reduce-v2 v3.2.3¶

Mercurial revision 5786:5c8b45563631 | 2026-08-04

Description¶

reduce-v2 is a tool used to filter Mog2D archives using a Lanczos time filter. It is developed and used by CTOH (Centre de Topographie des Océans et de l’Hydrosphère). The tool computes and writes clx-formatted filtered Mog2D archives.

Usage¶

reduce-v2 [OPTIONS]

Options¶

Note: If a default is not specified, the option is mandatory.

Input/Output Options¶

Option	Description
`-h <name>`	Root name for elevation archives. Default: `analysis`.
`-p <name>`	Root name for pressure archives. Default: `forcing`.
`-iF <format>`, `-f <format>`	Input archive format: `clx` or `cdf`.
`-oF <format>`	Output archive format: `clx` or `cdf`.
`-i <path>`	Path for input archives. Default: `./`.
`-o <path>`	Path for output filtered archives. Default: `./`.

Filtering Options¶

Option	Description
`-w <days>`	Filtering window in days. Default: `20.0`.
`-start <MM/YYYY>`	Starting month for filtering request.
`-end <MM/YYYY>`	Ending month for filtering request.
`-r <int>`	Ratio factor for archive reduction. Default: `1`.
`-m <method>`	Detiding method to remove S2 signal: `analysis`, `climatology`, or `none`. Default: `analysis`.
`--pressure-only`	Skip elevation processing.
`--ssh-only`	Skip pressure processing.
`-hf`	Also remove high-frequency signals with a 12.5-hour filter.

Advanced Options¶

Option	Description
`-no_default`	Disable default values for `-h` and `-p`.
`-pressure_factor <factor>`	Pressure factor. Default: `1.0`.
`-mesh <file>`	Path to the mesh file.
`-ssh <varname>`	Variable name for elevation (default: `elevation`).
`-pressure <varname>`	Variable name for pressure (default: `p`).

Deprecated Options¶

Option	Replacement
`-d`	Use `-m` instead.

Examples¶

Basic Filtering¶

Filter elevation and pressure archives from January 2000 to December 2000:

reduce-v2 -start 01/2000 -end 12/2000 \
  -i ./input_data \
  -o ./output_data \
  -iF cdf -oF cdf

Filter with Custom Root Names¶

Use custom root names for elevation and pressure archives:

reduce-v2 -h custom_elevation -p custom_pressure \
  -start 01/2000 -end 12/2000 \
  -i ./input_data \
  -o ./output_data

Detide with Climatology Method¶

Remove S2 signal using the climatology method:

reduce-v2 -m climatology \
  -start 01/2000 -end 12/2000 \
  -i ./input_data \
  -o ./output_data

High-Frequency Filtering¶

Remove high-frequency signals (12.5-hour filter):

reduce-v2 -hf \
  -start 01/2000 -end 12/2000 \
  -i ./input_data \
  -o ./output_data

Pressure-Only Filtering¶

Skip elevation and filter only pressure archives:

reduce-v2 --pressure-only \
  -p custom_pressure \
  -start 01/2000 -end 12/2000 \
  -i ./input_data \
  -o ./output_data

Custom Filtering Window¶

Use a custom filtering window of 30 days:

reduce-v2 -w 30.0 \
  -start 01/2000 -end 12/2000 \
  -i ./input_data \
  -o ./output_data

Resampling¶

Reduce archive size with a resampling factor of 2:

reduce-v2 -r 2 \
  -start 01/2000 -end 12/2000 \
  -i ./input_data \
  -o ./output_data

Environment Variables¶

reduce-v2 uses OpenMP (version 201511) for parallelization. Key environment variables:

Variable	Description
`OMP_NUM_THREADS`	Number of threads to use.
`OMP_SCHEDULE`	Runtime schedule type and chunk size.
`OMP_DYNAMIC`	Enable/disable dynamic thread adjustment.
`OMP_NESTED`	Enable/disable nested parallelism.

Example:

OMP_NUM_THREADS=6 reduce-v2 -start 01/2000 -end 12/2000 -i ./input_data -o ./output_data

Note: If running on a busy machine, limit threads to the number of free CPUs to avoid performance degradation.

Notes¶

Input Formats:

Supported formats: clx (binary, deprecated) and cdf (NetCDF).
NetCDF (cdf) is the recommended format.

Detiding Methods:

analysis: Uses harmonic analysis to remove S2 signal.
climatology: Uses precomputed climatology (requires S2-elevation-atlas.nc or S2.ele.s2c).
none: No detiding is applied.

High-Frequency Filtering:

The -hf option applies an additional 12.5-hour filter to remove high-frequency signals.

Resampling:

The -r option reduces the number of frames in the output archives by the specified factor.

Output:

Filtered archives are saved in the specified output directory (-o).
Output filenames include the root name, year, and month (e.g., analysis-filtered-2000.01.nc).

Performance:

For large datasets, ensure the output directory (-o) is on a fast storage device (e.g., SSD).
Adjust OMP_NUM_THREADS based on available CPU resources.