海洋流速测量技术研究

我国海洋测量技术最近几年取得了很大的发展。重点介绍数据采集与处理和信息管理，以及测量基础理论与应用研究领域的主要进展情况，并对这一技术未来发展趋势作了展望。海洋流速测量是海洋科学研究的熏要组成部分，海洋流速测量仪不仅可以为海洋科学研究提供重要支持，还在水文水资源研究、防洪预报、水资源管理和国防等多个领域具有广阔的应用前景。时差流速仪是利用超声波在水流的不同方向的传播速度存在差异这一特点来实现的，只要估计出超声波在各个方向的传播时延就可以计算出流速。     

一种基于方向平滑约束优化的多尺度光流算法

提出了一种采用方向平滑约束的多尺度光流算法.该算法在多尺度的拉普拉斯金字塔框架下,利用差值平方和(SSD)区域匹配方法实现对搜索区域内的流速及其协方差矩阵的估计,然后利用方向平滑约束对估计的流速进行传播和优化,方向平滑约束可以有效地抑制对遮挡和运动不连续处的过度平滑.人工和真实图像序列的仿真实验都获得了满意的结果.     

波浪浮标数据处理算法研究

利用数学中的多项式拟合算法,消除了数据处理过程中简单积分产生趋势项而对海浪参数估计带来的间接误差,提高了海态参数反演精度。实例仿真和实际数据测量结果表明,运用此方法处理波浪浮标数据时可以得到更加精准的海浪波高、周期等参数。     

选带细化频谱分析在超声波流量测量中的应用

通过中频调制为基础提取流体速度方向信息,引入选带细化频谱分析技术对解调后多普勒信号进行高精度的频谱估计,该方法主要有三个方面的优点:能判断流速的方向;降低流速测量下限;提高了流速测量的动态响应速度、实时性以及稳定性.在此基础上,以数字信号处理器(DSP)为平台设计了超声流量计,实验分析表明1 024点ZOOM-FFT算法在选定频带范围内与16 384点FFT有相近的分辨率.     

基于频偏应答的ADCP流速现场校准方法研究

针对声学多普勒流速剖面仪(ADCP)现场校准困难的问题,介绍了一种基于频偏应答的ADCP流速现场校准方法。通过声信号应答器,设置回发信号相对于发射信号的频偏实现速度矢量的模拟,并以频率为溯源量,对ADCP发射的信号及应答器回发频偏信号进行频率校准,进而实现ADCP流速参数的现场校准。研制了一套基于频偏应答的ADCP流速现场校准装置,在实验室消声水池条件下,以四波束300kHz ADCP为校准对象,开展了1～2m/s的流速校准实验,进行不确定度分析。结果表明,该装置对流速校准的不确定度达到1％模拟流速＋7mm/s,验证了该校准方法的可行性。     

宽带声学多普勒流速剖面仪回波信号模型分析

宽带声学多普勒流速剖面仪（Broadband Acoustic Doppler Current Profile,BBADCP）通过接收海洋体积混响信号进行频偏估计,体积散射模型的准确性决定了理论仿真的正确性。针对BBADCP的信号模型特点,建立了散射体单元散射叠加效应的海洋体积回波时空特性及散射模型,推导了叠加噪声后散射回波的具体表达式。通过散射回波的离散化,把各参数（幅度、频率、调制）分离开来,单独考虑各参数对测速精度的影响。利用复协方差算法对水流流速进行估计,分析了信噪比、水流流速、紊流效应等因素对BBADCP流速估计的影响,验证了体积散射模型的正确性。     

