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FF-SAR for CryoSat-2 Service User Manual

Introduction

The G-POD Service FF-SAR (Fully Focused SAR) for CryoSat-2 is a web platform that provides the capability to process on line and on demand CryoSat-2 SAR data, from FBR data products until FF-SAR Level1b products.  

The service is based on AREALT-FF1 Processor Prototype that has been developed by Aresys (http://www.aresys.it) in the framework of ESA contracts for Sentinel-6 and CryoSat. The AREALT-FF1 Processor produces FF-SAR altimetry waveforms exploiting the focusing technique in the 2D transformed frequency domain proposed in 1.

The AREALT-FF1 Processor will make use of the G-POD (Grid-Processing On Demand) distributed computing platform to deliver timely the output Level1b products. These output data products are generated in standard NetCDF format.

Using the G-POD graphic interface, it is possible to easily select the geographical area of interest along with the time of interest (based on the Cryosat-2 SAR FBR data products availability in the service's catalogue). After the task submission, it is possible to follow, in real time, the status of the processing task.

You find more information about how to use the generic G-POD graphic interface at the G-POD wiki page available at http://wiki.services.eoportal.org/tiki-index.php?page=GPOD%20User%20Manual

The on line FF-SAR service is available at https://gpod.eo.esa.int/services/FFSAR_Aresys_CRYOSAT/.

 

Description of the Processing Parameters in the G-POD graphic interface

The processor prototype is versatile in the sense that the users can customize and adapt the processing, according their specific requirements, setting a list of configurable options. 

In the G-POD web interface, user can enter easily this list of processing options via a series of drop-down menu.  Here, you find them listed with a basic description of their significance.
 
Processing Parameter Values Description
Range oversampling factor
  • 1
  • 2

User can decide wheter to apply zero padding prior to range compression: 1 if the zero padding has not to be applied, 2 if a zero padding by a factor of 2 has to be applied. It is worth recalling that the instrument samples the waveforms with a 320 MHz clock, providing a nominal_sampling = c / 320e6 / 2 = ~0.468m (with c = speed of light). Applying an oversampling factor waveform_sampling = nominal_sampling / range_oversampling_factor. Note that the altimeter range resolution is fixed and given by the chirp bandwidth of 320 MHz: c / 320e6 / 2 = ~0.468m.

Processed bandwidth factor
  • 0.25
  • 0.50
  • 0.75
  • 1.00

User can decide the fraction of the Doppler bandwidth that is processed to generate the FF-SAR single look waveforms, allowing to control the along-track resolution. Under some approximation the theoretical along-track resolution at -3dB is at_resolution = 1.073*velocity/processed_bandwidth (with velocity the satellite velocity and processed_bandwidth equal to the processed bandwidth factor multiplied by the instrument Pulse Repetition Frequency).

Multilook posting rate
  • 1
  • 20
  • 80
  • 100
  • 200
  • 500
User can decide the posting rate of the FF-SAR multi look waveforms. The processing parameter represents the approximate waveform spacing in frequency (Hz). The actual spacing will vary slightly along the orbit depending on orbital parameters.
 
Output Format

The FF-SAR Level1b data products generated in output are in standard NetCDF format. The NetCDF format is self-explanatory with all the data field significance described in the attributes.

The file naming convention for those files is :

L1B_FF_ML_starttime_stoptime.nc

where:

  • starttime is the time of the first sample in the Leve1b product in the format YYYYMMDDThhmmss
  • stoptime is the time of the last sample in the Level1b products in the format YYYYMMDDThhmmss

In the Level1b product, the following conventions are adopted

  • The Reference Time for the TAI Datation is 01/01/2000 00:00:00
  • The Vertical Datum for altitude reference is the WGS84 Ellipsoid

 

How to access to the service
The service is open and free of charge.
In order to be granted  the access to the service, you need to have an EO-SSO account (for EO-SSO registration, go hereand afterwards, you need to submit an e-mail to G-POD team (write to eo-gpod@esa.int), requesting the activation of the service for your EO-SSO user account.
 
Acronyms
EO-SSO: Earth Observation Single Sign-On
FBR: Full Bit Rate
FF-SAR: Fully Focused SAR
G-POD: Grid Processing On Demand
SAR: Synthetic Aperture Radar
WGS: World Geodetic System
 
References

1 Guccione, P.; Scagliola, M.; Giudici, D. 2D Frequency Domain Fully
Focused SAR Processing for High PRF Radar Altimeters. Remote Sens. 2018,
10, 1943. https://doi.org/10.3390/rs10121943


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Page last modified on Thursday 09 of July 2020 18:08:37 CEST by .