Jason Microwave Radiometer Performance and On-Orbit Calibration

Results are presented from the on-orbit calibration of the Jason Microwave Radiometer (JMR). The JMR brightness temperatures (TBs) are calibrated at the hottest and coldest ends of the instrument's dynamic range, using Amazon rain forest and vicarious cold on-Earth theoretical brightness temperature references. The retrieved path delay values are validated using collocated TOPEX Microwave Radiometer and Radiosonde Observation path delay (PD) values. Offsets of 1–4 K in the JMR TBs and 8–12 mm in the JMR PDs, relative to TMR measurements, were initially observed. There were also initial TB offsets of 2 K between the satellite's yaw state. The calibration was adjusted by tuning coefficients in the antenna temperature calibration algorithm and the antenna pattern correction algorithm. The calibrated path delay values are demonstrated to have no significant bias or scale errors with consistent performance in all nonprecipitating weather conditions. The uncertainty of the individual path delay measurements is estimated to be 0.74 cm ± 0.15, which exceeds the mission goal of 1.2 cm RMS.     

Jason Microwave Radiometer Performance and On-Orbit Calibration

Results are presented from the on-orbit calibration of the Jason Microwave Radiometer (JMR). The JMR brightness temperatures (TBs) are calibrated at the hottest and coldest ends of the instrument's dynamic range, using Amazon rain forest and vicarious cold on-Earth theoretical brightness temperature references. The retrieved path delay values are validated using collocated TOPEX Microwave Radiometer and Radiosonde Observation path delay (PD) values. Offsets of 1-4 K in the JMR TBs and 8-12 mm in the JMR PDs, relative to TMR measurements, were initially observed. There were also initial TB offsets of 2 K between the satellite's yaw state. The calibration was adjusted by tuning coefficients in the antenna temperature calibration algorithm and the antenna pattern correction algorithm. The calibrated path delay values are demonstrated to have no significant bias or scale errors with consistent performance in all nonprecipitating weather conditions. The uncertainty of the individual path delay measurements is estimated to be 0.74 cm ± 0.15, which exceeds the mission goal of 1.2 cm RMS.     

Correcting for Cryoprecipitation in the Calibration of IR Channels of the MSU-MR Radiometer

Izvestiya, Atmospheric and Oceanic Physics - The presence of cryoprecipitation, which forms a thin film on the input windows of infrared (IR) detectors and distorts the signal, is a major issue in...     

The Use of Artificial Neuron Networks for Retrieval Temperature and Humidity Sounding of the Atmosphere According to the Data of the MTVZA-GY Microwave Radiometer Installed on the Meteor-M No. 2-2 Satellite

Izvestiya, Atmospheric and Oceanic Physics - We consider the application of artificial neural networks for remote temperature and humidity profiles sounding of the atmosphere according to the data...     

风云一号遥感器可见光通道大气程辐射之间的关系

本文利用光谱辐射计测量的大气程辐射资料,研究了相应于“风云一号”卫星上改进型甚高分辨率扫描辐射计(CAVHRR)4个可见光通道的大气程辐射量(N_a)之间的关系。结果表明它们满足((N_a(λ))/(N_a(λ_0)))=A(λ/λ_0)~B的关系。 经回归分析得:A为1.0887,B为3.6587。式中λ_0是CAVHRR第二通道的中心波长,即λ_0=0.875μm,λ是CAVHRR其他3个通道中心波长。     

Algorithm for the Atmospheric Correction of Shortwave Channels of the MSU-MR Radiometer of the Meteor-M No. 2 Satellite

Izvestiya, Atmospheric and Oceanic Physics - The problem of atmospheric correction for shortwave channels of a multispectral low-resolution scanning radiometer onboard the Meteor-M No. 2 satellite...     

基于星载微波辐射计的海洋大气参数反演算法研究

利用3个辐射传输模式对无冰无降水情况下的星载微波辐射计亮温测量进行仿真研究,通过模拟计算结果与同步卫星数据之间的比较分析,确定了用于反演算法研究的前向模式;利用该模式,提出了基于物理的星载微波辐射计海洋大气参数(包括海面风速、海表温度、大气垂直积分水汽量以及积分液态水量)多重线性回归算法。     

多波束测深系统的安装校准

以多波束测深系统应用中所涉及的不同坐标系统为基础，将安装校准和数据校准分离，主要介绍安装偏差的来源、误差性质、校准目的和校准方法；同时，对多波束的主要部分——换能器的安装校准进行了详细的论述。     

光谱仪绝对辐亮度定标

保证现场测量离水辐射率精度的关键工作之一是对现场测量辐射计进行严格的实验室定标。本文就1999年8月进行的一次PIS-B定标试验，简述辐亮度定标的主要方法及数据处理方法。     

