1.7. ALOS PALSAR 产品介绍

1.7.1. ALOS PALSAR 简介

ALOS PALSAR 是先进陆地观测卫星 (Advanced Land Observing Satellite, ALOS) 上搭载的相控阵型L-波段合成孔径雷达 (Phased Array type L-band Synthetic Aperture Radar, PALSAR), 由日本宇宙航空探索局地球观测研究中心研制, 于2006年开始服役, 2011年结束服役.

1.7.2. ALOS PALSAR 平台参数与工作模式

ALOS PALSAR 具有三种工作模式, 分别为: 精细模式, 扫描模式和极化模式, 其具体参数参见文献 [Shimada.2019.Imaging] TABLE 2-3, 现总结如下表 表 1.6 所示.

表 1.6 ALOS PALSAR 精细模式下平台参数

参数

符号

值

单位

平台高度

\(H\)

691500

m

平台速度

\(V_r\)

7172

m/s

距离向天线长度

\(L_r\)

2.9

m

方位向天线长度

\(L_a\)

8.9

m

雷达波长

\(\lambda\)

0.236057

m

雷达载频

\(f_c\)

1.27

GHz

脉冲宽度

\(T_p\)

27.0

\(μs\)

距离向调频率

\(K_r\)

-1.037e+12

Hz/s

距离向带宽

\(B_r\)

28, 14

MHz

距离向采样率

\(F_{rs}\)

32, 16

MHz

距离向采样数

\(N_{r}\)

10344, 5616

方位向调频率

\(K_a\)

2122.96

Hz/s

方位向采样率

\(F_{as}=PRF\)

<2700, 2164.50

Hz

方位向采样数

\(N_{a}\)

不定

多普勒中心频率

\(f_{\eta_c}\)

1257.769

Hz

成像分辨率

\(\Delta_a × \Delta_r\)

\(5 × 5\)

m

幅宽

70km

m

入射角

\(\theta_i\)

约 38.7

\(°\)

斜视角

\(\theta_s\)

0

\(°\)

危险

文献 [Shimada.2019.Imaging] 中表 2-3 中所给速度为波束掠过地面的速度 \(V_g = 6700\), 根据平台高度等参数可以计算出卫星速度 \(V_s=7514\), 从而计算出实际有效速度为 \(V_r=7100\). 在距离徙动校正时用的是 \(V_r\), 若使用 \(V_g\), 则校正失效, 成像模糊. 另外, 该等效速度仅为近似速度, 如对于 IMG-HH-ALPSRP050500980-H1(sl=1el=35345) 数据, 实际取 \(V_r=7172\) 时, 成像效果最好(几乎无需自聚焦); 当有效速度计算不准确时, 可通过自聚焦改善成像效果.

1.7.3. ALOS PALSAR 产品

有关 ALOS PALSAR 的信息可在 这里 和 这里 查看. ALOS PALSAR 有

产品格式说明

数据下载

从 ASF 上可以下载 ALOS PALSAR 系列卫星产品数据,

1.7.4. ALOS PALSAR 数据读取

原始数据读取

与RADARSAT和ERS产品类似, ALOS PALSAR产品数据采用CEOS(参见 CEOS 小节)格式存储数据, ALOS PALSAR产品文件结构描述参考文件 [EarthObservationResearchCenter.2006] (可以从 这里 ), 下面简要介绍原始数据的文件结构及数据提取. 本节以从ASF上下载温哥华地区精细模式下的数据 ALPSRP050500980-L1.0.zip 原始回波数据文件为例进行讲解. 数据的读取可以采用本书开发的Python工具包 iprs, 其中在本书作者开发的 iprs 工具包中, 定义的SAR信号数据映射字典如 代码 1.12 所示.

