhanced visualization, and mapping applications     

空间碎片多光谱探测相机光学系统设计

为了实现对空间碎片探测,提出了一种空间碎片多光谱探测相机光学系统,由可见光相机、长波红外相机、中波红外相机光学系统组成,三个相机共用主、次镜,在三路相机光学系统中同时加入校正组件平衡校正像差,可见光相机焦距为1000mm,视场为1.2,长波红外相机焦距为-250mm,视场为2.75,中波红外相机焦距为-500mm,视场为1.38,考虑了温度对相机像质的影响,采用热膨胀性系数小的材料作为反射镜基底,分析了三个相机光学系统在空间环境下（205℃）温度环境下的像质变化,设计结果能满足使用要求。     

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.     

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     

High dynamic range video reconstruction from a stereo camera setup

To overcome the dynamic range limitations in images taken with regular consumer cameras, several methods exist for creating high dynamic range (HDR) content. Current low-budget solutions apply a temporal exposure bracketing which is not applicable for dynamic scenes or HDR video. In this article, a framework is presented that utilizes two cameras to realize a spatial exposure bracketing, for which the different exposures are distributed among the cameras. Such a setup allows for HDR images of dynamic scenes and HDR video due to its frame by frame operating principle, but faces challenges in the stereo matching and HDR generation steps. Therefore, the modules in this framework are selected to alleviate these challenges and to properly handle under- and oversaturated regions. In comparison to existing work, the camera response calculation is shifted to an offline process and a masking with a saturation map before the actual HDR generation is proposed. The first aspect enables the use of more complex camera setups with different sensors and provides robust camera responses. The second one makes sure that only necessary pixel values are used from the additional camera view, and thus, reduces errors in the final HDR image. The resulting HDR images are compared with the quality metric HDR-VDP-2 and numerical results are given for the first time. For the Middlebury test images, an average gain of 52 points on a 0-100 mean opinion score is achieved in comparison to temporal exposure bracketing with camera motion. Finally, HDR video results are provided.     

Collaborative sensing in a distributed PTZ camera network

The performance of dynamic scene algorithms often suffers because of the inability to effectively acquire features on the targets, particularly when they are distributed over a wide field of view. In this paper, we propose an integrated analysis and control framework for a pan, tilt, zoom (PTZ) camera network in order to maximize various scene understanding performance criteria (e.g., tracking accuracy, best shot, and image resolution) through dynamic camera-to-target assignment and efficient feature acquisition. Moreover, we consider the situation where processing is distributed across the network since it is often unrealistic to have all the image data at a central location. In such situations, the cameras, although autonomous, must collaborate among themselves because each camera's PTZ parameter entails constraints on the others. Motivated by recent work in cooperative control of sensor networks, we propose a distributed optimization strategy, which can be modeled as a game involving the cameras and targets. The cameras gain by reducing the error covariance of the tracked targets or through higher resolution feature acquisition, which, however, comes at the risk of losing the dynamic target. Through the optimization of this reward-versus-risk tradeoff, we are able to control the PTZ parameters of the cameras and assign them to targets dynamically. The tracks, upon which the control algorithm is dependent, are obtained through a consensus estimation algorithm whereby cameras can arrive at a consensus on the state of each target through a negotiation strategy. We analyze the performance of this collaborative sensing strategy in active camera networks in a simulation environment, as well as a real-life camera network.     

一种适用于分布式摄像机网络的SCIWCF算法

本文使用容积卡尔曼滤波器来处理分布式摄像机网络中的目标跟踪问题.平方根容积信息滤波（Square-Root Cubature Information Filter,SCIF）是容积卡尔曼滤波的一种扩展,其具有有效性和可靠性等方面优势,有利于对多源信息进行信息融合.然而当该算法应用于像摄像机网络这种大规模网络时,如果采用一般的集中式处理,中心节点可能会承受较大的计算压力.针对这个问题,本文首先将平方根容积信息滤波器进行了扩展,提出分布式平方根容积信息滤波器,使其能适应大规模网络.另外在摄像机网络中,由于摄像机装置在一个较大的区域内,由于摄像机观测区域有限,目标可能会出现在观察的盲区,这样就会存在某些摄像机的测量数据无效.针对这个问题,本文提出了平方根容积信息加权一致性滤波器（Square-Root Cubature Information Weighted Consensus Filter,SCIWCF）对状态信息和信息矩阵加权,减小这些无效信息在一致性算法的作用,从而提高整体的滤波性能.仿真实验结果表明,本文提出的算法能够在摄像机网络中对目标进行有效跟踪,在估计精度和滤波器稳定性等方面要优于传统的信息滤波.     

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     

国外传输型航空相机的发展现状与展望

航空相机是获取地面信息的重要技术手段之一,传输型航空相机是目前国外航空相机发展的主流。本文从传输型航空相机实际应用的角度出发,分析了目前国外的线阵、面阵、红外与双波段航空相机的发展现状与技术特点,并对国外航空相机的发展趋势进行了总结与展望。