Vicarious calibration of ASTER thermal infrared bands

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on the Terra satellite has five bands in the thermal infrared (TIR) spectral region between 8-12 /spl mu/m. The TIR bands have been regularly validated in-flight using ground validation targets. Validation results are presented from 79 experiments conducted under clear sky conditions. Validation involved predicting the at-sensor radiance for each band using a radiative transfer model, driven by surface and atmospheric measurements from each experiment, and then comparing the predicted radiance with the ASTER measured radiance. The results indicate the average difference between the predicted and the ASTER measured radiances was no more than 0.5% or 0.4 K in any TIR band, demonstrating that the TIR bands have exceeded the preflight design accuracy of <1 K for an at-sensor brightness temperature range of 270-340 K. The predicted and the ASTER measured radiances were then used to assess how well the onboard calibration accounted for any changes in both the instrument gain and offset over time. The results indicate that the gain and offset were correctly determined using the onboard blackbody, and indicate a responsivity decline over the first 1400 days of the Terra mission.     

Interband calibration over clouds for POLDER space sensor

The Polarization and Directionality of the Earth's Reflectance (POLDER) spatial polarimeter was onboard the Advanced Earth Observation Satellite (ADEOS) satellite that flew from August 1996 to June 30, 1997. POLDER measured both multidirectional reflectance and polarization in visible and near-infrared spectral bands with a very wide field of view. An accurate absolute radiometric calibration is essential for the scientific exploitation of radiance measurements of the Earth. POLDER inflight radiometric calibration has been performed at the Centre National d'Etudes Spatiales (CNES), French National Space Studies Center, from measurements taken only on well-characterized targets. This paper presents the results of the POLDER in-flight radiometric interband calibration over clouds for channels 443 and 490 nm. The method is based on the comparison of measurements to simulations. Selected measurements correspond to observations over oceans for high, thick convective cumulonimbus and for low, thick stratocumulus. Simulations are calculated using the discrete ordinate computing method. An error budget considers the sensitivity of this calibration method to cloud microphysics, to cloud top altitude, and to aerosols and gaseous loading. Calibration results are discussed for different simulated cloud models     

基于相关光子宽谱段自校准辐射基准源的定标新方法

针对我国空间科学的未来发展和应用需求,以及目前星上定标和在轨定标方法的局限性,提出一种基于自发参量下转换效应的自校准宽谱段（450~1500 nm）辐射基准源设计方案。该辐射基准源系统主要由宽波段参量下转换、观测与自校准复用光路、多路光子计数与符合探测、信号采集与测量控制等4个主要功能模块构成。辐射基准源兼有星上自校准和自主观测功能,能够在不依赖于外部基准的条件下实现高精度的自校准,保障对地高精度观测,为其他卫星有效载荷提供高精度的量值传递标准。     

MODIS的HJ-1B红外通道星上定标系数交叉验证

HJ-1B卫星自发射以红外通道共进行了7次星上黑体定标,针对星上定标系数的验证工作开展较少,以MODIS第31、32通道为参考源,分别基于光谱响应差异和线性统计关系两种方法对HJ-1B红外通道星上定标系数进行验证.首先,计算两个传感器表观辐亮度的匹配关系,进而计算出HJ-1B红外通道的等效离表亮温,通过与HJ-1B红外通道基于星上定标系数反演得到的离表亮温进行比较,实现对星上定标系数的验证.通过半高宽法、矩方法和查找表法这三种不同的方法计算得到了2009年9月14日星上定标系数.结果表明:三种方法中,查找表法精度较高, 且HJ-1B查找表法星上定标系数反演亮温与基于光谱响应差异和线性统计关系计算的等效亮温偏差较小,分别为0.02 K和0.81 K.这两种交叉验证方法的精度均在1 K以内,证明了该方法的可行性,且基于光谱响应差异的验证方法精度更高.该研究为光学载荷在轨辐射定标的验证提供了理论基础.     

基于中阶梯光栅的光谱定标装置设计方法

针对紫外-可见光波段高光谱成像仪光谱定标装置的设计进行研究,论述了中阶梯光栅的光学原理,根据光谱定标原理,利用中阶梯光栅工作角度大、衍射级次高、光谱分辨率高的优点,建立了基于中阶梯光栅的光谱定标装置,提出了基于中阶梯光栅的光谱成像仪光谱定标装置的设计方法。以大气探测卫星Aura 上所搭载的臭氧观测仪为例论述了光谱定标装置的设计过程,仿真分析了光谱定标装置带宽对光谱定标精度的影响,给出了衍射级次、光谱分辨率、平行光管焦距等光谱定标装置主要性能参数的设计计算方法,为基于中阶梯光栅的光谱成像仪光谱定标装置的设计提供了依据。     

In-Flight Absolute Radiometric Calibration of the Thematic Mapper

Ground spectral reflectance and atmospheric spectral optical depth measurements made at White Sands, New Mexico on January 3, 1983, were used with an atmospheric radiative transfer program to determine the spectral radiance at the entrance pupil of the Landsat-4 Thematic Mapper (TM). A comparison with the output digital counts of the TM, when imaging the measured ground area, provided an absolute calibration for five detectors in TM bands 2, 3, and 4. By reference to an adjacent, larger uniform area, the calibration was extended to all 16 detectors in each of the three bands. Pre-flight calibration results agreed with these inflight measurements to 6.6, 2.4, and 12.9 percent in bands 2, 3, and 4, respectively.     

