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Development of Methods for Measuring Ocean Wavelengths by Radar Altimeters

雷达高度计测量海洋波长方法的发展

基本信息

批准号：
04555087
负责人：
YOSHITOMI Kuniaki
金额：
$ 4.48万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1994
项目状态：
已结题

项目摘要

To determine ocean wavelengths by data processing, we need to know both of ocean waves and raw scattering data from ocean waves. Assuming that ocean waves are characterized by the Pierson-Moskowitz spectrum, we approximate the spectrum by using line spectra. Once defining the spectra and giving the significant waveheight H_<1/3> and wavelength L_<1/3> of the ocean wave, we can express the ocean wave as the sum of some aperiodic functions. By calculating electromagnetic wave pulses scattered from the approximate ocean wave, we can obtain the pulse train received with altimeters and make sure that the train has the first and second statistics similar to those of SKYLAB and SEASAT.The pulse train has therefore been simulated by computer for each ocean wave with the parameters of H_<1/3> and L_<1/3> ; and we have the database of the pulse train of SKYLAB and SEASAT for ocean waves of H_<1/3>=2.56-4.56m and L_<1/3>=25.6-91.4m. We now try the extension of the database to other altimeters and ocean waves.Using the database, the mean return pulse-waveforms have been obtainde for variable L_<1/3> and constant H_<1/3>, and show that if there is no noise, the L_<1/3> may be determined within 5m accuracy because of the fluctuation of received pulse power from the mean. If noise is added to the fluctuation and the standard deviation of received power is assumed to be 3dB,the resolution of L_<1/3> is reduced to 15m for both altimeters of SKYLAB and SEASAT.Development of the method based on pulse correlation is a forthcoming study.When ocean surfaces are assumed to be a homogeneous Gaussian random field, we can calculate the mean return pulse-waveform directly by using the probability density of random surfaces through the law of large numbers. This result makes clear the relation of the mean pulse waveforms and random surfaces.

为了通过数据处理确定海洋波长，我们需要知道海浪和海浪的原始散射数据。假设海浪的特征是皮尔逊-莫斯科维茨谱，我们近似的频谱使用线频谱。一旦定义了海浪的谱，给出了海浪的有效波高H <1/3>和波长L <1/3>，我们就可以把海浪表示成若干非周期函数的和。通过计算近似海浪散射的电磁波脉冲，得到高度计接收的脉冲序列，并保证该序列具有与SKYLAB和SEASAT相似的第一、第二统计量，从而对每种海浪，以H_（1/3）和L_（1/3）为参数，用计算机模拟了脉冲序列;并建立了H_（1/3）=2.56-4.56m和L_（1/3）=25.6-91.4m海浪的SKYLAB和SEASAT脉冲序列数据库。本文尝试将该数据库推广到其它的高度计和海浪，并利用该数据库得到了L_（1/3）和H_（1/3）的平均回波波形，表明在无噪声条件下，由于接收脉冲功率相对于平均回波波形的波动，L_（1/3）的测量精度可达5米。如果在起伏中加入噪声，并假定接收功率的标准偏差为3dB，SKYLAB和SEASAT高度计的L_（1/3）分辨率都降到15 m。利用随机面的概率密度，通过大数定律，可以直接计算平均回波脉冲波形。这一结果明确了平均脉冲波形与随机表面的关系。