On-board Calibration Research Articles

A Calibration Method of Three-axis Magnetic Sensor Based on Ellipsoid Fitting

It is very essential for a magnetic sensor to be calibrated before use because of various disturbances. However, Constrained by maneuverability of carriers, sample data distribute in a quite limited area, traditional calibration approach using ordinary least-square ellipsoid fitting algorithm makes large error or even cannot compensate properly. In this paper, a new onboard calibration method based on ellipsoid fitting is presented, without requiring external reference. Sample data are obtained in the restricted area by rotating carrier in three simple traces, ellipsoid coefficient are calculated using constrained least squares algorithm. The proposed method is contrasted with the traditional method via software simulation and experimental test; the results indicate that the new calibration method is stable and reliable, and superior to the traditional approach.

Low Mass Calibration Target for MM-Wave Remote Sensing Instruments

The reliability of millimeter and sub-millimeter wave radiometer measurements is dependent on the accuracy of the loads they employ as calibration targets. In the recent past on-board calibration loads have been developed for a variety of satellite remote sensing instruments. Unfortunately some of these have suffered from calibration inaccuracies which had poor thermal performance of the calibration target as the root cause. Stringent performance parameters of the calibration target such as low reflectivity, high temperature uniformity, low mass and low power consumption combined with low volumetric requirements remain a challenge for the space instrument developer. In this paper we present a novel multi-layer absorber concept for a calibration load which offers an excellent compromise between very good radiometric performance and temperature uniformity and the mass and volumetric constraints required by space-borne calibration targets.

Derive a MODIS-Based Calibration for the AVHRR Reflective Solar Channels of the NOAA KLM Operational Satellites

The Advanced Very High Resolution Radiometer (AVHRR) has been on board the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites (POSs) beginning with the Television Infrared Observation Satellite N launched in October 1978. Since then, a series of AVHRR sensors have collected over 30 years of continuous daily global observations. Recently, the NOAA K, L, and M POSs have provided an improved monitoring of the Earth's environment. The AVHRR instrument carried on NOAA-15 (NOAA-K) was launched in May 1998. It is followed by NOAA-16 to NOAA-18 (NOAA-L, NOAA-M, and NOAA-N), Metop-A, and NOAA-19 (NOAA-N'). All of them have been operating to date. An accurate and consistent calibration for the AVHRR reflective solar channels has been challenging as there is no onboard calibrator and vicarious calibration often needs to accumulate large number of reliable observations to derive any meaningful long-term trends. In this paper, we use the Committee on Earth Observation Satellites-endorsed calibration/validation Libya-4 (28.55 N, 23.39 W) desert site to track the long-term stability of reflective solar channels of the NOAA KLM AVHRR. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Terra and Aqua platforms is used as a reference to recalibrate the NOAA KLM trends. This study is focused on evaluating the calibration accuracy for the visible and near-infrared channels of each AVHRR instrument using MODIS channels 1 (620-670 nm) and 2 (841-876 nm). A site-specific bidirectional reflectance distribution function developed based on observations made by MODIS is used to normalize AVHRR-observed reflectances. Impacts of atmospheric water vapor on AVHRR-to-MODIS reflectance ratios are corrected with measured total water-vapor contents derived using the split-window temperature difference technique. Finally, MODIS-based AVHRR calibration results, which track the AVHRR on-orbit change, are applied on top of the AVHRR prelaunch values and presented in the form of quadratic polynomials as a function of time. All recalibrated AVHRR reflectances are compared with those provided from a Level 1B product. Additional validation is performed using NOAA-17 AVHRR observations acquired over Antarctic Dome Concordia site where the impact due to atmospheric water vapor is believed to be extremely small.

Rayleigh, Deep Convective Clouds, and Cross-Sensor Desert Vicarious Calibration Validation for the PROBA-V Mission

PROBA-V is a remote sensing satellite mission for global monitoring of vegetation. It is designed to offer almost daily coverage of all land masses and to provide data continuity with the VGT2 instrument aboard SPOT-5. Accurate radiometric calibration is key to the success of the mission; therefore, a comprehensive system for in-flight radiometric calibration has been developed. Without no onboard calibration devices, this in-flight calibration will rely fully on vicarious methods. In total nine techniques for vicarious calibration have been implemented and tested in order to meet the radiometric mission requirements. Three key methods that contribute largely to the calibration performance are presented in this paper: Rayleigh, deep convective clouds, and cross-sensor calibration over stable desert sites. As the PROBA-V sensor has still to be launched, calibration algorithm verification is performed using data from the spectrally very similar SPOT-VGT1 and SPOT-VGT2 sensors.

