1.时间转换
用matlab从jason-2的nc文件中读出的时间（time_20hz）单位，从数据说明中可以看出是以秒为单位，从2000-01-01 00:00:00.0开始：
time_20hz:
---------------------------
time field
[tai_utc_difference] is the difference between TAI and UTC reference time (seconds) for the first measurement of the data set. [leap_second] is the UTC time at which a leap second occurs in the data set, if any. After this UTC time, the [tai_utc_difference] is increased by 1 second
Dimensions: time=3204 meas_ind=20
- _FillValue: 18446744073709552000.000000
- calendar: gregorian
- leap_second: 0000-00-00 00:00:00
- standard_name: time
- tai_utc_difference: -33.000000
- units: seconds since 2000-01-01 00:00:00.0如果要还原成日期怎么办？
简单的做法是，直接在excel中处理一下就可以了。
| time_20hz （列号：L） | 天 (列号：M) | (列号：N) | (列号：O) |
|---|---|---|---|
| 269091209.6 | =L2/3600/24=3114.481592 | 2000/1/1 | =M2+N2=2008/7/11 11:33 |
2.作图时横坐标时间刻度问题
先看看这个：matlab作时间相关的图
以jason2为例，jason读取的时间是从2000-01-01 00:00:00.0开始的秒数，所以不能直接将其转换为天数，需要将2000-01-01 00:00:00.0转换为天数后与其相加，再作相应的图，大概用法如下：
time1 = datenum('2000/1/1') + time0;