# 寻找马航MH370进展 06/18/2014更新

——————————————————————————————————————————

06:36 6/19/2014

"While there remain a number of uncertainties and some disagreements as to the interpretation of aspects of the data, our best estimates of a location of the aircraft (is) near 36.02 South 88.57 East," according to the statement, which was approved by 10 named experts.

——————————————————————————————————————————

21:06 6/18/2014

CNN：Outside group tells governments where to search for Flight 370

A group of independent experts -- who prodded authorities to release satellite data on Malaysia Airlines Flight 370 -- says it thinks it knows the approximate location of the missing aircraft.
Five separate computer models all place the plane in a tight cluster of spots in the south Indian Ocean — hundreds of miles southwest of the previous search site.

——————————————————————————————————————————
20:01 5/27/2014
Inmarsat公布了卫星数据——————————————————————————————————————————
21:02 5/27/2014

Inmarsat的卫星定时与MH370飞机上的发动机监控模块通信，通信过程无人为扰动的可能性，因此是判断飞机未知的重要信息。
Inmarsat提供了了两种测量数据BTO和BFO，分别是通信信号的时间偏移和频率偏移，前者可以推算卫星与飞机之间的距离，后者可以根据多普勒效应推算飞机的速度（具体对利用多普勒效应推算MH370未知的原理见Ping Rings from the Inmarsat-3F1 Data），结合两者完成对飞机位置的判断。

Understanding the Burst Timing Offset (BTO) values:

The round trip time for a message is a combination of:
round trip time for a message 是指一条卫星报文传递的时间 包含传播时延和处理时延

1. Time from the ground station → satellite → aircraft → satellite → ground station
这一部分讲的是卫星报文的传递路径 从地面站->卫星->飞机->卫星->地面站
这个路径的长短影响着传播时延因为
传播时延 = 传播路径长度/光速
根据传播时延推算路径长度是确定飞机位置的重要参数，术语是测距定位，GPS主要就是靠测距定位。

2. Processing time within the ground station, satellite and aircraft terminal, which are constant
报文在传递过程中，不仅传播路径消耗时间 ，卫星、地面站、飞机上的无线电台收发、处理报文需要的时间也影响总的时延，称之为处理时延（Processing time）。Inmarsat的报告认为不同报文的处理时延是固定的，考虑到卫星传输的特性，这一看法是合理的。

The BTO is a value (in microseconds) relative to a terminal at a nominal fixed location. Only R-Channel messages are used.

The BTO therefore allows the determination of the distance between the satellite and the aircraft. It does not provide the actual aircraft location

Understanding the Burst Frequency Offset (BFO) values:
Burst Frequency Offset (BFO)是指由于飞机高速运动产生的信号的频率偏差。需要注意的是，参与MH370卫星通信的海事卫星部署于地球静止轨道（GEO），相对于地球静止，本身并不引入多普勒频率偏移。（后面还有具体解释）

The transmission signal path from the aircraft has two components affected by Doppler shift; between the satellite and aircraft, and between the satellite and ground station.

The following need to be considered when computing the expected frequency offset:
o Inmarsat Classic Aero mobile terminals are designed to correct for aircraft Doppler effects on their transmit signals. The terminal type used on MH370 assumes a stationary satellite at a fixed orbital position

o An individual aircraft terminal will have a fixed frequency bias

\$\$
f_{2} = f_{1} + f_{d}+f_{o}
\$\$

o Satellite, terminal and ground station oscillator stability

o The correction applied by the Automatic Frequency Control (AFC) system in the ground station partially compensates for the satellite to ground station Doppler