Comparison Among Cross, Onboard and Vicarious Calibrations for Terra/ASTER/VNIR

Comparative study on radiometric calibration methods among onboard, cross and vicarious calibration for visible to near infrared radiometers onboard satellites is conducted. The data sources of the aforementioned three calibration methods are different and independent. Therefore, it may say that the reliable Radiometric Calibration Accuracy: RCC would be the RCC which are resemble each other two of three RCCs. As experimental results, it is found that vicarious and cross calibration are reliable than onboard calibration. Also vicarious calibration based cross calibration method is proposed here. The proposed cross calibration method should be superior to the conventional cross calibration method based on band-to-band data comparison. Through experiments, it is also found that the proposed cross calibration is better than the conventional cross calibration. The radiometric calibration accuracy of the conventional cross calibration method can be evaluated by using the proposed cross calibration method.

Multisite Calibration Tracking for FY-3A MERSI Solar Bands

The MEdium-Resolution Spectral Imager (MERSI), onboard the second-generation Chinese polar-orbit meteorological satellite FY-3A, is a MODIS-like sensor with 19 solar bands and one thermal infrared band. Although there is a visible onboard calibration device, it can only be used for tracking temporal instrument degradation. The vicarious calibration (VC) campaign at the Dunhuang site, conducted once a year, has been the main postlaunch absolute radiometric calibration method for MERSI in the solar bands. To increase the in-flight calibration frequency, a multisite radiometric calibration tracking method is presented. This method relies on simulated radiation over several stable sites, and a daily calibration updating model is built from long-term trending of calibration coefficient series. The MERSI calibration reference is evaluated against the observations of Aqua MODIS, showing mean relative biases within 5% from 0.4 to 2.1 μm . The short-wave channels of MERSI are found to experience large degradation, particularly the 412-nm band with an annual degradation rate of 9.7%, whereas the red and near-infrared bands are relatively stable with annual degradation rates within ±1%. Several approaches have been used to analyze the reliability of MERSI calibration results. A comparison of the calibration slopes shows that the relative biases between the multisite method and the annual Dunhuang VC campaign are below 3.8%. Aqua MODIS is used as a reference to monitor the data quality of the recalibrated MERSI. A double-difference analysis shows that the mean relative biases are almost within 5% over stable deserts, and the synchronous nadir observation analysis also reveals good agreement.

Calibration for the Solar Reflective Bands of Medium Resolution Spectral Imager Onboard FY-3A

The Medium Resolution Spectral Imager (MERSI) is a key instrument onboard Fengyun-3 (FY-3), the second generation of polar-orbiting meteorological satellites in China. This paper summarizes the knowledge of MERSI instrument in terms of sensor design, calibration algorithm, prelaunch and on-orbit characterization, and performance verification. The calibration monitoring of its reflective solar bands (RSBs) is primarily conducted using a visible onboard calibrator and found that it has a significant degradation on the order of 10% in its shorter RSB bands (<; 500 nm), with the largest in band 8 of about 20% during the past two years. However, the performance at longer wavelength bands is relatively stable with a change of less than 5%. It is shown that the postlaunch calibration of the two short-wavelength infrared bands has frequent fluctuations because of random jumps in their electronic gains. These results are consistently verified by two kinds of vicarious calibration (VC) methods: China Radiometric Calibration Sites VC and intercalibration using Terra/Moderate Resolution Imaging Spectroradiometer over Dunhuang desert. The overall uncertainty in the MERSI top-of-atmosphere radiance or reflectance is less than 5%. These results provide the important reference and evaluation for the update of the FY-3A/MERSI calibration coefficients.

OBSERVATIONS OF HIGH-ENERGY COSMIC-RAY ELECTRONS FROM 30 GeV TO 3 TeV WITH EMULSION CHAMBERS

We have performed a series of cosmic-ray electron observations using the balloon-borne emulsion chambers since 1968. While we previously reported the results from subsets of the exposures, the final results of the total exposures up to 2001 are presented here. Our successive experiments have yielded the total exposure of 8.19 m^2 sr day at the altitudes of 4.0 - 9.4 g/cm^2. The performance of the emulsion chambers was examined by accelerator beam tests and Monte-Carlo simulations, and the on-board calibrations were carried out by using the flight data. In this work we present the cosmic-ray electron spectrum in the energy range from 30 GeV to 3 TeV at the top of the atmosphere, which is well represented by a power-law function with an index of -3.28+-0.10. The observed data can be also interpreted in terms of diffusive propagation models. The evidence of cosmic-ray electrons up to 3 TeV suggests the existence of cosmic-ray electron sources at distances within ~1 kpc and times within ~1x10^5 yr ago.

