基于HY-2卫星高度计机载校飞数据的有效波高信息提取及初步分析

利用HY-2卫星雷达高度计校飞数据,开展了有效波高信息提取及精度比对研究。首先对其进行波形筛选、1s平均和去噪,然后基于Hayne海面回波模型进行波形拟合,提取出波高均方根并得到有效波高,并与浮标和同轨迹的Jason-1卫星高度计有效波高进行了比较。结果表明,本次校飞其高度计测波精度存在系统偏差,初步分析可能是其数据未经仪器校正等原因导致。     

中国近岸海域高度计JASON-1测量数据的波形重构算法研究

卫星雷达高度计的测量数据目前已被广泛应用于各个领域,但高度计在近海的测量数据却一直不可用,一方面是因为高度计在近岸海域的回波波形测量受陆地回波的影响,另一方面是因为一些校正量对近海不准确,如大气湿对流层校正、海洋潮汐校正以及大气高频因数校正等。通过对高度计在近海测量的回波波形进行重构处理,可以缩短近海数据不可用的距离,提高数据的数量和质量。以我国海域及邻近海域(14°~45°N,105°~130°E)为研究区域,采用四种波形重构算法(海洋算法、重力中心偏离算法、冰层算法二和阈值算法)对JASON-1高度计1 a共31个周期的测量波形重新进行了计算,比较了轨道交叉点处升轨和降轨的海面高度异常值以及海面高度值与验潮站的实测水位,结果表明重力中心偏离法比其他三种算法更适合我国近海的测高波形重构:计算结果精度最高,有效数目最多。     

印度尼西亚近海潮汐潮流的数值模拟

利用FVCOM海洋数值模式计算了印尼近海的M2,S2,K1,O1分潮的分布,计算范围从20°S～20°N,90°～150°E,计算网格分辨率在印尼海域岛屿平均为1/12度,在大陆边界平均为1/5度,在开边界平均为1/2度.计算结果与104个TOPEX/Poseidon卫星高度计交叉点数据和79个验潮站数据进行比较,符合良好;与高度计交叉点比较,M2分潮振幅的均方根差为6 cm,迟角为7°;S2分潮的振幅偏差为3 cm,迟角偏差为8°;K1分潮振幅的偏差为6 cm,迟角偏差为10°;O1分潮振幅偏差为3 cm,迟角偏差为10°.根据计算结果给出了4个分潮的潮汐、潮流、潮余流和潮能通量密度分布图.     

基于现场的卫星高度计定标技术研究

卫星高度计数据的广泛应用离不开准确的现场定标检验工作。在青岛千里岩海上试验的基础上,分别使用GNSS浮标法和潮汐法对Jason-2卫星高度计进行了定标。其结果显示:(1)GNSS浮标法使用高精度GNSS数据处理软件GAMIT/GLOBK及其Track模块,对GNSS浮标数据进行高精度处理,得到的高度计偏差为+195.7 mm,该方法可以消除大地水准面和潮位的影响,精度较高;(2)在潮汐法中,利用FVCOM海洋模式模拟了千里岩周边的潮位,并对比了GNSS浮标测得的潮位结果,二者的标准偏差达到了1.3 cm,满足高度计定标的要求,结合EGM2008计算的大地水准面和平均动力地形,得到的高度计偏差结果为+150.9±35.1 mm,该方法受限较多,精度较差。但两种方法最终得到的高度计偏差与国际其他定标场的结果相当。     

TOPEX/POSEIDON高度计资料用于中国近海M2分潮的同化反演

以整个中国海为研究区域,把开边界取在TOPEX/POSEIDON(T/P)高度计资料数据点,利用趋近插值法将高度计资料同化到二维非线性潮汐数值模式中,反演了中国近海M2分潮的分布.计算结果与60个验潮站资料比较,符合良好振幅平均绝对偏差为6.7cm,相角偏差为5.5°,均方根偏差为12.6cm.根据计算结果给出东中国海和南海M2分潮的同潮图,与相关文献比较,符合良好.研究结果表明,以本方法利用T/P资料来反演中国海潮汐是可行的.     

