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 (Broadview 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, with only power -YES, with power and phase	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:

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
Choose the Default Tide Model	FES2004 FES2014b TPXO8 TPXO9	Flag to command the Default tide model used in the product (choose between FES2004, FES2014b, TPXO8 TPXO9)
Choose the Default Mean Sea Surface Model	DTU15 DTU18 CLS-CNES15	Flag to command the Default mean sea surface model used in the product (choose between DTU15, DTU18,CLS-CNES15)

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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 here) and 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