Cross Calibration of Formosat-2 Remote Sensing Instrument (RSI) Using Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)

The present paper describes the cross calibration of the Remote Sensing Instrument (RSI) onboard Formosat-2 using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra as a reference, which has been continuously calibrated by means of the onboard and vicarious calibration methods. The data integration system for multi-satellite sensor databases on the Global Earth Observation Grid (GEO Grid) is used in order to find pairs of images acquired by both satellite optical sensors over the radiometric calibration sites on the same days. Radiative transfer simulations that consider different imaging conditions using the Second Simulation of a Satellite Signal in the Solar Spectrum (6S) code are performed based on the Moderate-resolution Imaging Spectroradiometer (MODIS) atmosphere and land products, and the optimum methodology for this cross calibration is discussed under the assumption of no ground-based measurements. The derived calibration coefficients are normalized by the values of preflight calibration and are compared with the results of in-flight cross calibration by the Centre National d'Etudes Spatiales (CNES) and vicarious calibration described in our previous paper. The average degradations of sensor sensitivity since preflight calibration until 2009 are estimated to be 10% (Band2), 11% (Band3), and 8% (Band4). The derived long-term degradation trends are almost consistent with the results of our vicarious calibration within the precision. The cross-calibration methodology used in the present paper facilitates the in-flight radiometric calibration of satellite optical sensors.

Automatic Calibration of the 3D Vector Magnetometer

Embedded sensors are an emerging trend in mobile consumer devices. In this work a new algorithm is derived for the onboard calibration of three-axis magnetometers. The proposed calibration method is written in the sensor frame, and compensates for the combined effect of all linear time-invariant distortions, namely soft iron, hard iron, three-dimensional sensor non-orthogonally, scale factors, null-shift, arbitrary bias, among others. The new algorithm can be separated into two steps: In the first step, obtain the ellipsoid fitting parameters from comparing the difference between the measured value and the actual vector. In a second step, a calibration algorithm is adopted to compensate for magnetometers distortions. According to the model parameters the measured data is corrected to improve the precision of magnetometer. Simulation and experimental results with sensors data are presented and discussed, supporting the application of the algorithm to commercial and military platforms.

Absolute radiometric calibration of the KOMPSAT-2 multispectral camera using a reflectance-based method and empirical comparison with IKONOS and QuickBird images

This paper presents absolute radiometric calibration coefficients (gains) that explain the relationship between the digital number (DN) and at-sensor radiance for the multispectral camera (MSC) on Korea's first high-resolution satellite (KOMPSAT-2). Absolute radiometric calibration was performed using a reflectance-based method. In addition, the suitability of vicarious results from radiance- and reflectance-based validations was analyzed with reference to IKONOS and QuickBird images. The latter are spectrally similar to KOMPSAT-2 images and have been validated in a large number of studies. For all bands, the R 2 values of fitted lines for the gain ranged from 0.82 to 0.94, representing an improvement compared to previous findings for the KOMPSAT-2 MSC. To analyze the suitability of the vicarious results, same-pixel at-sensor radiances across different spectral bands were compared. In all bands, except the red band of QuickBird, the at-sensor radiances of KOMPSAT-2 MSC were highly correlated with those of IKONOS and QuickBird. In addition, same-pixel comparisons of reflectance across different spectral bands showed that the slopes of the least-squares lines for each band were similar to the results of the radiance comparison. The standard deviation among top of atmosphere (TOA) reflectances was within 0.019 for all bands. To calculate the tasseled cap transformation (TCT) coefficients for the KOMPSAT-2 MSC, an empirical method was applied using radiometric normalization. The results were similar to those obtained using the TCT coefficients for IKONOS and QuickBird in the brightness, greenness, and wetness components. The TCT images showed similar patterns. The absolute radiometric calibration coefficients presented here appear to be a good standard for maintaining the optical quality of the KOMPSAT-2 MSC, for which prelaunch, on-board, and vicarious calibration data are lacking.

An On-Board External Calibration Method for Aperture Synthesis Radiometer by Rotation

The on-board calibration of aperture synthesis radiometers (ASRs) with large arrays by the standard method of noise injection would seriously increase hardware requirements and system complexity. To avoid the use of noise injection, an external phase calibration method with antenna array rotation is proposed in this letter, which uses the observation scene as reference without needing for an external calibrator. The relationship of the visibility samples before and after the rotation is established and used to solve for the instrumental phase errors. The proposed method has been proved to be valid by simulations as well as some preliminary experimental results. It is applicable to geostationary ASRs with rotating array such as the geostationary atmospheric sounder.