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。     

JASON-2卫星高度计波高数据同化对中国渤黄海海浪数值预报影响研究

利用原国家海洋局北海分局浮标所测有效波高数据对Jason-2卫星高度计所测有效波高数据进行验证,采用50km空间窗和0.5h时间窗,得到219个时空配准点。对配准结果进行统计分析表明,Jason-2卫星高度计测得有效波高与浮标测量结果存在-0.277m的偏差,均方根误差为0.372m。利用最小二乘回归(OLR)对Jason-2有效波高数据进行校正可使其均方根误差下降至0.247m,减少34.5%。基于第三代海浪模式WAVEWATCH III对Jason-2有效波高数据进行最优插值同化试验,其中背景误差相关函数取为指数形式,相关距离尺度选为500km。与浮标观测数据比较表明,同化后模式有效波高均方根误差比未同化时减少11.56%,,能够有效地改善模式精度。以此为初始场进行为期3d的数值预报实验。与未同化实验相比,卫星高度计有效波高数据同化对模式0～72 h预报有不同程度的改善,改善程度随预报时间的增加而降低。     

利用T/P 卫星高度计资料调和分析南海潮汐信息

利用j,v模型调和分析1992～2002年共10 a的TOPEX/Poseidon(T/P)海面高度距平资料,提取了南海K1,O1,P1,Q1,M2,S2,N2和K2等8个主要分潮的潮汐调和常数。分析比较了卫星上下行轨道的19个交叉点的振幅和迟角,其中M2,S2,K1和O1的平均向量均方根偏差分别是1.5,1.1,2.5和1.4 cm;将交叉点的调和常数与TPXO7.2模式的结果进行了比较,结果表明M2,S2,K1和O1分潮振幅的绝对平均误差均小于3 cm,迟角的最大绝对平均误差为7.8°。选取了与卫星轨道较近的8个验潮站,对验潮站的实测数据调和常数和本文所得调和常数进行了比较,结果显示K1分潮的向量均方根偏差为4.7 cm,M2分潮的向量均方根偏差为3.7 cm。论文结果表明利用j,v模型调和分析方法对南海海域卫星高度计资料进行潮汐信息提取是可靠的,并可为局部重力场的研究提供海洋潮汐改正数据,有一定的参考价值。     

高度计大气温度校正的方法及其应用分析

大气中水汽造成的路径延迟的测量误差是目前卫星高度计存在误差的重要原因,这种误差对高度计算数据的分析应用产生很大的影响。介绍了高度计大气工校正的２种方法,并对它们的结果做了比较。最后分析了大气温度校正对高度计数据应用的影响。     

基于我国沿海GPS站点数据提取天顶水汽含量的方法对比研究

基于我国沿海地基GPS数据与海洋站气象数据,利用相关干对流层模型、湿对流层模型等,提取了东海沿海北茭、崇武2个GPS站天顶水汽含量,并与MODIS水汽产品数据做比对分析。结果表明:Elgered干对流层模型与Beivs湿对流层模型组合而成的提取方法较好,其平均偏差小于0.50 mm、均方根误差小于5.10 mm,其结果检验了沿海GPS提取水汽含量的可行性与有效性。     

Preliminary calibration results of the HY-2B altimeter’s SSH at China’s Wanshan calibration site

Satellite altimeter needs to be calibrated to evaluate the accuracy of sea surface height data. The dedicated altimeter calibration field needs to establish a special calibration strategy and needs to evaluate its calibration ability. This paper describes absolute calibration of HY-2B altimeter SSH using the GPS calibration method at the newly Wanshan calibration site, located in the Wanshan Islands, China. There are two HY-2B altimeter passes across the Wanshan calibration site. Pass No. 362 is descending and the ground track passes the east of Dan’gan Island. Pass No. 375 is ascending and crosses the Zhiwan Island. The GPS data processing strategy of Wanshan calibration site was established and the accuracy of GPS calibration method of Wanshan calibration site was evaluated. Meanwhile, the processing strategies of the HY-2B altimeter for the Wanshan calibration site were established, and a dedicated geoid model data were used to benefit the calibration accuracy. The time-averaged HY-2B altimeter bias was approximately 2.12 cm with a standard deviation of 2.08 cm. The performance of the HY-2B correction microwave radiometer was also evaluated in terms of the wet troposphere path delay and showed a mean difference ?0.2 cm with a 1.4 cm standard deviation with respect to the in situ GPS radiosonde.     

