Converting waterfall into data

Satellites & Observations
1

I’ve got wondered that if waterfall and audio, data shows same contents, can we convert each format into others?

More specific, i wonder how can i convert waterfall images into data files?

2

A quick answer to your questions:

  1. Waterfall, audio don’t show the same contents but they come from the same (raw I/Q) source. So, it is not possible to go from one format to the other.

  2. It can happen, to get data (points on time and frequency with a certain power in dB) but it will be too complicated to implement.

Some related information that may give you more answers:

Waterfall is the complete visualization of the I/Q data, however each point of waterfall comes as a result of a function that gets several I/Q data measurements and outputs the point and its power. Also each point is affected by the duration of the observation and the frequency Doppler.

As the image size of the waterfall has the same dimensions, a difference in duration will change the amount of the I/Q data used for each point.

The Doppler correction applied dynamically during the observation, this means that the point you see in the waterfall is on the computed, based on TLE, frequency that we expect satellite to transmit it and not the one that we actually received it.

So, in order to convert waterfall points to data, you will need to reverse the Doppler correction in order to find the right frequency and extract from the color scale the power in dB, and all these dynamically as both change in each waterfall.

Audio is partial (not full bandwidth) and compressed (ogg) representation of I/Q data. It includes the Doppler correction and also has no information about the power of the reception.

Waterfall Data (currently also known as Artifacts, but not to be confused when we use the same word artifacts to describe all the byproducts of an observation (waterfall, waterfall data, audio, demodulated data, raw I/Q)) is probably what you are looking for. It is a file with metadata and data that can be transformed to a waterfall image/visualization. Currently is in an experimental stage, and it is produced by limited stations that have set their client to produce and upload them in SatNOGS DB. The Waterfall Data can be found in https://db.satnogs.org/api/artifacts/ endpoint.

Let us know if the above are clear and let us know what are you trying to achieve, maybe we can provide ideas/solutions.

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