Filtering Oceanographic Current Meter Data for Tidal Removal

In summary: I'm still searching some tutorial on Octave.In summary, the conversation is about filtering oceanographic current meter data to remove the tidal component. The suggested method is to take the Fourier transform of the data and erase the spike at the tidal frequency. It is also recommended to design a notch filter or highpass filter with a center frequency of 12 Hz. Some members suggest using MATLAB or Octave for this task. There is also a discussion about the advantages of Octave and a recommendation to use it for filtering and signal or image processing. The conversation ends with the user expressing interest in learning more about wavelet transform using filters.
  • #1
Glowfish
2
0
Hi
I am working with current meter data (oceanographic) and have to filter my timeseries to remove the tidal component (frequency 12h). I have not worked with filters before and would appreciate any help.
Thanks
 
Mathematics news on Phys.org
  • #2
You need to take the Fourier transform of your data; this will give you a representation of your data as a spectrum of frequencies. I suppose there should be a spike at the tidal frequency (twice per day, or 1/12 per hour, or whatever units you use). Then simply erase that spike, and transform your data back into the time domain.
 
  • #3
Ben Niehoff said:
You need to take the Fourier transform of your data; this will give you a representation of your data as a spectrum of frequencies. I suppose there should be a spike at the tidal frequency (twice per day, or 1/12 per hour, or whatever units you use). Then simply erase that spike, and transform your data back into the time domain.


Better yet, design a notch filter with good characteristics, and a center frequency of 12 Hz. Taking an FFT, zeroing out coefficients, and then inverse transforming gives a terrible filter.

Probably this thread should be moved to EE or something like that?
 
  • #4
If you have access to MATLAB, it makes filtering datasets quite easy. Let us know what tools you have to work with.

- Warren
 
  • #5
quadraphonics said:
Better yet, design a notch filter with good characteristics, and a center frequency of 12 Hz. Taking an FFT, zeroing out coefficients, and then inverse transforming gives a terrible filter.

Probably this thread should be moved to EE or something like that?

Think it's a simple typo -- quadraphonics meant (1/12) Hz.
 
  • #6
berkeman said:
Think it's a simple typo -- quadraphonics meant (1/12) Hz.

Indeed; thanks for that.

A simple highpass filter might also be a good choice, if there isn't any interesting information below 1/12 Hz.
 
  • #7
berkeman said:
Think it's a simple typo -- quadraphonics meant (1/12) Hz.

Actually, this is also a typo. The frequency is 1 / 12 hours, or 2.31481481 x 10-5 Hz. :biggrin:

- Warren
 
  • #8
chroot said:
Actually, this is also a typo. The frequency is 1 / 12 hours, or 2.31481481 x 10-5 Hz. :biggrin:

- Warren

Ack! I'd better get back to work... :redface:
 
  • #9
berkeman said:
Think it's a simple typo -- quadraphonics meant (1/12) Hz.

Okay, I got a lot of advice but still not sure what to do. Unfortunately I don't have matlab. At the moment I'm working with excel and excelstat which allows me to do FFT and spectral analysis.
How do I design a notch filter or a highpass filter in excel with a frequency of 1/12 hr?
Baby steps please.:redface:
Lisa
 
  • #10
If you're not familiar with any kind of filter design, we cannot really help you. It's too sophisticated a problem to walk you through on a forum.

If you'd like, you can probably use the free program Octave to perform your actual filtering. (Octave is a free MATLAB clone.) I'd be happy to design your filter coefficients for you.

- Warren
 
  • #11
It will be great if someone could give a basis lesson on filter. I understand that discrete wavelet transform can also be efficiently implemented using filters.

Thanks chroot for the information on Octave. It's new to me. Do you recommend it? What are the advantages of this software? I have some little knowledge about Matlab. Do Octave have good toolbox, in particular for signal or image processing?
 
  • #12
What are the advantages of this software?
It's a Matlab clone and it's free.
 
  • #13
That's good start. Hopefully there is no copyright violation when using free clone software. Do you recommend any good website that I can download the Octave.

At the moment, however, I'm trying to understand https://www.physicsforums.com/showthread.php?t=32703" first. Not yet on MATLAB programming. Hopeful later I will be able to write program on wavelet transform using filters.
 
Last edited by a moderator:
  • #15
I have already download Octave version 3.0.1. Thanks Science Advisor CRGreathouse.

Have try simple commands and it works :smile: I will figure out later how to run a m-file.
 

What is "Filtering Oceanographic Current Meter Data for Tidal Removal"?

"Filtering Oceanographic Current Meter Data for Tidal Removal" is a process used by scientists to remove tidal signals from ocean current data. This allows for a clearer understanding of the underlying ocean currents, without the influence of tides.

Why is filtering oceanographic current meter data for tidal removal important?

Filtering oceanographic current meter data for tidal removal is important because tides can significantly affect ocean currents and can obscure important patterns or trends in the data. Removing tidal signals allows for a more accurate analysis of the underlying ocean currents.

What techniques are used to filter oceanographic current meter data for tidal removal?

There are several techniques used to filter oceanographic current meter data for tidal removal, including harmonic analysis, bandpass filtering, and spectral analysis. These techniques involve identifying and removing the tidal signals from the data, while preserving the non-tidal components.

What challenges are associated with filtering oceanographic current meter data for tidal removal?

One of the main challenges of filtering oceanographic current meter data for tidal removal is accurately identifying and separating the tidal signals from the non-tidal signals. This requires a thorough understanding of tidal patterns and variations in the ocean currents.

How can filtered oceanographic current meter data for tidal removal be used in scientific research?

Filtered oceanographic current meter data for tidal removal can be used in a variety of scientific research, such as studying ocean circulation patterns, tracking changes in ocean currents over time, and predicting the impact of tides on marine ecosystems. It can also be used in conjunction with other data sources to better understand the complex interactions between tides and ocean currents.

Similar threads

Kalman Filtering with missing observations
    • General Math
Replies
6
Views
2K
A few questions about airflow and filters...
    • Mechanical Engineering
Replies
5
Views
1K
Engineering Linear Filters for Removing Impulsive noise
    • Engineering and Comp Sci Homework Help
Replies
2
Views
844
I Noise Whiteness hypothesis in Kalman filtering
    • Set Theory, Logic, Probability, Statistics
Replies
4
Views
888
I How would one convert measured magnitudes of a satellite object to radiant intensity?
    • Astronomy and Astrophysics
Replies
0
Views
196
(Control) Derivative filter and discrete model
    • General Engineering
Replies
0
Views
689
I Regression Prediction with Time Series Data
    • General Math
Replies
1
Views
806
Detection of ground level ozone with light
    • Materials and Chemical Engineering
Replies
12
Views
526
A Editing in Freq domain and applying inverse FFT
    • General Math
Replies
6
Views
971
Engineering Questions about the workings of a phase locked loop
    • Engineering and Comp Sci Homework Help
Replies
10
Views
1K

Hot Threads

Recent Insights

Back
Top