HY-2A卫星雷达高度计海面高度测量分析与评估

HY-2A卫星是我国首颗自主海洋动力环境卫星,已连续运行6年多。卫星上搭载的主载荷雷达高度计能够实现全天候、全天时全球海面高度、有效波高和海面风速的观测,这些观测数据已经广泛用于海洋防灾减灾、资源开发和海上安全等领域。为了全面了解HY-2A卫星雷达高度计多年来的整体观测性能,本文选取了2012年10月26日至2017年8月27日间的全部观测数据IGDR产品进行综合评价。通过自交叉和与Jason-2互交叉两种手段对HY-2A卫星雷达高度计测高能力进行评估。计算HY-2A升降轨自交叉点的测高不符值,发现HY-2A卫星雷达高度计在近全球海域内、升降轨高度异常差小于30cm的限制条件下,平均绝对高度误差为5.81cm,高度异常标准差为7.76cm;限制观测区域为南北纬60°范围内、海面高度异常升降轨交叉点处的差小于10cm的情况下,平均绝对误差可达3.95cm,海面高度异常标准差达4.76cm。通过和Jason-2卫星的互交叉,发现在南北纬66°范围内,交叉点高度异常差小于30cm的情况下,HY-2A和Jason-2的海面高度异常平均绝对误差为5.86cm,标准差为7.52cm,如果在该海域内将海面高度异常差限制在10cm内,平均绝对误差和标准差分别达到4.19cm和4.98cm。HY-2A卫星雷达高度计已经达到国际同类卫星雷达高度计测高水平,可以满足海洋科学研究、海洋环流反演等的需求。     

Evaluation of tidal error in altimetry data in the Asian marginal seas

The magnitude and geographical distribution of the error in the Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO) altimetry data associated with tidal correction around Asian marginal seas has been revealed. The errors were evaluated by harmonic analysis of the AVISO corrected sea surface heights data (CorSSH). Errors of more than 15 cm of tidal correction were recognized in the western and northern parts of the Yellow Sea, Celebes Sea, Kuril Islands, and the northwestern part of the Okhotsk Sea. It was found that the CorSSH and sea level anomaly (SLA) data downloaded from the AVISO are not available for direct use in those marginal seas. To reduce the tidal correction error, the harmonic constants calculated from the latest tide model and regional tide model were applied as the tidal correction of the Altimetry data. The tidal errors in the Yellow Sea and the northwestern part of the Okhotsk Sea were reduced by approximately 20 cm and 10 cm, respectively. Root mean square differences between the harmonic constants derived from tide models and those derived from altimetry data were calculated. The root mean square differences were large in the Yellow and the Okhotsk Seas. Root sum squares for four principal tidal constituents in the Yellow and East China Seas and Okhotsk Sea were 7.72 cm and 8.36 cm, respectively.     

First Calibration Results for the SARAL/AltiKa Altimetric Mission Using the Gavdos Permanent Facilities

This work presents the first calibration results for the SARAL/AltiKa altimetric mission using the Gavdos permanent calibration facilities. The results cover one year of altimetric observations from April 2013 to March 2014 and include 11 calibration values for the altimeter bias. The reference ascending orbit No. 571 of SARAL/AltiKa has been used for this altimeter assessment. This satellite pass is coming from south and nears Gavdos, where it finally passes through its west coastal tip, only 6 km off the main calibration location. The selected calibration regions in the south sea of Gavdos range from about 8 km to 20 km south off the point of closest approach. Several reference surfaces have been chosen for this altimeter evaluation based on gravimetric, but detailed regional geoid, as well as combination of it with other altimetric models.