Offshore Absolute Calibration of Space-Borne Radar Altimeters

Absolute calibration of sea level measurements collected from space-borne radar altimeters is usually performed with respect to collocated sea level in situ records from tide gauges or GPS buoys (Ménard et al. 1994 Ménard, Y., Jeansou, E. and Vincent, P. 1994. Calibration of the TOPEX-Poseidon altimeters at Lampedusa: Additional results at Harves. J. Geophys Res., 99(C12): 24487–24504. http://dx.doi.org/10.1029%2F94JC01300 [Google Scholar]; Haines et al. 1996 Haines, B. J., Christensen, E. J., Norman, R. A., Parke, M. E., Born, G. H. and Gill, S. K. 1996. Altimeter calibration and geophysical monitoring from collocated measurements at the Harvest oil platform. EOS Trans. Suppl., 77(22): W16 [Google Scholar]; Bonnefond et al. 2003; Haines et al. 2003 Haines, B. J., Dong, D., Born, G. H. and Gill, S. K. 2003. The Harvest experiment: Monitoring Jason-1 and TOPEX/Poseidon from a California offshore platform. Mar. Geod., 26: 239–259. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]; Schum et al. 2003 Schum, C. K., Yi, Y., Cheng, K., Kuo, C., Braun, A., Calmant, S. and Chambers, D. 2003. Calibration of Jason-1 Altimeter over Lake Erie. Mar. Geod., 26: 335–354.  [Google Scholar]; Watson et al. 2003 Watson, C., Coleman, R., White, N., Church, J. and Govind, R. 2003. Absolute calibration of TOPEX/ Poseidon and Jason-1 using GPS buoys in Bass Strait, Australia. Mar. Geod., 26: 285–304. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]; Watson et al. 2004 Watson, C., White, N., Coleman, R., Church, J., Morgan, P. and Govind, R. 2004. TOPEX/Poseidon and Jason-1: Absolute calibration in Bass Strait, Australia. Mar. Geod., 27: 107–131. http://dx.doi.org/10.1080%2F01490410490465373[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]). Such a method allows regular and long-term control of altimetric systems with independent records. However, this approach is based on a single, geographically dependent point. In order to obtain more significant and accurate bias and drift estimates, there is a strong interest in multiplying the number of calibration opportunities. This article describes a method, called the “offshore method” that was developed to extend the single-point approach to a wider regional scale. The principle is to compare altimeter and tide gauge sea level data not only at the point of closest approach of an overflying pass, but also at distant points along adjacent satellite passes. However, connecting sea level satellite measurements with more distant in situ data requires a more accurate determination of the geoid and mean ocean dynamic topography slopes, and also of the ocean dynamical changes. In this demonstration experiment, 10 years of averaged TOPEX/Poseidon mean sea level profiles are used to precisely determine the geoid and the mean ocean circulation slope. The Mog2d barotropic ocean model (Carerre et Lyard 2003 Carrère, L. and Lyard, F. 2003. Modelling the barotropic response of the global ocean to atmospheric wind and pressure forcing-comparisons with observations. GRL, 30(6): 1275 [Google Scholar]) is used to improve our estimate of the ocean dynamics term. The method is first validated with Jason-1 data, off Corsica, where the dedicated calibration site of Senetosa provides independent reference data. The method is then applied to TOPEX/Poseidon on its new orbit and to Geosat Follow On. The results demonstrate that it is feasible to make altimeter calibrations a few tens to hundreds of kilometers away from a dedicated site, as long as accurate mean sea level altimeter profiles can be used to ensure the connection with reference tide gauges.     

剖面仪/表面仪绝对辐射定标

保证现场测量离水辐射率精度的关键工作之一是现场测量设备进行严格的实验室定标,本文就１９９９年９月进行的一次实验室绝对辐射定标试验,简述辐照度,辐亮度定标的主要方法及数据处理方法。     

微波辐射计遥感海洋盐度的研究进展

介绍了微波辐射计遥感海洋盐度的原理,回顾了在海水微波辐射亮度温度模型,机载、星载微波辐射计遥感海洋盐度实验,以及星载微波辐射计研究计划方面的进展。指出了为提高海洋盐度测量精度和空间分辨率,在盐度遥感机理、微波辐射计、及盐度反演研究方面的发展趋势。     

基于Jason-2校正辐射计的降雨率估计算法研究

采用Jason-2校正辐射计的亮温数据与GPM Ku波段测雨雷达的降雨率数据,开展基于Jason-2校正辐射计的降雨率估计算法研究。为避免波束填充效应,对Ku波段测雨雷达降雨率数据进行网格化处理,分别构建3×3,5×5及7×7网格的建模数据集和验证数据集,通过建模数据集建立了3种基于校正辐射计的降雨率估计算法研究,并通过验证数据集进行检验。结果表明:对GPM Ku波段测雨雷达的降雨数据进行3×3,5×5及7×7的网格化处理,可以在降雨率估计算法研究时有效避免波束填充效应,7×7网格化处理方法效果最优。对3种不同的算法比对,发现利用校正辐射计3个通道亮温信息的线性组合形式估计降雨率效果最优,相对偏差可达42.33%。     