ADCP流速仪检定拖车驱动方案探讨

近年ADCP流速仪在国内应用不断增多,急需建设可以检定ADCP流速仪的检测平台规范水利行业产品应用。ADCP流速仪检定水槽的长、宽、深等尺寸设计,必须根据ADCP流速仪产品特点进行专门设计。相比以往检定水槽,ADCP水槽的宽度增加很多,相对应的检定拖车的跨度也会增加很多,导致检定拖车的车重增加很多,而大型检定拖车的驱动设计方案是系统设计成败的关键。根据ADCP流速仪检测特点,该文提出基于交流伺服同步电机的ADCP流速仪检定拖车混合动力驱动(4驱/2驱)设计方案:高速段(0.2~6 m/s)采用四轮驱动,低速段(0.01~0.2 m/s)采用2轮驱动,很好地解决工作速度段大跨度下速度准确度控制难题,满足ADCP流速仪不同速度段检定需求。     

相控阵ADCP编码信号相移波束形成

相对于活塞式声学多普勒流速剖面仪,相控阵声学多普勒流速剖面仪的换能器体积大大缩小,并且依托相控阵本身的物理特性,无需进行声速补偿。利用窄带相控阵声学多普勒流速剖面仪系统进行编码信号的发射与接收,从而提高相控阵声学多普勒流速剖面仪的设备性能。首先介绍了相控阵ADCP的波束形成方法,然后分别介绍了相控阵的相移波束形成和时延波束形成原理,对编码信号相移相控波束形成情况下,相控阵发射和接收信号波束开角进行了对比,并对作用距离、测量精度、系统复杂度等系统性能进行了分析。分析结果表明:窄带相控阵声学多普勒流速剖面仪可以进行编码信号的发射和接收,能够提高系统的空间分辨率和测量精度,从而提高相控阵声学多普勒流速剖面仪的性能。     

国内相控阵ADCP技术的开发研究

声学多普勒海流剖面仪（ADCP）是海洋勘测领域的一项高新技术,ADCP的相控阵技术在换能器阵体积重量不增大的条件下进一步提高了测量范围和测速精度。本文着重介绍我们开发相控阵ADCP的情况及实时处理的湖上试验结果。试验表明相控阵ADCP测流原理是可行的,测量精度可达到1cm/s。     

基于互功率谱相位谱的混凝土结构中应力波波速的估计

在应用冲击反射法进行无损估计时，应力波波速测量是一项非常重要的工作。本文研究了时间延迟估计方法中用互功率谱的相位谱进行时间延迟估计的算法，并将其应用到波速估计中，取得了比较满意的结果。     

Optical remote sensing of marine constituents in coastal waters: a feasibility study

Optical remote sensing of ocean color is a well-established technique for inferring ocean properties. However, most retrieval algorithms are based on the assumption that the radiance received by satellite instruments is affected only by the phytoplankton pigment concentration and correlated substances. This assumption works well for open ocean water but becomes questionable for coastal waters. To reduce uncertainties associated with this assumption, we developed a new algorithm for the retrieval of marine constituents in a coastal environment. We assumed that ocean color can be adequately described by a three-component model made up of chlorophyll a, suspended matter, and yellow substance. The simultaneous retrieval of these three marine constituents and of the atmospheric aerosol content was accomplished through an inverse-modeling scheme in which the difference between simulated radiances exiting the atmosphere and radiances measured with a satellite sensor was minimized. Simulated radiances were generated with a comprehensive radiative transfer model that is applicable to the coupled atmosphere-ocean system. The method of simulated annealing was used to minimize the difference between measured and simulated radiances. To evaluate the retrieval algorithm, we used simulated (instead of measured) satellite-received radiances that were generated for specified concentrations of aerosols and marine constituents, and we tested the ability of the algorithm to retrieve assumed concentrations. Our results require experimental validation but show that the retrieval of marine constituents in coastal waters is possible.     

