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SWOT L3 KaRIn and Nadir Ocean Data Products

This tutorial will introduce you to some sample SWOT L3 data products and show you how to download these data from AVISO and perform basic plots using Python related libraries.

The Sea Level Anomaly is represented by the SSHA fields in L3 LR SSH products. These fields are described as follow:

SLA field	Calibrated	Edited	Filtered
ssha_unedited	X
ssha	X	X
ssha_noiseless	X	X	X

1. Introduction

1.1 Tutorial Objectives

Present SWOT sample L3 data products (Basic and Expert versions)
Show you how to find and visualize SWOT Sea Level Anomaly (SLA) data sets from AVISO FTP server
Download locally SWOT KaRIn (2D swath) and nadir (along-track) altimetry combined data

1.2 Import + code

[ ]:

# Install Cartopy with mamba to avoid discrepancies
# ! mamba install -q -c conda-forge cartopy

[1]:

import requests
import numpy as np
import xarray as xr

import os
import ftplib
from getpass import getpass
import cartopy.crs as ccrs
import cartopy.feature as cft
import cartopy.mpl.geoaxes as cmplgeo
import cartopy.mpl.gridliner as cmplgrid
import matplotlib.pyplot as plt
# %matplotlib inline

[2]:

def ftp_data_access(ftp_path, filename, username=None, password=None, local_filepath=None):
    # Set up FTP server details
    ftpAVISO = 'ftp-access.aviso.altimetry.fr'

    try:
        # Prompt for username and password
        if not username:
            username = input("Enter username for AVISO: ")
        if not password:
            password = getpass(prompt=f"Enter password for {username}: ")

        # 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():
                if not local_filepath: local_filepath = input("Enter the local directory to save the file: ")
                return download_file_from_ftp(ftp, filename, local_filepath)
            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 download_file_from_ftp(ftp, filename, target_directory):
    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 {local_filepath}")
            return local_filepath
    except Exception as e:
        print(f"Error downloading {filename}: {e}")

2. Download from FTP

2.1 Parameters

Define a local filepath to download files

[3]:

local_filepath='downloads'

Select regional boundaries

[4]:

localbox=[-50, -40, 40, 55] # Gulf Stream

2.2 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: ········

2.3 Download data

[7]:

# Define directories
ftp_path_basic = '/swot_products/l3_karin_nadir/l3_lr_ssh/v1_0_2/Basic/cycle_016/'
filename_basic = 'SWOT_L3_LR_SSH_Basic_016_339_20240610T063906_20240610T073032_v1.0.2.nc'

# FTP download
half_orbit_basic = ftp_data_access(ftp_path_basic, filename_basic, username, password, local_filepath)
half_orbit_basic

Connection Established 220 192.168.10.119 FTP server ready
Downloaded SWOT_L3_LR_SSH_Basic_016_339_20240610T063906_20240610T073032_v1.0.2.nc to downloads/SWOT_L3_LR_SSH_Basic_016_339_20240610T063906_20240610T073032_v1.0.2.nc

[7]:

'downloads/SWOT_L3_LR_SSH_Basic_016_339_20240610T063906_20240610T073032_v1.0.2.nc'

[8]:

# Define directories
ftp_path_expert = '/swot_products/l3_karin_nadir/l3_lr_ssh/v1_0_2/Expert/cycle_016/'
filename_expert = 'SWOT_L3_LR_SSH_Expert_016_339_20240610T063906_20240610T073032_v1.0.2.nc'

# FTP download
half_orbit_expert = ftp_data_access(ftp_path_expert, filename_expert, username, password, local_filepath)
half_orbit_expert

Connection Established 220 192.168.10.119 FTP server ready
Downloaded SWOT_L3_LR_SSH_Expert_016_339_20240610T063906_20240610T073032_v1.0.2.nc to downloads/SWOT_L3_LR_SSH_Expert_016_339_20240610T063906_20240610T073032_v1.0.2.nc

[8]:

'downloads/SWOT_L3_LR_SSH_Expert_016_339_20240610T063906_20240610T073032_v1.0.2.nc'

Download notebook.

SWOT L3 KaRIn and Nadir Ocean Data Products

1. Introduction

1.1 Tutorial Objectives

1.2 Import + code

2. Download from FTP

2.1 Parameters

Select regional boundaries

2.2 Authentication parameters

2.3 Download data

3. Basic product

3.1 Sea level anomalies

3.2 Plot sea level anomaly at nadir

3.3 Remove sea level anomaly at nadir

4. Expert product

4.1 Sea level anomalies

4.2 Sigma 0