One-Centimeter Orbit Determination for Jason-1: New GPS-Based Strategies

The U.S./French Jason-1 satellite is carrying a state-of-the-art GPS receiver to support precise orbit determination (POD) requirements. The performance of the Jason-1 “BlackJack” GPS receiver was strongly reflected in early POD results from the mission, enabling radial accuracies of 1–2 cm soon after the satellite's 2001 launch. We have made further advances in the GPS-based POD for Jason-1, most notably in describing the phase center variations of the on-board GPS antenna. We have also adopted new geopotential models from the Gravity Recovery and Climate Experiment (GRACE). The new strategies have enabled us to better exploit the unique contributions of the BlackJack GPS tracking data in the POD process. Results of both internal and external (e.g., laser ranging) comparisons indicate that orbit accuracies of 1 cm (radial RMS) are being achieved for Jason-1 using GPS data alone.     

Comparison of the Ku-Band Range Noise Level and the Relative Sea-State Bias of the Jason-1, TOPEX,and Poseidon-1 Radar Altimeters Special Issue: Jason-1 Calibration/Validation

TOPEX/Poseidon is a well known success, with the operational altimeter (TOPEX) and the experimental one (Poseidon-1), providing data of unprecedented quality. However, there are two major differences between the TOPEX and Poseidon-1 radar altimeters on board TOPEX/Poseidon. The first is related to the estimated range noise; the second is linked to the sea-state bias (SSB) model estimates. Since the recent launch of the Jason-1 radar altimeter (also called Poseidon-2), we have been cross-comparing these three systems to better characterize each of them. Analyzing standard user products, we have found that Jason-1 is behaving like Poseidon-1 and thus shows the same observed differences when compared with TOPEX. A comparative analysis of their features was performed, starting from the on-board acquisition of the ocean return and ending with the ground generation of the high level accuracy oceanographic product. The results lead us to believe that the sources for these differences lie in both the waveform tracking processing and the presence or abscence of a retracking procedure whether on-board or on ground. Because Poseidon-1 and Jason-1 waveforms are retracked while TOPEX waveforms are not in the products distributed to the users, we have applied the same ground retracking algorithm to the waveforms of the three radar altimeters to get consistent data sets. The analysis of the outputs has shown that: (a) the noise level for the three radar altimeters is definitively the same, and (b) the source of the relative SSB between Jason-1 and TOPEX lies in the different behavior of the on-board tracking softwares.     

Simultaneous Ocean Wave Measurements by the Jason and Topex Satellites,with Buoy and Model Comparisons Special Issue: Jason-1 Calibration/Validation

The verification phase of the Jason-1 satellite altimeter mission presents a unique opportunity for comparing near-simultaneous, independent satellite measurements. Here we examine simultaneous significant wave height measurements by the Jason-1 and TOPEX/Poseidon altimeters. These data are also compared with in situ measurements from deep-ocean buoys and with predicted wave heights from the Wave Watch III operational model. The rms difference between Jason and TOPEX wave heights is 28 cm, and this can be lowered by half through improved outlier editing and filtering of high-frequency noise. Noise is slightly larger in the Jason dataset, exceeding TOPEX by about 7 cm rms at frequencies above 0.05 Hz, which is the frequency at which the coherence between TOPEX and Jason measurements drops to zero. Jason wave heights are more prone to outliers, especially during periods of moderate to high backscatter. Buoy comparisons confirm previous reports that TOPEX wave heights are roughly 5% smaller than buoy measurements for waves between 2 and 5 m; Jason heights in general are 3% smaller than TOPEX. Spurious dips in the TOPEX density function for 3- and 6-m waves, a problem that has existed since the beginning of the mission, can be solved by waveform retracking.     

Near-Real–Time GPS-Based Orbit Determination and Sea Surface Height Observations from the Jason-1 Mission Special Issue: Jason-1 Calibration/Validation

The Jason-1 Operational Sensor Data Record (OSDR) is intended as a wind and wave product that is aimed towards near-real–time (NRT) meteorological applications. However, the OSDR provides most of the information that is required to determine altimetric sea surface heights in NRT. The exceptions include a sufficiently accurate orbit altitude, and pressure fields to determine the dry troposphere path delay correction. An orbit altitude field is provided on the OSDR but has accuracies that range between 8–25 cm (RMS). However, tracking data from the on-board BlackJack GPS receiver are available with sufficiently short latency for use in the computation of NRT GPS-based orbit solutions. The orbit altitudes from these NRT orbit solutions have typical accuracies of < 3.0 cm (RMS) with a latency of 1–3 h, and < 2.5 cm (RMS) with a latency of 3–5 h. Meanwhile, forecast global pressure fields from the National Center for Environmental Prediction (NCEP) are available for the NRT computation of the dry troposphere correction. In combination, the Jason-1 OSDR, the NRT GPS-based orbit solutions, and the NCEP pressure fields can be used to compute sea surface height observations from the Jason-1 mission with typical latencies of 3–5 h, and have differences with those from the 2–3 day latency Interim Geophysical Data Records of < 5 cm (RMS). The NRT altimetric sea surface height observations are potentially of benefit to forecasting, tactical oceanography, and natural hazard monitoring.     