Based on these observations and the gravimetric geoid model, the altimeter bias for the SARAL/AltiKa is determined as mean value of ?46mm ±10mm, and a median of ?42 mm ±10 mm, using GDR-T data at 40 Hz rate. A preliminary cross-over analysis of the sea surface heights at a location south of Gavdos showed that SARAL/AltiKa measure less than Jason-2 by 4.6 cm. These bias values are consistent with those provided by Corsica, Harvest, and Karavatti Cal/Val sites. The wet troposphere and the ionosphere delay values of satellite altimetric measurements are also compared against in-situ observations (?5 mm difference in wet troposphere and almost the same for the ionosphere) determined by a local array of permanent GNSS receivers, and meteorological sensors.     

神舟四号高度计波形数据预处理和信息提取

神舟四号(SZ-4)高度计在国内首次提供了星载雷达高度计回波波形数据.本文中作者分析了SZ-4高度计回波波形的特点,完成波形数据的预处理,并在此基础上完成初步的信息提取.在数据预处理方面,通过SZ-4高度计水陆边界处波形的特点,提出了波形最大幅度控制的方法,筛选回波波形.在波形归一化处理过程中,发现SZ-4高度计波形中存在双峰现象,并指出第二个峰为异常波形区.在波形信息提取方面,利用波形重新跟踪得到的半功率点计算出SZ-4高度计高度跟踪补偿误差,并根据高度计天线指向角和回波波形下降沿斜率之间的关系,从波形后沿提取天线指向角信息.分析结果表明,SZ-4高度计天线指向比较平稳,而跟踪补偿由于变化较大,在计算海面高度时,应作为一项误差源被考虑到.     

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.     

Improvement of Sea Surface Height Measurements of HY-2A Satellite Altimeter Using Jason-2

Abstract

HY-2A, which was launched on 16 August 2011, is the Chinese first microwave ocean dynamics environment satellite. Analyses of HY-2A daily sea-level anomaly data and HY-2A–Jason-2 (H-J) dual crossover sea-level anomaly differences show that HY-2A has measurement differences that mainly refer to an orbit error. H-J crossover differences and HY-2A–HY-2A (H-H) crossover differences give an estimate of the HY-2A orbit error. Smoothing cubic-spline functions are then used to obtain a continuous estimation of the HY-2A orbit error over time. On the basis of the simultaneous global minimization of H-J dual crossover differences and H-H crossover differences, the HY-2A observation error is efficiently reduced and height measurement data that are more precise are obtained. Specifically, the range bias/trend of the HY-2A altimeter is removed effectively and the root mean square of H-J crossover sea-level anomaly differences decrease from above 60?cm to 5.64?cm, and the standard deviation of H-J crossover differences decreases from 6.68 to 5.64?cm. Furthermore, the rms and standard deviations of H-H crossover differences both decrease from 7.46 to 6.55?cm. The results show that HY-2A after correction has a measurement accuracy and precision that are comparable to those of Jason-2.     

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.     

台湾海峡海表气溶胶干沉降通量研究

在已改进的Williams模型中,应用GW03海表动力学粗糙度参数化方案,考虑波浪对干沉降速率的影响,结合卫星资料和再分析资料,计算了台湾海峡海表气溶胶干沉降速率,并利用2006～2007年走航观测结果计算了台湾海峡总悬浮颗粒物的入海通量.其结果表明：台湾海峡海表气溶胶干沉降速率及总悬浮颗粒物干沉降通量具有明显的时空变化特征.台湾海峡海表气溶胶干沉降速率范围为5.83～6.17 cm/s,平均值为6.00 cm/s.其中冬季气溶胶干沉降速率最大,平均值为6.08 cm/s;夏季气溶胶干沉降速率最小,平均值为5.85 cm/s.台湾海峡气溶胶总悬浮颗粒物的干沉降通量也呈现出冬季的高[均值为7.31μg/（m2.s）],夏季的低[均值为2.23μg/（m2.s）]的特征.从空间分布上看,台湾海峡海表气溶胶干沉降速率出现1个高值中心,位于台湾海峡北部海域.总悬浮颗粒物干沉降通量出现2个高值中心和1个低值中心,分别位于台湾海峡北部海域、汕头至厦门海域和南海中北部海域.