JMART (Joint Multi-Altimetry Radar processing Toolkit)

Description

JMART is a altimeter data processor toolkit written in Python 3 (3.9.6). It implements in particular the fully-focused SAR (FF-SAR) processing to process Sentinel-3/Sentinel-6 L1a products.

Input

1. Sentinel-3/Sentinel-6 L1A netCDF4 products for reading pulse signals.
2. Sentinel-3/Sentinel-6 L2 netCDF4 products for geophysical corrections.
3. configuration file.

Input Data Downloading

1. Sentinel-3 L1A/L2 altimetry data from Copernicus (https://dataspace.copernicus.eu/). The data can be obtained via the copernicus api, see https://documentation.dataspace.copernicus.eu/APIs/SentinelHub.html on how to use it.

2. Sentinel-6 L1A/L2 altimetry data from EUMETSAT (https://data.eumetsat.int/). The data can be obtained via the EUMETSAT Data Access Client (EUMDAC) client, see https://user.eumetsat.int/resources/user-guides/eumetsat-data-access-client-eumdac-guide on how to set it up.

Output

1. L1b and L2 auto-descriptive netCDF4 files,
2. Command files to launch l1b and l2 processing,
3. log files for l1b and l2 processing.
4. slurm files if use HPC

Prerequisites

• Users are required to install a distribution of Python, such as miniconda and create an environment including Python 3.9.6.

• Once the installation of miniconda is completed, create a specific environment (e.g. named "jmart"):

	conda create -n jmart python=3.9.6

• The environment shall then be activated with:

	conda activate jmart

• In the activated environment, please install the following python packages :

On Linux:

  pip install numpy==1.21.3
  pip install scipy==1.7.1
  pip install netcdf4==1.5.7
  pip install pyproj==3.3.0
  pip install pyshp==2.1.3
  pip install tqdm==4.62.3
  pip install numexpr==2.7.3
  pip install matplotlib==3.4.3

on HPC (example in JSC):

  module --force purge

  module load Stages/2023
  module load StdEnv/2023

  module load SciPy-bundle
  module load netcdf4-python
  module load pyproj
  module load Cartopy 
  module load tqdm

• Once the environment is created, we suggested to put the bash script for calling the environment into file loadenv.

Get starting

To process sequentially all L1a products of a specific folder with JMART, point the directory of the processor and do:

    python launch_jmart_processor.py -c config/test.cfg

Specific options

• -c : to specify the path to the configuration file, as an example:

python launch_jmart_processor.py -c config/config.cfg

will launch all the L1a files of input directory indicated in the configuration file (input_dir)

• -slurm : creates a slurm job in slurm using srun to control jobs

python launch_jmart_processor.py -c config/config.cfg -slurm

• -dryrun : creates bash command files only, as an example:

python launch_jmart_processor.py -c config/config.cfg -dryrun

will create the bash command file(s) without launching them.

• -ncpu : numer of cpus per task been used, mainly for l2 processing, as an example:

python launch_jmart_processor.py -c config/config.cfg -ncpu 8

• -a : account for job in HPC

• -p : partition for job in HPC

• -t : walltime for job in HPC, HH:MM:SS

• -TMPDIR : TMPDIR for job running first in HPC, if not given, using default ./data/temp/

As a complete example running in HPC for submiting the slurm automatically:

python launch_jmart_processor.py -c config/config.cfg -ncpu 8 -a myproject -p batch -t 04:00:00 -TMPDIR ./data/temp/ -slurm

References

• Joint Multi-Altimeter Reprocessing Toolkits (JMART/v1.0)
• Sentinel-3/Sentinel-6 Product L2
• IPF-SR-1 07.07 Processing Guide

Contact Information

• Author: Jiaming Chen
• Contact: chenjiaming@uni-bonn.de
• Contributor: Luciana Fenoglio

FFSAR Level 1B Non-Time Critical Product Description

Product Overview

This document describes the Sentinel-3A/-3B SRAL (Synthetic Aperture Radar Altimeter) Level 1B Non-Time Critical (NT) product. The product filename is based on S3A_SR_1_BFF_BS_*.nc.