利用海洋卫星HY-1数据反演叶绿素a的浓度

利用去包络线法分析了叶绿素的光谱特征,构造了一种新的指数NDPI（Normalized Difference Pigment Index）反映海洋中的浮游植物。以辽东湾为研究区,通过我国第一颗海洋水色卫星HY-1数据获得NDPI值,再根据实测数据建立了叶绿素a浓度反演模型。和波段比值法及类似SeaWiFS的OCAv4算法比较,NDPI算法优势明显,算法稳定。根据该算法反演整个海区的叶绿素a分布,和前人的现场调查有很好的一致性。结果表明HY-1可用于海洋叶绿素反演,用NDPI算法能获得实时大面积海域叶绿素a浓度。     

Wavelet power spectrum-based autofocusing algorithm for time delayed and integration charge coupled device space camera

A novel autofocusing algorithm using the directional wavelet power spectrum is proposed for time delayed and integration charge coupled device (TDI CCD) space cameras, which overcomes the difficulty of focus measure for the real-time change of imaging scenes. Using the multiresolution and band-pass characteristics of wavelet transform to improve the power spectrum based on fast Fourier transform (FFT), the wavelet power spectrum is less sensitive to the variance of scenes. Moreover, the new focus measure can effectively eliminate the impact of image motion mismatching by the directional selection. We test the proposed method's performance on synthetic images as well as a real ground experiment for one TDI CCD prototype camera, and compare it with the focus measure based on the existing FFT spectrum. The simulation results show that the new focus measure can effectively express the defocused states for the real remote sensing images. The error ratio is only 0.112, while the prevalent algorithm based on the FFT spectrum is as high as 0.4. Compared with the FFT-based method, the proposed algorithm performs at a high reliability in the real imaging experiments, where it reduces the instability from 0.600 to 0.161. Two experimental results demonstrate that the proposed algorithm has the characteristics of good monotonicity, high sensitivity, and accuracy. The new algorithm can satisfy the autofocusing requirements for TDI CCD space cameras.     

Signal-to-noise ratio analysis to estimate ocean wave heights from X-band marine radar image time series

This work analyses the structure of the different contributions to the image spectrum derived by the three-dimensional Fourier decomposition of sea clutter time series measured by ordinary X-band marine radars. The goal of this investigation is to derive a method to estimate the significant wave height of the ocean wave fields imaged by the radar. The proposed method is an extension of a technique developed for the analysis of ocean wave fields by using synthetic aperture radar systems. The basic idea behind this method is that the significant wave height is linearly dependent on the square root of the signal-to-noise ratio, where the signal is assumed as the radar analysis estimation of the wave spectral energy and the noise is computed as the energy due to the sea surface roughness, which is closely related to the speckle of the radar image. The proposed method to estimate wave heights is validated using data sets of sea clutter images measured by a marine radar and significant wave heights derived from measurements taken by a buoy used as reference sensor.     

通用型高频宽带ADCP信号处理系统设计与实现

文章介绍了一种高频采集、数字解调滤波的通用型高频宽带声学多普勒流速剖面仪(Acoustic Doppler Current Profilers,ADCP)信号处理系统的设计和实现过程。该系统以现场可编程逻辑门阵列(Field Programmable Gate Array,FPGA)+数字信号处理器(Digital Signal Processor,DSP)+低功耗单片机(Mixed Signal Processor 430,MSP430)为架构平台,利用三者在信号处理领域的不同优势,采用软硬件协同设计的方式,解决了高频ADCP高采样率、高数据处理能力及低功耗的应用需求,在保证数据处理速度的基础上实现了相位的严格正交,且通过参数化配置实现了多频段、多功能的通用性设计,可适用于不同频段的走航式及自容式ADCP中。经湖上试验验证,该系统测速精度高,性能稳定可靠,达到了预期的设计指标。该系统的软硬件划分方式对其他高频海洋设备的研制具有一定的参考价值。     