Onboard calibration and monitoring for the SWIFT instrument

The SWIFT (Stratospheric Wind Interferometer for Transport studies) instrument is a proposed space-based field-widened Doppler Michelson interferometer designed to measure stratospheric winds and ozone densities using a passive optical technique called Doppler Michelson imaging interferometry. The onboard calibration and monitoring procedures for the SWIFT instrument are described in this paper. Sample results of the simulations of onboard calibration measurements are presented and discussed. This paper also discusses the results of the derivation of the calibrations and monitoring requirements for the SWIFT instrument. SWIFT's measurement technique and viewing geometry are briefly described. The reference phase calibration and filter monitoring for the SWIFT instrument are two of the main critical design issues. In this paper it is shown that in order to meet SWIFT's science requirements, Michelson interferometer optical path difference monitoring corresponding to a phase calibration accuracy of ∼10−3 radians, filter passband monitoring corresponding to phase accuracy of ∼5 × 10−3 radians and a thermal stability of 10−3 K s−1 are required.

The ChemCam Instrument Suite on the Mars Science Laboratory (MSL) Rover: Body Unit and Combined System Tests

The ChemCam instrument suite on the Mars Science Laboratory (MSL) rover Curiosity provides remote compositional information using the first laser-induced breakdown spectrometer (LIBS) on a planetary mission, and provides sample texture and morphology data using a remote micro-imager (RMI). Overall, ChemCam supports MSL with five capabilities: remote classification of rock and soil characteristics; quantitative elemental compositions including light elements like hydrogen and some elements to which LIBS is uniquely sensitive (e.g., Li, Be, Rb, Sr, Ba); remote removal of surface dust and depth profiling through surface coatings; context imaging; and passive spectroscopy over the 240–905 nm range. ChemCam is built in two sections: The mast unit, consisting of a laser, telescope, RMI, and associated electronics, resides on the rover’s mast, and is described in a companion paper. ChemCam’s body unit, which is mounted in the body of the rover, comprises an optical demultiplexer, three spectrometers, detectors, their coolers, and associated electronics and data handling logic. Additional instrument components include a 6 m optical fiber which transfers the LIBS light from the telescope to the body unit, and a set of onboard calibration targets. ChemCam was integrated and tested at Los Alamos National Laboratory where it also underwent LIBS calibration with 69 geological standards prior to integration with the rover. Post-integration testing used coordinated mast and instrument commands, including LIBS line scans on rock targets during system-level thermal-vacuum tests. In this paper we describe the body unit, optical fiber, and calibration targets, and the assembly, testing, and verification of the instrument prior to launch.

Extracting the dynamics of urban expansion in China using DMSP-OLS nighttime light data from 1992 to 2008

Timely and accurate information about the dynamics of urban expansion is vital to reveal the relationships between urban expansion and the ecosystem, to optimize land use patterns, and to promote the effective development of cities in China. Nighttime stable light data from the Defense Meteorological Satellite Program's Operational Line-scan System (DMSP-OLS) Nighttime Lights Time Series dataset provide a new source of information that can quickly reveal the dynamics of urban expansion. However, the DMSP-OLS sensor has no on-board calibration, which makes it difficult to directly compare time series data from multiple satellites. This study developed a new method for systematically correcting multi-year multi-satellite nighttime stable lights data and rapidly extracting the dynamics of urban expansion based on this corrected data for China from 1992 to 2008. The results revealed that the proposed method effectively reduced abnormal discrepancy within the nighttime stable light data and improved continuity and comparability. The dynamics of urban expansion in China from 1992 to 2008 were extracted with an average overall accuracy of 82.74% and an average Kappa of 0.40.

On-Board Calibration Methods for Mechanical Distortions of Satellite Phased Array Antennas

In satellite phased-array antennas, mechanical distortions, which may be due to vibrations caused when launching the satellite into the orbit or thermal variations in the orbit, result in significant degradation of electrical performance. In this paper, two on-board calibration methods are proposed for such mechanical distortions: One compensates for the element phase differences resulting from mechanical distortions, and the other is used to set the best-fit phase distribution obtained from the measured phases. The latter method is effective even at a low signal-to-noise ratio (SNR). The proposed methods have been validated by experiments, through which the theoretically predicted calibration accuracy of the methods has been successfully reproduced.

