RA Altimeter onboard ERS Level 2 Altimetry Ocean Product

Description

Product		ERS OPR
Credits		Ifremer/CERSAT for ESA
Sources		RA onboard ERS-1 [series ERS-1] RA onboard ERS-2 [series ERS-2]
Niveau		2
Couverture spatiale		Global
Résolution spatiale		7 km
Média		WWW , CDROM , FTP , DVD ,
Format
Résumé This product provides data sets from the ERS radar altimeter. This sensor is a Ku band (13.8 GHz) nadir pointing active microwave sensor providing, along the satellite track, measurements of the echoes from ocean surface, from which wind speed modulus, wave height and sea surface elevation can be retrieved (using precision orbits derived from the onboard laser retro-reflector). The datasets in the product include - over dated and geolocated 7 km wide cells (sensor footprint) - all sensor parameters, range and altitude elements used for geophysical quantities retrievement, all backscatter coefficient, wind speed, significant wave height elements computed, but also the ATSR/RW radiometer data (brightness temperature at 23.8 GHz and 36.5 GHz, water vapour content, liquid water content) used to correct altimeter measurements. Land cells are flagged. The OPR product is freely distributed to ESA-approved investigators (authorization must be requested to ESA/ESRIN Order Desk) on exabyte, CDROM or through the CERSAT WWW extraction service. The data are organized in swath format, with each record consisting of a cell. Each file covers one ERS pass (half orbit extending from pole to pole). A CDROM or an exabyte contains a whole ERS cycle (35 days). This product is available in 2 different versions. The level 1, called OPR1, is an intermediate product processed with the preliminary orbit, The level 2, called OPR2 is the final product processed with the precise orbit.

Couverture temporelle

Satellite	Résolution temporelle	Couverture temporelle
ERS-1		du 01/08/1991 au 02/06/1996
ERS-2		depuis 04/04/1995

The OPR product is available for both ERS-1 and ERS-2 missions

Distribution des données

Access to the data is restricted to ESA-approved users. Authorization must be requested to ESA Order Desk. There is a file per ERS half-orbit.

The format of data files on a medium follows either the CCSDS convention (Consultative Comittee on Space Data System), largely used in satellite data distribution) or the CEOS (Comittee on Earth Observation Satellites), depending on the phase of the satellite during the acquisition.

ERS-1

Phase	Cycle length (days)	Start	End	Format
A	3	01 Aug. 1991	10 Dec. 1991	CEOS
B	3	28 Dec. 1991	30 Mar. 1992	CEOS
C	35	14 Apr.1992	20 Dec.1993	CCSDS
D	3	23 Dec. 1993	10 Apr. 1994	CEOS
E	168	10 Apr. 1994	26 Sep. 1994	CEOS
F	168	28 Sep. 1994	21 Mar. 1995	CEOS
G	3	21 Mar. 1995	17 May 1996	CCSDS

ERS-2

Phase	Cycle length (days)	Start	End	Format
(one phase only)	35	21 Apr. 1995	today	CCSDS

Le tableau ci-dessous fournit quelques indicateurs de volumétrie pour le produit 19 :

Format	Granularité	Taille
uncompressed	half revolution	600,00 Ko
uncompressed	day	17,58 Mo
uncompressed	week	123,05 Mo

Il convient donc de prendre en considération ces indications avant d'opter pour un des différents moyens d'accès à ce produit mis à la disposition des utilisateurs :

WWW

Note

OPR data subsetting and dowload according to temporal and/or geographical criteria can be performed through the download form. This form is restricted to ESA-approved users (login and password must be requested to ESA) : fill in the form - without forgetting your email - and submit. You will receive a request notification by e-mail. The data subsets are made available to you as an uncompressed tar file (referenced in the e-mail), to be found on the IFREMER ftp server (address : ftp.ifremer.fr), under the directory "/pub/ifremer/cersat/tmp" when logged as anonymous.

CDROM

mailto:eohelp@esa.int

Note

The OPR data are also distributed on CDROM or exabyte. Each CDROM or exabyte generally stores 35 days of data (duration of a cycle). These medium is intended for users working on large amount of data (or long period of time) or requiring frequent access to the data. The CDROM and exabyte can be sent to ESA-approved users (ask at ESA Order Desk) on request to CERSAT User Service.

FTP

ftp://ftp.ifremer.fr/pub/ifremer/cersat/dpaf

Note

The intermediate product (OPR1) is available on the ifremer ftp site (ftp.ifremer.fr/pub/ifremer/cersat/dpaf) for the 4 last weeks.

DVD

mailto:eohelp@esa.int

Note

The OPR data are also distributed on CDROM or exabyte. Each CDROM or exabyte generally stores 35 days of data (duration of a cycle). These medium is intended for users working on large amount of data (or long period of time) or requiring frequent access to the data. The CDROM and exabyte can be sent to ESA-approved users (ask at ESA Order Desk) on request to CERSAT User Service.

Outils

Documentations