Basic Information

• Mission: Sentinel-3A/-3B
• Sensors:
  • Primary: SRAL (Synthetic Aperture Radar Altimeter)
  • Secondary: GNSS, DORIS
• Product Type: Altimeter L1B Non Time Critical
• Processing Institution: Uni-Bonn IGG|APMG
• Processing Software: IPF-SR-1 07.07
• Reference Ellipsoid: WGS84
• Semi-major Axis: 6378137.0 m
• Ellipsoid Flattening: 0.00335281066474748

Temporal Information

• First Measurement Time: start time of the satellite measurement
• Last Measurement Time: stop time of the satellite measurement
• Time Reference: Seconds since 2000-01-01 00:00:00 (UTC)

Product Characteristics

• Posting Rate: 80 Hz
• Range Extension Factor: 1
• Zero-padding Factor (zp): 2
• Hamming Window:
  • Azimuth: Applied
  • Range: Not applied
• Number of Burst Blocks: 180
• Surface Types:
  • 0: Open ocean or semi-enclosed seas
  • 1: Enclosed seas or lakes
  • 2: Continental ice
  • 3: Land

Data Groups

1. Main Data Group (/data/ku)

Contains multi-looked waveforms and associated parameters:

Key Variables:

• time: UTC time of measurement (seconds since 2000-01-01)
• latitude, longitude: Satellite position (degrees)
• altitude: Satellite height above ellipsoid (meters)
• power_waveform: Oversampled power waveforms (128 samples × 256 oversampled)
• msc: Magnitude Squared Coherence of single-looks (0-1)
• doppler_freqs: Doppler frequencies for each look (Hz)
• thermal_noise: Estimated thermal noise level (dB)
• surface_classification_flag: Surface type classification
• tracker_range_calibrated: 1-way range from satellite to surface (m)

2. Single-Look Complex Data Group (/data_sl/ku)

Contains single-look complex (SLC) data:

Key Variables:

• i_slc, q_slc: In-phase and quadrature components of SLC waveforms
• iq_scale_factor: Scaling factor to convert I/Q samples to voltage
• time: UTC time of SLC measurements

Variable Details

Platform Parameters

Variable	Description	Units
altitude	Satellite height above reference ellipsoid	meters
latitude/longitude	Satellite position	degrees
position_vector	Satellite position in ITRF (x,y,z)	meters
velocity_vector	Satellite velocity in ITRF (x,y,z)	m/s
off_nadir_[pitch/roll/yaw]_angle_pf	Platform pointing angles	degrees

Waveform Parameters

Variable	Description	Units
power_waveform	Calibrated multi-looked power waveform	counts
i_slc/q_slc	Single-look complex components	counts
iq_scale_factor	I/Q scaling factor	volts
pulse_repetition_interval	Time between pulses	seconds
sig0_scaling_factor	Scaling for sigma0 calculation	dB
rcs_scaling_factor	Scaling for RCS calculation	dBsm

Geophysical Parameters

Variable	Description	Units
tracker_range_calibrated	1-way range to surface	meters
radial_velocity	Platform velocity toward surface	m/s
separation_between_waveform	Along-track waveform spacing	meters

Processing Notes

1. Waveform Scaling: Power waveforms are scaled to fit 2-byte integers
2. Time Reference: All times are referenced to UTC with TAI-UTC difference of 37s
3. Coordinate System: ITRF for position/velocity, WGS84 for geodetic coordinates
4. Surface Classification: Based on MODIS and GlobCover data

Power Waveform from counts to watt

The real waveform in watt can be derived from the power_waveform and sig0_scaling_factor using the following formula:

Conversion Formula

$$ P_{\mathrm{waveform}} = \mathrm{power_waveform} \times 10^{\frac{\mathrm{sig0_scaling_factor}}{10}} $$

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FFSAR Level 2 Non-Time Critical Product Documentation

Product Identification

• Filename: S3A_SR_2_BFF_HY_*.nc
• Mission: Sentinel-3A/-3B
• Sensor: SRAL (Synthetic Aperture Radar Altimeter)
• Processing Level: L2 (Non-Time Critical)
• Institution: Uni-Bonn IGG|APMG

Temporal Coverage

• Start Time: start time of the satellite measurement
• End Time: stop time of the satellite measurement
• Time Reference: Seconds since 2000-01-01 00:00:00 UTC

Spatial Coverage

• Latitude Range: latitude processing range
• Longitude Range: longitude processing range
• Reference Ellipsoid: WGS84
  • Semi-major axis: 6,378,137.0 m
  • Flattening: 0.00335281066474748