星载EMI在轨光谱定标方法研究

于2018年5月9日搭载高分五号卫星发射的大气痕量气体差分吸收光谱仪(EMI)为紫外可见波段高分辨率成像光谱仪.为考察其在轨光谱性能,首先采用波长寻峰法即以太阳Fraunhofer线作为特征峰以快速获取载荷的光谱范围,然后采用谱线匹配法获取载荷空间维度的光谱弯曲值,最后采用光谱拟合法获取光谱分辨率的变化.寻峰法通过与标...     

风云三号MERSI数据提取北冰洋海冰信息方法研究

海冰是制约北冰洋航路开发最为重要的因素之一,FY-3卫星上搭载的中分辨率光谱成像仪（MERSI)扫描范围大,一天之内可获得5次以上极地同一地区观测数据,有利于北冰洋海冰状况的动态监测。以格陵兰岛附近海域为研究区域,利用2011年6月13日MERSI多波段数据,经过辐射定标、投影定位等预处理后,以两波段比值和归一化差分积雪指数(NDSI)作为判别指标,采用最大类间方差阈值法对指标图像进行分割,实现海冰、海水和云的区分,准确获取格陵兰岛附近海冰分布信息。该研究可为国产卫星数据在北冰洋航路选择和航运安全保障方面的应用提供技术支持。     

MIRAS reference radiometer: a fully polarimetric noise injection radiometer

A prototype reference radiometer for the Microwave Imaging Radiometer Using Aperture Synthesis (MIRAS) instrument of the Soil Moisture and Ocean Salinity satellite has been developed. The reference radiometer is an L-band fully polarimetric noise injection radiometer (NIR). The main purposes of the NIR are: 1) to provide precise measurement of the average fully polarimetric brightness temperature scene for absolute calibration of the MIRAS image map and 2) to measure the noise temperature level of the noise distribution network of the MIRAS for individual receiver calibration. The performance of the NIR is a decisive factor of the MIRAS performance. In this paper we present the operation principles and calibration procedures of the NIR, a measurement technique called blind correlation making measurements of full Stokes vector possible with the noise injection method, and finally experimental results verifying certain aspects of the design.     

HJ-1B卫星IRS传感器热红外通道交叉定标

以TERRA卫星中分辨率成像光谱仪(MODIS)传感器热红外通道的星上定标结果为标准,采用交叉定标方法获取HJ-lB卫星红外多光谱相机(IRS)传感器热红外通道定标系数.首先,获取两个传感器的对应通道,利用MODTRAN模拟光谱响应、观测角、大气条件和温度变化对匹配因子的影响.然后确定此研究只考虑对应通道的波谱响应和地表温度差异,并计算出不同地表温度下匹配因子的变化趋势.选择7次不同时间双星同步观测青海湖区域的图像作为交叉定标数据,根据MODIS的辐射亮度和匹配因子计算出IRS传感器热红外通道的辐射亮度,最后,将得到的辐射亮度和DN值进行线性回归,获得IRS热红外通道的定标系数.将此次定标结果与HJ-1B卫星IRS传感器热红外通道星上4次黑体定标结果进行比较,定标结果一致性较好.     

Terra MODIS on-orbit spectral characterization and performance

The Moderate Resolution Imaging Spectroradiometer (MODIS) protoflight model onboard the National Aeronautics and Space Administration's Earth Observing System Terra spacecraft has been in operation for over five years since its launch in December 1999. It makes measurements using 36 spectral bands with wavelengths from 0.41 to 14.5 /spl mu/m. Bands 1-19 and 26 with wavelengths below 2.2 /spl mu/m, the reflective solar bands (RSBs), collect daytime reflected solar radiance at three nadir spatial resolutions: 0.25 km (bands 1-2), 0.5 km (bands 3-7), and 1 km (bands 8-19 and 26). Bands 20-25 and 27-36, the thermal emissive bands, collect both daytime and nighttime thermal emissions, at 1-km nadir spatial resolution. The MODIS spectral characterization was performed prelaunch at the system level. One of the MODIS onboard calibrators, the Spectroradiometric Calibration Assembly (SRCA), was designed to perform on-orbit spectral characterization of the MODIS RSB. This paper provides a brief overview of MODIS prelaunch spectral characterization, but focuses primarily on the algorithms and results of using the SRCA for on-orbit spectral characterization. Discussions are provided on the RSB center wavelength measurements and their relative spectral response retrievals, comparisons of on-orbit results with those from prelaunch measurements, and the dependence of center wavelength shifts on instrument temperature. For Terra MODIS, the center wavelength shifts over the past five years are less than 0.5 nm for most RSBs, indicating excellent stability of the instrument's spectral characteristics. Similar spectral performance has also been obtained from the Aqua MODIS (launched in May 2002) SRCA measurements.     

