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VISAN Documentation
VISAN is a visualization and analysis tool for atmospheric data. With this application you can read product data from atmospheric instruments for missions such as Sentinel-5P, Aeolus, GOME-2, IASI, OMI, etc. but also from model data such as CAMS or ground based data such as those provided NDACC and EVDC. You can apply a wide range of mathematical operations to this data, and you will be able to create 2D and worldmap plots.
VISAN is the graphical front-end application for the Atmospheric Toolbox. The CODA and HARP software are installed as dependencies of VISAN and provide the functionality to ingest data from the atmospheric product files. This data can then be further processed using the analysis and visualization components that are built-in into VISAN.
The VISAN application is fully Open Source software and builds on top of existing Open Source packages such as Python, wxPython, VTK, CODA, HARP, etc.
A central Open Source package used within VISAN is the powerful high-level programming and scripting language Python. You will interact with VISAN through a Python-driven command line interface. This Python interface provides both easy interactive use and the possibility to implement scripts for advanced and/or repetitive types of analysis. Most of the code of the VISAN application itself was also written using the Python language.
Python provides a flexible way to add useful functionality. There are many freely available extension packages available for Python. When you install VISAN it will also install some important packages for your convenience, but you can easily add more. One extension that has already been added is the Numpy package, which provides a set of high-performance mathematical functions such as linear algebra operations, convolutions, Fourier transforms, etcetera.
Below you will find an overview of the documentation that is provided with VISAN.
Release Notes
For the latest release notes concerning this version of VISAN, look at the release page on GitHub.
Installing and Running VISAN
VISAN can only be installed as a conda package. There are packages available for Windows (64-bit), macOS (64-bit) and Linux (64-bit).
In order to install VISAN you will thus first have to install Anaconda or Miniconda for Python 3.
Using your Anaconda/Miniconda installation create and activate a conda environment in which you want to install VISAN. We recommend creating a dedicated environment for VISAN:
$ conda create -n visan $ conda activate visan
When you have activated the conda environment, install VISAN in the environment by running the following command:
conda install -c conda-forge visan
This will automatically also install the CODA and HARP software as dependencies in the same environment.
You can also install additional python packages in the conda environment, such as matplotlib, which will then be available from within VISAN as well. Make sure to always pass '-c conda-forge' when you call 'conda install' to install additional packages. This should make sure that the versions of your additional packages are ones that work correctly together with VISAN.
User Manual
The User Manual gives a description of the graphical components of VISAN such as the main window and the plot windows. The manual also explains the basic VISAN functionality needed to successfully use the application. Tutorials on VISAN can be found on the main Atmospheric Toolbox website.
Reference Manual
The Reference Manual provides an overview of all VISAN-specific functions (i.e. functions that are not part of the Python or Numpy packages).
External documentation
CODA
CODA deals with direct access to product data. The CODA interface for Python is a combination of the low level CODA functions for direct product access (using Cursor objects as used in the C and Fortran interfaces) and the high level CODA functions (using the fetch style functions as used in the MATLAB and IDL interfaces).
A description of the CODA Python interface can be found in the CODA documentation.
HARP
CODA and HARP provide two complementary ways of accessing and dealing with product data. Whereas CODA provides access to the data using the same structure as the data is stored in the product, HARP performs a conversion of the product data to a simplified harmonized datastructure (the HARP data format). The Python interface of HARP included with VISAN allows ingestion of atmospheric data into a Python representation of this HARP data format, but also provides a wide variety of operations that can be performed on the data such as filtering, regridding, unit conversion, application of averaging kernels, etc.
A description of the HARP Python interface can be found in the HARP documentation.
CODA Product Format Definition documentation
For products that do not use a self-describing data format CODA requires Product Format Definitions, stored in .codadef files, to interpret the format of the data. A textual description of the Product Format Definitions for the .codadef files that come with VISAN can be found in the Product Format Definition documentation. If you want to know how a data file is structured and where you can find specific data within a file this is the documentation you should consult.
Python
Python is the language in which you provide commands to the VISAN application. It is a very flexible and easy to learn language that can be used to create both small scripts as well as complete applications.
Numpy
Numpy is an extension package for Python that provides a set of high performance mathematical functions such as linear algebra operations, convolutions, Fourier transforms, etcetera. The special Numpy 'array' data structures are used throughout the VISAN application. For instance, all array data that you retrieve via an ingest through CODA or HARP will be stored using these special array types. If you want to perform mathematical operations on these arrays you should thus use the functions from this package.