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GPOD CryoSat-2 SARvatore Software Prototype User Manual


Introduction

The G-POD Service, SARvatore (SAR Versatile Altimetric Toolkit for Ocean Research & Exploitation)  for CryoSat-2, is a web platform that provides the capability to process on line and on demand CryoSat-2 SAR data, from L1a (FBR) data products until SAR Level-2 geophysical data products.

The service is based on SARvatore Processor Prototype that has been developed entirely by Salvatore Dinardo in the scope of the EOP-SER Altimetry Team (Salvatore Dinardo, Bruno Manuel Lucas, Jerome Benveniste) in ESA-ESRIN.

The processor has been  further upgraded (SARINvatore) to accept in input L1a (FBR) SARIN data products and build SARIN Level-2 geophysical data products as well.

The Processors will make use of the G-POD (Grid-Processing On Demand) distributed computing platform to deliver timely the output data products.

These output data products are generated in standard NetCDF format (using CF Convention), and they are compatible with BRAT (Basic Radar Altimetry Toolbox) and other NetCDF tools.

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.

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You find more information about how to use the generic G-POD graphic interface at the G-POD wiki page available here.

The on line SAR service is available here.

The on line SARIN service is availabe here.

List of option entries in the G-POD graphic interface

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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. The configurable options are divided according to the processing level they refer to (L1b and L2). Here, you find them listed with a basic description of their significance.

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     L1b Processing Options:

Option Name Option Value Option Description

Filter out Duplicated CryoSat-2 Products during the processing time 

- Enable

- Disable

Enable to filter out duplicated products during the processing.

If activated, duplicated products (from different baselines) will not be processed : only the product with highest baseline rank will be processed

Data Posting Rate 20Hz/80Hz

- 20 Hz

- 80 Hz

Flag to set the data posting rate: 20 Hz (canonic posting rate) or 80 Hz (finer posting rate)
Hamming weighting Window 
 - Apply only in coastal zone 
 
 - Yes, apply it
 
 - No. do not apply it
 
User can decide here whether to apply a Hamming weighting window on the SAR burst data, do not apply it, or to apply it only for  surface location in coastal area (more info at REF1) 
Exact Beam-Forming   
 - Approximated
 
 - Exact   
User can decide here whether to operate an exact  Beam-Forming or an approximated Beam-Forming (more info at REF1)    
FFT Zero-Padding

- Yes, apply Zero-Padding

- No, don't apply Zero-

  Padding

User can decide here whether to operate the Zero-Padding prior to the range FFT (section 4.8 in REF1). Zero-Padding is indicated for coastal zone and sea-ice analysis
Radar Receiving Window Size 

- 128 Range Bins

- 256 Range Bins

User can select here the size of the radar receiving window: 128 range bins (standard) or 256 range bins (extended). Extended window is indicated for coastal zone analysis

Antenna Pattern Compensation

- NO

- YES

Flag to activate the antenna pattern compensation on the Stack Data 

Dump SAR Stack Data in output

-NO

-YES

User can command here to post in output SAR/SARIN Stack Data Products for each selected pass.

Beware: SAR/SARIN Stack Data Products are quite bulky (usually one GB for medium-size product); we recommend to process SAR/SARIN Stack Data singuarly or max 5 passes at the time: contact G-POD team for massive production of SAR/SARIN Stack Data 

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    L2 Processing Options:

5

Option Name Option Value Option Description
 Restrict the re-tracking on specific surfaces 
 
 - Process all
 
 - Process only open sea       points
 
 - Process only water        
   points
User can decide here whether to process the whole pass, only points in open sea or only water points (points in open sea, costal zone and inland water)
PTR width alphap parameter 
 
 - LUT
 
 - Constant
 
User can decide here  whether to use a LUT (Look-Up Table) or a constant for PTR (Point Target Response) alphap parameter 
SAMOSA Model Generation 