Onboard calibration of the ASTER instrument

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a high spatial resolution optical sensor for observing the Earth carried on the National Aeronautics and Space Administration Terra satellite. ASTER consists of three radiometers covering the following regions: visible and near-infrared (VNIR), shortwave infrared (SWIR), and thermal infrared (TIR). The preflight calibration of VNIR and SWIR utilized standard large integrating spheres whose radiance levels were traceable to primary standard fixed-point blackbodies. The onboard calibration devices for the VNIR and SWIR consist of two halogen lamps with photodiode monitors. In orbit, all three bands of the VNIR showed rapid decreases in the output signal while all SWIR bands remained stable. The TIR onboard blackbody was calibrated against a standard blackbody from 100-400 K in a vacuum chamber before launch. The TIR is unable to see the dark space. The temperature of the TIR onboard blackbody remains at 270 K for a short-term calibration to determine any offset and is varied from 270-340 K for a long-term calibration of both the offset and gain. The long-term calibration just after launch was consistent with the prelaunch calibration but then showed a steady decrease of the TIR response over the five years of operation to date.     

Comparing the ocean color measurements between MOS and SeaWiFS: avicarious intercalibration approach for MOS

The Modular Optoelectronic Scanner (MOS) was launched in the spring of 1996 on the Indian IRS-P3 satellite. With the successful launch of NASA's Sea-viewing Wide Field of-view Sensor (SeaWiFS) in the summer of 1997, there are now two ocean color missions in concurrent operation, and there is interest to compare data from these two sensors. In this paper, we describe our efforts to retrieve ocean-optical properties from both SeaWiFS and MOS using consistent methods. We first briefly review the atmospheric correction, which removes more than 90% of the observed radiances in the visible, and then we describe how the atmospheric-correction algorithm used for the SeaWiFS data can be modified for application to other ocean color sensors. Next, since the retrieved water-leaving radiances in the visible between MOS and SeaWiFS are significantly different, we developed a vicarious intercalibration method to recalibrate the MOS spectral bands based on the optical properties of the ocean and atmosphere derived from the coincident SeaWiFS measurements. Furthermore, because of the strange calibration behavior of the MOS 750 nm band, we modified the atmospheric correction such that the MOS 685 and 868 nm bands can also be used. We present and discuss the MOS-retrieved, ocean-optical properties before and after the vicarious calibration using both the MOS 685 and 750 nm coupled with 868 nm bands in comparison with results from SeaWiFS and demonstrate the efficacy of this approach. We show that it is possible and efficient to vicariously intercalibrate sensors between one and another     

MODIS On-Orbit Spatial Characterization Using Ground Targets

The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor is currently being operated on both Terra and Aqua spacecrafts. MODIS uses 36 bands arranged in four focal plane assemblies (FPAs)—visible, near infrared, short- and middle-wavelength infrared, and long-wavelength infrared. Misregistrations between spectral bands and FPAs and changes of spatial characterization on-orbit could impact the quality of science data products generated with multiple bands located on different FPAs. In this paper, an approach is presented to compute the MODIS band-to-band registration (BBR) using ground measurements. A special ground scene with unique features is selected to calculate the spatial registration along-scan and along-track. The monthly and yearly spatial deviations are calculated for the bands of both Terra and Aqua MODIS except for some ocean bands, cloud bands, and the Aqua MODIS band 6. The comparison with results derived from the spectroradiometric calibration assembly, a device operated on-orbit to track the BBR shift between any two of the spectral bands, generally shows good agreement. The measured differences between these two approaches are typically less than 100 m in the scan direction and 200 m in the track direction. This approach can provide more frequent characterization of the MODIS BBR and is extremely useful for other sensors that do not have an onboard spatial characterization device.      

