ASTER instrument on Terra spacecraft is operating over 4 years since early 2000. The total number of acquired data exceeds 800 thousand scenes. The radiometric coefficients are frequently updated to compensate the degradation. The geometric performance is kept in good accuracy since the initial normal operation stage. The performance for radiometric, geometric and stereo capabilities will be comprehensively presented.
The advanced spaceborne thermal emission and reflection radiometer (ASTER) was developed by the MInistry of Economy, Trade and Industry (METI) for installation in the EOS-AM1 spacecraft. The ASTER consists of a visible and near-infrared radiometer (VNIR), a short-wave infrared radiometer (SWIR) and a thermal infrared radiometer (TIR). Two cryocoolers are required to cool the infrared detectors for the SWIR and TIR subsystems. Two cryocoolers have been operating in orbit for over 22000 hours. The temperature of each detector was stabilized in the allowable temperature range. Long-term data have been acquired on the cooling performance and power consumption under normal operation for each cryocooler, the following are described; outline of ground test results and performance of the ASTER cryocooler in orbit for over 22000 hours.
An image correlation tool, which can calculate co-variance of sub-images with an arbitrary window size, was developed. The tool has been applied to the evaluation of image quality of ASTER data products. Other application to the DEM creation is presented. The tool is also promising for the image navigation method to detect the attitude fluctuation of the satellite.
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) launched on NASA's Terra satellite in December 1999 provides anew tool for Earth observations. ASTER provides high-resolution, 15m(VNIR), 30m (SWIR) and 90m (TIR) coverage for limited areas with unique multispectal SWIR and TIR coverage and 15 m stereo coverage for DEM generation. These data have been used extensively for volcano and glacier monitoring. ASTER observations of over 1000 volcanoes around the world represent a significant increase in our ability to monitor volcanic activity and to map the products of eruptions. The SWIR channels have been used for mapping hot areas with temperatures up to 350 C and the multispectral TIR data have been used to map ash and SO<sub>2</sub> plumes. ASTER data are being used in the Global Land Ice Measurements from Space (GLIMS) project to map and catalog the approximately 80,000 glaciers. The objective is to acquire multiple observations to detect changes in ice margins and surface feature velocities. ASTER data acquired over the Jornada Experimental range in New Mexico have been used to extract spectral emissivities in the 8 to 12 micrometer range. These TIR data were also used in models to estimate the surface energy fluxes. Similar analysis of data acquired over the El Reno Oklahoma test site has shown that our satellite estimates of the surface fluxes agree reasonably well with ground measurements.
The mechanism of the crosstalk phenomena in the ASTER/SWIR subsystem, which has six bands in the wavelength of 1.6 - 2.43 micrometers region, is investigated. It is found that the incident light to a detector array of the band 4 of the SWIR subsystem is reflected at an electrical wiring at the focal plane. It is transported to detectors of other bands by multiple reflections through the bandpass filter in front of detectors. By analyzing SWIR images around islands and peninsulas, crosstalk components in images are estimated. For this purpose, the crosstalk correction software is developed. Parameters of the crosstalk phenomena, i.e., the amount of stray light and the influential area of stray light, are determined by image analysis. It is found that the spectral separation performance of the SWIR subsystem is enhanced using the correction software in this study, which leads to more accurate spectral studies of SWIR images and is promising in exploiting natural resources.
Japanese remote sensor ASTER was successfully launched on the NASA's Satellite Terra on December 18, 1999 by the cooperation between METI and NASA HQ, and ASTER is working without any major problems and continues to provide ASTER data. This is a result of the cooperation between US and Japan, especially ASTER Science Team, NASA GSFC, JPL, JAROS and ERSDAC. After the period of the Initial Checkout, ASTER GDS started ASTER data distribution to the public, and ASTER data is currently available without any restriction. In this paper, activities of ASTER operation and some scientific results are provided.
ASTER instrument on NASA Terra spacecraft has an along-track stereoscopic capability using one of the near infrared spectral bands. To acquire the stereo data, ASTER has two telescopes, one for nadir and another for backward viewing, with a base-to-height ratio of 0.6. The spatial resolution is 15 m in horizontal plane. Parameters such as the line-of- sight vectors and the pointing axis were adjusted during initial operation period to generate the Level-1 data products with the high quality stereo system performance. The accuracy of the stereo data generated from the Level-1A data is better than 10 m without GCP correction for individual scenes. Geolocation accuracy that is important for the DEM data sets is better than 50 m. This seems to be limited by the spacecraft position accuracy. The stereo system configuration, the method of parameter adjustment, DEM generation algorithm, and the final performance are described.