代码 1.12 ALOS PALSAR Data File Signal Data Record Descriptor Dictionary defined in iprs
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SarDataFileSignalDataRecordALOSPALSAR = {
    'Record sequence number': [(1, 4), '1B4', 0],
    'l-st record sub-type code': [(5, 5), '1B1', 0],
    'Record type code': [(6, 6), '1B1', 0],
    '2-nd record sub-type code': [(7, 7), '1B1', 0],
    '3-rd record sub-type code': [(8, 8), '1B1', 0],
    'Length of this record': [(9, 12), '1B4', 0],
    # PREFIX DATA - GENERAL INFORMATION
    'SAR image data line number': [(13, 16), '1B4', 0],
    'SAR image data record index (indicates the record sequence number of the image line)': [(17, 20), '1B4', 0],
    'Actual count of left-fill pixels': [(21, 24), '1B4', 0],
    'Actual count of data pixels': [(25, 28), '1B4', 0],
    'Actual count of right-fill pixels': [(29, 32), '1B4', 0],
    # PREFIX DATA-SENSOR PARAMETERS
    'Sensor parameters update flag (1=data in this section is an update 0=data is a repeat)': [(33, 36), '1B4', 0],
    'Sensor acquisition year (UT)': [(37, 40), '1B4', 0],
    'Sensor acquisition day of year (UT) ': [(41, 44), '1B4', 0],
    'Sensor acquisition msecs of day (UT)': [(45, 48), '1B4', 0],
    'SAR channel indicator (sequence number in multi-channel SAR data, polarization)': [(49, 50), '1B2', 0],
    'SAR channel code (0 = L, 1 = 5, 2 = C, 3 = X, 4 = KU and 5 = KA channel)': [(51, 52), '1B2', 0],
    'Transmitted polarization': [(53, 54), '1B2', 0],
    'Received polarization': [(55, 56), '1B2', 0],
    'PRF [mHz]': [(57, 60), '1B4', 0],
    'Scan ID for SCAN SAR mode ( 1 - 5 ) except Wide Observation mode = always 0': [(61, 64), '1B4', 0],
    'Onboard Range compressed flag (0 = no/1 = yes) = always 0': [(65, 66), '1B2', 0],
    'Pulse (chirp) type designator (0 = "LINEARbFMbCHIRPb",1 = "PHASEbMODULATORS") = always 0': [(67, 68), '1B2', 0],
    'Chirp length (nano-secs)': [(69, 72), '1B4', 0],
    'Chirp constant coefficient (Hz) (nominal value)': [(73, 76), '1B4', 0],
    'Chirp linear coefficient (Hz/usec) (nominal value)': [(77, 80), '1B4', 0],
    'Chirp quadratic coefficient (Hz/Wsec,)': [(81, 84), '1B4', 0],
    'spare Always blank(0) filled1': [(85, 88), '1B4', 0],
    'spare Always blank(0) filled2': [(89, 92), '1B4', 0],
    'Receiver gain (dB) nominal value': [(93, 96), '1B4', 0],
    'Nought line flag (0 = no(Right Line)/1 = yes(Loss Line))': [(97, 100), '1B4', 0],
    'Electronic antenna squint angle (millionths of degrees)= always blank (0) filled': [(101, 104), '1B4', 0],
    'Antenna mechanical elevation angle from nadir (millionths of degrees)= always blank (0) filled': [(105, 108), '1B4', 0],
    'Electronic antenna squint angle (millionths of degrees)': [(109, 112), '1B4', 0],
    'Mechanical antenna squint angle (millionths of degrees)= always blank (0) filled': [(113, 116), '1B4', 0],
    'Slant range to 1st data sample (m)': [(117, 120), '1B4', 0],
    'Data record window position (i.e.. sample delay) (nano-secs)': [(121, 124), '1B4', 0],
    'spare Always blank(0) filled3': [(125, 128), '1B4', 0],
    # PREFIX DATA-PLATFORM REFERENCE INFORMATION
    'Platform information': [(129, 192), '1B64', 0],
    # PREFIX DATA - SENSOR/FACILITY SPECIFIC, AUXILIARY DATA
    'Always blank (0) filled1': [(193, 284), '1B92', 0],
    'Counter of PALSAR frame': [(285, 288), '1B4', 0],
    'PALSAR auxiliary data': [(289, 388), '1B100', 0],
    'Always blank (0) filled2': [(389, 412), '1B24', 0],
    # SAR RAW SIGNAL DATA
    'Raw Data': [(413, 414), '2B1', 0]  # [I, Q]
}

使用 iprs 读取的文件 ALPSRP050500980-L1.0/IMG-HH-ALPSRP050500980-H1.0__A 的记录信息见 代码 1.13 所示.