Optimization of a semianalytical ocean color model for global-scale applications

Semianalytical (SA) ocean color models have advantages over conventional band ratio algorithms in that multiple ocean properties can be retrieved simultaneously from a single water-leaving radiance spectrum. However, the complexity of SA models has stalled their development, and operational implementation as optimal SA parameter values are hard to determine because of limitations in development data sets and the lack of robust tuning procedures. We present a procedure for optimizing SA ocean color models for global applications. The SA model to be optimized retrieves simultaneous estimates for chlorophyll (Chl) concentration, the absorption coefficient for dissolved and detrital materials [a(cdm)(443)], and the particulate backscatter coefficient [b(bp)(443)] from measurements of the normalized water-leaving radiance spectrum. Parameters for the model are tuned by simulated annealing as the global optimization protocol. We first evaluate the robustness of the tuning method using synthetic data sets, and we then apply the tuning procedure to an in situ data set. With the tuned SA parameters, the accuracy of retrievals found with the globally optimized model (the Garver-Siegel-Maritorena model version 1; hereafter GSM01) is excellent and results are comparable with the current Sea-viewing Wide Field-of-view sensor (SeaWiFS) algorithm for Chl. The advantage of the GSM01 model is that simultaneous retrievals of a(cdm)(443) and b(bp)(443) are made that greatly extend the nature of global applications that can be explored. Current limitations and further developments of the model are discussed.     

声学坐底式波浪仪的上位机设计

声学坐底式波浪仪包括水下测量系统和陆上处理主机,研究了陆上主机的上位机软件设计方法,并重点研究波浪估计算法在上位机软件的实现方法。波浪估计算法计算复杂,在上位机软件开发环境delphi 7下实现困难,文章采用delphi7和matlab 7.0混合编程方法实现上位机中的波浪估计功能,该混合编程方法实现更为简单,开发周期短。通过实测数据的验证,上位机软件与RD公司商用软件WAVESMON的波浪估计结果是一致的,证明了上位机软件的波浪估计结果是准确的,所设计上位机软件可有效满足波浪仪陆上处理系统的波浪处理需求。     

子带锐化互相关算法

本文分析了互谱相关算法在多目标或存在干扰情况下,估计效果不理想的原因,将分频段处理的思想引入到互谱相关算法中,并将各频段的处理结果进行尖锐化和加权处理,提出子带锐化互相关算法,解决了互谱相关算法在多目标或存在干扰的情况下估计效果不理想的问题。通过理论分析,仿真和海试数据的处理证明,算法在多目标,强干扰的情况下仍可很好的估计目标的方位,并且可以同时得到目标的频率信息,根据目标频带的不同还可以分辨相同方位角入射的不同声源。     

Diffuse reflectance of oceanic waters. III. Implication of bidirectionality for the remote-sensing problem

The upwelling radiance field beneath the ocean surface and the emerging radiance field are not generally isotropic. Their bidirectional structure depends on the illumination conditions (the Sun's position in particular) and on the optical properties of the water body. In oceanic case 1 waters, these properties can be related, for each wavelength λ, to the chlorophyll (Chl) concentration. We aim to quantify systematically the variations of spectral radiances that emerge from an ocean with varying Chl when we change the geometric conditions, namely, the zenith-Sun angle, the viewing angle, and the azimuth difference between the solar and observational vertical planes. The consequences of these important variations on the interpretation of marine signals, as detected by a satelliteborne ocean color sensor, are analyzed. In particular, the derivation of radiometric quantities, such as R (λ), the spectral reflectance, or [ L(w)(λ)](N), the normalized water-leaving radiance that is free from directional effects, is examined, as well as the retrieval of Chl. We propose a practical method that is based on the use of precomputed lookup tables to provide values of the f/Q ratio in all the necessary conditions[ f relates (R(λ) to the backscattering and absorption coefficients, whereas Q is the ratio of upwelling irradiance to any upwelling radiance]. The f/Q ratio, besides being dependent on the geometric configuration (the three angles mentioned above), also varies with λ and with the bio-optical state, conveniently depicted by Chl. Because Chl is one of the entries for the lookup table, it has to be derived at the beginning of the process, before the radiometric quantities R(λ) or [L(W)(λ)](N) can be produced. The determination of Chl can be made through an iterative process, computationally fast, using the information at two wavelengths. In this attempt to remove the bidirectional effect, the commonly accepted view relative to the data-processing strategy is somewhat modified, i.e., reversed, as the Chl index becomes a prerequisite parameter that must be identified prior to the derivation of the fundamental radiometric quantities at all wavelengths.