The ASTER system is flying on the Terra spacecraft since December 18, 1999. After the instrument check, multispectral images ranging from visible to thermal infrared have been provided using three subsystems, i.e., VNIR, SWIR and TIR. To deliver data products with high quality from the viewpoint of the geolocation and band-to-band registration performance, the fundamental program called the Level-1 processing has been developed. On December 1, 2000, the official data products (Version 1.0) were released, where the band-to-band registration accuracy in the subsystem was better than 0.3 pixels and that between subsystems was better than 0.5 pixels. On May 1, 2001, the validated data products have been released by improving the geometric performance, where the band-to-band registration in the subsystem is better than 0.1 pixels and that between subsystems is better than 0.2 pixels. In this paper, the characteristics of the images and the effect of geometric parameters on the image quality of the ASTER system, which consists of four telescopes and a cross-track pointing function, are analyzed by image matching method based on a cross-correlation function.
12 The Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) was one of the mission instruments selected by NASA to fly on the EOS-AM1 spacecraft. The EOS- AM1 (Terra) spacecraft was launched from Vandenberg Air Force Base, December 18, 1999. The ASTER consists of a visible and near-infrared radiometer (VNIR), a short-wave infrared radiometer (SWIR) and a thermal infrared radiometer (TIR). Two cryocoolers are required to cool down the infrared detectors for the SWIR and the TIR. Two cold plates act as a heatsink for each compressor unit and maintain in temperature in the range between 20 degree(s)C and 25 degree(s)C by a capillary-pump heat-transfer system (CPHTS). Therefore, environmental temperature conditions are the same for the two compressor units. While the TIR expander unit is thermal controlled by a local radiator with a heat pipe, the SWIR expander unit employs radiative cooling for thermal control. The performance of ASTER cryocooler was evaluation to operate normally, based on the data obtained in the functional checkout in orbit. The SWIR cryocooler cools the detector to the operating temperature of 77 K in the cooldown time of 22 minutes. The TIR cryocooler cools the detector to the operating temperature of 80 K in the cooldown time of 23 minutes. The temperature of each detector was stabilized in the allowable temperature range. A clear image was obtained in the initial checkout of each radiometer in their observation mode.
12 The ASTER system was launched successfully on board the Terra spacecraft on December 18, 1999. The system obtains multispectral images ranging from visible to thermal infrared region by combining three subsystems composed of four telescopes. To deliver data products with high quality from the viewpoint of the geolocation and band-to-band registration performance, the fundamental program called the Level-1 processing has been developed. The geometric validation procedure of ASTER, which consists of four telescopes and a cross-track pointing function, is carried out during the initial checkout period. Image matching method based on a cross-correlation function was used to register images of each band.
Proc. SPIE. 4169, Sensors, Systems, and Next-Generation Satellites IV
KEYWORDS: Thermography, Signal to noise ratio, Short wave infrared radiation, Telescopes, Multispectral imaging, Data acquisition, Infrared radiation, Radiometry, Modulation transfer functions, Spatial resolution
12 The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a high spatial resolution multispectral imaging radiometer, and is onboard the NASA's Terra spacecraft launched on December 18, 1999. It spectrally covers the visible and near-infrared, short-wave- infrared, and thermal infrared regions with 14 spectral bands, and creates high-spatial-resolution (15-90 m) multispectral images of the Earth's surface. The observation performances of the ASTER instrument were evaluated by the early images, e.g. spatial resolution, modulation transfer functions (MTF), signal-to-noise-ratios (SNRs), band-to-band registrations, and so on. It was confirmed that the ASTER instrument generally exceeds the specified observation performance, and the early images exhibit excellent quality even in the preliminary processing level. In the initial check-out phase, ASTER was operationally used for intensive monitoring of volcanic eruptions in Japan, and successfully provided useful information to volcanologists.
