Regional in situ validation of satellite altimeters: Calibration and cross-calibration results at the Corsican sites

The in situ validation of the satellite altimeter sea surface heights is generally performed either at a few local points directly flown over by the satellites or using the global tide gauge network. A regional in situ calibration method was developed by NOVELTIS in order to monitor the altimeter data quality in a perimeter of several hundred kilometres around a given in situ calibration site. The primary advantage of this technique is its applicability not only for missions flying over dedicated sites but also for missions on interleaved or non repetitive orbits. This article presents the altimeter bias estimates obtained with this method at the Corsican calibration site, for the Jason-1 mission on its nominal and interleaved orbits as well as for the Jason-2 and Envisat missions. The various regional bias estimates (8.2 cm and 7.4 cm for Jason-1 respectively on the nominal and interleaved orbits in Senetosa, 16.4 cm for Jason-2 in Senetosa and 47.0 cm for Envisat in Ajaccio, with an accuracy between 2.5 cm and 4 cm depending on the mission) are compared with the results obtained by the other in situ calibration teams. This comparison demonstrates the coherency at the centimetre level, the stability and the generic character of the method, which would also be of benefit to the new and future altimeter missions such as Cryosat-2, SARAL/AltiKa, Sentinel-3, Jason-3, Jason-CS.     

Calibration of Envisat radar altimeter over Lake Issykkul

This study presents the results of calibration/validation (C/V) of Envisat satellite radar altimeter over Lake Issykkul located in Kyrgyzstan, which was chosen as a dedicated radar altimetry C/V site in 2004. The objectives are to estimate the absolute altimeter bias of Envisat and its orbit based on cross-over analysis with TOPEX/Poseidon (T/P), Jason-1 and Jason-2 over the ocean. We have used a new method of GPS data processing in a kinematic mode, developed at the Groupe de Recherche de Geodesie Spatiale (GRGS), which allows us to calculate the position of the GPS antenna without needing a GPS reference station. The C/V is conducted using various equipments: a local GPS network, a moving GPS antenna along the satellites tracks over Lake Issykkul, In Situ level gauges and weather stations. The absolute bias obtained for Envisat from field campaigns conducted in 2009 and 2010 is between 62.1 and 63.4 ± 3.7 cm, using the Ice-1 retracking algorithm, and between 46.9 and 51.2 cm with the ocean retracking algorithm. These results differ by about 10 cm from previous studies, principally due to improvement of the C/V procedure. Apart from the new algorithm for GPS data processing and the orbit error reduction, more attention has been paid to the GPS antenna height calculation, and we have reduced the errors induced by seiche over Lake Issykkul. This has been assured using cruise data along the Envisat satellite track at the exact date of the pass of the satellite for the two campaigns. The calculation of the Envisat radar altimeter bias with respect to the GPS levelling is essential to allow the continuity of multi-mission data on the same orbit, with the expected launch of SARAL/Altika mission in 2012. Implications for hydrology in particular, will be to produce long term homogeneous and reliable time series of lake levels worldwide.     

差动式激光多普勒技术在冲击校准测试中的应用

本文介绍了利用差动式激光多普勒技术实现高加速冲击校准的原理、方法和实际的光学系统。     

专用测试设备校准探讨

与军工产品科研生产密切相关的专用测试设备的校准,是军工产品质量保证的关键因素,越 来越受到生产研制和使用方的重视.不断完善专用测试设备的校准方法,使之更科学、更规范,是计量部门一直致力研究的问题.本文介绍了专用测试设备的特点、现状、专用测试设备现场校准及自动校准的必要性和特殊性,对专用测试设备的校准方法及不确定度评定等作了论述,并展望了专用测试设备校准的发展方向.     

加速度计的校准

介绍了振动传感器——加速度计的校准方法及其误差分析,着重介绍了加速度计校准的最新方法,即随机校准,提出了改进的随机校准方法,并作了相应的误差分析。对各种校准方法如正弦比较法、激光干涉仪法、随机校准法进行了比较,作了试验研究。     

差分GPS的原理和实现方法

GPS卫星无线电导航系统预计在1995年投入正式运行。GPS信号中的P码仅供美军和特别用户使用,C/A码则向全世界民用开放。C/A码受选择可用性(SA)影响,导航静度下降到一个适当水平。为提高GPS定位精度,各国都争相研究差分GPS(DGPS)。本文从GPS误差入手,主要就DGPS原理和实现方法进行讨论。     

交流电能表检定装置的测量不确定度评定

为了避免用传统误差体系的概念表示测量结果可能引起的不足，近年来在国内外科技文献中，讨论测量结果的误差时都已采用了测量不确定度来表示。根据测量不确定度的评定与表示方法，通过对交流电能表检定装置的各项误差源的分析，对交流电能表检定装置的不确定度进行了分析，最后对0．02级三相交流电能表检定装置的不确定度进行评定。     

经纬仪竖直角测角标准偏差检定方法的研究

从竖直角的定义出发，分析了目前国内外经缜义竖直角检定方法及其不足，提出了一套较为完整的检定方案。     

ICP－AES内标法测定合金中常量成分

合金中的常量成分的分析多有杉湿法化学法进行滴定分析或重量法分析，分析方法复杂、周期长。高频电感耦合等离子体发射光谱（ICP－AES）具有分析速度快、线性范围宽、能同时分析的特点，进一步改善其精密度，可应用于合金常量含量元素分析。本文用内标法改善ICP-AES分析结果的精密度，对比了用与不同内标法的结果，并测定了标准样品的常量成分，分析了内标元素的加入对结果的影响。     

“燃油非稳态流量校准装置”初探

非稳态流量计量是一个国内外都没有解决的难题。其中很重要的原因是缺乏可信的非稳态流量校准装置，因而无法得知流量计的动态特性。本文以飞机发动机燃油系统的涡轮流量计为例，阐述了有关非稳态流量校准装置的基本理论和实施方案