我试图了解如何使用谐波常数创建潮汐预测表.
我使用了Bridgeport的谐波常数(http://tidesandcurrents.noaa.gov/data_menu.shtml?stn=8467150%20Bridgeport,%20CT&type=Harmonic%20Constituents)
并使用此python脚本总结了潮汐组件 -
import math
import time
tidalepoch = 0
epoch = time.mktime(time.gmtime()) - tidalepoch
f = open('bridgeport.txt', 'r')
M_PI = 3.14159
lines = f.readlines()
t = epoch - 24 * 3600
i = -24
while t < epoch:
height = 0
for line in lines:
x = line.split()
A = float(x[2]) # amplitude
B = float(x[3]) # phase
B *= M_PI / 180.0
C = float(x[4]) # speed
C *= M_PI / 648000
# h = R cost (wt - phi)
height += A * math.cos(C * t - B)
print str(i) + " " + str(height + 3.61999)
i += 1
t += 3600
每天为"今天"打印一个高度.由此产生的高度大约在我预期的范围内,-0.5到7.5英尺,但是对于日期不正确.
我是在正确的轨道上吗？我如何确定潮汐时代？在维基百科的Doodsen示例中(http://en.wikipedia.org/wiki/Arthur_Thomas_Doodson),他们使用0来获得1991年9月1日的结果.但是它们的谐波值与当前发布的谐波值不同,并且该日期确实如此.似乎不适合我.
这是我的bridgeport.txt文件的内容 -
1 M2 3.251 109.6 28.9841042
2 S2 0.515 135.9 30.0000000
3 N2 0.656 87.6 28.4397295
4 K1 0.318 191.6 15.0410686
5 M4 0.039 127.4 57.9682084
6 O1 0.210 219.5 13.9430356
7 M6 0.044 353.9 86.9523127
8 MK3 0.023 198.8 44.0251729
9 S4 0.000 0.0 60.0000000
10 MN4 0.024 97.2 57.4238337
11 NU2 0.148 89.8 28.5125831
12 S6 0.000 0.0 90.0000000
13 MU2 0.000 0.0 27.9682084
14 2N2 0.077 65.6 27.8953548
15 OO1 0.017 228.7 16.1391017
16 LAM2 0.068 131.1 29.4556253
17 S1 0.031 175.5 15.0000000
18 M1 0.024 264.4 14.4966939
19 J1 0.021 237.0 15.5854433
20 MM 0.000 0.0 0.5443747
21 SSA 0.072 61.2 0.0821373
22 SA 0.207 132.0 0.0410686
23 MSF 0.000 0.0 1.0158958
24 MF 0.000 0.0 1.0980331
25 RHO 0.015 258.1 13.4715145
26 Q1 0.059 205.7 13.3986609
27 T2 0.054 106.4 29.9589333
28 R2 0.004 136.9 30.0410667
29 2Q1 0.014 238.8 12.8542862
30 P1 0.098 204.1 14.9589314
31 2SM2 0.000 0.0 31.0158958
32 M3 0.012 200.1 43.4761563
33 L2 0.162 134.1 29.5284789
34 2MK3 0.015 203.7 42.9271398
35 K2 0.150 134.7 30.0821373
36 M8 0.000 0.0 115.9364166
37 MS4 0.000 0.0 58.9841042
小智 4
如果您使用 C，一种方法是使用 libTCD http://www.flaterco.com/xtide/libtcd.html来存储组成数据，这为访问数据提供了一个良好的框架。
要进行计算，您需要将纪元调整为当年的开始。该代码使用 libTCD 中的函数，并且基于 xTide 中使用的算法。
TIDE_RECORD record;
int readStatus = read_tide_record(self.stationID, &record);
int epochStartSeconds = staringSecondForYear(year);
for (unsigned constituentNumber=0; constituentNumber<constituentCount; constituentNumber++) {
float constituentAmplitude = record.amplitude[constituentNumber];
float nodeFactor = get_node_factor(constituentNumber, year);
amplitudes[constituentNumber] = constituentAmplitude * nodeFactor;
float constituentEpoch = deg2rad(-record.epoch[constituentNumber]);
float equilibrium = deg2rad(get_equilibrium(constituentNumber, year));
phases[constituentNumber] = constituentEpoch + equilibrium;
}
然后计算自年初以来的潮汐偏移量：
- (float)getHeightForTimeSince1970:(long)date {
//calculate the time to use for this calculation
int secondsSinceEpoch = date - epochStartSeconds;
float height = 0;
for(int i = 0; i < constituentCount; i++) {
float degreesPerHour = get_speed(i);
float radiansPerSecond = degreesPerHour * M_PI / 648000.0;
height += amplitudes[i] * cos(radiansPerSecond * secondsSinceEpoch + phases[i]);
}
height += record.datum_offset;
return height;
}