ASTER is a multispectral imager which covers wide spectral region from visible to thermal infrared with 14 spectral bands, and will fly on EOS-AM1 in 1999. To meet this wide spectral coverage, ASTER has three optical sensing subsystems (multi-telescope system), VNIR, SWIR and TIR. This multi- telescope configuration requires highly refined ground processing for the generation of Level-1 data products that are radiometrically calibrated and geometrically corrected. A prototype Level-1 processing software system is developed to satisfy these requirements. System design concept adopted includes; (1) 'Automatic Processing,' (2)'ALL-IN-ONE-CONCEPT' in which the processing is carried out using information included in Level-0 data product only, (3) 'MODULE INDEPENDENCE' in which only process control module independently control other modules to change any operational conditions. (4) 'FLEXIBILITY' in which important operation parameters are set from an external component to make the processing condition change easier. The adaptability and the performance of the developed software system are evaluated using simulation data.
The ASTER system is a multispectral imager which covers a spectral range from visible to thermal infrared light by combining three subsystems composed of four telescopes. To ensure the high-quality data products concerning to the geolocation and band-to-band matching performance, the geometric registration is needed. This paper describes the geometric validation procedure for a multi-telescope imager with a cross-track pointing function. The strategy for the maintenance of database files and the preparation a GCP library is also shown.
The advanced spaceborne thermal emission and reflection radiometer (ASTER) is a facility instrument which has been selected by NASA to fly on the EOS-AM1 platform in 1998. Two independent cryocoolers are needed to cool down infrared detectors for the short-wave infrared radiometer (SWIR; 1.6 - 2.4 micrometer) and the thermal infrared radiometer (TIR; 8.3 - 11.3 micrometer). The goal in the development of the ASTER cryocooler is a durability of over 50,000 hours and mechanical vibration forces below 0.1 N in the frequency range from 40 Hz to 135 Hz in the directions of all three axes. A split- Stirling cycle cryocooler with clearance seals and linear electric motors is employed for this purpose. The compressor design for this adopts a piston driving mechanism which has a twin-opposed piston configuration, into one compression space. The mechanical vibration caused by an expander displacer is reduced by an active balancer. The cryocoolers for SWIR and TIR have a cooling capacity of 1.2 W at 70 K with power consumption lower than 55 W without control electronics. Two cryocoolers were evaluated from the viewpoint of cooling performance and mechanical vibration forces, and are presently undergoing life tests. The design concept and cryocooler performance test results which are indispensable for enduring a long life in space are described.
The ASTER (advanced spaceborne thermal emission radiometer) includes three telescopes sensitive to different wavelengths. As the telescopes are capable of changing sight directions, some band to band registration technique among images with different spectrum characteristics will be necessary. In this study, we propose a new registration method using image matching to deal with these problems and experimental results for airborne images are shown. This method is based on chip matching technique and consists of three processes. The experimental results were better than the results of the conventional method. The algorithm will be included to the ASTER level 1 data processing and the requirement that the band-to-band registration error should be less than 0.3 pixel will be achieved.
Advanced spaceborne thermal emission and reflection radiometer (ASTER) short wave infrared radiometer (SWIR) is planned to be launched with EOS-AM1 in 1998. SWIR has six bands and the linear detector arrays of all the bands are located on the same focal plane in parallel each other. Therefore parallax occurs between the six bands data. Large parallax causes errors in multiband data processing and so it is necessary to eliminate influential parallax from observation image. For the purpose of correcting parallax, we have developed a parallax estimation method for ASTER SWIR bands. To estimate parallax, image matching method is employed. But image matching method is not always effective. Cloud or featureless area in the image misleads the image matching process into a wrong result. So to prevent such misleading and to judge the validity of the result of the image matching method, coarse digital elevation model (DEM) data of which the cell size is about 1 km is introduced.
Orthoimage products are planned to be produced at ASTER ground data system (GDS), this will be useful for general applications users. The major problem in orthoimage generation is a big computation load for terrain correction. In this paper, a high speed orthoimage generation method is proposed. The proposed method is based on the next four basic ideas: (1) The DEM products produced at ASTER GDS are used as fundamental information for terrain correction. ASTER DEM is generated by stereo matching on the basis of area correlation algorithm. Therefore the terrain correction for every pixel is ineffective. (2) As ASTER DEM products have ground coordinates corresponding to every other pixel on observation images, it is easy to transform observation image coordinates into orthoimage coordinates by using the ECR coordination. (3) In order to eliminate iterative calculations for determination of relations from orthoimage coordinate to observation coordinate, inverse transformations are directly obtained from relationship between a block on the observation image and its projection onto the orthoimage coordinate system. (4) Pixels in the block projected on orthoimage are transformed into the observation image coordinate. Then, image values are interpolated at the image observation coordinate. As a result, the proposed method can be executed with similar computation load to geometric transformation without terrain correction.
