SEPwC Tidal Analysis Coursework

Introduction

Your task is to write code to read in multiple tidal data files (each a different year) for a single tidal station. You should then calculate the M2 and S2 tidal components and also the rate of sea-level rise per year, for that station.

The tests

The test suite uses two data files from the 1940's from the Aberdeen tide gauge station. The test will check reading in these data, joining multiple years and calculating tidal constituents.

You can run the tests by running pytest or pytest test/test_tides.py from the main directory. Try it now, before you make any changes!

You can run a single test using:

pytest test/test_tides.py::TestTidalAnalysis::test_reading_data

You can run the unit tests only:

pytest test/test_tides.py::TestTidalAnalysis

The regression tests check the whole code:

pytest test/test_tides.py::TestRegression

The data

There are three directories with data for Whitby, Aberdeen and Dover for the years 2000 to 2019. Your code must be able to read in all the data files in one of those directories and perform the analysis by the user suppying the folder. You should be able to run:

python3 tidal_analysis.py data/whitby

for example to calculate the stats for Whitby. The program should print the tidal data, the sea-level rise and the longest contiguous period of data (i.e. without any missing data) from the data loaded.

Each file in the folder contains the tidal elevation and residual for a year. There are records every 15 to 60 minutes. The files are laid out like this:

Port:              P038
Site:              Aberdeen
Latitude:          57.14325
Longitude:         -2.07451
Start Date:        01JAN1946-00.00.00
End Date:          31DEC1946-23.00.00
Contributor:       National Oceanography Centre, Liverpool
Datum information: The data refer to Admiralty Chart Datum (ACD)
Parameter code:    ASLVZZ01 = Surface elevation (unspecified datum) of the water body                      
  Cycle    Date      Time      ASLVZZ01     Residual  
 Number yyyy mm dd hh mi ssf           f            f 
     1) 1946/01/01 00:00:00      3.6329      -0.1522  
     2) 1946/01/01 01:00:00      3.4195      -0.1547  
     3) 1946/01/01 02:00:00      2.9013      -0.2043  
     4) 1946/01/01 03:00:00      2.2612      -0.2170  
     5) 1946/01/01 04:00:00      1.6821      -0.2059  
     6) 1946/01/01 05:00:00      1.2859      -0.1926  

The headers should be ignored by your program. The data should consist of the at minimum a datetime column and a column called Sea Level which is the ASLVZZ01 data.

The UK Tidal Database has the following M2 and S2 amplitudes for our three stations of interest:

Station Name	M2 Amplitude	S2 Amplitude
Whitby	1.659 m	0.558 m
Aberdeen	1.307 m	0.441 m
Dover	2.243 m	0.701 m

Your code should return value similar to these, but they don't have to be identical.

Hints and tips

Use pandas to load data and manage most of the data wrangling.

The `scipy.stats' module can do the linear regression to work out sea-level rise. You may find it easier to work out the rise per day and multiply by 365 to get metres per year.

uptide can calculate the tidal constuents, but any nan (i.e missing data) must be removed prior to working out tidal constiuents.

To search for files of a certain type within a directory, use the glob module.

Regular experssions might be useful for removing the dodgy values (N, M, T), so something like:

my_data.replace(to_replace=".*M$",value={'A':np.nan},regex=True,inplace=True)

will replace any value ending in M in the column A in the pandas dataframe my_data. Note I've done this inplace so I don't need to reassign into another variable.

To convert datetimes to numbers to do a linear regression (see above), there are a few ways, but using the date2num function in matplotlib.dates, which converts a datetime to the number of days since 01-01-1970.

The rules

You cannot alter any of the assert comments in test/test_tides.py

If you alter any function names in the main code, you can alter the name in the test file to match; however the rest of the test must remain unchanged. This will be checked.

If you wish to add more tests, please do, but place them in a separate file in the test directory. Remember to name the file test_something.py. You must also make sure the class name(s) are different to those in test/test_tides.py.

You can also add extra functionality, but the command-line interface must pass the tests set.