# Proposal of a data format for interchanging radiosonde flight data between a receiving station and server connected to multiple receiving stations

For this purpose the APRS format is pretty much used exclusively up to this point. This protocol is however not designed for this task, and is lacking in various points (authentification, data ambiguity, transfer of raw data)

The proposed format consists of various blocks. the first block named "general" is obligatory, all other blocks are optional. This makes it possible for blocks to be added in the future. In general, no authentification is used. if authentication is required by the server, a "authentication" block containing the receiving stations digital signature which had to be whitelisted beforehand. For each radiosonde transmission format, a specialised "raw_sondetype" block exists, which contains the specific raw data for the sonde type, which makes it possible to keep a log of raw data, for example if the open-source algorithms for ptu calculation are refined. As an example for a possible extension block, a "tof" block for determining the location of frame-based encrypted radiosondes like the RS41-SGM is proposed as well.

The proposed format should not only work for ham radio use, but should also have the goal to be useful for meteorological use as well.

## general
(* are required fields. If data is missing here, no frame should be sent. Optional fields should be NULL if no information is provided)
The minimal viable block should at least contain frequency, position and time, as these three are enough to uniquely identify each sonde among different receivieng stations. The act of assigning a unique id to each flight can only occur at the server side. A serial should never be used as an id by itself, as multiple flights of the same sonde can and will occur. Maybe it is possible for servers to share id information between them. Also, for most standard sondes, a id like serial_flightnumber would be fine.

receiver-frequency*: nominal transmission frequncy
receiver-frequency-afc: actual transmission frequency
receiver-name: name of the receiving station
receiver-latitude: latitude of the receiving station
receiver-longitude: longitude of the receiving station

frame-timestamp*: timestamp of the received timestamp. If no timestamp is provided or with frameless sondes, gps-time when receiving last piece of what will be sent out as a frame
frame-id: id of the current frame

sonde_serial: serial of the sonde
sonde-ontime: time after the sonde has been switched on
sonde-type: this has to be quite an elaborate contruct as many things have to be considered here, for example when the type is not clear from the transmission, when xdata is used etc.

sonde-horizontal-speed: horizontal speed of the sonde
sonde-vertical-speed: vertical speed of the sonde
sonde-direction: heading of the sonde
sonde-latitude*: latitude of the sonde
sonde-longitude*: longitude of the sonde
sonde-altitude: gps-altitude of the sonde

sonde-pressure: barometric pressure as measured by the sonde
sonde-temperature: air temperature as measured by the sonde
sonde-humidity: relative humidity as measured by the sonde
sonde-voltage: battery voltage of the sonde

## raw-raw_sondetype
Those have to be determined on a sonde-by-sonde basis. For example, for the RS41 this could contain of a field for each block of the RS41s frame, as this is easy validateable and transferable

## authentification
signature of the receiving station using a known and trusted implementation, for example of RSA

## tof
(in principle it is bad practice to use serials as ids here, but it will most likely never occur that reference sondes with no serial are used and it is way easier)
target-serial: serial of the sonde with unknown position
reference_1_serial: serial of reference sonde 1
reference_1_time_difference: time in nanoseconds between reception frame begin of reference 1 and unknown sonde
reference_2_serial: serial of reference sonde 2
reference_2_time_difference: time in nanoseconds between reception frame begin of reference 2 and unknown sonde
reference_3_serial: serial of reference sonde 3
reference_3_time_difference: time in nanoseconds between reception frame begin of reference 3 and unknown sonde