ASTER instrument is a high performance spatial imager on board the EOS-AM1 spacecraft, which will be launched in June 1998. The ASTER raw data will be captured by U.S. ground system via TDRSS, processed to level-0 data, and then transferred to the ASTER Ground Data System in Japan for level-1 data products generation. The ASTER Ground Data System consists of the Communication and System Management System (CSMS), ASTER Operation Segment (AOS), Science Data Processing Segment (SDPS), and Direct Receiving Station (DRS). The ASTER Ground Data System adopts a challenging design concept to handle approximately 780 sets of scenes of 14 spectral bands one stereo band (about 80 Gbytes) per day.
ASTER is an advanced multispectral imager with high spatial, spectral, and radiometric resolutions for EOS-AM1 spacecraft which will be launched with four other instruments in June 1998. The ASTER instrument covers a wide spectral region from visible to thermal infrared by 14 spectral bands. To meet a wide spectral coverage, optical sensing units of ASTER are separated into three subsystems, that is the visible and near infrared subsystem, the short wave infrared subsystem and the thermal infrared subsystem, depending on spectral region. Moreover, ASTER has an in-track stereoscopic viewing capability by a near infrared band. To acquire the stereo data the VNIR subsystem has two telescopes for the nadir and backward viewings. Several new technologies are adopted as design challenges to realize the high performance. The validity of these new technologies is verified through the evaluation of the engineering model.
The advanced spaceborne thermal emission and reflection radiometer (ASTER) is an instrument which was selected by NASA to fly on the EOS-AM1 platform in 1998. Two cryocoolers are required to cool infrared detectors for the short-wave infrared radiometer (SWIR) and thermal infrared radiometer (TIR). The mission lifetime of the EOS-AM1 platform is expected to be 5 years, and accordingly, an operation lifetime more than 5 years is required for ASTER cryocoolers. The goals in the development of the ASTER cryocoolers are realization of a operation lifetime of over 50,000 hours and mechanical vibration forces below 0.1 N in the frequency range from 40 Hz to 135 Hz in the driection of all three axes. A split- Stirling cycle cryocoolers with clearance seals and linear motors is employed for this purpose. The compressor design adopts a piston driving mechanism which has a twin-opposed piston configuration in one compression space. The mechanical vibration caused by a displacer in the expander unit is reduced by an active balancer. Cryocoolers for SWIR and TIR have cooling capacity of 1.2 W at 70 K with power consumption lower than 55 W without control electronics. Several engineering models (EM) have been fabricated and are presently undergoing performance and life tests. Results of cryocooler verification tests and effects of jitter of mechanical vibration on the ASTER instrument are described.
ASTER is an advanced multispectral imager with high spatial, spectral, and radiometric performances for an EOS-AM1 polar orbiting platform which will be launched with four other instruments in June 1998 and covers a wide spectral region from visible to thermal infrared by 14 spectral bands. To meet a wide spectral coverage, optical sensing units of ASTER are separated into three subsystems, that is, visible and near infrared subsystem, a short wave infrared subsystem, and a thermal infrared subsystem, depending on the spectral region from a technical point of view. This ASTER instrument configuration with multi-telescopes leads to necessity of the ground processing on the generation of level-1 data products which are radiometrically calibrated and geometrically registered. The concept of level-1 processing algorithm on the ASTER Ground Data System is described.
ASTER is an advanced multispectral imager with a high spatial, spectral and radiometric resolutions for EOS-AM1 platform which will be launched in June 1998. ASTER covers a wide spectral region from visible to thermal infrared by 14 spectral bands. Moreover, ASTER has a stereoscopic viewing capability by a near infrared band. Excellent observational performance can be expected by a pushbroom type visible and near infrared radiometer (VNIR subsystem) with a high spatial resolution of 15 m, a pushbroom type short wave infrared radiometer (SWIR subsystem) with a high spectral resolution and a whiskbroom type thermal infrared radiometer (TIR subsystem) with high spatial, spectral and radiometric resolutions. Long life mechanical cryocoolers are developed to enhance the performances of the SWIR and the TIR subsystems.