- Use SAMOSA 2

- Use SAMOSA 3

- Use SAMOSA+

User can decide here which SAMOSA generation model to use in the processing (SAMOSA 2 or SAMOSA 3 or SAMOSA+).
The SAMOSA 3 is a truncated version of SAMOSA 2 (only zero-order term); more info at REF2.
SAMOSA+ is the SAMOSA2 model tailored for inland water, sea ice and coastal zone domain

Single-Look or Multi-Look Model 

-Single-Look

-Multi-Look

Flag to command the application of the Multilooking on the Waveform Model (Single-Look or Multi-Look). Single-Look option is indicated for quick runs over sea ice and inland water while Multi-Look is the most accurate and is advised for ocean applications

Dump RIP in output

-NO

-YES

Flag to append Range Integrated Power (RIP) in the output netCDF data product 

Dump SAR Echo Waveforms in Output

- NO

-YES

User can command here to attach in the output product the SAR Echo Waveforms
 
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Adopted Conventions

 
  • The Reference Time for the TAI Datation is 01/01/2000 00:00:00
  • The Vertical Datum for altitude reference is the WGS84 Ellipsoid
  • The Curve Best-Fitting Scheme, used in the re-tracking stage, is a

    Bounded Levenberg-Marquardt Least-Squares Estimation Algorithm (LEVMAR-LSE).

  • The SAR Power Return Waveform Model, used in the re-tracking stage, is the SAMOSA Model (REF2)
  • Static bias has been applied to the range, sigma nought and antenna

    mispointing measurements. The values of the static biases are reported 

    in the output NetCDF data products.

  • The orbital altitude has been corrected for a Time Tag Bias. The value of  the applied time tag bias is reported in the output NetCDF data products.
  • The measurements are posted both at  rate of 20 Hz and of 1 Hz.
  • The sea state bias has not been applied to the sea level anomaly  measurements.
  • All the default geophysical path corrections are from the CryoSat-2 FBR products; refer to CryoSat-2 mission handbook to know the exact source of these corrections
  • No a priori data editing has been applied to the 20 Hz measurements.
  • The misfit between SAR Waveform Model and SAR Waveform Data has been computed as:   

                             sqrt( 1/128*sum(residual)^2 )*100


   where residuals are the differences between model's waveform power and 
   data's waveform power, normalized for the waveform power's maximum value.
 

Output Format

 

The L2 data products generated in output are in standard NetCDF format (CF-convention), fully compatible with BRAT.

The file naming convention for those files is :

RES_FBR_INPUT_FILENAME.nc

where:

FBR_INPUT_FILENAME is the filename of the SAR FBR data file given in input

(for more details on the input filename, please check the product specification

The netCDF format is self-explanatory with all the data field significance described in the attributes.

Along with the NetCDF file, it is provided in output a .png picture of the radar data image (Radar Echogram) and a kml file of the satellite pass ground-track.

Selecting the corresponding option, user can decide to post in output also the SAR Stack Data Products, still in netcdf format.

The naming convention for those stack data products is :

STK_FBR_INPUT_FILENAME.nc

They will be held in the STACK folder inside the .tgz output package
 
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.
 

Contact Us

 

For any question, bugs and support, please contact us at:

altimetry.info@esa.int

For G-POD specific questions please contact:

eo-gpod@esa.int 

 
Acronyms
 
SAR: Synthetic Aperture Radar
SARIN: Synthetic Aperture Radar Interferometry
WGS: World Geodetic System
EOP-SER: Earth Observation Programmes: Science, Exploitation, Research
CF: Climate & Forecast
FBR: Full Bit Rate
G-POD: Grid Processing On Demand
LUT: Look-Up Table
L1a: Level 1a
L1b: Level 1b
EO-SSO: Earth Observation Single Sign-On
 

References

 

REF1:  Guidelines for the SAR (Delay-Doppler) L1b Processing, ESA, 2013, available here

REF2 :  SAR Altimeter Backscattered Waveform Model (SAMOSA Model Paper), IEEE-TGARSS


Contributors to this page: Salvatore.Dinardo .

Page last modified on Wednesday 08 of March 2017 15:57:42 CET by Salvatore.Dinardo.