|||
int2 <- function (v) { floor(v); }
dt_ext <- function(y, jsd){ #二次曲线外推,用于数值外插
dy = (y - 1820)/100;
return (-20 + jsd * dy * dy);
}
dt_calc <- function(y){ #传入年, 返回世界时UT与原子时(力学时 TD)之差, ΔT = TD - UT
y0 = dt_at[length(dt_at) - 1]; #表中最后一年
t0 = dt_at[length(dt_at)]; #表中最后一年的 deltatT
if(y >= y0){
jsd = 31; # sjd是y1年之后的加速度估计。
# 瑞士星历表jsd=31, NASA网站jsd=32, skmap的jsd=29
if(y > y0 + 100){
return(dt_ext(y, jsd))
};
v = dt_ext(y, jsd); #二次曲线外推
dv = dt_ext(y0, jsd) - t0; # ye年的二次外推与te的差
return (v - dv*(y0 + 100 - y)/100);
}
d = dt_at;
for(i in seq(1, length(d), by = 5) ) {
if(y < d[i + 5]) break; # 判断年所在的区间
}
t1 = (y - d[i]) / (d[i + 5] - d[i]) * 10 #### 三次插值, 保证精确性
t2 = t1 * t1
t3 = t2 * t1;
res <- d[i + 1] +d[i + 2] * t1 +d[i + 3] * t2 +d[i + 4] * t3
return( res );
}
# TD - UT1 插值表
dt_at = c(
-4000, 108371.7, -13036.80, 392.000, 0.0000,
-500, 17201.0, -627.82, 16.170, -0.3413,
-150, 12200.6, -346.41, 5.403, -0.1593,
150, 9113.8, -328.13, -1.647, 0.0377,
500, 5707.5, -391.41, 0.915, 0.3145,
900, 2203.4, -283.45, 13.034, -0.1778,
1300, 490.1, -57.35, 2.085, -0.0072,
1600, 120.0, -9.81, -1.532, 0.1403,
1700, 10.2, -0.91, 0.510, -0.0370,
1800, 13.4, -0.72, 0.202, -0.0193,
1830, 7.8, -1.81, 0.416, -0.0247,
1860, 8.3, -0.13, -0.406, 0.0292,
1880, -5.4, 0.32, -0.183, 0.0173,
1900, -2.3, 2.06, 0.169, -0.0135,
1920, 21.2, 1.69, -0.304, 0.0167,
1940, 24.2, 1.22, -0.064, 0.0031,
1960, 33.2, 0.51, 0.231, -0.0109,
1980, 51.0, 1.29, -0.026, 0.0032,
2000, 63.87, 0.1, 0, 0,
2005, 64.7, 0.4, 0, 0, #一次项记为x, 则 10x=0.4秒/年*(2015-2005), 解得x=0.4
2015, 69
);
## 输入年, 计算delta T
dt_calc(1800)
dt_calc(1960)
dt_calc(1965)
dt_calc(2012)
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