The advanced spaceborne thermal emission and reflection radiometer (ASTER), a multi- spectral imaging radiometer with 14 spectral bands, is a research facility instrument that will be launched in 1998 on NASA's EOS-AM1 platform. Characteristics of the ASTER data can be summarized as (1) wide spectral coverage from the visible to thermal infrared regions, (2) multispectral thermal infrared data with high spectral and spatial resolution and (3) stereoscopic capability in the along track direction. ASTER is currently being designed to meet the requirements given by the ASTER science team.
Proc. SPIE. 1939, Sensor Systems for the Early Earth Observing System Platforms
KEYWORDS: Thermography, Infrared imaging, Short wave infrared radiation, Radio optics, Sensors, Data acquisition, Infrared radiation, Modulation transfer functions, Spatial resolution, Space operations
ASTER is an advanced multispectral optical imager with a high spatial resolution, and covers a wide spectral region from visible to thermal infrared. In addition, ASTER has a stereoscopic viewing capability in the along-track direction. Excellent observational performances are expected by trying several technical challenges. High radiometric resolutions will be achieved by employing pushbroom scanning in visible, near infrared, and short wave infrared bands without sacrificing spatial resolutions. An adoption of active coolers will enhance the performance of short wave and thermal infrared bands. Major predicted observational performances of ASTER in the EM design phase are described.
A compact thermal video camera with very high sensitivity has been developed by using a self-scanned 128 InSb linear array photodiode. Two-dimensional images are formed by a self- scanning function of the linear array focal plane assembly in the horizontal direction and by a vibration mirror in the vertical direction. Images with 128 X 128 pixel number are obtained every 1/30 seconds. A small size InSb detector array with a total length of 7.68 mm is utilized in order to build the compact system. In addition, special consideration is given to a configuration of optics, vibration mirror, and focal plane assembly. Real-time signal processing by a microprocessor is carried out to compensate inhomogeneous sensitivities and irradiances for each detector. The standard NTSC TV format is employed for output video signals. The thermal video camera developed had a very high radiometric sensitivity. Minimum resolvable temperature difference (MRTD) is estimated at about 0.02 K for 300 K target. The stable operation is possible without blackbody reference, because of very small stray radiation.
Two long life mechanical cryocoolers for the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument of the EOS-A platform are intended to cool down infrared detectors for short-wave infrared and thermal infrared bands. The ASTER cryocoolers based on a split-Stirling cycle have to meet the requirements of a long operation life of 50,000 h and low mechanical vibration.
ASTER is an advanced multispectral imager with a high spatial, spectral and radiometric resolutions for EOS-A platform. ASTER covers a wide spectral region from visible to thermal infrared by 14 spectral bands. Moreover, ASTER has a stereoscopic viewing capability by a near infrared band. Significant design challenges are realization of a pushbroom type visible and near infrared radiometer (VNIR subsystem) with a high spatial resolution of 15 m, a pushbroom type short wave infrared radiometer (SWIR subsystem) with high spectral resolution and a whiskbroom type thermal infrared radiometer (TIR subsystem) with a high spatial, spectral and radiometric resolutions. Long life mechanical coolers for the SWIR and the TIR subsystems are also components with a technical risk.
The Ocean Color and Temperature Scanner (OCTS) is a piece of observation equipment that measures ocean color and temperature from a scientific satellite. The OCTS is equipped with two focal plane assemblies: one observes ocean color in the range of visible to near infrared, and the other measures ocean temperature in the infrared region. We report here results of the so-called break boad model of the latter focal plane assembly. This focal plane assembly contains four infrared detectors that are cooled to 100 K by radiational cooling. We have evaluated this cooled focal plane assembly, and have confirmed that it has satisfied such NEP (noise equivalent power) values, registration accuracy and power consumption as are required in view of the OCTS performance characteristics.
A compact focal plane assembly which consists of a linear array of 128 InSb photodiodes and two Si-MOSFET multiplexer IC chips has been developed. The design and fabrication of the photodiode array, the readout circuit on the focal plane, the hybrid packaging, and the operation of the focal plane assembly are described. A small InSb pixel size of 60 microns is used, and the total length of the array is 7.60 mm. A measured radiometric resolution of 0.04 K NE Delta T is obtained for a 300 K target with a simple circuit configuration under the TV-compatible operation.