Applying Low-Pass Filter through bash EddyID command

[acapet]

Hi !

The use of --cut-wavelength and --order option allows to apply a high pass Bessel filter on altimetry fields before identification when using the bash command EddyID.

Alternatively, through python, Low-pass filter are also available.

I'm using experimental altimetry datasets which are quite noisy at the moment, and the noise lead to a significant decrease (~30%) in the number of identified eddies. To solve this, I'd like to attempt appyling a low-pass filter with a small spatial scale (~5km?).

Is it possible to do so through the bash command EddyID, or do I have to use the python approach ?

Thanks !

[AntSimi]

Hi!

Unfortunately, EddyId doesn't allow this :(.
But with some quick modification it could be possible here for application and here for options
It could be a welcome PR!
Just for knowledge method will refuse a wavelength under 2 times grid step.
If you need more informations, don't hesitate!
Antoine

[AntSimi]

classic use

This command will provide identification on a grid where we try to remove scale bigger than 700km

EddyId \
    src/py_eddy_tracker/data/nrt_global_allsat_phy_l4_20190223_20190226.nc \
    20190223 adt ugos vgos longitude latitude /tmp/ --cut 700 --fil 1 --fit_err 70

EddyInfos will show the radius distribution

EddyInfos /tmp/Anticyclonic_20190223.nc 

-- /tmp/Anticyclonic_20190223.nc -- 
    | 3342 observations from 25255 to 25255 (1 days, ~3342 obs/day)
    |   Speed area      : 35.18 Mkm²/day
    |   Effective area  : 48.24 Mkm²/day
    ----Distribution in Amplitude:
    |   Amplitude bounds (cm)        0.00      1.00      2.00      3.00      4.00      5.00     10.00    500.00
    |   Percent of eddies         :      18.76     23.94     15.50      9.84      6.28     15.62     10.05
    ----Distribution in Radius:
    |   Speed radius (km)            0.00     15.00     30.00     45.00     60.00     75.00    100.00    200.00   2000.00
    |   Percent of eddies         :       0.00      5.24     33.00     26.06     15.02     13.17      7.36      0.15
    |   Effective radius (km)        0.00     15.00     30.00     45.00     60.00     75.00    100.00    200.00   2000.00
    |   Percent of eddies         :       0.00      4.13     24.36     22.50     16.13     17.89     14.60      0.39
    ----Distribution in Latitude
        Latitude bounds            -90.00    -60.00    -15.00     15.00     60.00     90.00
        Percent of eddies         :       7.51     46.56     13.02     30.13      2.78
        Percent of speed area     :       4.26     42.12     26.79     25.60      1.22
        Percent of effective area :       4.45     43.46     25.20     25.62      1.27
        Mean speed radius (km)    :      44.76     55.92     83.79     54.81     40.96
        Mean effective radius (km):      53.18     65.70     95.19     63.62     48.56
        Mean amplitude (cm)       :       3.52      5.23      2.09      4.24      3.14

New options

This command will provide identification on a grid where we try to keep only scale between 150km and 700km

EddyId \
    src/py_eddy_tracker/data/nrt_global_allsat_phy_l4_20190223_20190226.nc \
    20190223 adt ugos vgos longitude latitude /tmp/ --cut 150 700 --fil 1 --fit_err 70

This operation will create more bigger eddies and reduce population of little eddies

EddyInfos /tmp/Anticyclonic_20190223.nc

-- /tmp/Anticyclonic_20190223.nc -- 
    | 2429 observations from 25255 to 25255 (1 days, ~2429 obs/day)
    |   Speed area      : 40.91 Mkm²/day
    |   Effective area  : 57.59 Mkm²/day
    ----Distribution in Amplitude:
    |   Amplitude bounds (cm)        0.00      1.00      2.00      3.00      4.00      5.00     10.00    500.00
    |   Percent of eddies         :      23.26     23.26     13.71      8.23      6.09     16.10      9.35
    ----Distribution in Radius:
    |   Speed radius (km)            0.00     15.00     30.00     45.00     60.00     75.00    100.00    200.00   2000.00
    |   Percent of eddies         :       0.00      1.98     17.91     23.34     19.39     19.31     17.58      0.49
    |   Effective radius (km)        0.00     15.00     30.00     45.00     60.00     75.00    100.00    200.00   2000.00
    |   Percent of eddies         :       0.00      0.74     10.95     16.55     16.26     23.05     31.25      1.19
    ----Distribution in Latitude
        Latitude bounds            -90.00    -60.00    -15.00     15.00     60.00     90.00
        Percent of eddies         :       6.30     47.18     16.26     28.20      2.06
        Percent of speed area     :       3.85     41.76     28.26     25.05      1.09
        Percent of effective area :       4.02     43.40     26.05     25.48      1.06
        Mean speed radius (km)    :      57.27     69.30     96.67     68.96     55.22
        Mean effective radius (km):      69.78     84.23    111.67     83.28     64.24
        Mean amplitude (cm)       :       2.84      5.22      2.04      4.39      2.37

Identification match

EddyQuickCompare /tmp/Anticyclonic_20190223.nc /tmp/Anticyclonic_20190223_pass_band.nc --invalid 2
[ref] /tmp/Anticyclonic_20190223.nc -> 3342 obs
[0] /tmp/Anticyclonic_20190223_pass_band.nc -> 2429 obs
          nomatch      multi_match        low       intermediate       high          parent          twin          complex    
[ 0]    27.6% (924)    8.1% (272)     3.5% (118)     5.3% (178)    55.4% (1850)     0.0% (0)      7.2% (240)      1.0% (32)   
          nomatch      multi_match        low       intermediate       high          parent          twin          complex    
[ 0]    6.3% (153)     5.4% (130)     4.9% (118)     7.3% (178)    76.2% (1850)    4.9% (120)      0.0% (0)       0.4% (10)

• 27 % of original structure are not present in pass band dataset
• 6 % of structure are new in pass band dataset
• 4.9% of structure in pass band dataset enclosed two eddies from original one
• 55.4% of original dataset have a good correlation in pass band dataset