Normalization Reading and Writing for Radio Baseband Data

Very Long Baseline Interferometry (VLBI) is an observing technique by which signals from a number of radio telescopes at different locations over the world can be combined to produce extremely high angular resolution. With high resolution and high sensitivity give higher standards for the design of terminal equipment of radio astronomy. The radio signals received at each individual telescope are saved onto hard disk now in a lot of well-defined formats data, for example the Mark IV/Mark5B/VDIF format. All of these data obey the rules, every package contains frame header and frame data, while maybe both raw binary data and ascii file to describe the data allocation. Although the rules same, the details are different. So before correlation these data, we should decode and combine these raw data first, and then send the data to hardware/software correlator for generating visibility data. But for now there is still not a well structured software to decode/encode all of these data, in this paper we will describe a framework to reading and writing radio baseband data, with the aim to simplify data process standardization. The framework will supply the following features: decode supported radio baseband formats(with same API), encoding some defined information into baseband data for simulation(this feature will generate fake data for the reading functions), read multiple files as if it was a single file, write to a bunch of files based on some rules(these functions are for the general VLBI observation which will store a lot of small size files). The framework introduced in this article can be used for new data format just adding some new a piece of code.