Processing Information

• Software Version: IPF-SR-1 07.07
• Retracking Algorithms:
  • OCOG_SAR (Offset Center of Gravity)
  • PTR (Point Target response)
  • SAM+ (SAMOSA+ model)
• OCOG Threshold: 0.8
• Posting Rate: 80 Hz
• Range Extension Factor: 1
• Zero-padding Factor: 2

Data Groups

1. Main Data Group (/data/ku)

Contains geophysical parameters derived from retracking algorithms:

Geophysical Parameters

Variable	Description	Units	Scale Factor
altitude	Satellite height above ellipsoid	m	0.0001
latitude/longitude	Satellite position	degrees	1e-06
sig0_scaling_factor	Sigma0 scaling factor	dB	1e-06
rcs_scaling_factor	Radar cross-section scaling	dBsm	1e-06
tracker_range_calibrated	1-way range to surface	m	0.0001

Retracker Outputs

OCOG Retracker:

• range_ocog: Corrected range (m)
• sig0_ocog: Backscatter coefficient (dB)
• amplitude_ocog: Waveform amplitude
• epoch_ocog: Retracking epoch (s)

PTR Retracker:

• range_ptr: Corrected range (m)
• sig0_ptr: Backscatter coefficient (dB)
• amplitude_ptr: Waveform amplitude
• epoch_ptr: Retracking epoch (s)
• misfit_ptr: Model misfit error

SAM+ Retracker:

• range_samp: Corrected range (m)
• sig0_samp: Backscatter coefficient (dB)
• swh_samp: Significant wave height (m)
• amplitude_samp: Waveform amplitude
• epoch_samp: Retracking epoch (s)
• misfit_samp: Model misfit error

2. Geophysical Data Group (/data_01)

Contains environmental corrections and auxiliary data:

Altimeter Corrections

Correction	Description	Units	Scale Factor
iono_cor_gim	Ionospheric (GIM)	m	0.0001
iono_cor_alt	Ionospheric (altimeter)	m	0.0001
model_wet_tropo_cor_zero_altitude	Wet tropospheric (model)	m	0.0001
model_dry_tropo_cor_zero_altitude	Dry tropospheric (model)	m	0.0001
sea_state_bias	Sea state bias	m	0.0001
dac	Dynamic atmospheric correction	m	0.0001

Tide Models

• Ocean Tides:
  • ocean_tide_sol1 Solution 1 (GOT4.10)
  • ocean_tide_sol2 Solution 2 (FES2014)
  • Includes load tide and equilibrium components
• Solid Earth Tide: solid_earth_tide using Cartwright and Tayler tables
• Pole Tide: pole_tide using Desai model

Auxiliary Data

Variable	Description	Units	Scale Factor
geoid	Geoid height (EGM2008)	m	0.0001
mean_sea_surface	MSS height (DTU21)	m	0.0001
wind_speed_alt	Altimeter wind speed	m/s	0.01
rain_flag	Precipitation flag	-	-
distance_to_coast	Distance to nearest coast	m	100

Quality Flags

• surface_classification_flag:
  • 0: Open ocean/semi-enclosed seas
  • 1: Enclosed seas/lakes
  • 2: Continental ice
  • 3: Land
• oceanlike_flag:
  • 1: Open ocean
  • 0: Non-open ocean
• rain_flag:
  • 0: No rain
  • 1: Rain
  • 2-5: Various probability levels

Usage Notes

1. Range Corrections: Apply all relevant corrections to obtain sea surface height: $$ \begin{aligned} \text{SSH} &= \text{altitude} - \text{range}_{\text{ocog/ptr/samp}} - \text{Correction} \ \text{Correction} &= \text{Geophysical Correction} + \text{Tide Correction} \ \text{Geophysical Correction} &= \text{iono_cor_gim} + \text{wet_tropo} + \text{dry_tropo} \ \text{Tide Correction} &= \text{solid_earth_tide} + \text{pole_tide} + \text{ocean_tide} + \text{dac} + \text{sea_state_bias} \end{aligned} $$
2. Sigma0 Calculation: Backscatter coefficients are already fully calibrated

$$ \sigma^{0} = \mathrm{sig0}_{\mathrm{ocog/ptr/samp}} + \mathrm{sig0_scaling_factor} $$

3. Retracker Selection: SAM+ is recommended. oceanlike_flag can be used for selecting the good waveform from Ocean.