多角度偏振辐射计星上积分球结构设计及检测

In order to calibrate the six apertures of a multi-angle polarizing radiometer synchronously and to meet the need of full beam path calibration.a six-hole ellipsoid integrating sphere calibration source was designed according to the optical characteristics and structural constraint of the polarizing radiometer.Then the consistency,uniformity and polarization of the integrating sphere output were tested.In the test,the consistency was directly measured by using the scaled spectral radiometer,while the uniformity was detected by using the scanning method combined a lens and apertures in consideration of the small outlet of the integrating sphere.Furthermore,the degree of polarization was detected by a linear polarization detector designed based on the Marius extinction law.Experiments demonstrate that the detection methods and data processing have enhanced the signal-to-noise ratio as well as the accuracy of the system.It is shown that the brightness consistency of paired openings for the integrating sphere is better than 99.5%,the surface uniformity is better than 99%,and the degree of polarization is below 1%,which satisfies the needs of radiometric calibration of the multi-angle polarizing radiometer.

环境一号B 星红外多光谱相机综合辐射定标

The infrared multispectral camera (IRS) of HJ-1B is subject to several influences that cause perfor- mance degradation while in orbit. Absolute radiometric calibration can effectively adjust the measured radiometric accuracy of the sensor, improving the radiometric performance of remote sensing data. Based on the characteris- tics of the IRS on-board calibration system, this paper uses data recorded from a test site in August 2010 to carry out a radiometric calibration of the IRS thermal infrared channel, verify the calibration coefficients and correct their accuracy. The results show that absolute calibration can avoid the limitations of the on-board calibration system and that the calibration coefficients of IRS are accurate and reliable enough to meet the requirements of quantitative applications.

결함안전 기능을 고려한 교정 반사경 구동장치

일반적으로 탑재 교정을 위한 교정 반사경 구동장치는 교정임무 수행 시에는 주광경로 상의 전개위치로 반사경을 구동하며, 교정 후에는 주광경로와 이격된 수납위치로 반사경을 구동한다. 교정 반사경 구동장치의 결함 발생 시에는 반사경이 전개된 상태로 남아 주광경로를 차단하지 않도록 반사경을 강제 수납한다. 본 논문에서 제안한 결함 안전장치를 가지는 교정용 반사경 구동장치는 구동을 위한 스텝모터, 전개 및 수납 상태확인을 위한 마이크로 스위치, 베어링과 스프링의 기능을 동시에 갖는 피봇베어링 등으로 구성된다. 본 논문에서는 상기의 기능을 갖는 교정 반사경 구동장치 구현을 위한 구동장치 구성을 제안하였으며, 구성요소의 최적화 설계치를 도출하고 기능시험을 통해 결함안전 기능을 갖는 교정 반사경 구동장치의 유효성을 검증하였다. Calibration mirror mechanism has been widely used for on-board calibration with black body. The calibration mirror is deployed to reflect the radiation energy from the black body to the image sensor for calibrating the sensor system. After the calibration, the calibration mirror is stowed not to hide a main optical path. It also has a fail-safe function which can stow the mirror by just removing the input power of motor when the calibration mirror is stopped at certain position during the calibration. In the present work, the operation concept, design, torque analysis and functional test results of the calibration mirror mechanism with the aforementioned function have been introduced and investigated.

Gamma-Ray Burst Polarimeter (GAP) aboard the Small Solar Power Sail Demonstrator IKAROS

Abstract The small solar-power sail demonstrator ``IKAROS'' is a Japanese engineering verification spacecraft launched by the H-IIA rocket on 2010 May 21 at Japan Aerospace Exploration Agency (JAXA) Tanegashima Space Center. IKAROS has a 20 m diameter sail, which is made of a thin polyimide membrane. The sail converts the solar radiation-pressure into the propulsion force of IKAROS, and accelerates the spacecraft. The Gamma-Ray Burst Polarimeter (GAP) aboard IKAROS is the first polarimeter specifically designed to measure the polarization of Gamma-Ray Bursts (GRBs) from space, and will do so in the cruising phase of the IKAROS mission. GAP is a modest detector of 3.8 kg in weight and 17 cm in size with an energy range of between 50–300 keV. The GAP detector is now a member of the interplanetary network (IPN) for determining the GRB direction. The detection principle of gamma-ray polarization is the anisotropy of the Compton scattering. Coincidence between the central plastic Compton scattering medium and discrete CsI detectors distributed around the sides of the plastic defines the Compton-scattering angle, which is expected to show an angular dependence if polarization is present in a given GRB. In this paper, we present the GAP detector and its ground-based and onboard calibrations.