An Assessment of Jason-1 Microwave Radiometer Measurements and Products

In the context of the sea level survey at the mm level, it is necessary all along the lifetime of the altimeter mission to survey the quality of the products from the microwave radiometer. The calibration of the brightness temperatures has been validated using reference brightness temperatures over selected continental areas as well as simulations for a wide range of oceanic and atmospheric situations. The validation of the wet path delay is performed by comparison with radiosonde measurements and pointed out that both the JMR and the TMR estimate wet path delay around 5 mm higher than the one measured by radiosondes. Furthermore, it appeared that the correction of the TMR drift degrades the product with respect to radiosonde measurements. The monitoring of the brightness temperatures since launch shows a mean drift around +0.1 K/year for the 18.7 GHz, -0.6 K/year for the 23.8 GHz channel, and around -0.4 K/year for the 34 GHz channel.     

An Assessment of Jason-1 Microwave Radiometer Measurements and Products

In the context of the sea level survey at the mm level, it is necessary all along the lifetime of the altimeter mission to survey the quality of the products from the microwave radiometer. The calibration of the brightness temperatures has been validated using reference brightness temperatures over selected continental areas as well as simulations for a wide range of oceanic and atmospheric situations. The validation of the wet path delay is performed by comparison with radiosonde measurements and pointed out that both the JMR and the TMR estimate wet path delay around 5 mm higher than the one measured by radiosondes. Furthermore, it appeared that the correction of the TMR drift degrades the product with respect to radiosonde measurements. The monitoring of the brightness temperatures since launch shows a mean drift around +0.1 K/year for the 18.7 GHz, ?0.6 K/year for the 23.8 GHz channel, and around ?0.4 K/year for the 34 GHz channel.     

星载微波辐射计空间分辨率增强算法研究

由于天线尺寸和重量受到限制,星载微波辐射计的空间分辨率通常都比较低.同时在测量地理参数时往往要用到辐射计的多个频率通道测量值,这就需要把不同通道的空间分辨率统一成某个较高空间分辨率.因此,出于应用的目的,利用微波辐射计空间分辨率增强算法来得到较高分辨率的图像很有必要.简单介绍了增强星载微波辐射计图像空间分辨率的几种算法,详细叙述了Backus-Gilbert反演算法的原理.设计了带有一些地物特征的人工合成图像,并使用BG反演算法对一模拟辐射计的生成图像进行了增强处理.从处理前后的图像对比可知,无论辐射计测量是否含有噪声,BG反演算法都很好地提高了辐射计生成图像的空间分辨率.在考虑噪声时,通过分析增强处理后图像与人工合成图像之间的相关性,仔细挑选协调参数,对分辨率和噪声进行了较好的折中处理.     

SARAL/AltiKa Absolute Calibration from the Multi-Mission Corsica Facilities

The geodetic Corsica site was set up in 1998 in order to perform altimeter calibration of the TOPEX/Poseidon (T/P) mission and subsequently, Jason-1 and OSTM/Jason-2. The scope of the site was widened in 2005 in order to undertake the calibration of the Envisat mission and most recently of SARAL/AltiKa. Here we present the first results from the latter mission using both indirect and direct calibration/validation approaches. The indirect approach utilizes a coastal tide gauge and, as a consequence, the altimeter derived sea surface height (SSH) needs to be corrected for the geoid slope. The direct approach utilizes a novel GPS-based system deployed offshore under the satellite ground track that permits a direct comparison with the altimeter derived SSH. The advantages and disadvantages of both systems (GPS-based and tide gauges) and methods (direct or indirect) will be described and discussed. Our results for O/IGD-R data show a very good consistency for these three kinds of products: their derived absolute SSH biases are consistent within 17 mm and their associated standard deviation ranges from 31 to 35 mm. The AltiKa absolute SSH bias derived from GPS-zodiac measurement using the direct method is ?54 ±10 mm based on the first 13 cycles.     

波束角偏差对多波束测量的影响及校正

波束角偏差是影响多波束系统测量精度的因素之一,严重时导致测量的海底地形成凸凹形状的伪地形。论述了波束角偏差产生的原因以及对多波束系统测量精度的影响,介绍了借用EM系列多波束系统配置的横向参数校准软件对波束角偏差进行校正的方法,经实际应用,该方法很好地校正了波束角偏差,提高了测量数据的精度。     

Absolute Calibration of the Jason-1 Altimeter Using UK Tide Gauges

This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1-61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.     

Absolute Calibration of the Jason-1 Altimeter Using UK Tide Gauges

This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1–61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.