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Download SWOT from AVISO

This notebook explains how to explore and retrieve available SWOT LR data from AVISO’s THREDDS Data Server and FTP Server, presented here.

L2 data can be explored at: https://tds.aviso.altimetry.fr/thredds/L2/L2-SWOT-DATA/L2-SWOT.html

L3 data can be explored at: https://tds.aviso.altimetry.fr/thredds/catalog/dataset-l3-swot-karin-nadir-validated/l3_lr_ssh/catalog.html

Tutorial Objectives

Discover Aviso’s Thredds Data Server catalogue
Download files through HTTP and FTP
Download a dataset through Opendap

Import + code

[1]:

import warnings
warnings.filterwarnings('ignore')

[2]:

import os
import re
from getpass import getpass
import threddsclient
import numpy as np
import requests as rq
import ftplib
import xarray as xr
from xarray.backends import PydapDataStore

[13]:

def _get_filename_from_cd(cd):
    """ Get filename from content-disposition """
    if not cd:
        return None
    fname = re.findall('filename="(.+)"', cd)
    if len(fname) == 0:
        return None
    return fname[0]

def http_download_file(dataset_url:str, output_path:str):
    response = rq.get(dataset_url, auth=(username, password))

    try:
        response.raise_for_status()
    except rq.exceptions.HTTPError as err:
        raise Exception(err)

    filename = _get_filename_from_cd(response.headers['content-disposition'])
    file_path = os.path.join(output_path, filename)

    open(file_path, 'wb').write(response.content)
    return file_path

def _download_file(ftp:str, filename:str, target_directory:str):
    try:
        local_filepath = os.path.join(target_directory, filename)
        with open(local_filepath, 'wb') as file:
            ftp.retrbinary('RETR %s' % filename, file.write)
            print(f"Downloaded {filename} to {target_directory}")
            return local_filepath
    except Exception as e:
        print(f"Error downloading {filename}: {e}")

def ftp_download_file(ftp_path:str, filename:str, output_path:str):
    # Set up FTP server details
    ftpAVISO = 'ftp-access.aviso.altimetry.fr'
    try:
        # Logging into FTP server using provided credentials
        with ftplib.FTP(ftpAVISO) as ftp:
            ftp.login(username, password)
            ftp.cwd(ftp_path)
            print(f"Connection Established {ftp.getwelcome()}")

            # Check if the file exists in the directory
            if filename in ftp.nlst():
                return _download_file(ftp, filename, output_path)
            else:
                print(f"File {filename} does not exist in the directory {ftp_path}.")
    except ftplib.error_perm as e:
        print(f"FTP error: {e}")
    except Exception as e:
        print(f"Error: {e}")

def open_dataset(dataset_url):
    """ Open the dataset at dataset_url.
    Args:
        dataset_url

    Returns:
        xr.Dataset
    """
    session = rq.Session()
    session.auth = (username, password)
    try:
        store = PydapDataStore.open(dataset_url, session=session, timeout=300, user_charset='UTF-8')
        return xr.open_dataset(store)
    except Exception as e:
        print(f"Something wrong with opendap url {dataset_url}: {e}")

Parameters

Define existing output folder to save results

[4]:

output_dir = "downloads"

Authentication parameters

Enter your AVISO+ credentials

[5]:

username = input("Enter username:")

Enter username: aviso-swot@altimetry.fr

[6]:

password = getpass(f"Enter password for {username}:")

Enter password for aviso-swot@altimetry.fr: ········

Download files through HTTP

To find the data you want to download, you can explore the Swot LR L2 or Swot LR L3 catalogues.

Copy the FileServer url to download data through HTTP :

[7]:

swot_lr_dataset_url = "https://tds.aviso.altimetry.fr/thredds/fileServer/dataset-l2-swot-karin-lr-ssh-validated/PIC0/Basic/cycle_014/SWOT_L2_LR_SSH_Basic_014_001_20240417T111950_20240417T121118_PIC0_01.nc"

[8]:

swot_lr_file = http_download_file(swot_lr_dataset_url, output_dir)
swot_lr_file

[8]:

'downloads/SWOT_L2_LR_SSH_Basic_014_001_20240417T111950_20240417T121118_PIC0_01.nc'

Download files through FTP

Files available through FTP follow the same file tree as in the THREDDS Data Server.

Data	FTP starting point	Browsing files URL
Swot LR L2	/swot_products/l2_karin/l2_lr_ssh	https://tds.aviso.altimetry.fr/thredds/catalog/dataset-l2-swot-karin-lr-ssh-validated/catalog.html
Swot LR L3	/swot_products/l3_karin_nadir/l3_lr_ssh	https://tds.aviso.altimetry.fr/thredds/catalog/dataset-l3-swot-karin-nadir-validated/l3_lr_ssh/catalog.html

[9]:

ftp_path = '/swot_products/l2_karin/l2_lr_ssh/PIC0/Expert/cycle_008/'
ftp_file = 'SWOT_L2_LR_SSH_Expert_008_001_20231214T064919_20231214T074047_PIC0_01.nc'

[10]:

swot_lr_file = ftp_download_file(ftp_path, ftp_file, output_dir)
swot_lr_file

Connection Established 220 192.168.10.119 FTP server ready
Downloaded SWOT_L2_LR_SSH_Expert_008_001_20231214T064919_20231214T074047_PIC0_01.nc to downloads

[10]:

'downloads/SWOT_L2_LR_SSH_Expert_008_001_20231214T064919_20231214T074047_PIC0_01.nc'

Load a dataset via OPeNDAP

To find the data you want to load, you can explore the Swot LR L2 or Swot LR L3 catalogues.

Copy the OPeNDAP url to load dataset through Opendap :

[11]:

swot_lr_dataset_url = "https://tds.aviso.altimetry.fr/thredds/dodsC/dataset-l3-swot-karin-nadir-validated/l3_lr_ssh/v1_0_2/Basic/cycle_014/SWOT_L3_LR_SSH_Basic_014_001_20240417T111950_20240417T121116_v1.0.2.nc"

[14]:

swot_lr_dataset = open_dataset(swot_lr_dataset_url)
swot_lr_dataset

Store the dataset to a NetCDF file

[ ]:

# Set encoding for each variable
for var in list(ds.keys()):
    ds[var].encoding = {'zlib':True, 'complevel':5}

[21]:

ds.to_netcdf(os.path.join(output_dir, 'dataset.nc'))