Jason-1: Assessment of the System Performances Special Issue: Jason-1 Calibration/Validation

On 7 December 2001, Jason-1 was successfully launched by a Boeing Delta II rocket from the Vandenberg Air Force Base, California. The Jason-1 satellite will maintain the high accuracy altimeter service provided since 1992 by TOPEX/Poseidon (T/P), ensuring the continuity in observing and monitoring the Ocean Dynamics (intraseasonal to interannual changes, mean sea level, tides, etc.). Despite one-fourth the mass and power, the Jason-1 system has been designed to have basically the same performance as T/P, measuring sea surface topography at a centimetric level. This new CNES/NASA mission also provides near real-time data for sea state and ocean forecast. The first two months of the Jason-1 mission have been dedicated to the assessment of the overall system. The goals of this assessment phase were: 1. To assess the behavior of the spacecraft at the platform and payload levels (Jason-1 being the first program to call on the PROTEUS versatile multimission platform for Low and Medium Earth Orbit Missions developed in partnership between Alcatel Space and CNES); 2. To verify that platform performance requirements are met with respect to Jason-1 requirements; 3. To verify that payload instruments performance requirements evaluated at instrument level are met; 4. To assess the performance of the Jason-1 Ground System. This article will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications. Provision of data to the Jason-1 Science Working Team started at the end of March 2002. This is the goal of a six-month phase after closure of the initial assessment phase to derive the error budget of the system in terms of altimetry user products.     

基于T/P 和Jason-1 高度计数据的渤黄东海潮汐信息提取

对19 a 的TOPEX/POSEIDON(以下称T/P)和Jason-1 卫星高度计测高数据进行调和分析, 得到渤黄东海海域的8 个主要分潮(M2、S2、N2、K2、K1、O1、P1 和Q1)。提出一种将两类卫星高度计数据统一的方法, 消除了因两类卫星高度计校正算法等不同所导致的相互之间的偏差。变轨后的T/P与Jason-1 卫星加密了高度计对潮汐观测的空间分布。通过对交叉点处升轨与降轨的潮汐调和分析结果进行比较, 检验调和分析方法及高度计数据的可靠性; 将基于高度计数据的调和分析结果与验潮站资料进行比较, 以检验其正确性。4 个主要分潮(M2、S2、K1、O1)振幅之差的均方根介于1.0~1.8 cm, 迟角之差的均方根介于4.1°~7.8°。与已有研究结果相比, 调和分析结果的精确性有所提高。在此基础上, 综合变轨前后两类高度计测高数据的调和分析结果, 给出并分析了渤黄东海4 个主要分潮的同潮图。     

TJ-1模拟月壤承载特性的现场试验研究

采用TJ-1模拟月壤作为试验材料,通过静力触探、静载荷试验的对比分析,探讨适合月壤承载力计算的经验公式,以期为未来载人登月时宇航员和着陆器登陆可能涉及到有关月面承载能力的问题提供必要的参考。首先,使用近255 t TJ-1模拟月壤人工制备出13 m×12 m×1.2 m试验用地基,后在试验地基均匀布置6个静力触探测点和2个静载荷试验测点进行测试。针对太沙基承载力计算半经验公式以及规范和国内外学者提出的12个适合中密实砂土静力触探承载力计算的经验公式,对试验结果进行探讨。发现直接运用太沙基提出的半经验公式计算月壤承载力结果明显偏小,而由联合试验小组提出的经验公式 能够用来近似计算月壤地基承载力。计算结果表明,该经验公式在计算承载力时能够与静载荷试验值较好的吻合。     

First record of Biecheleria cincta (Dinophyceae) from Chinese coasts, with morphological and molecular characterization of the strains

The presence of Biecheleria cincta (=Woloszynskia cincta) in the Chinese coasts is reported for the first time. In scanning electron microscope, three to five series of vesicles and an elongated apical vesicle (EAV) were visible in the epicone, and both the hypocone and the cingulum had three series of vesicles each. Thin sections revealed that B. cincta possesses stalked pyrenoids and an unusual eyespot consisting of a stack of cisternae with brick-like materials (type E), thus supporting its transfer from Woloszynskia to Biecheleria. Spiny cysts formed spontaneously in culture, with an encystment rate of around 20%. Both large subunit ribosomal DNA (LSU rDNA) and internal transcribed spacer region (ITS) sequences in 12 strains from the Chinese coasts were determined. Phylogenetic analyses based on LSU rDNA and ITS sequences using Bayesian inference and maximum likelihood revealed two distinct ribotypes (referred to as ribotype A and B) in B. cincta. ITS region pairwise distances within B. cincta ranged from 0.024 to 0.072, suggesting the existence of a complex of cryptic species.     

Remote forcing of Indian Ocean warming on Northwest Pacific during E1 Nino decaying years： a FOAM model approach

This paper attempts to analyze in detail the remote influence of the Indian Ocean Basin warming on the Northwest Pacific （NWP） during the year of decaying E1 Nifio. Observation data and the Fast Ocean- Atmosphere coupled Model 1.5 were used to investigate the triggering conditions under which the remote influence is formed between the positive sea surface temperature （SST） anomaly in the North Indian Ocean and the Anomalous Northwest Pacific anticyclone （ANWPA）. Our research show that it is only when there is a contributory background wind field over the Indian Ocean, i,e., when the Indian Summer Monsoon （ISM） reaches its peak, that the warmer SST anomaly in the North Indian Ocean incites significant easterly wind anomalies in the lower atmosphere of the Indo-West tropical Pacific. This then produces the remote influence on the ANWPA. Therefore, the SST anomaly in the North Indian Ocean might interfere with the prediction of the East Asia Summer Monsoon in the year of decaying E1 Nifio. Both the sustaining effect of local negative SST anomalies in the NWP, and the remote effect of positive SST anomalies in the North Indian Ocean on the ANWPA, should be considered in further research.