代码 1.13 Signal data record of file IMG-HH-ALPSRP050500980-H1.0__A
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Record sequence number [(1, 4), '1B4', [2]]
l-st record sub-type code [(5, 5), '1B1', [50]]
Record type code [(6, 6), '1B1', [10]]
2-nd record sub-type code [(7, 7), '1B1', [18]]
3-rd record sub-type code [(8, 8), '1B1', [20]]
Length of this record [(9, 12), '1B4', [21100]]
SAR image data line number [(13, 16), '1B4', [1]]
SAR image data record index (indicates the record sequence number of the image line) [(17, 20), '1B4', [1]]
Actual count of left-fill pixels [(21, 24), '1B4', [0]]
Actual count of data pixels [(25, 28), '1B4', [10304]]
Actual count of right-fill pixels [(29, 32), '1B4', [40]]
Sensor parameters update flag (1=data in this section is an update 0=data is a repeat) [(33, 36), '1B4', [1]]
Sensor acquisition year (UT) [(37, 40), '1B4', [2007]]
Sensor acquisition day of year (UT)  [(41, 44), '1B4', [5]]
Sensor acquisition msecs of day (UT) [(45, 48), '1B4', [23518945]]
SAR channel indicator (sequence number in multi-channel SAR data, polarization) [(49, 50), '1B2', [1]]
SAR channel code (0 = L, 1 = 5, 2 = C, 3 = X, 4 = KU and 5 = KA channel) [(51, 52), '1B2', [0]]
Transmitted polarization [(53, 54), '1B2', [0]]
Received polarization [(55, 56), '1B2', [0]]
PRF [mHz] [(57, 60), '1B4', [2155172]]
Scan ID for SCAN SAR mode ( 1 - 5 ) except Wide Observation mode = always 0 [(61, 64), '1B4', [0]]
Onboard Range compressed flag (0 = no/1 = yes) = always 0 [(65, 66), '1B2', [0]]
Pulse (chirp) type designator (0 = "LINEARbFMbCHIRPb",1 = "PHASEbMODULATORS") = always 0 [(67, 68), '1B2', [0]]
Chirp length (nano-secs) [(69, 72), '1B4', [27000]]
Chirp constant coefficient (Hz) (nominal value) [(73, 76), '1B4', [0]]
Chirp linear coefficient (Hz/usec) (nominal value) [(77, 80), '1B4', [1232940752]]
Chirp quadratic coefficient (Hz/Wsec,) [(81, 84), '1B4', [0]]
spare Always blank(0) filled1 [(85, 88), '1B4', [0]]
spare Always blank(0) filled2 [(89, 92), '1B4', [0]]
Receiver gain (dB) nominal value [(93, 96), '1B4', [24]]
Nought line flag (0 = no(Right Line)/1 = yes(Loss Line)) [(97, 100), '1B4', [0]]
Electronic antenna squint angle (millionths of degrees)= always blank (0) filled [(101, 104), '1B4', [0]]
Antenna mechanical elevation angle from nadir (millionths of degrees)= always blank (0) filled [(105, 108), '1B4', [0]]
Electronic antenna squint angle (millionths of degrees) [(109, 112), '1B4', [0]]
Mechanical antenna squint angle (millionths of degrees)= always blank (0) filled [(113, 116), '1B4', [0]]
Slant range to 1st data sample (m) [(117, 120), '1B4', [850614]]
Data record window position (i.e.. sample delay) (nano-secs) [(121, 124), '1B4', [106684]]
spare Always blank(0) filled3 [(125, 128), '1B4', [0]]
Platform information [(129, 192), '1B64', [0]]
Always blank (0) filled1 [(193, 284), '1B92', [0]]
Counter of PALSAR frame [(285, 288), '1B4', [752607]]
PALSAR auxiliary data [(289, 388), '1B100', [263129968205480992023280643085359307138574792461797720331625355555552187227123992216825909049138802819234429379486614773355864556286127397455858336090606728798761926618935967276621537709384105360275969343101570371356070712498890271222661120]]
Always blank (0) filled2 [(389, 412), '1B24', [0]]
Raw Data [(413, 414), '2B1', [29, 20]]

可见该文件中共包含, 脉冲重复频率为 \(2155.172Hz\), 脉冲宽度为 \(27μs\), 第一个样本斜距为 \(850614m\).

警告

需要注意的是, IQ通道数据在写入前被施加了直流偏置, 它们的值可以从 SAR Leader File Descriptor Record 记录中读取, 映射格式如下, 即为16位浮点数, 读取的本小节数据中的直流偏置的值均为15.5:

Number

Bytes

Format

Description

66

819 － 834

F16.7

DC Bias for I-component

67

835 － 850

F16.7

DC Bias for Q-componen

1.7.5. ALOS PALSAR 数据成像

对上一小节中读取的温哥华地区的数据, 采用调频变标方法成像 (调频变标成像) 小节. 由于原始数据较大, 且方位向采样点数一般远大于距离向采样点数, 故这里仅给出降采样的成像结果图以及多视处理后的结果图.