Calculating number of years for PR metrics using irregular time index

[RenanBRibeiro]

When working with data that features highly irregular time steps, such as altimetry data, the method for calculating years in metrics.py may produce inaccurate counts of years. This, in turn, affects the calculation used to identify and order peak numbers. Consequently, the computation of Peak Ratio (PR) may be flawed, relying solely on a singular event.

By introducing additional print statements and making minor modifications to the code, the outcome is altered as follows:

# Calculate number of years
    dt_int = time[1:].values - time[0:-1].values
    dt_int_mode = float(stats.mode(dt_int, keepdims=False)[0]) / 1e9  # in seconds
    N_years = dt_int_mode / 24 / 3600 / 365.25 * len(time)
 # changing code here
    print(N_years)
    dt = time[-1] - time[0]
    N_years = dt.days / 365.25
    print(N_years)
 # changing code here

Output

0.18286146601769462
10.992470910335387

my data is from 2013 to 2023, so ~11years.

I understand that this simple calculation dt = time[-1] - time[0] can also cause problems when we have many gaps in the data, but in this case it works well.

[jsmariegaard]

@daniel-caichac-DHI - peak ratio sounds like something for you? Any comments on this?

[daniel-caichac-DHI]

Agree with Renan, that the peak ratio if you have many gaps in you data, could be wrong as the number of years are not true.
This could actually be an improvement.
Now, on a altimmetry topic, the PR on altimetry data is not good anyway, for a different reason though. The peak over threshold algorithm will mark thing as peak which are not necessarily a peak. Let me show an example picture.

Black line : Continuos measurement from a non-existen buoy in a point
Red line: Altimetry data at the ~same location (lots of gaps)
Blue points: Detected points.

As you can see, P1 could be falsely detected as a peak, because it has more than 36h between peaks, and fulfills all criteria.
Peak Ratio on discontinuous altimetry data is dangerous.

Palle is a little bit more blunt about it and is saying it does not make sense to make a peak-ratio on satellite data.
Maybe Renan could ask him for more details?

[RenanBRibeiro]

Thank you Daniel, for the feedback.
Regarding PR on altimetry. It's true! It makes no sense to calculate the PR with this type of data. Thanks again!