# Harmonic decomposition ## Background Harmonic decomposition is an effective technique to separate anisotropic and dipping components from radius and transverse RFs ([Bianchi et al., 2010](https://doi.org/10.1029/2009JB007061])). This technique not only used to estimate azimuthal crustal anisotropy and crustal layer dipping , but used to extract isotropic component of RF for 1D RF inversion. In the Seispy, the command `rfharmo` is accessible for computing the harmonic decomposition, plotting different components after the decomposition, and save the isotropic component to a local SAC file. ``` usage: Harmonic decomposition for extracting anisotropic and isotropic features from the radial and transverse RFs [-h] [-t tb/te] [-s dt] [-o outpath] [-e enf] [-p figure_path] rfpath positional arguments: rfpath Path to PRFs optional arguments: -h, --help show this help message and exit -t tb/te Time window from tb to te for trimming RFs, NOTE: do not insert space before this argument, defaults to -2/10 -s dt Resample RFs with sampling interval of dt -o outpath Specify output path for saving constant component. -e enf Enlarge factor, defaults to 2 -p figure_path Figure output path, defaults to ./ ``` ## Download this example Users can download the same file as [`ex-rfani.tar.gz`](https://osf.io/download/4hk6d/): - Unzip the file to any directory. ```shell wget https://osf.io/download/4hk6d/ -O ex-rfani.tar.gz tar -xzf ex-rfani.tar.gz ``` ## Run this example Change directory to `ex-rfani` and just run following in the command line ``` rfharmo -o./ ``` - The RFs are trimmed from -2s to 10s as default. - Append `-o./` to specify the output path to save the isotropic component as SAC format (`SC.LTA_constant_R.sac`). - The result of `SC.LTA_harmonic_trans.png` is automatically saved to current directory as default. :::{figure-md} fig-target Result of harmonic decomposition in SC.LTA :::