Detection of calibration drifts in spaceborne microwave radiometersusing a vicarious cold reference

The coldest possible brightness temperatures observed by a downward-looking microwave radiometer from space are often produced by calm oceans under cloud-free skies and very low humidity. This set of conditions tends to occur with sufficient regularity that an orbiting radiometer will accumulate a useful number of observations within a period of a few days to weeks. Histograms of the radiometer's coldest measurements provide an anchor point against which very small drifts in absolute calibration can be detected. This technique is applied to the TOPEX microwave radiometer (TMR), and a statistically significant drift of several tenths of a Kelvin per year is clearly detected in one of the channels. TMR housekeeping calibration data indicates a likely cause for the drift, as small changes in the isolation of latching ferrite circulators that are used in the onboard calibration-switch assembly. This method can easily be adapted to other microwave radiometers, especially imagers operating at frequencies in the atmospheric windows. In addition to detecting long-term instrument drifts with high precision, the method also provides a means for cross-calibrating different instruments. The cold reference provides a common tie point, even between sensors operating at different polarizations and/or incidence angles     

星载大气痕量气体差分吸收光谱仪定标机构设计

星载大气痕量气体差分吸收光谱仪(星载仪器)搭载于太阳同步轨道卫星上,应用于定量监测全球空气质量变化以及污染气体的分布输运过程。星上定标是成像光谱仪获取数据定量化应用的基础,星载仪器采用太阳光定标方式和标准灯定标方式进行在轨定标。需对星上定标方式采用的定标机构进行分析和合理的设计,以保证星载仪器在轨定标的可靠性和精度。     

利用MODIS对FY-2E/VISSR红外窗区和水汽通道的交叉绝对辐射定标

介绍了利用高精度的TERRA/MODIS观测资料对FY-2E红外窗区和水汽吸收通道进行绝对交叉定标的方法,并选用2010年5、7和12三个月的卫星数据进行了交叉定标计算.结果表明,交叉定标系数计算亮温与MODIS匹配点处实测结果非常接近,约90％的亮温偏差小于1K,其中高温区结果更稳定,偏差小于低温区,这主要是由于低温区杂散光影响显著造成的.总的说来,借助TERRA/MODIS可以实现对FY-2E/VISSR的高频次高精度的绝对定标,为FY-2E在轨替代定标提供重要的方法基础.     

Evaluation of radiative transfer simulations over bright desert calibration sites

The Spinning Enhanced Visible and Infrared Imager (SEVIRI), the Meteosat Second Generation main radiometer, measures the reflected solar radiation within three spectral bands centered at 0.6, 0.8, and 1.6 /spl mu/m, and within a broadband. This broadband is similar to the solar channel of the radiometer onboard the first generation of METEOSAT satellites. The operational absolute calibration of these channels relies on modeled radiances over bright desert sites, as no in-flight calibration device is available. These simulated radiances represent, therefore, the "reference" against which SEVIRI is calibrated. The present study describes the radiative properties of these targets and evaluates the uncertainties associated with the characterization of this "reference", i.e. the modeled radiances. To this end, top-of-atmosphere simulated radiances are compared with several thousands of calibrated observations acquired by the European Remote Sensing 2/Along-Track Scanning Radiometer 2 (ERS2/ATSR-2), SeaStar/Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Syste/spl grave/me Pour l'Observation de la Terre 4 (SPOT-4/VEGETATION), and the Environmental Research Satellite/Medium Resolution Imaging Spectrometer (ENVISAT/MERIS) instruments over the SEVIRI desert calibration sites. Results show that the mean relative bias between observation and simulation does not exceed 3% in the red and near-infrared spectral bands with respect to the first two instruments.     

风云二号B星星载扫描辐射计水汽通道定标方法

FY-2B静止气象卫里扫描辐射计水汽通道发射前定标在实验室真空罐内进行．发射在轨后,可以利用里上黑体监视探测器性能变化,但由于呈上黑体光路与目标光路不同,无法进行水汽通道的在轨全光路定标．介绍了FY-2B水汽通道的发射前定标、利用在轨电定标确定量化关系进行的定标处理以及与NOAA-17卫里HIRS／3通道12的相对定标方法．     

红外相机实时绝对辐射定标技术研究

辐射定标技术是实现定量遥感的关键环节。近年来,随着红外遥测技术愈发成熟,星上红外辐射定标已成为空间定量遥感技术的重要发展方向。文中从红外相机实时绝对辐射定标的背景出发,提出了半光路星上绝对辐射定标和基于多温度场的场地绝对辐射定标方法,结合实验数据,分别采用星上定标、场地定标、交叉定标三种方案进行在轨绝对辐射定标实验验证,并对其适用场景进行了分析。结果表明,通过结合半、全光路定标数据处理和转换技术,利用水面场和陆面场的场地绝对辐射定标方法,优选合适的定标场地,同时在陆面场中增加典型地物场景实现多温度场定标的方法,所提出的辐射定标方法实现了实时高精度绝对辐射定标,定标精度优于1.5 K。